TECHNICAL MANUAL 
FOR LOW PRESSURE 
CHAMBER OPERATORS 
DIVISION OF AVIATION MEDICINE 
BUREAU OF MEDICINE AND SURGERY  
(S| 
Jf t5 
AVIATION HYGIENE TRAINING UNIT 
U. S. NAVAL AIR STATION, SAN OlEGO This manual has been prepared for the Instruc- 
tion of Low Pressure Chamber Technicians, The 
Bureau of Medicine & Surgery desires to acknow- 
ledge the contributions made by the following 
officers to the preparation of this manual: 
Lt. Comdr. C. F. CELL, (MC) USN 
Lt. Comdr. R. M. CARR, (MC) USNR 
Lt. Comdr. F. W. GROSS, (MC) USN 
Lt. Comdr. H. L. JONES, (MC) USN 
Lt. (jg) M. C. SHELESNYAK, H-V(S) USNR ERRATA 
Page 6, diagram, pressure at 20,000 feet, change from 379 to 349. 
Page 30, paragraph 2, line 2, change "the anoxia" to "acute anoxia." 
Page 35* paragraph 1, line 1, change "undectable" to "undetectable", 
page 44* paragraph 3* line 5* change "32.3 feet per second" to 
"32*3 feet per second per second". TABLE OF CONTENTS 
PART ONE: AVIaTION HYGIENE 
Form, Function, and Environment 1 
Fundamentals of Physiology 4 
Physics of Atmosphere 6 
Heart in Aviation 11 
Respiration: Anatomy (one) 16 
Physiology (two) 19 
Anoxia 28 
Aeroembolism 36 
Acceleration 43 
Gastrointestinal Tract 49 
Ear and Sinus 51 
Temperature 55 
Airsickness 57 
Fatigue 58 
Bodily Care 62 
Carbon Monoxide and Noxious Gases 63 
Night Vision 69 
PART TWO: BAROCHAMBER TECHNOLOGY 
Barochaober: Theory 71 
Barochamber: Operations 72 
(Duties of Technician) 74 
Navy Oxygen Equipment 77 
Safety Rules 86 FORE WORD 
The instruction of several classes ott 
hospital carpamen as Low Pressure Cham- 
ber Technicians has resulted in the pre- 
paration of this manual. Its sole pur- 
pose is for instruction of future class- 
es, and as a reference following their 
qualification. 
Full credit for the compilation of the 
text is given the following officers! 
C.F.GELL, Lieut.Cmdr. (M» U.S.N, 
R.M.CARR, Lieut .Cmdr. (M3) U.S.N.R. 
F»W.GROSS, Lieut .Cmdr. (M3) U.S.N. 
H.L.JONES, Lieut.Cmdr. (M3) U.S.N. 
M.C .SHELESNYAK, Lieut, (jg) H-V{S) U.S.N.R. 
Lieut.Shelesnyak was also largely res- 
ponsible for the editing and the illus- 
trations. Helpful suggestions were also 
made by former students and enlisted 
personnel Attached to the Low Pressure 
Chamber. 
i< • s # mltel£&r 
(Japtain (M3) U.S.N, FOR M - FUNCTION f. ENVIRONMENT 
The subject of the following discussions is the physi- 
ology of aviation. The problems of the physiology of avi- 
ation are essentially the same as those of any other physi- 
ology, namely the problems of the working of living matter. 
The special aspects of aviation physiology are introduced 
by the fact that flying is carried on in an environment 
different than that of ordinary living, and by the exist- 
ence of a relationship between body function and environ- 
ment. Living matter is greatly influenced by its environ- 
ment - that is, it responds and reacts to all and anything 
about it - inside and out: heat, cold, exercise, air, wa- 
ter, food, feelings - everything. 
Let us examine this relationship between function and 
environment. It will help in the understanding of the prob- 
lems of aviation. To begin with, let us look at life or 
living. The task of defining life or living is a rash en- 
terprise and actually of little value. For the understand- 
ing of man it is more important to appreciate certain es- 
sential characteristics of what we call life(or living pro- 
cesses). Needless to say, there are many com- 
plexities, and simplifications must be made. 
Biologists (students of living matter and pro- 
cesses) begin with a discussion of the unit of 
living matter, the cell, and its substance,pro- 
toplasm. When protoplasm is first mentioned, a 
long array of its characteristics follows and 
includes irritability, contractility, capacity 
to reproduce,conduct impulses, assimilate food- stuffs, secrete, etc. Protoplasm ie Justly called 
the physico-chemical basis of living, the structu- JBSy 
ral unit of living matter is the cell, which con- H&anil 
sists basically of a membrane wall {the cell wall), 
protoplasm, and a control unit within the cell (the W 
nucleus). Wherever cells specialize in a particular 
characteristic or function of protoplasm, and arc 
grouped together, the mass is called tissue. For 
exanple, cells specializing in conduction of impul- I 
ses constitute nerve tissue; cells specializing in 
contraction constitute muscle tissue. It is an at- 
tribute of living matter to adjust and alter its 9 
form(or structure) to its function, and vice versa, 
and as a result the structures of various tissues 
and the cells composing them are modified according 
to functions. Incidentally basic characteristics of proto- 
plasm usually persist, even though specialization has oc- 
curred. 
The body is composed of tissue, which in turn is made 
up of cells. Although each cell has its individuality, the 
body must be considered as a single unit - as a whole. This 
concept of considering the body as a single unit made up of 
many small units all reacting to various conditions and in 
turn influencing the whole body is known as the concept of 
the organism as a whole. 
The concept can be visualized in a way by watching the 
response of a cat to a strange dog. 
First the eyes and the nose pick up stimuli, light 
wavss and chemicals, and report via nerves to the 
brain; from the brain "messages11 are flashed - fear 
is instilled - the adrenal medulla secretes adrena- 
lin - the muscles tense for action -the hair stands 
on end to afford more protection in combat - the 
heart beats faster -glucose and oxygen are utilized 
at greater rate - and so forth. Many separate parts 
all coordinated into action of the organism as a 
whole. 
We are particularly interested in the 
reaction to its environment. Environment, in the 
widest sense, means everything - everything which 
is outside and inside of the body. The temperature, 
humidity, light, sound, smell, - the feelings, ex-* 
periences, thoughts, all go into the making of the environment, and, as such, influence the bodily reactions. 
The bodily functions react to the various states of energy 
and matter of the surrounding environment, and long periods 
of constant or repeated exposure to particular conditions 
may result in bodily adaptations. 
During the many thousands of years of en- 
velopment, plant and animal forms have 
evolved and adjusted to their environ- 
ment. VJitness the animal and plant life 
of the desert - cacti, llama, camel, and 
hosts of others do well under desert con- 
ditions. Fish are peculiarly adapted for living in the wa- 
ter, birds for flying, and so on and on. The long time in- 
fluences and adaptations made us what we are. 
Aside from the responses to evolutionary influences, 
the body has a remarkable capacity to adjust to immediate 
environmental changes. These responses are of course limi- 
ted. For example, man can live on the Sahara Desert or in 
Greenland, at the equator or in the polar regions, but he 
cannot live in temperature above 160 degrees F, nor bciow 
-100 degrees F. Man can rest quietly or perform work in an 
amount equivalent to about one-fourth horsepower. He can 
adjust to various conditions of the environment within a 
limited range. 
The natural en- vironment of man is 
the earth1s surface, and even there with- 
in limitations .With- in the range of con- 
ditions upon the sur- face of the earth 
man actf usts moderate- ly well. The realm 
of flying, of aviation, presents, however, a new and dif- 
ferent environment, one which extends beyond the limits of 
man's natural adjustability. The fact that aviation pre- 
sents new conditions - new conditions in regard to environ- 
ment, positional relations, light, sound, vibrations, etc., 
and that the functioning of the organisra(physiology) reacts 
to changes in the state of the environment, forms the basis 
of the ohysiolocv of aviation. 
We shall examine some of the fundamentals of physiolo- 
gy, and then study the environment of aviation: the atmos- 
phere. FUNDAMENTALS OF PHYSIOLOGY 
Physiology is concerned with the problems related to 
how the living organism works in its normal surround- 
ings and how it reacts to its abnormal surroundings. A 
man walks. We see how he manages to regulate the orderly 
movements of arms, legs, and body without thinking about it. 
To understand even such an apparently simple procedure, we 
explore the workings of various parts. We study the muscle 
movements, the circulation of blood, the nerve control, and 
various other processes. 
In the study and understanding of bodily behavior a 
synthetic or unifying point of view must be accepted. This 
point of view is expressed in the concept of the organism 
as a whole. This concept deals with the individual organ- 
ism as it adapts Itself to the demands of the changing en- 
vironment and variable activity. The point of view reveals 
the existence of some unifying or integrating force which 
coordinates the workings of the various separate cells, 
tissues, and organ systems into a unity of the organism as 
a whole. These integrating or unifying forces act through** 
out life, regulate the growth and development and function 
of various parts of the organism, and make the parts con- 
form to the needs of the whole. 
The human body is often considered an engine. This is 
partly correct, but from one point of view the body bears 
very little resemblance to man-made machines. Man-made ma- 
chines, within wide limits, are stable whether the machine 
is acting or at rest. There is no such state of stability 
in the human machine. The living organism does maintain a 
semblance of a constant state, but on close examination we 
see that this constant state of the living organism ia due 
to many integrated chemical and physical constantly 
making fine adjustments to conditions imposed upai the tacjy. 
In this task the blood plays a most important role as an 
instrument of keeping a uniform internal environment. The 
blood provides this internal environment* and is in close 
contact with every single cell in the body. The blood sup- 
plies the tissue with foodstuffs, with oxygen for carrying 
on oxidation which releases energy for maintaining activity 
of the cells, and the blood also removes the waste and ex- 
cess products. In order that each cell carry on its activity, and in 
turn that the organism carry on its activities, it is nec- 
essary to have a source of energy. The problem is essen- 
tially the same for the body as it is for any other engine. 
Energy is needed for activity, and the amount of energy 
needed is dependent upon the demands made by the degree of 
activity. This means simply that a man running at top 
speed demands more energy than one at rest, that an ac- 
tively growing child nedds more than a senile old man. The 
pattern followed by the energy requirements and utiliza- 
tions of the body is the same as any engine and follows 
the laws of thermodynamics. The organism has as its source 
of energy the foodstuffs, in specially processed states, 
which it has ingested and stored; the release of these en- 
ergies are essentially controlled by the oxidation (the 
combining with oxygen or burning) of these foodstuffs. The 
energy exchanges in the body are called the metabolic pro- 
cesses, and a resting man will have a certain rate of en- 
ergy release which is called the basal metabolic rate. The 
energy exchanges under conditions of activity are greater, 
and so are the metabolic rates. In the proper understand- 
ing of physiological processes it is important to realize 
that energy is needed for every function, and fundamental- 
ly the energy is gotten by the chemical reactions of the 
oxygen-foodstuff combination. 
The adjustments which the body - cells, tissue, and 
organs - makes in order to maintain stability of the or- 
ganism as a whole, need energy and this constant function- 
ing assumes the greatest share of the metabolic activity. 
Whenever a new demand is made, whether it arise from a 
change in internal environment, such as the ingestion (ta- 
king in) of foodstuffs, or a disease process, such as an 
infectious disease, or from an external change such as a 
drop in the surrounding temperature or a marked change in 
the altitude of the organism, or increased physical exer- 
tion - the energy demands of the body are increased, and 
more foodstuff is used and more oxygen is needed. In our 
study of the reaction of the organism to such changes in 
environment as are introduced in the performance of mo- 
dem flying we will see how the demands upon the body are 
increased, the limitation to which it is extended, and the 
means taken by man to extend the natural limitations. PHYSICS Of ATMOSPHERE 
No adequate understanding of the 
function of the human body can be made 
without an understanding of its envi- 
ronment. This is particularly true in 
regard to an adequate understanding of 
the bodily reactions in flight. The 
special state of the environment in 
which aircraft and aircraft personnel 
operate is the atmosphere. It is for 
this reason that we shall discuss the 
atmosphere of the earth with respect to 
the physics of the air in relation to 
human physiology. We shall concern our- 
selves with atmospheric composition, 
pressure, temperature, density, and so 
on, at sea level and at various alti- 
tudes. 
The earth is surrounded by an en- 
velop of a mixture of gases and water 
vapor which is held close to it by the 
force of gravity. This layer of gases 
is about 100 miles high, and contains 
about 18% of Nitrogen, 21% of Oxygen, 
and the remaining one percent contains 
traces of Carbon Dioxide, Hydrogen, He- 
lium, Neon, Argon, Krypton, and Xenon. 
We are primarily concerned with three 
components of the air, exclusive of wa- 
ter vapor. These three components are 
oxygen, nitrogen, and carbon dioxide. 
Each is important for a different rea- 
son. Oxygen is essential for living; 
it is as essential for the combustion 
of body fuels (foodstuffs) and the re- 
lease of body energy as it is for the 
combustion of engine fuel. Nitrogen is 
important because it takes up almost 
80g of the air, but has no particular 
value for living processes. Carbon di- 
oxide has an odd role; it is an insig- 
nificantly small percentage in the air, 
but is a waste product of respiration 
and as such composes 5% of the expired breath, A definite amount of carbon dioxide is necessary 
in the blood for the control of breathing and heart action 
but in an air sample where it is too great, life becomes 
intolerable. 
In order to test the composition of the atmosphere, 
samples of air have been collected by various means, in- 
cluding manned balloons,pilot balloons, 
and high altitude aircraft flights, at 
altitudes ranging from sea level to al- 
most 50 miles above sea level. The per- 
centage composition of gases is appro- 
ximately the same at all these levels. 
Water vapor of the atmosphere varies in 
the cloud areas but averages about 1.2& 
The percentage of water vapor gradually 
decreases with increasing altitude, un- 
til the air above 35 000 feet is prac- 
tically dry. This is evidenced by the 
lack of clouds in the stratosphere. 
Corv*f>ovK*n 
OoorU 
Briefly, we recall that there is a relationship be- 
tween the volume, temperature, pressure, and density of a 
gas. To examine the atmosphere in respect to its pressure, 
temperature, density, and so on, it is important to review 
the GAS LAWS, which are the physical laws to which gases 
conform in their behavior. Since air is a mixture of ga- 
ses, its behavior will conform to the gas laws. Take a gas 
filled cylinder with a tight-fitting piston; the greater 
the pressure exerted on the piston, the smaller the vol- 
ume - and if heat is applied the gas will expand and occu- 
py a greater volume. Of course, when pressure is reduced, 
the volume is increased, and when the piston is cooled the 
volume is decreased. 
In more technical language we state the gas laws as 
follows: (l) When the temperature remains constant, ike 
volume of a gas varies inversely as the pressure; that is, 
the greater the pressure the smaller the volume, and con- 
versely, the less the pressure the greater the volume, 
(py«p»V*(l))is the form in which this law is stated by the physicist) (2) When the pressure remains constant, the 
volume of a gas varies directly as the temperature, that 
is, the wanner the larger the volume, or, conversely, the 
colder the smaller the volume, (Physicists combine these 
as the Gas Law: 2 ) (3) Since the atmosphere is 
9.//-a fearI* 
iv.u s« mi || 
a mixture of gases etc,), another gas law, 
Daltons Law, is relevant. It is the law of Partial Pres- 
sures, and states: The pressure of a mixture of gases in 
a given space is equal to the sum of the pressures which 
each gas of a mixture would exert by itself if confined in 
that same space. In other words, each gas in a mixture of 
gases exerts a pressure proportional to the percentage of 
the whole which it occupies. (4) Another characteristic 
of gases which is important, especially in understanding 
the physics of the air in regard to physiology, is density. 
Density of a gas is the weight of a standard, unit of 'vtfume 
of gas, and can be visualized as the number of particles 
(molecules)per unit volume. The great- 
er the density the greater the number 
of molecules per unit of volume. The 
density of air (dry) is 1.293 kgm. per 
cu. meter. (A kilogram is equal to 2,2 
pounds; a meter is roughly a yard.) 
This measurement must be made under standard conditions, 
15° C. and 760 mms, of mercury pressure. 
Bearing in mind the gas laws, and the fact that air 
is a mixture of gases, we will examine the atmosphere. 
Since air has density (weight) then it exerts a pressure. 
In order to measure this pressure we employ an instrument 
called a Barometer (Baros - pressure, Metros - measure). 
A sixiqale barometer is made by filling a glass 
tube, which is sealed at one end, with mercury, and 
then inverting the tube in an open dish of mercury, 
so that the open end of the tube is below the sur- 
face of the mercury in the dish. The column of mer- 
cury in the tube will fall to a height dependent up- 
on the air pressure. At sea level (standard condi- 
tions) the column will be 29.92 inches, or 760 mms. 
high. In other .words, the atmospheric pressure Is 
great enough to support a column of mercury 760 mms, 
high. As a matter of fact, the weight of a column of air one inch square from sea level to the uppermost rea- 
ches of the atmosphere is about 15(14.7) pounds. The weight 
of 14.7 pounds per square inch is designated as one atmos- 
phere ,* 
Let us return to our mercury barometer(there are other 
types too) and start studying atmospheric pressure. If we 
begin a trip starting at soa level and climb up to a moun- 
tain peak, we notice that after we have climbed up 1000 ft. 
the column of mercury has dropped (gradually) from 760 mms. 
to 732.9 mms. At 5000 ft. above sea level the column is 
only 632.3 mbs. At 10 000 ft, the barometric pressure has 
dropped to 522,6 mms. We see clearly that as the altitude 
increases the atmospheric pressure decreases. 
This relationship has a significant and striking as- 
pect; namely, at 18 000 ft, the pressure has been reduced 
to 380 mms. (1/2 atmosphere); at 34 000 ft., to 190 mms, 
(l/4 atmosphere), and at 42 000 ft. to 128 mms. (l/6 at- 
mosphere), so that $/6 of the atmospheric pressure(read 
density) is concentrated in the lowest eight miles of 
the 100-mile atmosphere. With the decrease in baro- 
metric pressure as the altitude increases there is a 
corresponding decrease in partial pressure of oxy- 
gen. Eventually the partial pressure of oxygen 
gets so small that sufficient oxygon necessary for 
life is not available. 
This is true because the partial pressure of each com- 
ponent of a mixture of gases is the product of the percen- 
tage composition times barometric pressure and while at sea 
level (760 mms. Hg.) the partial pressure of oxygen in at- 
mosphere is 157 mms. (or an equivalent oxygen percentage of 
20,93), at 18 000 ft, (300 mms. Hg,), the partial pressure 
of oxygen is 79.3 mms, (or an equivalent oxygen percentage 
of 10,45). Therefore, the passage through the lungs into 
the blood of the required amount of oxygen essential for 
living tissue is determined by the partial pressure of oxy- 
gen in the atmosphere, and cannot take place above certain 
altitudes. Therefore, in order to maintain sufficient oxy- 
gen pressure, the percentage of oxygen in the inspired air 
must be increased (P O2 z % 0?* P Air), until finally 
oxygen must be used at high altitudes. The table shows the relationship between altitude, ba- 
rometric pressure, oxygen pressure, and oxygen percentage 
equivalent. 
Altitude 
(Feet) 
Barometric 
Pressure 
Oxygen 
Pressure 
Cran.Hg,). 
©2 Percent 
Equivalent 
0 
760 
I59VO 
20.96 
3,281 
670 
140,4 
18.40 
6,562 
593 
124.5 
16.40 
9,842 
524 
109.8 
14.50 
10,300 
506 
105.9 
13.00 
16,404 
410 
85.9 
11.30 
18,000 
380 
79.5 
10.00 
22,966 
320 
67.0 
8.80 
28,000 
253 
53.0 
6.90 
34,000 
187 
39.0 
5.16 
40,000 
149 
32.0 
4.20 
42,000 
128 
26.7 
3.52 
50,000 
90 
18.8 
2.40 
TEMPERATURE: The study of the structure of the atmosphere 
reveals an interesting relationship between the altitude 
and the air temperature. Roughly, there is a decrease in 
temperature of 2 C° for every 1000-foot rise in altitude. 
This approximate relationship is true until 35 to 36000 ft. 
is reached, whereafter the temperature remains rather cons- 
tant, varying between -55 to -65° C. This "constant” tem- 
perature zone is called the stratosphere, and this region 
of the atmosphere is free from water vapor (and consequent- 
ly icing problems) and free from storm effects. The extreme 
cold of high altitude has a direct bearing on physiologic 
function and will be discussed later. THE HEART IN 
AVI AT I ON 
Having discussed the re- 
lationship of function to en- 
vironment and some fundamen- 
tals of bodily function, and 
having examined the atmos- 
phere which is the body1s en- 
vironment, we shall proceed 
to a discussion of some of 
the bodily systems with spe- 
cial regard to their action 
in conditions of aviation. 
The cardio-vascular sys- 
tem, that is the heart, blood 
vessels, and the blood, has 
the important function of 
maintaining and controlling 
the internal equilibrium of 
the body. This means that it 
is the task of this system to (l) carry all essential mate- 
rial - foodstuffs, oxygen, minerals, vitamins, enzymes, and 
hormones - to the tissues, (2) to remove waste products from 
the tissues, and (3) to maintain the internal stability of 
the organ. The heart is the pumping device of this system, 
and its main function is to create adequate mechanical for- 
ces for the circulation of the blood throughout the body. 
To this end the heart is constructed of special types of 
musculature known as cardiac muscle, and from the very ear- 
ly stages of embryonic formation to the death of an indivi- 
dual this muscle continues periodic contractions. 
£cucHa •yOPCUlATtON 
In briefest outline we can say of its anatomy that the 
human heart consists of four chambers, namely, two auricles 
and two ventricles. The auricles are relatively light in 
musculature. They are the entrance chambers into which the 
blood arrives from the general circulation. Blood from the 
body returns via the right auricle and from the right auri- 
cle passes down into the right ventricle, which is a very 
muscular chamber and which pumps the blood through the pul- 
monary artery into the lungs. The blood which has been ox- 
ygenated, that is, mixed with oxygen, returns to the heart, 
via the pulmonary vein, into the left auricle, and passes 
from the left auricle into the left ventricle, which is the 
master pump chamber so to speak, and which pumps the oxyge- 
nated blood through the aorta and its subsequent branches 
and divisions throughout the body until smaller and smaller subdivisions of blood vessels, from large arteries to small 
arteries, to arterioles, through the capillaries, and then 
from the capillaries into the venules and veins back to the 
heart. The capillaries have intimate contact with the body 
tissue. 
In this discussion we arc concerned chiefly with the 
control of the heart rate and the blood vascular system, 
with especial regard for the changes which occur in flying. 
First let us understand that the blood vascular system, in, 
carrying on its main task of maintaining internal equili- 
brium, is a very dynamic and constantly changing system. 
A sudden shocking noise will increase the heart rate, A 
flattering remark or an embarrassing situation will result 
in a change in the caliber of the peripheral blood vessels, 
particularly around the face. A half-dozen quickened steps 
will quicken the heart rate. These are gross and obvious 
changes. There is an infinite and continuous series of 
changes to the internal and external environment to which 
the cardiovascular system is perpetually reacting. We shall 
concern ourselves with many of the various changes in the 
cardiovascular system which arc associated with conditions 
of flying, but in this particular discussion we will focus 
our attention upon the heart. We will concern ourselves 
with the normal heart rate and its control, with minute vo- 
lume, the relation of the heart to oxygen consumption, and 
the reaction of the heart to changes in altitude. 
From your experience in aviation medical examination 
you recall that great importance is placed upon the exami- 
nee1 s heart system. The circulatory efficiency rating (the 
Schneider Test), which has a very important place in the 
medical examiner1s routine,is an index primarily of cardio- 
vascular efficiency. The importance which is attached to 
the cardiovascular system and pulse rate, resting and after 
exercise, is a real and significant one. let us look to the 
reasons, 
The normal or average pulse rate of an adult, healthy 
male granges from 60 to 90. A word here about the meaning 
of “normal11 and “average11. You will be asked often by some 
enlisted man or officer, after you have taken his pulse and 
recorded, for example 84, “Is 84 normal pulse?11, or the fi- 
gure may be 72, or 68. There is a general impression that 
the normal pulse is a particular and finite number and this 
Impression is an erroneous one, based upon the lack of un- 
derstanding of the heart function. The average-sized per- 
son on measuring his height rarely asks whether 66J11 is THE normal height nor on weighing 168 lbs. does this person ask 
whether 168 is THE normal weight. Insofar as our body size 
is concerned we have accepted the fact that normal or ave- 
rage means normal or average within a range. A 23-yr, old 
man may be 5f4M or 5r3Mi he may be 61 or 6'1M, and there is 
no question about his height being a normal height. This 
same type of thinking must be associated with the pulse 
rate; as a matter of fact, very much more so, for, although 
the normal pulse rate ranges from say 60 to 90, it is per- 
fectly normal for a particular individual's pulse to range 
from 55 to 90 and higher, A man at rest or immediately af- 
ter waking in the morning, who has a pulse rate of 55, has 
a normal pulse. On Jumping out of bed and doing a few brisk 
setting-up exercises, it will be normal for his pulse to 
climb to 95> perhaps even 110, This concept of the normali- 
ty of variation, or the range of normal, is a very funda- 
mental one in all biological problems, and understanding it 
gives the student of physiology a real working tool. 
cohtRol 
(MTRIHSIC COHTfdt 
This variation in pulse rate is regulated by two fac- 
tors* The extrinsic nerve supply is composed of 
nerve, whidh tends to depress the heart rate, and the three 
cardiac nerves descending from the sympathetic chain in the 
neck. Stimulation of the cardiac nerves causes the heart 
rate to increase. The intrinsic nerve supply is composed 
of the sino-auricular node where the impulse, or exciting 
factor, arises. These impulses travel over the auricular 
muscle until they come to another structure, known as the 
A-V node (atrio-ventricular). This structure allows only a 
set number of impulses to go through it and down the bundle of (a communication system within the heart muscle), 
where the musculature of both ventricles are activated and 
ventricular contraction occurs. 
Each of these systems is independent of the other, but 
each one modifies the action of the other. If the extrinsic 
nerve supply is completely removed the heart will continue 
to beat with its independent rhythm. It is a result of im- 
pulses going to the brain from the carotid sinuses and from 
other sensory nerves from the skin, eyes, ears, etc,, and 
then to the heart from the brain through the extrinsic va- 
gus and sympathetic cardiac nerves which activate the dif- 
ferent pulse rates under various conditions. 
The blood supply for the heart, that is, the blood 
which nourishes the heart proper, is supplied via the two 
coronary arteries. These arteries arise in the aortic bulb 
and during cardiac diastole (relaxation) the openings are 
free and blood enters the arteries. During systole the car- 
diac muscle is contracted and the blood is forced into the 
cardiac sinus which opens into the right auricle. 
Now a word about pulse rates and blood pressure. An 
increase in pulse rate does not necessarily mean an in- 
crease in blood pressure, A rapid pulse may not be pushing 
as much blood out into the circulation as a slower rate 
with a more efficient stroke. The minute volume is the im- 
portant factor. The cardiac pudqp needs a sufficient volume 
of blood returning from the general circulation to allow it 
to contract properly. In shock-like states there is often 
found the very rapid, thready pulse, with a very low blood 
pressure. These rapid, ineffectual strokes of 120 a minute 
will not push out nearly as much blood as a slow efficient 
rate of 70 a minute. 
This condition is probably due to the fact that the 
heart is not receiving enough blood back from the periphe- 
ral circulation and consequently does not have a sufficient 
volume of blood to adequately fill the ventricles. There 
are other conditions in which the pulse rate is slow, but 
the blood pressure is still low and the person may be in 
shock. This is due to the fact that the stroke, or contrac- 
tion of the cardiac muscle: is too weak to push a sufficient 
volume of blood into the aorta. This is the type of cardiac 
response usually seen in anoxic shock. 
VJhile flying it is common to encounter conditions in 
which the heart must use more energy to pump- faster; the 
heart itself requires more oxygon and food. The nervous 
system must be able to transmit the initiating impulses ihen these conditions are met. The tone of the heart muscle must 
be normal to insure an adequate pressure within the vascu- 
lar system. 
It is apparent now why flying personnel must have good 
hearts. The changes which must be met by this organ in high 
altitude flying require a strong heart muscle to withstand 
the anoxia, and the general physical condition must be good 
to insure an adequate venous return to the right heart, A 
diseased heart muscle cannot be expected to respond ade- 
quately to conditions of anoxia under which perfectly ncmnl 
people fail. The nervous mechanism of the heart must bo 
normal to enable the cardiac muscle to receive the correct 
number of impulses in the right rhythm so that compensation 
may take place. The coronary arteries must be normal so 
that the aviator*s heart receives an adequate supply of ox- 
ygen. 
Relaxation 
CONTRACTION 
15 RESPIRATION PART ONE 
We have seen that the cardiovascular system has the 
important job of carrying supplies through the body. One 
substance essential for living is oxygen, and oxygen is car- 
ried throughout the body by the blood stream. As important 
as is the heart in circulating oxygen is the apparatus for 
introducing oxygen into the blood. That apparatus is the 
respiratory system. 
In order to fully understand the reasons for the need 
of accessory oxygen in flying at altitudes above the criti- 
cal level a knowledge of the physics of the atmosphere that 
surrounds us, as well as a knowledge of the physiology of 
respiration, is required. With this knowledge we can suc- 
cessfully tie together the chain of events in logical se- 
quence and arrive at an understanding. 
As you follow your daily tasks you are breathing con- 
tinuously, without any conscious effort. As seen by an ob- 
server it consists of the inhalation and exhalation of air 
through your nose and the respiratory passages, a process 
which occurs from twelve to sixteen times per minute. This, 
however, is only the first phase of respiration, known as 
external respiration. The second phase, known as internal 
respiration, consists of the gaseous interchange of oxygen, 
carbon dioxide# and water vapor between the lungs, blood 
stream, and tissue cells. 
The nose, pharynx, larynx, trachea, the 
large bronchi,and bronchioles serve as a pi- 
ping system from the outside to the lungs, 
through which the atmosphere is brought to 
the lung tissue. The main function of the 
nose with its projecting turbinates is to 
furnish a large surface over which incoming 
air can be warmed to avoid irritation fma 
cold and to remove gross Impurities, The im- 
purities are removed by hairs and mucous 
membrane in the nasal vestibule. 
Atm rmm 
thif 
LAM**, Tt 
fMmmtumi, 
7h Tm AtfMHgy 
TM* 
******f wm 
*rm r*f h—o. 
The trachea and large bronchi are part- 
ly surrounded by cartilagenous rings which 
make them semi-rigid. As the bronchi branch into bronchi- 
oles, this rigidity decreases until we reach the smaller 
bronchioles which are quite elastic. The entire respirato- 
ry tract is lined with ciliated epithelium. These hair cells have a continuous, sweeping, notion toward the nasal 
end of the tract, and they tend to sweep inpurities into 
the trachea, where they may be coughed up and ejected. The 
terminal divisions of the respiratory system are the alveo- 
li, or air sacs. These are microscopic air sacs which open , 
from the bronchioles. They are approximately l/25 inch in 
diameter and there are several million per lung. 
The total surface area of all the alveoli in the 
human lung has been estimated to be between 700 
and 800 square feet, roughly the area of a ten- 
nis court. The walls of the alveoli are moist 
and extremely thin,about 1/50,000 inch in thick- 
ness. The alveoli are surrounded individually 
by a plexus of capillaries, so that the only ac- 
tual separation between the air in the alveoli 
and the blood is the wall of the alveolus and the wall of 
the capillary. It is at this point that the exchange of 
gases between the body and its environment takes place. 
This gaseous exchange takes place across these two nestranos 
but they are so small they offer no material resistance. 
ALVSoLl 
o* 
The lungs lie in the right and left thoracic cavity. 
They are enclosed in a membrane known as the visceral pleu- 
ra, which is continuous with a similar membrane, the parie- 
tal pleura, which lines the walls of the thoracic cavity. 
Below the lungs lies a muscular membrane separating the 
thoracic cavity from the abdominal cavity, the diaphragm. 
The diaphragm is capable of decreasing or increasing the 
size of the thoracic .cavity by pushing up or down. The size 
of the thoracic cavity may also be changed by the elevation 
or depression of the ribs. 
t*spi*h r*o* 
f* HAL tno* Breathing occurs when the thoracic cavity is increased 
in size with the combined elevation of the ribs by the in- 
tercostal muscles, depression of the diaphragm, and relaxa- 
tion of the abdominal musculature* When this happens, the 
parietal and visceral pleura are separated, creating space 
with a negative pressure. Since nature will not tolerate a 
vacuum, it attempts to obliterate this space by drawing air 
into the respiratory passages and expanding the lungs. Re- 
laxation of the muscles involved results in depression of 
the ribs, elevation of the diaphragm. This, with the con- 
traction of the abdominal muscles, decreases the size of 
the thoracic cavity and forces the inhaled air out of the 
lungs. The average individual inhales about 500 ccs., or 
one pint, of air with each inspiration. This is known as 
The tidal aiij when multiplied by the number of breaths 
taken per minute, will give the volume of air inhaled and 
exhaled per minute. This is called the ventilation rate. 
and equals 6 to 8 liters per minute in the average man. The 
volume of air which can be oxhaled from the lungs after the 
deepest possible inhalation is termed vital capacity aid re- 
presents the maximum capacity to which the tidal volume may 
be increased. 
The human body is made up of millions of tissue cells. 
Every tissue in the body has its individual cellular compo- 
nent, which, while it differs in appearance, fundamentally 
is doing the same thing that all other cells are doing, oxi- 
dizing the basic foods, fats, proteins, and carbohydrates, 
developing beat and energy and creating carbon dioxide and 
water vapor as waste gases. Thus in order to keep these 
cells living it is necessary to keep them supplied continu- 
ously with oxygen, since the body has no arrangement for 
the storage of oxygen, and to relieve them of the waste ga- 
ses formed. This is internal respiration. RESPIRATION- PART TWO 
Internal and external respiration have to do with the 
exchange of gases from the outside of the body, through the 
lung, into the blood (external and from the blood into the 
tissues (internal). Since the gases, in the course of this 
exchange, conform to the physical laws for the behavior of 
gases in genera], let us review certain definitions and laws 
which apply: diffusion, Graham* s Law, solubility of gases, 
and Dalton*s Law of partial pressures. 
Diffusion is the tendency of a gas to distribute it- 
self uniformly within a confined space. The diffusion of 
gases is not influenced by the existence of semi-permeable 
membrane. Semi-permeable membranes are membranes which per- 
mit the flow of gases but restrain other particles. The 
body is composed of literally millions of such membranes, 
in fact, each cell wall is a semi-permeable membrane. The 
lining of the lung, that is the alveolar wall, is a semi- 
permeable membrane. The diffusion of the various gase a 
within the lung across this membrane, accounts for the pas- 
sage of oxygen, nitrogen, and carbon dioxide from the at- 
mosphere into the blood stream, and conversely. 
The amount of diffusion depends upon the relationship 
of concentrations on each side of the membrane. The natu- 
ral tendency is for the diffusing gases to balance them* 
selves on either side of the membrane and for the gases to 
move from the area of higher concentration to that of les- 
ser concentration. Rates of diffusion of gases are also 
dependent upon the density of the gases, namely, according 
to Graham* s Law, "The relative rate of diffusion of gases 
under the same conditions ore inversely proportional to the 
square roots of the density of those gases". From this wo 
see the importance of the phenomena of diffusion in the ex- 
change of gases in the body. Since the diffusion is depen- 
dent upon both the pressure and the density, the partial 
pressure of a gas, and, therefore, the law of partial pres- 
sure which demonstrates its beha- 
vior, is also very pertinent. 
In a mixture of gases the law 
of partial pressure obtains, that 
is, each gas exerts a pressure in- 
dependent of the others and equal to that which it would 
exert if it alone were confined to that volume. For example 
the total pressure of air at sea level is 760 mms« of mer- cury. The partial pres- 
sure of oxygerv a gas oc- 
cupying 20,6 of the air, 
is 152. At an altitude 
of 18 000 ft., where the 
atmospheric, or total 
pressure is only 380 mms., the partial pressure of oxygen 
(2056) is 76 mms. (or 20£ of 3S0). The partial pressure is 
important in our consideration of gaseous exchange in the 
body because the rate of diffusion of a gas, and the solu- 
tion of gas (in a solvent) are proportional, among other 
things, to the partial pressure of that gas. This impor- 
tance can be seen when the partial pressures of gas in the 
lung are examined. 
(The discrepancy between calculated partial pressures 
here and those given in the table on page 9 are due to the 
use of 2056 as oxygen percentage, for the sake of simplifi- 
cation, rather than 20.93% which is more accurate and used 
in the table.) 
The gases involved in respira- 
tion are oxygen, nitrogen, water 
vapor, and carbon dioxide, and the 
partial pressures of these gases as 
they enter the lungs are: approxi- 
mately, nitrogen 594, oxygen 149, 
water vapor 47 (water vapor tension 
of saturated air at 98.6® F.), and 
carbon dioxide 0,3 mms. of Hg. How- 
ever, on being drawn into the lung, 
where this atmospheric air mixes 
with tho alveolar,air, the partial 
pressures are altered and the 
gen has a pressure of 100 mms,, the 
carbon dioxide 40, the nitrogen and 
water vapor remaining the same. 
The water vapor in the alveo - 
li exerts a constant pressure re- 
gardless of altitude since this 
pressue is due to the fact that 
the alveolar air is saturated with 
water and the aqueous tension is 
dependent upon the temperature and 
the temperature remains 98.6° (body 
temperature). The carbon dioxide 
pressure also remains constant 
in a small rangq from 36 to 40 mms.. and is due to the continuous diffusion of carbon dioxide 
from the venous blood into the alveolus. The relative con- 
stancy of these two factors plays an important role in cal- 
culating alveolar partial pressures at high altitudes when 
breathing pure oxygen. This will be seen later. 
The chart shows partial pressures of the gases of the 
atmosphere and the partial pressures of the alveolar gasea 
When these pressures are examined in percentages, one sees 
that the nitrogen remains roughly the same but that there 
is a marked difference in the percentage of oxygen and 
carbon dioxide existing in the atmosphere and in the alve- 
olus. The atmosphere contains roughly 20£ oxygen and 0«3£ 
carbon dioxide, whereas the alveolus contains 13% oxygen 
and 3% carbon dioxide. This is the condition which exists 
at sea level. 
APPROXIMATE PARTIAL PRESSURES AT SEA LEVEL 
Atmosphere 
Alveolus 
Nitrogen 
80* 
80* 
Oxygen 
20 
15 
Carbon Dioxide 0,03 
5 
Water 
Varies 
47 nuns. 
The solubility of a gas is the ratio of concentration 
of the gas in the solution to the concentration of the gas 
above the solution. The solubility is dependent upon a 
number of factors: (l) the pressure of the gas, (2; the 
temperature of the gas, (3) the solvent, (4) the tenjpera- 
ture of the solvent, &nd(5) the solid substances contained 
within the solvent. In other words, the greater the pres- 
sure, the cooler the gas and the solvent and the freer the 
solvent is from impurity the greater the amount of gas 
which will go into solution. 
The mechanism by which the gases enters the blood 
stream And by which they are transported throughout the 
body can be described as follows: First, the laws of phy- 
sical diffusion govern the passage of the gases through 
the semi-permeable membranes (alveolar wall and capillary 
wall), and second, the transport of the gases by the blood 
involves mechanisms other than physical solution, namely, 
chemical combinations. 
Were the transport of the respiratory gases accom- 
plished by the physical solution of the gases in the fluid component of the blood, the amount of oxygen carried in 100 
ccs. of blood would be 0.2 ccs., and th* amount of carbon 
dioxide would be 0.3 ccs. Actually, et sea level pressures 
18 to 20 ccs. of oxygen are carried for each 100 ccs. of 
blood, and 40 to 50 ccs. of carbon dioxide. This remark- 
able increased ability for carrying of oxygen and carbon 
dioxide is due to the loose chemical combination of the ox- 
ygen with a substance which exists in the red blood cells, 
called hemoglobin, and in the case of carbon dioxide by the 
combination of carbon dioxide in the form of bicarbonate 
ions. 
Reference to the above oxygon dissociation curve will 
aid in understanding tha factors involved in the oxygen 
transport of the blood. 
(1) The chemical combination of oxygen and hemoglobin 
is a loose and reversible oik* that is, it combines with 
ease and it dissociates with eaaa. 
(2) The chemical combination of oxygen and hemoglobin 
is related to the pressure of oxygon (partial pressure of 
oxygen). Incidentally, this relationship is of particular 
pertinence in studying altitude physiology. Notice in the 
curve that the percent of oxygen saturation (vertical axis) 
increases with the increase of oxygen pressure (horizontal 
axis). 
(3) The affinity of hemoglobin for oxygen is high un- 
der high partial pressures and low under low partial pres- 
sures. This is evidenced in the S-shape of the curve and 
accounts for the ease with which hemoglobin takes on oxygen 
in the capillaries of the lung where the partial pressure 
is great, and the ease with which hemoglobin gives off oxy- gen from the capillaries to the body tissues where the 
partial pressure of oxygen is low. 
(4) The hydrogen ion concentration (pH), which moans 
the acidity or alkalinity, affects the oxygen-carrying ca- 
pacity of the hemoglobin. The blood maintains a very de- 
finite range of pH, but varies within that range. These 
variations are due chiefly to the carbon dioxide content 
of tho blood, which, in turn, is related to respiration. 
When one breathes deeply, the partial pressure of oarbon 
dioxide is increased and the blood becomes slightly more 
acid. When a substance is neutral, that is, neither acid 
nor alkaline, we denote the fact by stating its pH as 7.0, 
Maximum alkalinity is denoted by a pH of 14.0, and maximum 
acidity by a pH of 1,0, The blood shifts from a pH of 7.2 
(slightly alkaline) to a pH of 7.6. The relationship of 
the pH to the oxygen-carrying capacity of hemoglobin is 
clearly siown in these curves. Note, for example, that at 
a partial pressure of oxygen Of 30 mms, of Hg. that the 
percentage of oxygen saturation of the blood is 45 when 
the pH is 7.2, 57 when the pH is 7.4, and 70 when the pH 
is 7.6. 
(5) There is a relationship between the transport of 
oxygen and carbon dioxide, namely, that the greater the 
concentration of oogrgeh the less Oarbon dioxide, and the 
greater the concentration of carbon dioxide the less oxy- 
gen, Since the carbon dioxide leaves the body from the 
alveolar capillaries of the lungs the arterial blood can 
carry a great deal of oxygen, and since the oxygen leaves 
the capillaries In the tissues the venous blood can carry 
a great deal of carbon dioxide. 
Let us examine the gas tensions and the gaseous ex- 
change involved in respiration from the inspiration of air 
to the passage of gases across the alveolar membrane thru 
the transport of gases to the tissues, and from the tis- 
sues, via the blood, back to the lung, to the expiration 
of air. 
When air is inhaled at sea level it has a total pres- 
sure of 760 mms, of Hg., and an oxygen partial pressure of 
152. As has been pointed out above, on being mixed in the 
lung, the composition of air alters, so that the partial 
pressure of oxygen, carbon dioxide, nitrogen, and water 
vapor arc 106, 40, 567, and 47, respectively. This can be 
calculated in the following manner. The total pressure is 
760 ibbs. Of the 760 mms., 47 mms. is water vapor. 
760 (T.P. - 47 (W.V.) • 713 ("Dry" Air) Vtwu* 
QlcoO 
bioooj 
The percentage composition of alveolar air, 
because of the dilution and because of the 
existence of high concentrations of carbon 
dioxide, now is nitrogen 80%, oxygen 15%, 
and carbon dioxide 5%, Therefore, to arrive 
at the partial pressure of oxygen within 
the alveolus wc takd the product of the to- 
tal dry air times the percentage composi- 
tion of oxygen, or 
713 
5bI ms. 
The oxygen pressure in the alveolus of 106 
ms. is greater than t he oxygen pressure or 
tension in the venous blood. The oxygen 
tension in the venous blood has been mea- 
sured and shewn to be 40 mms. Therefore, 
according to the physical laws, the oxygon 
from the alveolus /diffuses across the mem- 
brane of the alveolar wall and the capil- 
lary wall into’thp blood; that is, from a 
region of high partial pressure to one of 
low partial pressure. Because of the car- 
rying capacity of hemoglobin the blood be- 
comes saturated to 95% of its oxygen satu- 
ration, ifhich iresults in an oxygen tension 
of 100** yf 103 in the arterial blood. The 
with its high tension of ox- 
ygen moves throughout the body. On coming 
in contact with the cellular tissues where 
the oxygen tension has been reduced because 
of the utilization of oxygen in metabolic 
processes (foodstuff plus oxygen to heat, 
energy, carbon dioxide, and water), the 
oxygen diffuses from its region of higher tension (the blood) to the region qf lesser tension (the 
tissues). At the same time the existence of a low carbon 
dioxide tension in the arterial blood results in the pas- 
sage of carbon dioxide from the tissues into the blood. 
This blood returns to the heart (venous blood); therefore, 
has a relatively low tension of oxygen and a high tension 
of carbon dioxide. On reaching the lung the conditions are 
reversed by the passage of carbon dioxide into the alveoli 
and by passage of oxygen from the alveoli into the blood. 
(This cycle is shown in diagramatic form) 
At an altitude of 18 000 ft., where the total pres- 
sure of air is reduced to 380 mns,, the alveolar partial 
pressures are oxygen $0, carbon dioxide 40, nitrogen 243> 
and water vapor 47* These figures are arrived at as fol- 
lows: Total pressure at 18 000 ft, is 380 inns, of Hg. The 
water vapor in the lung exerts a pressure of 47 mas., and 
therefore, must be subtracted; 
380 rame. (T.P.) 
-47 mms. (w,V.) 
333 mns. ("Dry11 alveolar air) 
The percentage of oxygen in alveolar air is 15; therefore, 
to arrive at the partial pressure of oxygen in the lung at 
18 000 ft,, take 15* of 333; 
333 mas. 
mas. 
This partial pressure of oxygen is so low that the arterial 
oxygon saturation is only 75* of its capacity. This low 
saturation results in Considerable handicap to the indivi- 
dual because of inadequate oxygen for bodily processes, 
(This will be more adequately discussed under the heading 
of ’’Anoxia”) 
To overcome the effects of the low partial pressure 
of oxygen at 15 000 ft. and altitudes above, the simple ex- 
pedient of breathing pure oxygen is carried out. The cal- 
culation of alveolar partial pressures while breathing 100 
percent oxygen is as follows: 
Total Atmospheric Pressure at 18 000 ft. 380 mm,Hg. 
Total Oxygen Pressure at 18 000 ft. 380 
Alveolar Carbon Dioxide -40 
Alveolar Hater Vapor -47 
Oxygen Pressure breathing 100* 02 at 18 000 ft, 293 ma. 
Total Atmospheric Pressure at 34 000 ft. 190 mm.Hg. 
Total Oxygen Pressure at 34 000 ft, 190 
Alveolar Carbon Dioxide -40 
Alveolar Water Vapor -47 
Oxygen Pressure breathing 100* ©2 at 34 000 ft, 103 mm, 
♦ ' At an altitude of 30 000 ft. the alveolar gases have 
a partial pressure as follows: oxygen 138, carbon dioxide 
40, nitrogen 0, water vapor 47. At an altitude of 34 000 
ft. the oxygen partial pressure is 100, and at an altitude 
of 40 000 ft. it has dropped to 57. In the accompanying 
diagram, showing the percent saturation of arterial blood 
at altitudes up to 44 000 ft., one can compare conditions 
breathing air and breathing oxygen. The left side of the 
curve, which shows oxygen saturation of blood breathing 
air, shows that imminent collapse is reached between the 
altitudes of 16 000 and 21 000 ft., whereas by breathing 
pure oxygen, right side of curve, imminent collapse is not 
approached until 43 to 44 000 ft. is reached. The failure 
of pure oxygen to maintain life above 44 000 ft. is due to 
ftftC«*T Off APT**iAL «xY6*N <AfAC«lY 
5# •% 
•6% 
|M ScnMl 
tii inmidfut C^M* 
the fact that the partial pressure of oxygen at that alti- 
tude, even though it is pure oxygen without diluting nitro- 
gen, is too low. 
RELATION OF ALTITUDE TO ARTERIAL OXYGEN SATURATION & ANOXIA 
Atmospheric Air 
Sea Level 9556 
6 000 ft. 93-95* 
12 000 ft, 85-92* 
15 000 ft. 77-87* 
18 000 ft. 63-78* 
20 000 ft. Below 65* 
100$ Oxygen 
Normal 37 000 ft. 
Lowest Normal 37 000 ft* 
Slight Handicap 40 000 ft. 
Narked Handicap 41 300 ft. 
Serious Handicap 42 500 ft. 
Imminent Collapse 43 500 ft. 
From our discussion of the anatomy of respiration it 
is apparent that the ventilation rate, or volume of air 
inhaled per minute, can be changed by either increasing 
the number of breaths taken per minute, or by increasing 
the tidal volume of each breath. The ventilation rate and 
the tidal volume are adjusted to meet the requirements of 
the body under most conditions on the ground. In order to 
understand the limitations of these adjustments, however. we must have an understanding of the mechanisms by which 
they are controlled. 
There is a voluntary and an involuntary control of 
respiration. By conscious effort it is possible to in- 
crease or decrease the rate of respiration for a short 
time. This, of course, upsets the equilibrium which is 
maintained by the involuntary mechanism. As soon as this 
voluntary control is relaxed the involuntary control mech- 
anism takes over and automatically restores the normal e- 
quilibrium. For example, should an individual, at rest, 
hyperventilate, that is, breathe faster and deeper than u- 
sual, the normal carbon dioxide content of the air sacs is 
reduced below 5*5£ and the oxygen content is raised above 
14.5£. As soon as the voluntary control is relaxed, the 
involuntary control slows down the breathing rate until 
the normal equilibrium is restored. 
Involuntary control is exercised by the brain. At 
the base of the posterior brain there is a region known as 
the respiratory center, which controls the nerve stimuli 
that activate the muscles of the chest and diaphragm. The 
respiratory center can control the rate and depth of res- 
piration by altering the rate and intensity of nervous imr- 
pulsos. Alterations in the nerve impulses are produced in 
two ways: (l) By changes in the character of nerve impul- 
ses arriving at the respiratory center from various con- 
trol stations lying outside of the brain; (2) By changes 
in the chemical composition of the blood flowing through 
the respiratory center. This is the most influential fac- 
tor of the two. The center is particularly sensitive to 
the carbon dioxide content of the blood. If the car b on 
dioxide content is increased, the respiratory center res- 
ponds by increasing the ventilation rate until the carbon 
dioxide content returns to normal. This adjustment is 
quite delicate and under ordinary conditions at rest the 
carbon dioxide content of the blood is maintained within 
very narrow limits. 
This effect of carbon dioxide, that is, its stimula- 
tion of the respiratory center, is utilised in life-saving 
equipment. Inhalators usually have tanks with mixtures of 
9556 oxygen and % carbon dioxide (or 9356 oxygen and 
bon dioxide), so that these gas mixtures can be given to 
people who have become asphixiated or who have difficulty 
in breathing. The carbon dioxide stimulates respiration, 
the oxygen supplies adequate partial pressure of oxygen 
for bodily function. AN O X I A 
In discussing anoxia there are three terms which are 
frequently met* the meaning of which the student should 
know. Anoxia is a term used to describe oxygen lack in the 
body. Hypoxia is a synonymous term. Anoxemia means an 
oxygen lack in the blood. 
Anoxia usually is classified as follows: (a) Anoxic, 
(b) Anemic, (c) Stagnant, and (d) Histotoxit. 
Anoxic Anoxia is that type in which 
there is a lack ot oxygen in the arterial 
blood; that is, the oxygen tension is low 
and, consequently, the hemoglobin is not 
saturated with oxygen. This type can be 
a result of several conditions. (l) Low 
tension of oxygen in the inspired air, 
such as occurs at high altitudes, breath- 
ing inert gasee, or anesthetic agents, 
(2) Abnormal conditions within the lungs, 
such as fluid in the alveoli from cardiac 
failure, edema from irritation caused by 
irritant vapors, mechanical obstruction 
of the air passages (diphtheria, foreign 
bodies, tumors), pneumonia, collapse of the lung following 
perforating injuries, advanced emphysema, (3) Shallow res- 
piratory movements from any causq apnea following voluntary 
forced respiration, overdistention of the gut from intesti- 
nal gases. (4) Malformations of the heart or blood vessels 
("Blue Babies"). 
iO¥ Oa 
/H 
'too* W 
CC 
The reduction of the arterial tension of oxygen is more 
serious than the lack of oxygen saturation. The velocity 
of oxidative processes has been determined by experimental 
methods to be proportional to the partial pressure of oxy- 
gen, Also, the increased respirations induced by this low- 
ered oxygen pressure wash out the carbon dioxide of the ar- 
terial blood and because of this fact the dissociation of 
oxyhemoglobin is much reduced. In fact, the tissues of the 
body are hampered in three ways in this type of anoxia: The 
rate of oxidation is diminished because of the lowered par- 
tial pressure of oxygen in the blood; there is less oxygen 
in the blood than normal; the low carbon dioxide pressure 
hampers the dissociation of oxyhemoglobin. This is the type 
of anoxia in which we are most interested in aviation hy- 
giene, because it is this type which our flight personnel 
will have to combat and which wc are attempting to help than 
overcome. Anemic Anoxia, usually is not so seri- 
ous* ’ The hemoglobin that is present is 
normal and there is no interference with 
tissue oxidation. There is not enough a- 
vailable hemoglobin to supply the needs of 
the tissues of the body under abnormal con- 
ditions. Unless it is far advanced, the 
patient, as long as he is quiet, experien- 
ces little or no discomfort. The principal 
causes of this type of anoxia are (1) he- 
morrhage, either acute or chronic, (2) a- 
nemia, primary or secondary, and (3) car- 
bon monoxide poisoning. 
Ct*k are 
deduced n 
* 
Stagnant Anoxia is due to a slowing 
down of the circulatory rate. This con- 
dition is usually local* but under cer- 
tain conditions may affect the entire bo- 
dy. The blood is normally saturated with 
oxygen and the tension is normal* Anoxia 
is developed because the slower circula- 
tory rate allows the blood to give up a 
greater percentage of its oxygen and some 
tissues do not receive a sufficient sup- 
ply because the arterial blood is starved 
by the time it reached the particular 
tissue. Any condition which improves the 
circulation will help relieve the anoxic state. The 
ing conditions may produce this type of anoxia; (1) Failure 
of the circulation (advanced heart disease), (2) impairment 
of venous return, and (3) shock. 
fafk of* 
bJ»ot\ -fiom 
fdoced 
Histotoxic Anoxia is a condition in 
which the cells are not able to utilize 
the oxygon which is brought to them. The 
tension and the saturation may be quite 
normal,This type of reaction may be caused 
by cyanides, alcohol, or any substance 
which interferes with the cellular respi- 
ration. Most of these substances inter- 
fere with the action of the enzymes which 
enable the cell to use the oxygen brought 
by the blood. 
S/emc» dor 
0% transit 
c% reduced. 
Ay 
af T&oyufn 
In addition to the above classifica- 
tions, anoxia may also be classified as follows: 
(A) Fulminating Anoxia. This is rapidly induced by 
sudden ascents to 28 000 feet without or breathing 
high concentrations of inert gases, as sometimes happens in our dirigible crashes when personnel are caught in high 
concentrations of escaping helium gas. Unconsciousness may 
develop in 45 to 90 seconds. This type of anoxia resembles 
asphyxia, but asphyxia is not anoxia. 
(B) Acute Anoxia. The difference between this type 
and the above is that the anoxia is not developed as quick* 
ly and is not as severe. This is the type of anoxia which 
you see every day in the low pressure chamber when the sub- 
jects are at 18 000 feet without oxygen. While every organ 
in the body is presumably affected in this type of anoxia, 
the central nervous system, the respiratory, the circulato- 
ry systems appear to be affected the most. The nature of 
the effect of this type of anoxia will be studied in detail 
later. 
(C) Chronic Anoxia. This is a condition which results 
from long exposure to high altitudes, and even in the ac- 
climatized individual there is a dyspnea on exertion. The 
symptomotology of this condition may be stated briefly as 
principally fatigue. Fatigue develops much faster than at 
sea level and recovery is much slower. This condition may 
also produce degenerative changes in some organs. We will 
examine this subject later in discussing mountain sickness. 
There are several variable factors at high altitudes 
which may affect the physiology of aviation personnel. They 
have been listed as follows: 
1. Lowered atmospheric pressure; 
2. Lowered partial pressure of ox ygen; 
3. Temperature; 
4* Humidity; 
5. Increased intensity of sunshine; 
6. Electrical conditions; 
7. Vibration. 
By far the most important of these conditions is the low- 
ered partial pressure of oxygen. It is the effect of this 
condition that we now study in detail and examine its ef- 
fect on the different organs and systems of the body. 
The effect of anoxia on the blood has been studied for 
many years and by many different investigators and from 
this mass of work the following conclusions may be drawn. 
In acute anoxia, such as we are dealing with, there is some 
evidence that the number of red blood colls is increased 
rather rapidly in most subjects, in the matter of an hour 
or so, and probably as a result of contraction of the spleen 
forcing a larger number of the cells into the blood stream. The effect of anoxia on the heart and circulation in 
acute anoxia results in the following changes in the blood 
vascular system. The pulse rate increases, as does the 
contraction of the heart, until the percentage composition 
of oxygen in the alveolar air falls to below 9%,after this 
critical level the rate may remain stationary or decrease, 
but the minute volume output of the heart rapidly falls 
until that time when the anoxia affects the heart muscle 
and the rate falls rapidly and a circulatory collapse oc- 
curs. There is no real evidence that the blood pressure 
changes to a significant degree. In cardiac failure one 
explanation is that the intramuscular pressure is respon- 
sible for the maintenance of venous pressure and conse- 
quently the venous return to the right side of the heart. 
In the circulatory collapse, according to this theory, the 
intramuscular pressure falls firsts followed by the failure 
of the venous return and consequent deficient filling of 
the heart and decrease in the amount of blood the heart is 
able to put into circulation. This is then followed by a 
fall in blood pressure, and the fast, thready pulse which 
we are so accustomed to seeing in shock. The pallor and 
sweating are a result of the contraction of the peripheral 
arterioles in an attempt to return the peripheral blood to 
the circulation. 
The respiratory system is profoundly affected by low- 
ered partial pressure of oxygen. There is a fall in the 
alveolar carbon dioxide pressure, which is due to the in- 
creased rate and depth of the respiratory movements. The 
increased rate and depth of respiratory excursions washes 
the carbon dioxide out of the alveolar air. This results 
in a fail of U*2 mms. Hg. of carbon dioxide pressure for 
each fall of 100 mms. Hg. of barometric pressure, (This 
is disputed by some workers) 
In acute anoxia there is an increase in the rate, the 
depth, and the minute volume of the respiration. The res- 
piratory center is evidently one of the most sensitive a- 
reas to the lowered oxygen partial pressure. It is be- 
lieved by some workers that with the decrease in oxygen 
the respiratory cerfcer becomes more sensitive to the car- 
bon dioxide, which would explain the increased rate and 
depth of respiration. After anoxia has progressed to the 
point where the cells of the respiratory center have a 
markedly reduced excitability respiration may cease. Other 
effects on the respiratory system in acute anoxia are a 
slight depression of the respiration while the body reco- 
vers from the loss of carbon dioxide and while the bicar- 
bonate is being reformed in the blood. Some subjects, when in the stage of acute anoxia, show a change in the pattern 
of respiration, a periodic breathing which resembles the 
well-known Chevne-Stokes Syndrome. The vital capacity is 
decreased approximately 1C# 
at an altitude of 15 000 ft. 
This is probably due to the 
dilatation of the alveolar blood vessels. 
Another system which alters its function during anoxia 
is the central nervous system. Nervous tissue is the least 
capable of withstanding oxygen want. In anoxic anoxia the 
blood vessels which supply the brain dilate early, but be- 
cause of the lowered oxygen pressure the brain has a defi- 
cient oxygen supply. At a simulated altitude of 26 000 ft, 
experimental studies have shown cortical cell changes(cells 
of the cortex of the cerebrum). Some of these changes may 
be irrevocable. Studies of the survival of nervous tissue 
completely deprived of oxjgon, even for a matter of minutes, 
show the pyramidal cells of the cerebral cortex are most 
sensitive, the cerebellar cells next, and the medullary cen- 
ters and spinal cord following, in that order. 
The spinal fluid pressure is increased, as is the in- 
tracranial pressure. The mechanism for producing this pres- 
sure is not known, but may be due to the increased perinea* 
bility of the capillary wails. 
The entire nervous system is affected in anoxia, the 
finer judgments and discriminations are lost firsl* followed 
by a train of events, such as increased reaction time, loss 
of initiative, and slowness of neuromuscular coordination. 
The after-effects of anoxia are headache, fatlgie, and slow 
recovery of finer judgment sense. The other organs of the 
body are also affected, but the changes just examined be- 
come so profound that death would result before secondary 
changes* 
The type of anoxic anoxia which is most common in avi- 
ation iflt of course, that which is associated with altitude. 
The decreasing atmospheric pressure with resultant decreas- 
ing partial pressure of oxygen in the inspired air results 
in a lowered oxygen tension in the arterial blood. Obvious- 
ly the degree of anoxia is directly related with the degree 
of lowered oxygen tension, which in turn is related to the 
altitude. At an altitude of 10 000 ft. there is a moderate 
or mild degree of anoxia which has no telltale effects for 
the first four or five hours. There are, however, definite 
subclinical effects and the finer or higher brain functions 
are dulled. With increase in altitude there is a more 
marked anoxia of such a degree that from 12 to 1556 of heal- thy adult personnel will faint or become unconscious with- 
in a half-hour at 18 000 ft, (The drawing demonstrates re- 
lative degrees of anoxia at various altitudes) 
As far as aviation personnel is concerned anoxia, even 
though it be of low grade and not severe enough to cause 
unconsciousness, is a very important condition. Low grade 
anoxia will affect the nervous system causing complete lack 
of critical judgment, a lack of motor coordination, and a 
false feeling of well-being. 
Overcoming the effects of anoxia forms the basis of a 
very valuable practice in aviation medic namely the uti- 
lization and training in the use of accessory oxygen equip- 
ment at altitudes over 10 000 ft. The natural lowered par- 
tial pressure of oxygen: is increased art 1 ArielJLy .by the use 
of such oxygen equipment. Thus by the use of accessory oxy- 
gen equipment aviation personnel can go from sea level to 
high altitudes day in and day out without any deleterious 
effects of anoxia. 
Individuals who live at moderately high altitudes ad- 
just themselves to their new environmental conditions. Du- 
ring that acclimitization to high altitudes the following 
events have been shown to occur: (l) An increase in total 
ventilation of the lungs due to stimulation of the respira- 
tory center (reflexes)j (2) Fall in carbon dioxide alveo- 
lar tension and rise in oxygen pressure; (3) Increase blood 
alkalinity, which is controlled to a reasonable degree by 
increased alkali excretion by the kidneys; (4) An in- 
creased number of red blood cells first by contraction of 
the spleen and later by stimulation of the redbone marrow; 
(5) An increase of hemoglobin in percentage and total a- 
mount; (6) An acceleration of the heart rate and an in- 
crease in cardiac output. 
There is some evidence that other changes occur, but 
the above are more or less definite. The repeated ascent 
of aviators to high altitudes does not result in acclimiti- 
zation. The changes occur slowly in people who live conti- 
nuously for a period of several days, weeks, or months un- 
der conditions of lowered partial pressure of oxygen. 
The importance of anoxia in aviation is so great that 
it is worth our while to reiterate salient points in the a- 
bove discussion. At the same time we will correlate the 
Bureau of Aeronautics Technical Order 43-40 with the symp- 
toms of anoxia at various altitudes. The Technical Order states that in all eases of flight 
over 15 000 ft., regardless of duration, accessory oxygen 
should be used. At an altitude of 15 000 ft* the blood sa- 
turation ranges from 77 to 87$. Within this range one finds 
considerable handicap in performance of any physical or 
mental activity. Headache, slight dizziness, a alight feel- 
ing of nausea, sluggishness, and a general feeling of hea- 
viness may be present; vision is slightly dinned, and a 
feeling of confusion may exist* The individual is partial- 
ly cyanotic; that is, nails, lips, and ear lobes may range 
from a light blue to a deep purple. As is true in all de- 
grees of anoxia, judgment is impaired* 
Above 15 000 ft., symptoms of anoxia persist and most 
of them are intensified; the vision is further dimmed and 
the cyanosis is increased. The general feeling, however, 
may be altered from that of weakness and sluggishness to a 
feeling of well-being and much akin to that associa- 
ted with certain stages of intoxication. Progressive in- 
crease in anoxia results of Course in severe taxing of the 
body, with an increasingly greater degree of malfunction, 
weakness, stupor, coma, and death* 
The Technical Order states that Navy personnel flying 
at an altitude of 12 000 ft* for two hours or more should 
use accessory oxygen* At an altitude of 12 000 ft, the ar- 
terial oxygen saturation ranges from 84 to 92$. There is 
appreciable handicap associated with oxygen saturation of 
only 64$ and since the effects of anoxia are accumulative 
it is clear that prolonged stay at a moderate altitude of 
12 (XX) ft. can have definite deleterious effects. The symp- 
toms associated with anoxia at this altitude £r a prolonged 
time are similar to those at 15 000 ft. The onset, however, 
is much more insidious and the decrease of critical judg- 
ment the more important effect. 
The Technical Order further state's that for stays at 
10 000 ft. of four hours or longer oxygen should be used. 
The situation here is similar to that at 12 000 ft*, except 
that since the altitude is slightly less a greater period 
of time for the accumulation of anoxic symptoms is necessa- 
ry. An important, recently recognized condition associated 
with prolonged flying at 9 to 10 000 ft. is the chronic low 
grade anoxia. Flying personnel who experience long missions 
at an altitude of 8 700 ft. find themselves extremely fa- 
tigued, irritable, suffering from insomnia, loss of appe- 
tite, and a general insidious weakness. This picture does 
not present itself when personnel use oxygen on prolonged 
moderate altitude flights, since by using oxygen the accu- mulative effects of this low grade, undectable anoxia are 
prevented. 
A particularly important effect of anoxia, even very 
low grade, is the decrease of night vision. This is cdie- 
cussed later. AEROEMBOU SM 
Aeroembolism is a disease produced as the result of 
subjecting the body to & rapid decrease of atmospheric 
pressure (decompression)> as in the course of an aircraft 
flight to very high altitudes. The condition is assumed 
to be due to the formation of nitrogen bubbles in the body 
tissues and fluids. 
Aeroembolism is distinguished from divers* bends 
(Caisson*s Disease) by the fact that it occurs from the 
decompression below one atmosphere of pressure, while di- 
vers* bends occur from decompression below two or three 
atmospheres. 
In discussing the cause of this condition it is help- 
ful to use an analogy. Almost everyone is acquainted with 
the machine that makes the common soda water in soda foun- 
tains, It consists essentially of a cylinder with piston, 
ordinary water, and a tank of compressed carbon dioxide. 
Water is put in the bottom 
of the cylinder and some of 
the carbon dioxide is allowed 
to flow into the space above 
the water. The piston is 
then depressed, and with the 
increase in pressure the 
carbon dioxide dissolves in 
the water. As long as this 
pressure is maintained, the 
carbon dioxide will stay in 
solution. However, if the 
pressure is decreased, either by lifting the piston or by 
letting the soda water flow into the outside air, the car- 
bon dioxide comes out of solution. This release of pres- 
sure is what accounts for the formation of bubbles and the 
foaming up of carbonated drinks when the bottle cap is re- 
moved. Now, how does this apply to the human body? 
The human being lives constantly in an atmosphere 
made up of S0% nitrogen and 20% oxygen at a total atmos- 
pheric pressure of about 15 pounds per square inc|i. Using 
our example above, we may compare the human oody with the 
water in the bottom of the cylinder and replace the carbon 
dioxide with the nitrogen and oxygen of the atmosphere. 
The "piston** (atmosphere) is set to exert 15 pounds of 
pressure per square inch. Under this pressure a certain amount of nitrogen and oxygen Is dissolved 
in the human tissues in a manner similar to 
the solution of carbon dioxide in mater. 
Since the body uses the oxygen in metabolic 
processes there is little of this gas exis- 
ting in the free and uncombined form* 
Insofar as the body is concerned, ni- 
trogen is an inert gas and exists in the 
dissolved, uncoabined form. As the body is 
taken to altitudes where the absolute pressure of the at- 
mosphere is decreased, or, as in our analogy, the piston is 
raised, the nitrogen comes out of solution from the body 
tissues and fluids in the form of nitrogen bubbles. (Thus, 
at sea level pressure the tissues of the body are always 
saturated with atmospheric nitrogen.} It is of interest 
that nitrogen is more soluble in fats and oils than in wa- 
ter, and, likewise, in the body the fats dissolve five to 
six times as much nitrogen per unit of mass as does the 
blood itself. 
The following is the sequence of events in aeroembo- 
lism. During ascent in aircraft, or in any other situation 
in which the atmospheric pressure is decreased, the partial 
pressure of the body nitrogen is greater than the partial 
pressure of the alveolar nitrogen. The nitrogen from the 
blood diffuses into the alveoli of the lungs, the nitrogen 
of the tissues enters the blood stream, and thonce into the 
lung. Thus, the body tends to rid itself of its excess 
(expanded) nitrogen. If the ascent is slow, and the nitro- 
gen in the body can be eliminated through the lungs as fast 
as it comes out of solution, no unusual symptoms occur. If, 
however, the pressure is decreased rapidly to at least one- 
half the original pressure, the nitrogen gas will come out 
of solution with such relative rapidity that bubbles will 
form in the tissues, blood, and body fluids. The most like- 
ly site for bubble formation is body tissue, which has high 
fat content and meagre capillary circulation. Wien bubbles 
become largo enough they block off capillaries, which cau- 
ses a decreased local blood supply. This blocking of blood 
circulation interferes with the normal functioning of the 
local parts, and provokes various symptoms. 
The symptoms of aeroembolism are conveniently grouped 
according to the affected site, as follows: 
1. Skin and mucous membranes 
2. Bones and muscles 
3. Respiratory system 
4. Semicircular canals 
5* Central nervous system The akin and cmcous membrane symptoms are popularly 
known as ,fThe Itch". These symptoms may be classed as pa- 
raesthesia (or false sensation), and presumably are caused 
by collections of nitrogen bubbles beneath the skin which 
irritate the sensory nerve endings. These symptoms mani- 
fest themselves in various ways. There may be a sandy sen- 
sation between the eyelids and the eye s • 
Frequently bubbles may be seen beneath 
the conjunctiva. There may be sensations of 
cooling or drying of the eyes. (This should 
not be confused with oxygen leak around the 
mask, or ex pirational blowing over the eyes) 
A generalized itching of the skin may occur, 
but it is more common for one area, usually 
near a large subcutaneous deposit of fat as 
around the waist or on the buttocks, to be 
affected. Scratching is only of temporary relief since the 
nitrogen bubbles are pushed from one area to another. The 
sensation of ants crawling over the body (called fornica- 
tion) is not uncommon. The sensation of excessive sweating 
when in reality the skin is perfectly dry, and of hot and 
cold flashes also fall in the general group of paraesthesia 
or false sensations. In some Individuals, bubbles of vary- 
ing sizes may be felt or seen beneath the skin and mucous 
membranes, particularly beneath the palmar skin of the fin- 
gers and beneath the ocular conjunctiva. This is called 
subcutaneous crepitation. In most cases the symptoms dis- 
appear immediatelv upon reaching lower altitudes (increased 
external pressure), A small percentage of cases retain 
subcutaneous induration and erythema for several days. None 
of these symptoms is incapacitating, but they are annoying. 
The occurrence of these symptoms indicates the onset of ae- 
roembolism and should warn of the possibility of the deve- 
lopment of more severe symptoms. 
Symptoms of the Joints and muscles are 
commonly referred to as "The Bends", Some 
observers believe the exact origin of the 
pain in the bones and muscles due to the 
blocking of capillaries supplying the area 
involved, while others believe it is due to 
the gas (nitrogen) pressure on or under the 
periosteum or the insertions of tendons a- 
bout the Joint. While movable Joints are 
most Commonly affected, pain is frequently 
felt in the region of the biceps and the poste'rior'thigh 
muscles. The pain has been grouped into four arbitrary 
types, as follows: 
38 Type 1, An aching in one or more areas, which is notice- 
able but not severe or incapacitating* 
Type 2. Pain is more severe than Type 1, and of such a de- 
gree that the subject restricts his movements. Al- 
though this pain is not incapacitating it defini- 
tely Icnrerm a man* s efficiency. 
Type 3. Pain is more severe than Type 2. The person is 
unable to move the member affected; he becomes 
pale, clammy, and if not relieved will become un- 
conscious. It is definitely incapacitating* 
Type 4* Pain appears with dramatic suddeness, and is very 
apt to render a men unconscious in a very short 
time unless given immediate relief. 
The bone and muscle symptoms are the most common cau- 
ses of incapacity from aeroembolism. It is obvious that a 
pilot or crew Jacob*? who is unable to move his leg or arm 
is a serious handicap to any mission. Descent to low alti- 
tude (greater pressure) effects immediate relief in most 
instances. Although there may b e some residual effects af- 
ter re compression they are not common. 
The involvement of the lungs in aeroembolism, popular- 
ly known as "The Chokes*, is due to the collection of ni- 
trogen bubbles in the circulation of the lungs. These bub- 
les irritate the mucous membranes of the respi- 
ratory tract and cause burning, substernal pain 
and unproductive and difficult cough and a sen- 
sation of choking. The Chokes have also been 
described "likte mixing a bromoseltser in the 
lungs'*• The symptoms increase the individual's 
apprehension, and may lead to collapse* It is 
definitely incapacitating and relief must be 
provided as soon as possible to prevent serious 
results. Fortunately the Chokes are much less common than 
the two groups of symptoms described above. Immediate re- 
lief without residual effect is gotten by descent. 
A condition, popularly known among deep sea divers as 
"The Staggers", may occur in aviators* It is 
presumably due to nitrogen bubbles in the fluid 
circulation in the semicircular canals, which 
Jff stimulate false sensations of position and mo- 
tion. The Individual is completely confused In 
regard to position and movement, and behaves 
accordingly, much like an intoxicated person. 
This condition is very incapacitating and the symptoms may persist for days, but fortunately its occur- 
rence is rare in aviation. 
Divers* "Paralysis1* is probably due to the blocking of 
cerebral or spinal capillaries, with a resultant ischemia 
(blood lack) to a certain area of the brain or spinal cord. 
Some believe it may be due to the direct 
pressure of nitrogen bubbles in the spinal 
fluid upon the nerve roots* It will result 
in paralysis of that part of the body con- 
trolled by the part of the brain or cord af- 
fected. Nitrogen bubbles have frequently 
been demonstrated in the spinal fluid at al- 
titude pressures equivalent to that found at 
18 000 ft. Since the spinal fluid has no 
direct connection with the circulating blood 
it is probable that the nitrogen is not rapidly eliminated. 
This has led some investigators to believe that most of the 
symptoms are due to pressure (these bubbles) on the central 
nervous system. Fortunately divers' paralysis is extremely 
rare in aviation. 
In the early days of high altitude bombing in this war 
a fairly large percentage of the bombers had to return to 
their bases without completing their mission, because per- 
sonnel developed incapacitating symptoms of aeroembolism. 
There were three methods open to correct this situation. 
The service could employ men for high altitude flying who 
were resistant to the effects of low atmospheric pressures- 
”Bend Resistant". The physico-chemical state of the body 
of those who were susceptible to aeroembolism could be al- 
tered to render them less susceptible. Or, the environment 
of the individual could be controlled so that he would not 
be exposed to low pressures, even though flying at high al- 
titudes. 
To aid in the selection of bend-re sistent personnel 
low pressure chambers were operated for the classification 
of individuals according to 
their ability to withstand 
the effects of low atmos- 
pheric pressures# with par- 
ticular reference to the 
development of the symptoms 
of aeroembolism. The graph 
shows the results of tests 
made on one group of one 
thousand individuals taken 
to 35 000 ft and kept there 
for one hour. The data re- 
tWAUKKV OtlT#H«rTtoi y linn 
fWKfcUfffcV y IKK 
\tcWwfr A*f vealed that the younger the individual the lose susceptible 
he is to the bends. Men in the older age groups, who have 
their valuable experience, need not, however, be eliminated 
from high altitude flying (except fighter craft), since by 
altering the physico-chemical state of the body a person 
can become resistant to bends. By breathing 100% oxygen, 
the partial pressure of alveolar nitrogen is greatly re- 
duced with a resultant diffusion of nitrogen from the blood 
and tissues and a reduction of the nitrogen stores of the 
body. This is the principle of the process, "Denitrogena- 
tion", or, as it is sometimes called, "Preoxygenation", Ac- 
cording to the best available evidence, the elimination of 
about of the body nitrogen before ascent to high alti- 
tude renders most people protection from serious or incapa- 
citating symptoms of aeroembolism. Fifty percent of the 
body nitrogen can be removed by breathing 10056 oxygen with 
especially designed mask for one hour, provided that the 
individual exercises for one-half of that time. Exercise 
hastens the circulation rate and therefore hastens the dif- 
fusion of nitrogen from the blood. 
Since denitrogenation also occurs during ascent to 
high altitudes and when 100% oxygen is breathed from the 
ground on up, the degree of nitrogen removal is greatly in- 
creased. The Bureau of Aeronautics Technical Order directs 
all personnel flying over 23 000 ft, to take oxygen from 
ground level up. 
Denitrogenation, however, is practical in only certain 
types of combat flying, namely, scheduled missions. Bomb- 
ing and observation plane personnel who are scheduled to 
fly at a certain time can begin breathing oxygen lug enough 
before that time to insure sufficient denitrogenation. 
Fighter pilots, however, who may have to fly at any time, 
and who must climb at maximum rates, find denitrogenation 
impractical, since it would entail their breathing oxygen 
for long hours while at the "ready". Therefore, for fight- 
er pilots the first and third alternatives only are appli- 
cable, that is, choice of personnel, or alteration of en- 
vironment. 
By maintaining the body within relatively high atmos- 
pheric pressure, even though the plane may be flying in a 
very high altitude, the development of aeroembolism can be 
prevented. That, of course, is the principle applied to 
the use of the pressure suit or the pressurized cabin pi am 
However, neither method is sufficiently developed at pre- 
sent to be practical for large scale combat flying. Although it is known that nitrogen bubbles fora in the 
tissues, and in the spinal fluid at 18 000 ft., it is rare 
to encounter any symptoms considered incapacitating below 
30 000 ft. Practically, then, so far as aviation is con- 
cerned , aeroembolism is a disease that occurs only above 
30 000 ft. 
Die probabilities of developing symptoms depend upon 
the rate of climb to the altitude and the length of time at 
that altitude. Thus a person mi£it be able to tolerate 
35 000 ft. for an hour, and yet become incapacitated with 
bends after an hour and five minutes. Also, an individual 
might be able to tolerate 35 000 ft. for several hours and 
yet develop incapacitating symptoms shortly after reaching 
40 000 ft. It farther depends upon the amount of muscular 
movement, and the degree of protection from cold. Too much 
movement, and chilling both abet the onset of the bends. 
The general physical condition, with special regard to fa- 
tigue, alcohol, and food, also enter. ACCELERATION 
The development of aircraft which are highly maneuver- 
able at great speeds has presented the aviation personnel 
and the flight surgeon, who is interested in maintaining 
maximal health and efficiency, with definite and important 
problems. The reactions of the human body to great veloci- 
ties, and especially to changes in rate or direction (or 
both) of velocity, may cause serious impairment of normal 
function. It is important to know the limits of these for- 
ces to which the pilot can be subjected, and how to over- 
come the damaging effects. To this end we are going to ex- 
amine the physical and medical aspects of motion through 
space. 
Velocity (or speed) is an expression of motion through 
space, and is usually indicated ai V *• d/t (or distance per 
time). It is important to know that V can be uniform or 
varying in rate, and can be a straight, or curved, or vary- 
ing direction. When a velocity is changing, the rate of 
increase, or decrease, is designated as acceleration (posi- 
tive for increase in rate, negative for decrease). 
The maximum velocity to which a man can be subjected 
has not been ascertained. Vfe do know, however, that if a 
man is protected from wind resistance he can travel, with 
little effect,as fast as 600 to 700 miles per hour, as long 
as the speed remains constant and the direction of flight 
is in a straight line. 
An aircraft in straight and level flight and traveling 
at a constant speed presents no problem to the crew. How- 
ever, whenever the direction or speed is altered, accelera- 
tions arc developed. The physiologic changes occurring as 
a result of development of high accelerations are profound 
and dramatic in thoir effect. The most common example is 
the "blacking-outn which occurs in pull-outs from dives or 
during prolonged tight turns. 
At present the high accelerations which occur in avia- 
tion and affect the pilot arc mostly developed by change in 
direction of flight, and due to the positive or negative 
lift of the wings. Although catapult take-offs and carrier 
landings develop relatively high accelerations, their phy- 
siological significance is limited because of their short 
duration. The effects of acceleration upon the body are due to the 
forces which act during the acceleration. These forces can 
be calculated from simple physical laws. First, the force 
developed in linear acceleration is 
f » m . a 
where f * fpree, m ■ mass, and a ■ acceleration. 
In other words, the force is proportional to the mass of 
the object and to the acceleration (or rate of change of 
velocity). 
Since moat of the acceleration developed 
in aircraft if due to change in direction, 
and change in direction of path of flight is 
always curvilinear, the centrifugal accele- 
rations are of particular Interest to us. 
The forces developed in centrifugal accele- 
rations are 
f « nar^/r 
where m c mass, v* is velocity squared, and 
r the radius of turn. 
From the examination of this formula it is 
clear that forces are increasingly greater 
with small radius of turn (e.g., tight turns 
or quick pull-outs) and very markedly increased (v*) by in- 
crease in velocity. 
In the assignment of A unit of force the pull or force 
of gravity has been accepted as the unit. According to the 
law of gravity, the earth exerts a force (or attraction)in 
all bodies, and if a body could fall through space without 
resistance, it would increase its velocity 32.3 feet per 
second. This is referred to as the acceleration of gravity. 
Under conditions of resting equilibrium the force of gravi- 
ty is exerted upon a supported body. This force is equal 
to the of the body, or designated as I G. 
Although the source of acceleration forces, that is, 
whether they arise from linear or centrifugal acceleration, 
is of little concern beyond the fact that most of those de- 
veloped in flying are centrifugal, the axis of the body 
through which the forces act is of utmost importance. 
There arc certain conventional axes which are used in ae- 
ronautics and which we will adopt. They are three in lum- 
ber, designated as the transverse, vertical, and lateral 
axes. The transverse axis passes from propeller to tail; 
the vertical axis posses through the pilot, from head to 
food; the lateral axis passes along the wings, through the 
fuselage. In respect to the pilot 
and other aircraft passengers 
there are two essential direc- 
tions of acceleration: (1) the 
transverse, and (2) the verti- 
cal (or positive or gravitation- 
al) types. Transverse accele- 
rations are encountered in li- 
near direction with marked ve- 
locity rate changes, chiefly in 
catapult take-offs, carrier 
landings, and parachute lumps (on opening of chute and 
landing). The magnitude of "Ge" developed in all these 
cases is small, e.g., catapult starts develop 3 - 4 G, pa- 
rachute opening, 5 6 G, jump landings 8 - 9 G, but the 
duration of the force is so limited that the physiological 
effects are slight, as long as the body is not "thrown" a- 
gainst some barrier. 
Adequate protection against transverse 0 forces can 
be gotten by proper buckling-in belts and shoulder straps, 
so that the effects of the forces can be minimi zed. More- 
over, adequate buckling-in equipment greatly reduces the 
seriousness of most crash landings. Protection against 
accelerations developed in opening of parachute is limited 
to delaying the opening of the chute when leaving a very 
fast-moving craft, until speed of free fall (160 m.p.h.) 
is reached. The proper method of overcoming the forces of 
"G" in landing of parachutists is the same as "breaking" 
any fall, namely, spring-like bending of knee and rolling. 
The problem of positive acceleration is one of great- 
est importance. 
Changes in direction of motion account for moat of 
the conditions in combat aviation where accelerative for- 
ces are developed to such a degree that detrimental effe cts 
occur. The simplest and most usual change in direction is 
that which occurs when flying in a 
circle or a part of a circle, or when 
changing from a straight line to a cir- 
cle. These flight paths occur in the 
course of ordinary maneuvers, making 
turns, diving, and pulling out of a 
dive, etc. The movement of aircraft 
in a large circle around a particular 
focus results in a development of cen- 
trifugal forces. We can visualize the 
centrifugal forces by twirling a chest 
nut around on the end of a string. If we could arrange to have a spring scales between the chest- 
nut and the center of the circle we would discover that the 
weight of the chestnut increased as it was twirled around 
and also increased progressively as the string or radius of 
curvature was shortened. These conditions exist in air- 
craft, so that when a flyer is making a large radius turn 
there is usually no physiological effect. If, however, he 
were to make & tight or small 
turn at approximately the same 
speed, the centrifugal forces 
would bo of so large a degree 
that blood would be forced 
from his head toward his feet 
and the pooled blood of the 
limbs would be difficult to 
pump back to the brain* This 
would result in a graylng-out 
or ‘a blacking-out, with a loss 
of vision and possibly also of 
consciousness, A similar con- 
dition is experienced in the 
sharp pulling out of a dive 
when a pilot, moving in a re- 
latively straight line at a 
high rate of speed as he ap- 
proaches his bombing target, as he pulls the nose of his 
plane upward general accelerative forces tend to push the 
bodily fluids downward (that is, maintaining the same 
straight line path as the first phase of the dive), with a 
resultant graylng-out or blacking-out. 
The forces encountered in dives or turns are measured 
in Gs, Now, as an airplane describes a circle of a radius 
of 1600 ft., and at a speed of 200 nup.h., the centrifugal 
force will be 2G and the aviator will apparently weigh 30, 
that is, his own weight plus the centrifugal force. In o- 
ther words, the pilot weighing 150 lbs. would experience or 
apparently weigh 450 lbs. He would be pressed into his 
seat, his head and limbs and belly muscles would be pulled 
downward and his blood and tissue juices would become three 
times heavier. When the G forces exceed a certain limit 
the aviator experiences & gradual dimness of vision and 
blacking-out or loss of vision. If the forces are 
tained or Increased, the next stage is loss of conscious- 
ness, In order to overcome these effects and by adequate 
knowledge of the forces and conditions of blacking-out we 
can make certain protective arrangements, Vfe should exa- 
mine the heart and blood circulation* We know fro* our phy- 
siology that the left side of the heart is the pump system that autonatically adjusts its pumping forces to the work 
which it must do. It can lift against a pressure of 120 to 
250 rams, of mercury provided that the blood flow is main- 
tainable, VJhen the forces of acceleration are such that 
they increase the weight of the blood to a degree great c- 
nough so that the flow of blood cannot be maintained into 
the heart, the symptoms of anoxia, blood lack, particularly 
of the brain, appear suddenly and dramatically. The second 
reason why it is difficult for the blood to maintain its 
flow is that in the increased weight of the blood and for- 
ces pushing it toward the extremities, there is a pooling 
of blood in the lower limbs and lower part of the abdomen 
and this blood has great difficulty in returning to the 
heart. 
In order to overcome, to a certain degree, the effects 
of acceleration we carry out certain procedures which as- 
sist in the maintaining of blood flow to the heart* The 
first is the tensing and tightening up of the muscles of 
the lower extremities and of the apdanan. This can be done 
by conscious, or voluntary, 
muscular control, or, mechan- 
ically, by the use of a so- 
called "Anti-Black-Out Suit". 
The second is the reduction 
in the difference in level 
between the heart and the 
head. Since the heart must 
pump upstream, so to speak, 
from its level to the brain 
level, an upright position moans 
a maximum difference in level, 
whereas a crouching position, 
with the head lowered somewhat, 
means a reduced difference in 
level. The logical method for 
effecting this positional change 
and preventing the pooling of 
blood in the lower extremities 
would be a cockpit arrangement 
such that pilots of dive bomb- 
ers and fighters could handle 
their aircraft in a prone posi- 
tion. Under such conditions 
the centrifugal forces which 
act from head to foot in a sit- 
ting man would act from back to 
belly. Perhaps the best indi- 
cation of the effectiveness of 
a change in position in the overcoming of black-out can be gotten from the following 
comparative data. In an ordinary sitting position an ave- 
rage pilot can stand 3 to 4 G for a matter of 3 to 5 se- 
conds without blacking-out. If he crouches over, he can 
stand from 3 J to 5j G from 4 to 6 seconds. If he life down 
he can stand from II to 12 G for a period of 120 to ISO 
seconds. 
Another aspect of maintaining so-called G-tolerance, 
is the general bodily condition. A person in excellent 
physical condition, in excellent health, can withstand a 
greater amount of G-forco, over a greater period of time, 
than can a person who is suffering from any lapse in his 
physical condition. THE INTESTINAL T RAC T 
The stomach and intestinal tract nor- 
mally contain a variable amount of gas which 
is always maintained at a pressure approxi- 
mately equivalent to that of the atmosphere 
surrounding tho body* Intestinal gases,like 
all other gases, behave according to tho gas 
laws* Therefore, as the individual ascends 
in the atmosphere the volume of his intesti- 
nal gas will increase. 
Altitude 
Relative volume of gas 
0 ft* 
1 volume 
18 000 ft. 
2 volumes 
28 000 ft. 
3 volumes 
33 000 ft. 
4 volumes 
38 000 ft. 
5 volumes 
42 000 ft. 
6 volumes 
The effect of the 
expansion of gastro-in- 
testinal gases will vary 
somewhat with the origi- 
nal quantity of gases and 
with the rate of ascent. 
Thus, In the normal indi- 
viduil, at a slow rate of 
ascent of 200 to *>00 ft, per minute, a feeling of moderate 
abdominal distention will be felt at 12 000 to 16 000 ft., 
with sensations of movement of gas through the intestin a 1 
tract. At that altitude, belching and passage of flatus 
begins and tends to continue as the altitude increases. 
Slow ascent rarely causes incapacitating abdominal discom- 
fort, inasmuch as the expanded gases can be passed through 
the tract and eliminated. With rapid ascents of 2 000 ft, 
per minute, or more, the gas expands rapidly and tends to 
remain localized in the intestinal loops. This increases 
abdominal distention, and abdominal cramps of varying seve- 
rity may be experienced. The abdominal distention may also 
be great enough to cause upward pressure on the diaphragm 
and embarrass respiration; it may be of such severity as to 
distract the man from his task or incapacitate him. 
The greatest single factor determining the amount of 
gas in the intestinal tract is the quality and quantity of 
food ingested. The following is a list of "Diet Don’ts" 
for flying personnel, particularly before engaging in high 
altitude flights; 
Don’t eat excessively; 
Don’t eat gas-forming foods, such as beans, cabbage, 
raw apples, cucumbers, greasy moats, and spice; 
Don’t drink carbonated beverages, such as coca colas, 
gingerale, etc., or whipped drinks, as malted milks, milk 
shakes, etc* In mild cases, passage of gas, or descent will 
ordinarily relieve the distress immediately. In 
severe cases, it is not unusual for the cramps to 
last for 24 hours after descent to sea level pres-* 
sure. Vague, undefined gastro-intestinal complaints 
have been described as a result of repeated ascents 
jrith the attendant abdominal distention. EAR, NOSE, (i SINUS 
The nose and the ear are the moat frequent sites for 
disabling symptoms in flying personnel* In order to under- 
stand this statement, it is first necessary to understand 
the fundamental anatomy of the ear, nose, and throat* 
Referring to the diagram of the 
ear, it will be seen that it consists 
of a series of connecting canals be- 
tween the side of the head and the 
back of the throat, or pharynx. If 
it were not for the tympanic membrane 
or the ear drum, which lies at the 
inner end of the external canal, se- 
parating it from the middle ear cavi- 
ty, there would be an open passageway 
from the external ear to the throat, 
so that, literally, one could breathe 
through his ears. It will also be 
noted that the external canal is la^p 
and open to the outside, while the Eustachian tube, which 
connects the middle ear cavity to the throat, is small. Al- 
though the orifice of the Eustachian tube in the throat ap- 
pears open, it is actually only a closed slit, except when 
the proper throat muscles are brought into action. 
If the atmospheric pressure is decreased, the pressure 
in the external canal will change more rapidly than in the 
middle ear. The pressure in the middle ear will be rela- 
tively greater and the ear drum will tend to bulge out into 
the external ear canal. Before the pressure on both sides 
of the drum can be equalized, some of the air in the middle 
ear must force itself out through the Eustachian tube and 
escape into the throat. When this is done the ear drum will 
return to its normal position. (See diagram, next page) 
This process occurs in ascent in aircraft or in the 
low pressure chamber. Very small changes in pressure will 
result in a dull or full feeling in the ear*. If the indi- 
vidual swallows, or otherwise moves his throat muscles to 
facilitate passage of air from the middle ear to the throat 
the ears Mpopw; there is no longer that full or dull feel- 
ing which means that the oar drum has returned to its nor- 
mal position. This process is repeated time after time un- 
til the ascent is stopped. From a practical standpoint, 
Clearing the ears”,or equalizing the pressure, causes very 
little trouble on the ascent because the greater pressure COMING- 
Op/ 
GCMNG- 
-p O w ** f 
is in the middle ear and it 
will tend to force the air 
out through the Eustachian 
tube, even though no throat 
movements are made to faci- 
litate it. 
On the descent, howev- 
er, the story is different. 
If we descend from any gi- 
ven. altitude with the oar 
equalized, the 
‘pressure in the external 
ear will become relatively 
less. This will force the 
ear drum inward, toward the 
middle car. To equalize the 
pressure or clear the ears, 
air must pass through the 
Eustachian tube into the 
middle ear. But before this 
can be done the Eustachian 
tube orifice in the throat 
must be opened, and this is 
done only with voluntary 
movement of the throat mus- 
cles, as swallowing or yawn- 
ing, Practically, it has 
been found that if the awe- 
rage, normal individual 
swallows or yawns about 
every 300 ft. during des- 
cent he will be able to 
keep the ears clear. It 
must be emphasized that 
| this is a voluntairy action 
and if it is not carried 
out the relative pressure 
between the outside and 
inside of the drum will 
become so great that much 
t pain will be caused and a 
ruptured ear drum may re- 
sult. The least serious 
complication is a red, 
swollen, retracted ear 
drum, resulting in dull 
|pain and partial deafness 
for several days. Occa- 
sionally gross hemorrhage occurs into the middle ear, which will also result in tem- 
porary deafness, with possible sclerosis of the ossicles 
and some permanent deficiency in bearing. 
This condition, just described, is called Aero-Otitis 
Media, to distinguish it from Otitis Media due to bacteriaL 
invasion of the middle ear. However, true purulent otitis 
media may supervene due to the decrease in resistance of 
the middle car tissues. 
The average normal individual free of upper respirato- 
ry infection, with a little experience, can keep his ears 
"open”, even though descending at a very rapid rate. The 
common cold, however, may be said to be one of the greatest 
enemies of the aviator. Since, with the common cold there 
is swelling of the mucous membrane and lymphoid tissue of 
the throat, the orifice of the Eustachian tube may be in- 
volved. The orifice would be narrowed, and thus slower and 
more difficult to open. In some instances it might be im- 
possible to open. 
It is imperative that the flyer with an upper respira- 
tory infection report to the flight surgeon, and the flight 
surgeon should advise such a man to refrain from flying. It 
is better to be grounded for two to five days because of a 
cold than to be grounded indefinitely with damaged ear 
drums. 
An important factor about ear ventilation is the fact 
that ventilation must be exercised at all altitudes and, as 
a matter of fact, greater attention must be given it at low 
altitudes than at high altitudes. This is due to the fact 
that pressure differentials are greater near the earth*s 
surface than at very high altitude; that is, there is a 
difference in pressure of 28 mns. of Hg. between sea level 
and 1000 ft., whereas there is a difference of only 15 mms. 
between 20 and 21 000 ft. 
The paranasal sinuses are air-filled bony cavities 
lined with mucous membranes, situated within the bones of 
the anterior skull. There are four sets of sinuses: fron- 
tal sinuses (one above each eye in the frontal bones), the 
maxillary sinuses (antrums, located in the cheek bones) , 
ethmoidal sinuses (located just back of the root of the 
nose), and the sphenoidal sinuses (posterior to the nose, 
just beneath the brain)* These cavities cooiaunicate with 
the nose through one or more small openings. Under normal 
conditions with changes in pressure such as occurs in fly- 
ing from one altitude to another, the passage of air from 
the cavities takes place with case. However, if the opon- ings are obstructed by the 
presence of extraneous tis- 
sue or mucus or constricted 
by inflammatory or allergic 
swelling, the passage of air 
is restricted and a pressure 
differential between the si- 
nuses and the outside air 
results. This pressure dif- 
ferential will cause sharp, 
penetrating pain in the si- 
nus region. Peculiarly e- 
nough, the pain will occur both when there is negative 
pressure and when there is positive pressure in the sinu- 
ses, so that contrary to the usual situation in ear block 
greet pain may occur both on ascent and descent. This pain 
is frequently so intensely severe that collapse and uncon- 
sciousness occurs. 
Again the common cold is one of the most frequeit 
causes of sinus block. The swelling of the mucous mem- 
branes which results from the common cold causes closure 
of the sinus canals. This closure prevents the equlliza- 
tion of sinus pressure with the resultant condition des- 
cribed above. 
Here again the aviator must make it his responsibili- 
ty to seek the advice of the flight surgeon. Temporary 
grounding may prevent great pain, and possibly serious ac- 
cident, should the pain cause collapse. 
Treatment of ear and sinus block is carried out in 
the low pressure chamber by spraying the nose and throat 
with some astringent such as ephedrine, which shrinks the 
mucous membranes about the orifices of the sinus canals 
and Eustachian and permits them to open. Upon the advice 
and direction of the Flight Surgeon, shrinking of tho mu- 
cous membranes can be accomplished by flying personnel in 
the course of flight by the use of a Benzedrine Inhaler. 
However, this should be done only upon the advice ot a 
medical officer. In the event of sudden severe pain, ei- 
ther in flying or in the chamber, instant relief can be 
obtained by returning to a higher altitude. From there a 
slower descent should be made. 
Closing the mouth and nostrils and blowing, thus in- 
creasing the intranasal pressure, will frequently effect 
relief of both ear and sinus symptoms. This should not be 
done when other methods such as swallowing, yawning, chew- 
ing, yelling, or moving the lower jaw, are adequate. T EMPtRATUIlt 
The temperature range to which aviation personnel may 
be subjected under present combat conditions may ex- 
tend from 140° to minus 70° F, Since the production 
of heat and the regulation of body temperature are es- 
sential for normal living* aviation personnel must m 
cem itself with the environmental temperature. 
Heat is produced in the body as the result of oxida- 
tion of foods. Any exercise, even the slightest physical 
exertion, increases the production of heat above a resting 
rate. Ingestion of food will increase the production of 
heat, and the absorption of heat from exposure to the sunfs 
rays may increase basal heat production two- or threefold. 
These various mechanisms of producing heat are considered 
the chemical regulation of heat control. The loss of heat 
usually occurs through physical means, such as radiation, 
conviction, and conduction. The regulation of body temper- 
ature to approximately 98.6° F, under a variety of environ- 
mental conditions is done by the balancing of heat produc- 
tion with heat loss. The proper use of clothing is man*s 
main method for controlling heat loss. Because of this and 
because of the wide range of temperatures encountered in a- 
viation, adequate clothing for flying personnel is an im- 
portant consideration. 
An added consideration must be made in regard to high 
altitudes, since as the altitude increases the temperature 
decreases. This decrease in environmental temperature pro- 
vokes an increased effort on the bo<3y toward heat produc- 
tion and this, in turn, demands a greater amount of oxygen. 
We see here the beginning of what can become a vicious cir- 
cle, wherein the body reaches higher and higher altitudes 
and demands more and more oxygen for maintaining its tem- 
perature and at the same time enters an environment which 
has a decreasing partial pressure of oxygen. Shivering, 
which is an involuntary muscular exercise for increasing 
heat production, is effective, and at sea level causes no 
great demands upon the respiratory system. At an altitude 
of 35 000 ft,, however, the additional muscular activity of 
shivering causes a great drain on the already limited sup- 
ply of oxygen and can precipitate anoxic failure. 
Protection from cold in aircraft depends upon the fly- 
ing conditions and the aircraft. Fighter planes usually 
present no great problem since the cockpit of most fighters 
is close to the engine, large crew aircraft, where various members of the crew have battle stations distant from the 
heated pilot cabin, call for special clothing. Recent de- 
velopments include electrically-heated flying suits which 
are lightweight and of little bulk so that wearers can fit 
into small, cramped spaces which are isolated from the main 
section of the aircraft and by plugging their line into the 
power supply of the plane, can maintain a comfortable tem- 
perature, Protection must be given to the exposed parts of 
the face to prevent frostbite; this can be accomplished by 
use of protective salves. The eyes can be protected by the 
use of adequate goggles. 
The environmental temperature, especially that of high 
altitudes, must be taken into account in the use of oxygen 
equipment. Caution must be exercised and constant checking 
carried out in order to avoid freezing of equipment, parti- 
cularly since expired breath is always vapor-charged. A I \\ S IC K N £ S S 
Air sickness is comparable to sea sickness. The cau- 
ses are much the same in both cases. The symptoms are 
sweating,nausea, vomiting, often accompanied by dizziness, 
lassitude, depression. There is a great variation in the 
symptoms of different individuals. Some may get relief 
from vomiting; others may be depressed and nauseated with- 
out vomiting; some turn green; in general, the disease is 
very uncomfortable and incapacitating. History has usual- 
ly smiled at the ailing sea sick or air sick person and 
there has been much bravado on the part of those who at 
that particular moment are not suffering. Yet it is doubt- 
ful that there is any person who has never experienced a 
certain amount of air sickness or sea sickness. There are 
also some persons who are particularly sensitive to any 
changes in position and are chronic sufferers. Most per- 
sons, however, can usually overcome the bodily reaction s 
to motion by learning certain tricks in orientation, such 
as visual concentration on the horizon or some fixed spot 
in the horizon, andhy developing confidence in themselves 
that they will be able to withstand combinations -of unfa- 
vorable sensations by keeping themselves fit and occupied. 
Dietary indulgences, smoking excess, lack of adequate bo- 
dily care, are conducive to lowering the tolerance of the 
individual to air sickness. To avoid air sickness it i s 
advised to maintain a moderately full stomach, to fix vi- 
sual concentration on some point in the horizon, and to 
maintain adequate ventilation. 
Foul odors, especially those of hot oil, gasoline, 
and warned rubber, which are common in aircraft, and the 
presence of noxious gases, particularly very small amounts 
of carbon monoxide, coupled with relative lack of oxygen 
which begins to manifest itself above 5 000 ft,, are con- 
ducive to air sickness. FATIGUE 
Fatigue is a generalized condition of the body organ- 
ism due to excessive strain, coupled with inadequate recu- 
peration. It is a condition which involves each and every 
part of the body organism, and, although some particular 
system, such as the nervous system, fcastro-intestinal sys- 
tem, or the muscular system, may show more evidence of fa- 
tigue than others, it must be understood that it is a dis- 
ease of the entire body. The condition is associated with 
weariness, inefficiency, weakness, disinclination to con- 
tinue work, nervousness, and irritability. The condition 
also produces an intense demand for rest. The best example 
can be seen in cases of marked muscular fatigue after pro- 
longed exercise or physical exertion, when the body1s ur- 
gent need for rest in order to repair and rebuild exhausted 
and broken-down parts of the body causes the subject great 
weariness, unto sleep. Fatigue is also associated with e- 
motiohs, so that the degree of fatigue can be greater than 
one would expect from the sheer physical exertion iinvolved 
in flying. In other words,the emotional tension and strain 
of combat flying can play an important role in provoking 
fatigue, even though the subject has done relatively little 
physical exertion. 
I 
The fatigue of flying personnel is occupational in 
character. This fatigue, which is a generalized bodily fa- 
tigue, is incurred by the emotional stress, mental effort, 
and various amounts of physical activity experienced in fly- 
ing, Combat flying is much more fatiguing than routine fly- 
ing by virtue of the increased emotional duress and mental 
efforts involved and also the greater amount of physical 
activity demanded. Prior to the war, flight personnel rare- 
ly engaged in prolonged flights, and an average service pi- 
lot spent approximately 300 hours a year in the air. Under 
these conditions fatigue among flight personnel was not a 
pressing problem. Today, however, when flights of 20 hours 
or longer are common, and aviators may spend as many as 200 
hours a month in the air, the condition of aviation fatigue 
is an important one. There are certain conditions encoun- 
tered in aviation which are conducive to fatigue. 
The emotional stresses associated with flying, parti- 
cularly under combat conditions, cannot be minimized in con* 
sidering psycho-somatic reactions which result in condi- 
tions such as nervousness, anxiety, and fear. The amount 
of emotional stress is in part dependent upon the psychic 
make-up of the individual and depends upon the type of fly- 
ing, whether combat or patrol, diy or night, in good or bad weather. The pilot, having the responsibi- 
lity of command in control of the airplane 
and being more acutely aware of flight con- 
ditions, is more apt to suffer in this res- 
pect than the rest of the crew. Intense 
mental concentration is required of the pi- 
lot during the entire course of the flight 
and most of the cranial nerves are stimulated to an unusuaL 
degree. The eyes are in constant motion, continually roving 
the instrument panel and exploring the horizon. Accommoda- 
tion is frequently shifted as the pilot views the panel, 
terrain, and maps, and, in general, the concentration ef- 
fort demanded of the pilot and also the rest of the crew is 
beyond that found in almost any other routine work. 
Noise and vibration in aircraft effect the impact of 
sound and tactile impulses upon the sensory nerve endings 
in the body and provoke and stimulate the nervous system to 
a marked degree. Although at first glance the noise and 
vibration of aircraft may appear to be of relatively little 
importance, careful evaluation of these con- 
stant high grade stimuli reveals a very marked 
contributing factor in the development of fa- 
tigue . Aircraft comfortization, which includes 
adequate ventilation, proper air-conditioning, 
reduction of vibration and noise, has done a 
great deal for the reduction of these provoca- 
tive conditions in peace time commercial aircraft, but in 
service craft this degree of comfortization cannot be a- 
chieved. 
The spatial changes in aircraft are constantly setting 
up impulses which result in stimulation of the nerves of e- 
quilibration. The many impulses which are constantly sent 
to the brain and relayed to the muscles by associated path- 
ways and which result in muscular reactions, 
all tend to induce bodily fatigue. Minor 
shifts of the viscera within the abdominal ca- 
vity caused by postural changes also result in 
the elicitation of many stimuli from that re- 
gion to the brain. The magnitude, complexity, 
and constancy of these stimuli in flight by 
far exceed those encountered in normal terrestrial exis- 
tence . 
The rapid temperature changes associated with present- 
day flying, ranging up to and over 100° F., are also condu- 
cive to fatigue. The fact that the air temperature changes 
roughly 2 C. degrees per thousand feet of altitude accounts 
for a very marked and severe change of the body environment in regard to temperature change, in turn causing 
many bodily reactions which tend to compensate and 
maintain an even temperature equilibrium. Wearing 
very heavy flying gear at ground level in tropical 
or semi-tropical regions and then going to alti- 
tudes where even this heavy flying gear is not completely 
protective, subjects the body to such extremes that fatigue 
is inevitable. 
Ventilation usually is not within the comfort zone in 
aircraft. The lack of adequate ventilation results in the 
presence of unusual odors, gasoline, oil, rubber, etc., 
which may be deleterious to the health and sometimes are 
quite nauseating. The presence of noxious gases, particu- 
larly carbon monoxide, is always a potential danger, and e- 
ven though the concentration of gas present may be submini- 
mal, prolonged breathing of contaminated air is harmful. 
Anoxia is a special aspect of improper ven- 
tilation, chiefly inadequacy of osgrgen, and al- 
though the use of oxygen masks is directed by the 
Bureau there are many occasions in practice when 
personnel permit themselves to fly at altitudes 
which result in a low grade anoxia. This low 
grade anoxia reduces the capacity of the body tissue for 
natural, normal repair with resultant accumulation of bro- 
ken-down tissues and metabolic waste products. It is also 
true that in altitudes over 33 000 feet, even with pure mp* 
gen supply, there is a degree of anoxia. 
Continued fatigue in flight personnel may result in a 
condition known as staleness. In this condition men are e- 
motionally and physically unfit for active flying. Any num- 
ber of symptoms are present: excessive fatigue, increased 
irritability, loss of appetite, digestive disturbances with 
loss of weight, insomnia, nightmares, weariness, etc. 
The best treatment of stalcness and also of fatigue is 
a preventjjse treatment. This means that the flying time of 
aviation personnel should be limited within a given lorigth 
of time; it means that bodily comfort, rest, and recreation 
between missions should be stimulated and promoted; it means 
further, keeping the body in optimal condition of physical 
fitness, and it also means relieving as far as possible va- 
rious extraneous causes for emotional difficulties and con- 
flicts, such as worry over economic conditions, over the 
safety of the family and loved ones at home, etc. 
In summary it can be said that fatigue in flying per- 
sonnel is a generalized body condition resulting from pro- longed over*-stimulation, either high grade or low grade, of 
the body and its various parts, and a lack of adequate pe- 
riod of rest and recuperation between these periods of pro- 
vocation* Moreover, the best method for the handling of a- 
viation fatigue is the understanding of the condition as a 
generalized condition and the removal or reduction, to as 
great a degree as possible, of the various provocative fac- 
tors which produce fatigue. It is particularly important 
to realize the preventive aspects in the treatment of stale- 
ness and fatigue, since it has become a costly lesson thstb 
when fatigue is permitted to exist for too long a period of 
time the damage becomes irreparable and flying personnel 
suffer nervous "break-downsw, which makes them unfit for 
service activity for a very long period of time, if not for 
ever. BODILY CARE 
Flying personnel must pay particular attention to 
maintaining their bodies in the best physical condition, 
A flyer in an open airship is exposed to wind which, even 
at moderate altitudes, is colder than that at the eartHis 
surface, and drier; it tends to make the eyes water, dry 
and chap the skin, and cool the body. Goggles 
should be worn, helmets should be worn, and 
gloves should be worn. Exposed parts of the body 
can be protected partially by an application of 
cold cream or lanolin. Drafts should be avoided 
as much as possible in closed cockpits. 
The decrease of air temperatures with progressive in- 
crease in altitude results in constant lowering of the 
temperature of the environment of aviation personnel as 
they climb into the higher heights. When the skin becomes 
cold, nerve messages fleeing to the centers which regulate 
the body temperature excite the bodily mechanism for in- 
creased warmth, with a resultant increased use of oxygen. 
This is an important factor to realize in the course of 
high altitude flying. Furthermore, cold, when it becomes 
increased enough, influences bodily movements, makes the 
flyer particularly uncomfortable, and disturbs his concen- 
tration. Frostbites and freezing to death can occur un- 
less adequate protection ia taken. Adequate protection 
consists chiefly of the proper clothing and proper heat- 
ing* If flying must take place in cold climates then oxy- 
gen should be used at altitudes lower than the customary 
10 000 ft. 
Aviation personnel must be particularly careful in 
protection of the eyes and ears. For the protection of 
the eyes, properly fitted regulation goggles offer all 
that is necessary* These goggles should be tin-* 
ted for use in aircraft at sea, over snoir coun- 
try, and over deserts. The proper care of the 
eyes in night flying is not only of importance 
to the pilot as an individual, but of utmost im- 
portance in combat activity, since eyes which have become 
adapted to darkness and are keen in perceiving very fine 
differences in gray tonea are extremely sensitive to light 
and a sudden glare of a search light, or even a misdirec- 
ted landing field light can blind a pilot with serious re- 
sults. The protection of the ears from the constant druumingi 
vibrating noises, at various pitches and volume, which are 
part of aircraft, is important for two reasons. First, keen 
hearing is of help in detecting smooth function of the en- 
gines and also for adequate communication over the inter- 
communication system. The second is in regard to sound and 
fatigue. When the pilot is protected from sound and noise 
he is removing an element which plays a rather marked role 
in provoking pilot fatigue. 
General bodily condition, the maintenance of physical 
fitness is of obvious value. The aviation crow in its or- 
dinary routine work does not do much physical exercise, and 
yet the maintaining of maximum bodily fitness is of prime 
importance because it permits them to better withstand the 
tiring effects of flying. 
Adequate relaxed rest should be cherished by the air 
crew, since it is this period when the bodily tissues, mus- 
cles, nerves, etc,, hage an opportunity to repair and reju- 
venate, Rest includes not only sleep but also moderate re- 
laxing recreation, congenial comradeship, and interest in 
some activity, preferably something beyond and outside the 
scope of aviation. CARBON MONOX IDE 
The aviation industry, the flying, manufacturing, and 
servicing of aircraft, has hazards caused by the use and 
presence of harmful substances, such a* dopes, paints, 
cleaning material, aviation gasoline, exhaust gases, hot 
oil fumes, fire extinguishing compounds, etc. The proper- 
ly trained aviation medicine technician and barocham ber 
technician should acquaint himself with the various noxious 
gases and learn precautions necessary in the handling and 
use of these substances. 
Airplane dope consists of various materials used on 
fabric coverings of airplanes. Fumes of these substances 
are irritating to the nose and throat and skin, and some 
are particularly dangerous, since very small percentages 
produce marked symptoms, as anemia and bleeding into the 
skin. The best precaution to take against dopes is the 
proper ventilation of shops, use of adequate masks, and 
frequent periods of recesses in the outdoors* There is al- 
so great danger in dope rooms of the possibility of fire, 
since many compounds are highly inflammable. All flames 
and electrical sparking devices should be eliminated. The 
spraying of paint lacquer and dope is a very common proce- 
dure around aircraft, particularly sea craft, and persons 
engaged in this should be extremely careful and should 
wear respirators. 
Cleaning materials in aircraft shops can be (2) aque- 
ous, or watery, cleaners, and (b) volatile cleaners. The 
aqueous cleaners consist of soaps, cleaner and polisher, 
(neither of which is dangerous) and platers cleaner, heavy 
duty cleaner, aluminum cleaning ooopouns, carbon remover, 
phosphoric acid alcohol cleaner, which are all very irri- 
tant to the skin and from which there is a danger of se- 
vere burns to the skin and eyes. Precautions against con- 
tact must, therefore, be carefully exercised. The vola- 
tile cleaners are: gasoline, benzine, acetone, paint 
and varnish remover, alcohol, dry cleaning solvent, and 
carbon tetrachloride. All except the last are highly in- 
flammable and great caution must be used in regard to heat 
and flame. They are more or less toxic and their detri- 
mental effects occur through absorption through the akin 
or through inhalation. Breathing the vapors or spilling 
the liquid on clothing or exposed parts must be avoided. 
Carbon tetrachloride must not be allowed to come in con- 
tact with hot metal, since by heating it phosgene is gene- 
rated and phosgene is extremely poisonous. In addition to the usual dangers of ordinary gasoline, 
aviation gasoline contains an added substance, ethyl fluid 
(tetra ethyl lead), which is very toxic. The fumes of this 
fluid can cause unconsciousness and death; good ventilation 
is, therefore, essential. Intense heat (the desert sun, 
for example) can "boil over” motor gasoline. Then, when the 
plane starts up, the fumes can rapidly overcome the pilot. 
If desert conditions are encountered the safest thing is to 
wear an oxygen mask for several minutes after the take-off. 
Rubber gloves should be worn in handling the fluid, as the 
pure ethyl fluid can burn. If it does contact the skin, 
wash thoroughly with soap and water immediately. 
The principal compounds used in fire extinguishers in 
or about aircraft, are carbon dioxide and carbon tetrachlo- 
ride. Carbon dioxide gas is non-combustible* High concen- 
tration of carbon dioxide depresses the respiratory rate 
and can result in death. Carbon tetrachloride is a poison- 
ous volatile liquid and when inhaled it acts as an anesthe- 
tic, causing drowsiness, dizziness, headache, excitement, 
vomiting, anesthesia, and finally unconsciousness. 
If carbon tetrachloride, which has a characteristic o- 
dor, is detected in flight, the source should be checked 
and eliminated immediately and the cockpit ventilated. 
When sprayed on a fire or on hot metal, carbon tetra- 
chloride forms phosgene, a poisonous gas. Since inhalation 
of even a few “whiffs" of this gas may be fatal it must be 
avoided. Cr$sh crews are equipped with gas masks for this 
purpose. At the scene of an aircraft fire, whenever crash 
crews start spraying, get leeward of the fire. 
Exhaust gases from internal combustion engines used in 
aircraft usually contain methane, hydrogen, oxygen, carbon 
monoxide, carbon dioxide, and nitrogen. In addition, air- 
plane engines using ethyl gasoline will blow little solid 
particles out with the exhaust gases. These consist mainly 
of lead chloride, lead sulfate, and carbon particles. 
Certain of these above mentioned products are toxic if 
inhaled by flying personnel, and if the cockpit or cabin 
air is contaminated by them they should be removed to avoid 
serious effects. 
There are several factors concerned in the elimination 
of exhaust products from the interiors of airplanes. One of 
the most important of these is whether the engne is direct- 
ly in front of the fuselage, as in single- or tri-motored aircraft. Little trouble has been encountered with 2 or 4 
motored airplanes. Where an engine is immediately in front 
of the personnel compartment, the amount of exhaust gas 
entering it depends largely on the motor exhaust system, 
fo be absolutely certain that exhaust fumes are not 
getting isto cockpit or cabin is to analyze the air in 
those places. 
The greatest potential danger fro© noxious gases in 
aircraft from the exhaust carbon monoxide, It is a 
tasteless and odorless gas. It occurs in exhaust fumes 
from the incomplete combustion of carbon materials. The 
amount of carbon monoxide in exhaust gases varies from 1 
to 7%, with an average of 2*8%, However, the carton mono- 
xide of the exhaust becomes well mixed with atmospheric 
air before reaching the cockpit of an airplane and seldom 
exceeds a concentration of ,0456 at that point. Neverthe- 
less, even this small amount is known to be highly toxic. 
Carbon monoxide is dangerous because it produces an 
anoxia by diminishing the oxygen-carrying capacity of tho 
blood. The attraction of hemoglobin for carbon monoxide 
is 300 times as great as for oxygen, so that in a mixture 
of hemoglobin, oxygen, and carbon monoxide, the carbon mo- 
noxide's chances of combining with ttoa 'hemoglobin are 300 
times better than those of the oxygen. Moreover, the car- 
bon monoxide already present in the arterial blood acts to 
further increase the anoxia by preventing the release of 
oxygen from the blood to the tissues. Since the blood oxy- 
gen saturation is 
low at high alti- 
tudes, and since 
even a very small 
amount of carbon 
monoxide reduces 
the oxygen-carry- 
ing capacity of 
the blood, the 
danger of even 
traces of carbon 
monoxide at high 
altitudes is 0*2at 
For Example, at 
14 000 feet, tho 
arterial oxygen 
saturation is I85S 
and signs of anoxia may develop; if ,00556 carbon monoxide 
is present, signs of anoxia may develop at 11 600 feet. 
♦ 66 — and If ,0156 carbon monoxide is present, signs of anoxia may 
develop at 7 000 feet. The table shows the correlation of 
carbon monoxide concentration in the blood with the signs 
and symptoms of carbon monoxide poisoning, (Use chart for 
relation of blood carbon monoxide and atmospheric carbon 
monoxide) 
Carbon Monoxide, 
percent in blood 
Symptoms 
b-io 
None 
10-20 
Tightness across forehead, pos- 
sibly slight headache, dilatation 
of cutaneous blood vessels. 
20-30 
Headache, throbbing in temples. 
30-40 
Severe headache, weakness dizzi- 
ness, dimness of vision, nausea, 
and vomiting, and collapse. 
40-50 
Same as previous, with increased 
pulse rate and respiration, and 
more possibility of collapse. 
50-60 
Syncope, increased respiration 
and pulse, coma with intermit- 
tent convulsions, Cheyne-Stokes* 
type of respiration. 
60-70 
Coma, with intermittent convul- 
sions, depressed heart action - 
possibly death. 
70-80 
Weak pulse and slowed respira- 
tion, respiratory failure and 
death. 
Since carbon monoxide poisoning comes on so insidiously and 
since it is as dangerous as it is, preventive measures to 
keep it out of the cabins and cockpits of planes must be 
used. In order to control the carbon monoxide problem it 
is necessary to establish the allowable concentration of 
gas which is harmless and which can be measured by a prac- 
tical method. The use of the Hines Safety Appliance Company 
Indicator, which can measure as low as 0.00356, is an essen- 
tial part of the preventive measures against carbon mono- 
xide poisoning. All airplanes should be tested with this 
indicator, with readings taken at different altitudes, with 
different throttle and fuel mixture settings, and with va- 
rious cabin and ventilator openings. If any change in plane 
design is made, new tests are necessary* DANGEROUS CONCENTRATIONS OF CARBON MONOXIDE 
Concentration, percent 
Effect 
0*01, or 1 part in 10 000 
0.04, or 4 parts in 10 000 
0,06 to 0,07, or 6 to 7 
parts in 10 000 
0.10 to 0.12, or 10 to 12 
parts in 10 000 
0.35 or 35 parts In 10 000 
No symptoms for 2 hours 
No symptoms for 1 hour 
Headache and unpleasant 
symptoms in 1 hour 
Dangcrour for 1 hour 
Fatal in less than 1 hour 
Dangerous concentrations of carbon monoxide in aircraft 
compartments are indicated by: 
1, Subjective symptoms, such as throbbing headache, nau- 
sea, dizziness or dimming of vision, 
2. Odor of exhaust gases. 
3- Sounding of a warning signal. 
Required action is as follows; 
1. Open all cockpit hoods or windows and attempt to eli- 
minate any odor of exhaust fumes by ventilation. 
2. Attach oxygen masks and breathe pure oxygen until the 
symptoms disappear, 
3* Descend to lower altitude as soon as possible. 
4. Turn off exhaust heaters if such are in use. 
The treatment for carbon monoxide poisoning is the 
breathing of 95% oxygen with 5% carbon dioxide. NMiHT VISION 
Night vision is of special importance in military o- 
perations and since the mechanism differs from that of day 
vision we will consider some aspects of it* 
The main difference between night vision and day vi- 
sion, is that night vision is accomplished with the peri- 
pheral field of vision, whereas day vision is central. The 
factors which affect night vision are dark adaptation, al- 
titude , food, and individual variations* Dark adaptation 
is a chemical process within the retinal cells by which 
the visual sensitivity is improved almost ten thousandfold 
after a period of 30 minutes of darkness, A fraction of a 
second of full light can destroy the entire sensitivity 
increase which has been gained by the 30-minute darkness. 
Even small amounts of dial light can reduce the dark adap- 
tation, It has been found that red-lensed goggles qssist 
in dark adapting and in maintaining dark adaptation. 
Altitude plays a very important role in night vision. 
The sensitivity of the retinal cells and brain cells corv- 
trolling vision to oxygen lack is very acute and even the 
moderately low altitudes at reduced partial pressure of 
oxygen with the resultant reduced tissue oxygen can inter- 
fere with night vision. For this reason Technical Order 
of the Bureau of Aeronautics states that in all night fly- 
ing, regardless of altitude, accessory oxygen should be 
used. 
A chemical factor in the diet. Vitamin A, is also es- 
sential for adequate flight vision. An excess of this vi- 
tamin will not increase visual acuity, but any decrease 
from the normal amount will seriously influence alght vi- 
sion, In combat zones whore probabilities exist for re- 
duced rations, it is particularly important that flying 
personnel be supplied with adequate Vitamin A, 
Individual variation in regard to night vision is 
great and persons with keen vision can see as well with 
one-tenth the illumination as those with poorest night vi- 
sion, The individual can improve his own night vision by 
practicing peripheral seeing, that is, practicing to look 
through the side of his eyes rather than head-on. This can 
be done out of doors at night. 
In summary, the following suggestions can be made for 
improving the efficiency of night vision: 1. Developing dark adaptation prior to any night flights 
and maintaining that adaptation. 
2. Eliminating all non-essential limits within the air- 
craft and keeping essential ones very dim. 
3. Using red light in aircraft wherever possible. 
4. Using especially prepared charts and maps which can be 
visualized in red light. 
5. Using supplemental oxygen at all altitudes. 
6. Guarding against Vitamin A deficiency. 
7. Practicing peripheral vision. 0MIOCHAM8ER : THEORY 
Whenever th® scientist or the engineer wishes to study 
the behavior of some machine or some substance under a par- 
ticular condition, he builds an artificial environment and 
places the machine within that environment. To study the 
behavior of certain* types of airfoil* or wing structures of 
aircraft, the aeronautical engineer studies the new design 
of wing in an air tunnel. In this way he can subject the 
design to conditions of flight without going through the 
complete process of building a plane, and then flying it* 
As a matter of fact, the short-cut method of the wind tun- 
nel also affords a much greater opportunity for careful and 
controlled study. To study the behavior of an engine in 
polar regions, the engineer places the engine in a refrige- 
rated chamber and studies its performance. 
The low pressure chamber is a device by which the sci- 
entist can make artificial conditions which Are similar to 
the conditions of the atmosphere. 
Not all conditions of the atmos- 
phere can be simulated in the 
chamber, but as far as man* s be- 
havior ia concerned three very 
important conditions can be made. 
The low pressure chamber can be 
used to make artificial altitude 
conditions insofar as the pres- 
sure, the partial pressure of ga- 
see, and, in chill chambers, the temperature of the atmos- 
phere are concerned. By making high altitude conditions 
within a confined chamber on the ground level the reactions 
of man to high altitude can be studied and demonstrated on 
humans without the use of aircraft and without all the at- 
tendant difficulty and risk which is incurred in high alti- 
tude flying. Moreover, the use of the chamber permits a 
greater control of simulated altitudes and rates of ascent 
and descent. 
Another important factor about the low pressure cham- 
ber is the convenience with which subjects can b© observed 
from the outside of the chamber. This does not pertain on- 
ly to the seeing of the subjects through ports, and the 
speaking with them over the intercommunication system, but 
also to the use of measuring devices, such as electrocardi- 
ographs, photoelectric heraoglobinometers, which can be at- 
tached to the subjects inside the chamber and read and re- 
corded by outside observers. The essential structure of the lew pressure chamber is 
a reinforced substantial structure which can be sealed from 
the outside air. By an arrangement of a vacuum, or suction 
pump, the air Inside the chamber is removed at a rate com- 
parable to any desired rate of climb. An intake valve is 
always kept open so that there is a constant flow of fresh 
air into the chamber, and no foul air (contaminated with 
carbon dioxide from expired breath) is allowed to accumu- 
late. 5y adjustment of the intake and exhaust valves, the 
internal pressure of the chamber can be "set" at any de- 
sired pressure (altitude), and in this way high altitudes 
can be simulated at ground level. 
It is clear then that with the use of the low pressure 
chamber it is possible to study certain reactions of the 
human being under conditions of high altitudes (low atmos- 
pheric pressure) without leaving the ground. These special 
bodily reactions are those concerned directly with pressure 
changes and the changes in body cavities and body-contained 
air, and with the partial pressure changes of oxygen in re- 
gard to the metabolism (tissue*energy exchanges). The low 
pressure chamber affords an opportunity to study and expe- 
rience the influence of decreased pressure and of decreased 
oxygen, or oxygen lack. 
It is an established fact that with the increase in 
altitude the atmospheric temperature decreases, and at an 
approximate rate of one degree (centigrade) to every five 
hundred feet increment in altitude. Lew pressure chambers 
have been developed with proper refrigerating systems so 
that with simulated altitude changes parallel temperature 
changes ape introduced. This type of low pressure chamber 
is called a chill-chamber. The use of this chill-chamber 
affords an opportunity to study, not only the pressure and 
oxygen changes, but also the temperature changes. IBAKOCH AM BE R : OPERA T I ON 
The operation of the barochamber (low pressure cham- 
ber) is one of the important responsibilities and duties of 
the technician* The carrying out of this duty should be 
focused through three frames of reference. First, the fo- 
cus of the teacher. In other words, the barochamber is pri- 
marily a teaching device and all the operation and activity 
of such a unit should emphasize training and teaching as- 
pects of the simulated flights. The second focus or point 
of view should be that of the doctor, which means every ef- 
fort should be made toward keeping men in maximum flying 
fitness. The doctor ia concerned with maintaining the bar- 
rochamber as an estimate for aiding understanding of the 
body so that maximum physical fitness can be achieved by 
flying personnel. The third point of view is the engineer. 
The barochamber and its related equipment, oxygen equip- 
ment, pressure pump systems, and communication sys- 
tem, is a highly technicological unit and its proper opera- 
tion and understanding demands the engineer's point of view 
in regard to handling of the equipment and maintaining it, 
and a knowledge of its function. 
Detailed aspects of the operations of the various 
parts of the barochamber are, of course, dependent upon the 
specific equipment of the particular barochamber. The pump 
system is the system by which air is evacuated from the 
chamber at a rate to simulate various rates of climb, up to 
6, 7> and 8 000 ft. per minute. The pumps arc vacuum pumps 
and may be water or oil-sealed. Detailed and specific op- 
erational procedures must be mastered for each type of pumpt 
The communication system is usually an electronic in- 
tercommunication system, so that observers and subjects in- 
side the chamber can maintain contact with observers out- 
side, The operation of these units is usually very simple 
and consists principally of seeing that adequate connec- 
tions are made, that switches arc in their proper position, 
and that various volume controls are set. 
Oxygon equipment and oxygen supply obviously play an 
essential role in the operation of a barochamber, and a 
complete understanding of the nature and operation of the 
equipment is invaluable to the technician. The oxygen e- 
quipment used in the chamber is used not only to afford a 
supply of oxygen in case of emergency or to give adequate 
oxygen to maintain life at the higher altitudes, but also IT IS USED 3K THB BADOCHAMBER FOR TRAINING PURPOSES. To 
that end the technician must know the Havy equipment so 
that he may assist in the teaching of this equipment to 
the trainoes aid guide them in the course of routine runs. 
The more expert his understanding and teaching* the great- 
er his value to the service* 
Medical equipment involved in the operation of the 
be.rochatntx>r consists of equipment used in the examination 
of nasal passages and oars and equipment used for shrink- 
ing mucous membranes of the sinuses so that sinus and mid- 
dle ear ventilation con be expedited. There is also First 
Aid equipment * primarily stimulants which may be needed on 
occasion for resuscitation. The use and care of medical 
equipment follows the dictates of the use and care of all 
medical equipment in the hospital corps. Another medical 
aspect is the proper care of face masks. Since many men 
use the same face mask during the course of the day it is 
essential that the facepiece be sterilized after each use 
in order to avoid transmission of upper respiratory infec- 
tions. 
The teacher* s point of view is a very important one 
in the operation of the barochamber, and the proper under- 
standing and incorporation of this point of view results 
in treating the barochamber as a school. As such, every 
effort is made for the exhibiting of educational charts 
and diagrams, cutaway models of equipment, and having a- 
vailable various bulletins on aviation hygiene. The oper- 
ation of the barochamber usually elicits a great deal of 
inquiry from tho trainees and from the casual spectators 
end the technician can render aviation hygiene a particu- 
lar service in emphasizing and reiterating that the funda- 
mental function of tho operation of the barochamber is for 
the training of aviation personnel in the various aspects 
of aviation hygiene, including the effects of anoxia, mea- 
sures for avoiding anoxia, middle ear ventilation, bends, 
etc. 
Technicians assigned to duty at barochambers may be 
given any one of a number of assignments. The particular 
typo of assignment will* of course, depend upon the unit. 
In general, however, the duties can be classified as (1) 
general duties about the chamber, and (2) specific duties, 
such as controls operator, inside observer, outside obser- 
ver* recorder, equipment demonstrator, etc. 
In carrying out the general duties, the technician 
can find no bettor pattern than that stated under the the- 
ory and maintenance of a namely* that the ac- tivity should function as a training or teaching unit with 
the additional point of view of the medical officer and the 
engineer. The general duties around a barochamber, then, 
as the general duties in any unit in the Navy, call for mi- 
litary precision and exactness and dispatch. 
Specific duties relating to the barochamber as a teach- 
ing unit can be better visualized by taking each post sepa- 
rately. 
In order to be a better teaching service to the trai- 
nees and also in order to have present someone who has ade- 
quate medical training, to take care of any medical emer- 
gency at a high altitude in the chamber, the general pro- 
cedure is to have a trained technician or a medical officer 
participate as am inside observer in each flight of the ba- 
rocharaber. The duties and responsibilities of the inside 
observers are rather clearly defined hy the procedure of 
the run. At the present time this procedure consists of, 
first, an ear check, that is, a preliminary short flight to 
a certain altitude with drop to sea level during which the 
trainees are given an opportunity to demonstrate their ca- 
pacity to ventilate their middle ears. This is followed by 
preparations for a routine indoctrination flight, which con- 
sists of taking sea level pulses and giving a mental acuity 
test to the trainees at sea level. Following these two pro- 
cedures it is the custom to demonstrate again the oxygen 
equipment and to permit the trainees to go through check- 
lists for the use of their equipment. The flight gets un- 
der way, and the group climbs to an altitude of 18 000 ft., 
where the flight is levelled off. A 10-minute stay is car- 
ried out, during which time the inside observer pays parti- 
cular attention to all the signs and symptoms of the trai- 
nees and is on guard in case any trainee collapses or dirts 
because of lack of adequate oxygen. A good inside observer 
points out to the trainees the various anoxic changes that 
they are experiencing or that can bo seen in fellow crew 
members. At the end of a 5-minute interval at 18 000 ft. 
pulses arc taken and a cheek is made for gross tolerance. 
After the group has stayed at 18 000 ft. for 10 minutes it 
is given a second mental acuity test. At the completion of 
this test, which usually takes three minutes, the inside 
observer tells the men to put on their masks and as- 
sists those who need help. The observer then checks all 
the face pieces for fitness, ho carries out a drill in the 
flushing-out of the rebreather equipment, and when he has 
satisfied himself that all men have returned to a normal 
state and that each has an adequate and properly function- 
ing oxygen supply he signals the controls operator to climb 
to an altitude of 28 000 ft. At this altitude the observer is particularly alert 
regarding the possibilities of monfs lapsing into uncon- 
sciousness for lack of oxygen which may occur because of 
equipment failure, ill-fitting masks, etc. A third mental 
acuity test is taken at this altitude, pulses are taken, and 
the chamber begins to descend. 
The descent embodies an important responsibility for 
the inside observer and that is to see to it that the crew 
members make the necessary effort for ventilating their 
middle oars. On those occasions when a crew member experi- 
ences an ear block, the inside observer arranges for level- 
ling-off of the chamber or increasing its altitude and ad- 
vises and assists the trainee in overcoming his block. 
During the course of the flight and in its return a 
good inside observer continues emphasizing the fact that 
all that has happened in the chamber is for training. The 
tests and the pulse rates arc taken not to test a man but 
to show him that regardless of his zeal or desire under a 
alight degree of anoxia his performance is definitely poor 
and with oxygen at an altitude just under two miles his 
performance cannot be differentiated from that at sea level. 
The controls operator is the pilot, so to speak, of 
the barochamber, and by adequate handling of the intake and 
exhaust valves which connect the chamber to the pump the 
operator can maintain any flight path in regard to altitude 
climb and descent which he wishes. Controls operators 
should learn and understand the nature pf the equipment, 
the panel board which he uses for controlling the flight, 
namely the altimeter, the rate of climb meter, and the 
clock. The controls operator is also responsible for see- 
ing that the communication system is intact and in working 
order, and also that the water and power for pump systems 
arc in order. 
The proper and adequate keeping of records in the ba- 
r©chamber cannot bo overemphasized. The accurate keeping 
of records not only affords the unit an index of its acti- 
vity but affords opportunity for the unit to examine criti- 
cally its training program, to study the various conditions 
encountered in routine flights so that the staff can revise 
or control its program with maximum effectiveness. OX Y G E N EQUIPMENT 
The following notes arc presented for instruction and 
guidance in demonstrating oxygen breathing equipment to 
Navy personnel and are presented in the form of a lecture 
to the trainees in aviation hygiene. 
This part of your short course in Aviation Hygiene 
deals with standard Navy Oxygen Equipment, and its proper 
use. It is of great importance for you to learn "how to 
use this equipment properly, to understand how it works, 
and to practice its use so that you will become familiar 
with its use and feel comfortable while you are using it. 
The information regarding oxygen equipment which you are 
about to hear, and the Bureau of AeronautiCScTechnical Or- 
der 42-4Q, which has been given you and which you will find 
reprinted on the back of the small certificate which you 
will receive at the completion of your short course in 
Aviation Hygiene, are the two most vital and essential 
phases of Aviation Hygiene, 
Standard Navy Oxygen Equipment can be classified in- 
to four types. By good fortune each type is named in ac- 
cordance with the method by which it operates, and we dis- 
cuss all four, although the occasion may not arise for the 
use of all, in order that you may appreciate the develop- 
ment of tho equipment and also that you may better under- 
stand the latest models. 
In the first place, we must understand that oxygen 
as used in the Navy comes to us In a gas fora under high 
pressure in cylinders or oxygen bottles which are heavily 
walled metal cylinders containing oxygen 
under a head of 1800 lbs, pressure per 
square inch. The use of oxygen directly 
from such a bottle would result in da- 
mage and irritation of the nose and of 
the mouth because of its high pressure. 
Therefore, it is necessary in all types 
of equipment to have a mechanism lywhich 
the pressure is reduced from 1800 lbs, 
to from 9 to 12 or 15 lbs. The device 
used for lowering the pressure is called 
a "reduction valve"• There are various 
types of reduction valves. Some are se- 
parate from the rest of the equipment 
and others are incorporated within it* The earliest type of oxygen equipment, both insofar 
as its use and its development is concerned is the Constant 
Flow. This functions exactly as it is named, and the user 
of oxygen has a continuous and constant flow of oxygon from 
the oxygen source to his breathing apparatus* Of course, 
there is a reducing valve in the line* 
The Constant Flew in its primitive form 
consisted of an oxygen bottle, a redu- 
cing valve, a rubber hose connection, 
and a mouthpiece which appeared similar 
to an ordinary pipestem. The user in- 
serted the pipestem in the comer of 
his mouth and with a certain amount of 
practice was able to suck in air through 
one corner of his mouth and breathe out 
his breath through the other* Beyond the fact that this 
system was simple and supplied oxygen it had no virtues and 
all vices. It was uncomfortable to use, because it would 
irritate the tissue membrane and produce marked salivation 
(incidentally, it was given the name of "The Drool Tool" by 
old aviators). At high altitudes it would freeze. It took 
a great deal of training to learn to use it with 
even c small amount of efficiency. It was funda- 
mentally inefficient. It was tiring for the jaws 
of the user, and on those occasions when the pipe 
stem slipped from the mouth of the user it often 
became quite a task to fumble and fish around with heavy 
gloves for this fine rubber tubing and pipestem. Moreover, 
it was very wasteful insofar as the use of oxygon was con- 
cerned, for oxygen was being discharged whether the user 
was breathing in or breathing out. 
In order to have a more efficient apparatus, a second 
type, the Demand Regulator type, was designed, which deli- 
vers oxygen from a cylinder through a reducing valve to the 
user at rates automatically adjus- 
ted to the demand. In other words 
when the user inhales and demands 
oxygen he gets oxygen, and when 
exhales and has no need for oxygen 
no oxygen flows from the system, 
Ihe operation of this instrument 
is controlled by a small suction 
which is developed as one inhales, 
Dxygen is inspired from the cylin- 
der and the exhaled air is exhaus- 
ted to the atmosphere. The appa- 
ratus consists of a regulator, a 
facepiece, and a breathing hose. These are connected to the oxygen cylinder. The reducing 
valve is incorporated in the assembly and also a gauge, 
graduated per square inch, is installed on the regulator. 
The facepiece has two small exhalation vents which permit 
expelling air but prevent atmospheric air from entering in- 
to the breathing circuit on inspiration. 
There is a manually operated "Emergency Bypass Valve", 
which permits the user to convert the demand apparatus in- 
to a constant flow type in case the regulator fails to ope- 
rate properly and automatically. It is 
important to realize that when the user 
opens the bypass valve the consumption 
of oxygen will be greatly increased and 
his supply bottle will last for a much 
shorter time than it would at operation 
with the demand regulator. In practice 
the valve should be opened slowly and 
only a minimum flow should be used. 
The demand regulator Operates in the following manner* 
When the oxygen supply cylinder valve is opened, oxygen 
flows into the reducing valve, expanding the bellows and 
closing the valve* Second, on inhalation at the facepiece, 
a differential pressure is created 
across the diaphragm, pausing it to 
open the admission valve and oxygen 
flows through the valve and breath- 
ing tube to the- facepiece and user* 
Although this demand type ap- 
paratus operates satisfactorily, 
there is a certain amount of ineffi- 
ciency and waste of oxygen because 
of the fact that breathing out 
wastes 95 parts per hundred of oxy- 
gen. In order to make this clear, 
let us recall that expired breath contains roughly 5# cap- 
bon dioxide which contaminates the expired breath and makes 
it impossible for a person to rebroatho air. Now, in the 
case of breathing pure oxygen through a demand regulator 
one breathes in 100# oxygen and breathes out 95# oxygen 
plus 5# carbon dioxide. If an arrangement could be made 
for the removal of this 5# carbon dioxide then one could 
recover 95 parts per hundred of oxygen from each 
expired breath. That, essentially, is the mech- 
anism of the third type of oxygen equipment which 
we will discuss, namely the Rebreather Apparatus. 
By the use of a chemical filter it is possible to remove from the expired breath the contaminating carbon 
dioxide and also some of the water vapor* Let us look at 
a diagram of the re* 
breather type of equip- 
ment. We see first the 
oxygen supply bottle, 
then a breathing bag 
from which we see a 
hose connection leading 
to the face piece, and, 
since this is a closed 
system, the expired 
breath comes back down 
through a breathing tube 
and is passed through a 
canister which contains 
a chemical filter for 
the removal of carbon 
dioxide. In this aj>* 
paratus, the wearer 
breathes oxygen in a 
closed circuit and the 
exhaled oxygen is re- 
tained and used after purification by removal of the car- 
bon dioxide. The expired oxygen goes to the breathing bag 
and v/hen the bag becomes partly depleted a small trip- 
valve is opened and the oxygen supply is automatically re- 
plenished, In this way there is always a supply of oxygen 
necessary for normal function. 
Two types of oxygen rebreathing apparatus have been 
developed; an individual oxygen supply type, and a centre! 
or manifold oxygon supply type. The operation is essen- 
tially the same, the only difference being in the source 
of oxygen. The individual supply carries a small cylinder 
whereas the central supply is operated by a large central 
storage cylinder with out- 
lets along the oxygon line 
mounted in the fuselage. In 
the Chamber, as is true in 
most large aircraft, the cen- 
tral oxygen supply type is 
used. In the use of the re- 
breather type of apparatus 
it is essential to remember 
that the apparatus is more 
complicated than either the 
demand or constant flow and for that reason needs a more 
careful check* Whenever one uses the rebreather type of 
apparatus one should proceed to go through the following five steps in their check list* 
!• Oxygen supply. No apparatus will operate without 
an oxygen supply. If one uses the individual type appara- 
tus, one checks to see that the hose connections are pro- 
perly fixed between the oxygen bottle and the rebreather 
breathing bag and checks on the gauge to see that there is 
an adequate supply of oxygen for the duration of the 
flight. In the use of the central supply system it is ne- 
cessary to connect the oxygen hose line to the fuselage 
supply line and this is done by inserting the male plug 
into the female valve outlet. A small thumb button is de- 
pressed and the plug inserted and given a quarter-turn to 
the right until it fits snugly. In the use of the central 
supply system in aircraft it is of importance to check 
constantly in order to prevent the plane vibration from 
shaking the connection from its fitting. In general, a 
properly connected fitting will not shake loose; However, 
precautionary checking during flight is important. When 
the oxygen supply lines have been connected and the oxygen 
supply checked by the reading of the gauge, the user is 
ready for the second step in our check list. 
2, Canister. Under this item we consider first the 
canister, second its proper opening, third its proper in- 
sertion in the apparatus, and fourth its lifetime. Canis- 
ters are filled with a caustic, irrita- 
ting chemical, which, when it comes in 
contact with the skin, particularly the 
eyes, nose, or throat, can do a moderate 
amount of damage, it is, therefore, im- 
portant to open the canister with cau- 
tion for often, especially at altitudes 
above the ground, the air rushing out of 
the canister carries with it fine par- 
ticles of caustic, which, if they were 
directed toward some crewmato or toward 
the user’s face, would do damage. To 
open the canister properly, turn the end 
which you are opening away from you 
toward the deck and pull the small metal 
tab out in order to break the seal and then pull the co- 
vering open.. A small rubber wafer is inserted in the fac- 
tory and should be removed. Occasionally faulty canisters 
do not have this wafer and if such be the case discard the 
canister and take a new one. After opening one side, open 
the other and you are ready for the insertion of the ca- 
nister into the apparatus. A word here about opening the 
canister. This is a job meant for each man for his own 
canister; do not rely on your plane captain or your buddy for opening it* Since the life of a canister is United to 
two hours from the tine of opening, the only way you can he 
sure that yours is a fresh and new one is for you to open 
it and insert it* Having opened the ca- 
nister we now insert it, cither side up* 
See that it is aligned properly and not 
out of line, and then close the toggle* 
If the canister has been inserted proper- 
ly it will take no force to close the 
toggle* If force is necessary, the ca- 
nister has not been aligned properly and 
should be re-aligned. Forcing a toggle 
can result in the denting of the canis- 
ter ends with a resultant failure of ti- 
de qua te oxygen supply* 
3. Leaks. Having inserted the ca- 
nister, our next stop is to chock or re- 
breather system for possible leaks or faulty connections. 
This is done in the following way. The small button valve 
connected to the face piece is closed by pushing it down. 
This is done to close the system; otherwise the oxygen 
would flow from the tank through the breathing bag, through 
the nose connections, out into the 
room and the system could not be 
checked. Having closed this small 
valve the user then depresses or push- 
es the wishbone against tho breathing 
bag, until it begins to fill with oxy- 
gen. The bag should fill to a mode- 
rate taut fullness within five seconds. 
After the bag is filled, the tester 
removes his finger from the wishbone, 
keeping the face piece valve closed, 
and watches the bag for 10 or 15 seconds. 
If the bag remains as taut and full as it 
originally was, there are no leaks. If, on 
the other hand, the bag deflates, it is ne- 
cessary to look for the source of the leak. 
In doing this one rcchecks the oxygen line 
connection to see that it is fit and snug. 
Second, one checks the canister to see that 
it is seated properly and that its ends are 
not dented. If both arc in order, one then 
checks the breathing bag connection of the 
oxygen line tube. In order to do this it 
is necessary first to disconnect the other end of the oxy- 
gen line. Occasionally there is a washer seated in this 
connection. No washer should be in this place and if one is found it should be removed* A washer in this particu- 
lar place will reduce the pressure from its necessary 9 lbs, 
to 1 lb,, and is placed there at times in ignorance. If 
these three checks have been made and the equipment still 
leaks, exchange the apparatus for a now one. 
4. Face piece, Since no two people look the same, no 
two people's faces are built the same, and yet masks are 
essentially the same pattern. It is important, 
to check the mask to see whether it fits properly. The re- 
breather type mask is so built that it fits 
best when tho top straps are secured snugly 
and placed on the top of the head as far as 
possible. The bottom strap is only a safety 
strap and should go around the back of the 
neck loosely. If the user's nose bridge is 
either very sharp or very broad, it may be 
necessary to remold the nose piece of the 
taask, To do this there is a small malleable 
wire which can be adjusted. To check the 
mask for fitness one puts it on properly and 
then, with the nose connection clamped or 
kinked off by hand, one inhales. If the mask fits properly 
suction will result and the facepiece will collapse against 
the face. 
5. Washing or flushing out of the apparatus. This is 
done in order to fill the entire breathing bag and the hose 
connections with pure oxygen and is done simply by breath- 
ing in from the oxygen supply and breathing out to the at- 
mosphere. To expedite this there is a small face piece 
valve, the one which was 
closed in step three to 
check the system &r pos- 
sible and this face 
piece valve is manipula- 
ted in the following way. 
When tho user breathes in 
the valve is up, when he 
breathes out the valve is 
down. A simple way to re- 
member the process is to 
remember that breathing in the chest goes up; the valve 
goes up. Breathing out, the chest goes down; the valve 
goes down. In this way the user breathes pure oxygen in 
and breathes out to the atmosphere. This breathing in and 
breathing out with the valve up and down, respectively, is 
called ,fflushing out", and three or four flushes should be 
carried out at the following times. As soon as the appara- 
tus is put on it should be flushed out; every 10 or 15 mi- 
wivr 
or ' 
WttAlff 
**#r, nates in a flight; whenever the user belches or burpq 
since the intestinal gases arc part nitrogen it is impor- 
tant to remove this nitrogen from the system. 
This rebreather type of apparatus* which uses a mini- 
mum amount of oxygfen and which has a high degree of effi- 
ciency, must be used intelligently and with constant care 
to see that the oxygen lines are in order, that the canis- 
ter is not used too long, and that flushing out is done 
periodically and regularly. 
The fourth type of equipment, which is a recent de- 
velopment, is built upon the demand regulator principle 
and modified for a more efficient utilization of oxygen. 
You will recall in the regular demand type oxygen system 
10035 oxygen is delivered to the user with each inhalation. 
IOO56 oxygen is more than is necessary at altitudes above 
10 000 ft. and below %. Q00 ft., and, therefore, with the 
old demand type regulator there is always an excess of 
oxygen delivered to the user. For example, you will re- 
call from the doctor* s lecture that when IOO56 oxygen is 
being used at 18 000 ft., the oxygen pressure in the lung 
at that time is 293 was* of mercury, which is almost three 
times the amount necessary for normal bodily activity. 
The recent modification in demand type apparatus, which is 
called Dilutor Demand Regulator. corrects this waste of 
oxygen by mixing proper proportions of atmospheric air and 
oxygen (delivered from the cylinder), so that an internal 
lung pressure of oxygen of about 106 rams, is always main- 
tained. In other words, with the dilutor demand arrange- 
ment, the lung always has, with each inspiration, a pres- 
sure of oxygen comparable to that which exists at sea le- 
vel, breathing air. 
The dilutor demand regulator can be considered as 
three separate devices combined in one and by simple ad- 
justments any one of the three types can bo used. For ex- 
ample, under conditions of operation with the emergency 
valve opened, the regulator performs as a constant flow regulator. When the eme rgency valve is dosed and the di- 
lator demand valve is in its "OFF" position, then the regu- 
lator operates as an ordinary demand type regulator delive- 
ring 1005& oxygen to the user with each inhalation. When 
the valve is turned to its w0Nrt position, the device ope- 
rates to deliver enough oxygen to the user on each inhala- 
tion so that a pressure of approximately 107 mms, of mercu- 
ry is available in the lung. 
As far as the operation of 
this device is concerned, it is 
simple and quite automatic; the 
operator has to see, first, that 
there is an adequate oxygon sup- 
ply, and, second, that the oxygen 
supply is turned on. In most 
planes there is a flow indicator 
which offers the user an opportu- 
nity to see that oxygen is flow- 
ing, and then, after fitting at 
the mask, it is necessary only to 
see that the regulator valve is 
in its "ON" position. If this 
valve is not in its "ON” posi- 
tion, the user will be defeating the purpose of economy in- 
troduced by its use. These valves are so designed that the 
proportions of oxygen and air will be mixed or automatical- 
ly controlled by the atmospheric pressure, and there is 
less air in the mixture at 20 000 ft. than at 15 000, and 
less at 25 000 ft. than at 20 000, which means more oxygen 
at 25 000 ft. than at 20 000 ft,, etc, Vlhen an altitude of 
33 000 ft. is reached the valve is automatically closed and 
only pure oxygen reaches the user. 
This type of equipment is being introduced in various 
Navy aircraft and probably will be used by most Navy per- 
sonnel. There are two types of products on the market. The 
demonstration is a Pioncer-Bendix Model. The second type 
is the Aro-Mix, and, except for one slight difference,their 
performance and function are the same. This difference is 
that in using the Aro-Mix it is essential to put the regu- 
lator valve to its "OFF" position before opening the emer- 
gency valve for constant flow. S A f t T Y RULE S 
This chapter consists almost entirely of safety miles 
taken from the rules governing various trades in effect at 
U. 3. Naval Air Station, San Diego, California, They are 
divided into two sections. The following deal with the 
handling of gas cylinders, particularly oxygen. 
1. Do not store full gas cylinders 
in direct sunlight or in any hot 
place. 
2. Great care must be used to pre- 
vent the dropping or bumping of any 
gas cylinder. Cylinders must be 
kept in racks or stands or lashed 
to prevent them from being knocked 
over. 
3. Care must be taken to prevent 
the contamination by oil or grease 
with any part of the cylinder valve 
or hose, 
4. Leather washers must never be used on gas cylinder 
valves; the regular fiber washer or gasket must be used. 
5. The valve protector cap must be kept in place whenever 
cylinders are not in use. 
6. Cylinders must never be used for other than their de- 
signated kind of gas. 
7. Do not stand in front of gauges when opening the dis- 
charge valve. 
8. Handling of cylinders by cranes must be done only when 
proper racks are used. Rope or wire slings are forbidden. 
9. Remove regulators and place caps over valves when 
transporting cylinders by other than regular cylinder 
trucks, 
10. Cylinders must never be dropped or treated roughly, 
11. Leaky cylinders must be placed in the open immediately 
on being noticed. 
OIL <T 0-/G Prt , 
Hot hi** 12. Any charged or partially charged cylinder, of any 
site, is as potentially dangerous as a loaded shell and 
must always be handled as such. 
13. Should any charged or partially charged cylinder be- 
gin to discharge when not held, in a vise, every effort 
should be made to seize it or fall on it to prevent roll- 
ing. 
14* Cylinders shall never be voided of residual gas un- 
less an approved anti-coil safety cap is tightly screwed 
on the discharge orifice of the valve. Voiding shall be 
slowly, in the open air, at least 50 feet from open lights 
or fires. All other cylinders shall be securely damped 
in the cylinder vise. 
15. Oxygen and acetylene cylinders shall be stored sepa- 
rately in specially constructed storage locations. Cylin- 
ders shall be kept at a minimum and stored and shipped nth 
valve protecting caps in place. 
16. Use only the wrench provided for opening valves. 
17. Close valves only snug-tight and do not oil or grease 
them. 
18. Never handle the valve on a charged cylinder in such 
a way that it may unintentionally be opened, 
19. Never fill a cylinder beyond its rated capacity. 
20. To prevent explosion, use correct typo of safety disc 
properly installed. Allow no stoppage or abnormal res- 
trictions. in the discharge lines. 
21. Cylinder with a broken safety wire should be weighed 
to cheek its contents before use. 
22. Oxygen regulators shall be stamped with serial num- 
bers. Those in service shall be tested at intervals of 90 
days. 
23* Tests shall be conducted and logs maintained listing 
serial numbers and dates tested. 
The safety regulations below deal with the use of air 
plane dopes and solvents and noxious fuels* 
1. Working spaces must be kept clean and in complete or- 
der. 2. Extreme care shall be taken in handling and using sol- 
vents for cleaning. 
3. Inflammable solvents, when used for cleaning by hand 
shall be used only in approved safety cans. 
4. All heated objects shall bo kept free Of waste and re- 
sidue. 
5. No metals shall be struck together. Heavy nails, hobs 
or steel plates on solos or heels of shoes are prohibited. 
6. Steel scrapers for cleaning concrete floors in the 
presence of inflammables are prohibited. 
7. Only spark-proof tools and approved equipment shall be 
used in the presence of inflammables. 
8. No naked lights, automatic lighters, matches of any 
kind, or smoking will be tolerated in the presence of dope 
or solvents. 
9. No dope shall be stored in the shop, and none shall be 
handled in the shop in larger than one-gallon containers. 
All dope containers and brushes shall be removed at the end 
of the day and stored in fireproof lockers. 
10. Pirebills shall be posted and fire frills hold at re- 
gular intervals. 
11. Doors and windows shall be kept 
closed while doping. 
12. All pipe, ducts, or flues shall 
discharge out of doors at a safe point. 
13. Avoid excessive exposure to fumes. 
If overcome the immediate treatment is 
removal to fresh air, with artificial 
respiration, if necessary. Call the 
doctor. 
14. Protective cream shall be applied to skins sensitive 
to dope and solvents. 
15. Do not breathe fumes from welding, cutting, plating; 
pickling, painting, lead burning, galvanising, or molten 
metals. If adequate ventilation is not available, use fame 
type respirator. 
IV. V*<W«fOf« 
Gaum M<aSoiiaf 
|»AS Hft «\PV£>5iVP 
P»WC< «t AQ*>r 
54 (*»urfos*4*rm*iW 16. Attention is directed to the possible injurious toxic 
effect of fumes generated by metal spraying, particularly 
with cadmium, 
17. All metal spraying must be done in the open air or in 
well ventilated spaces, 
18. Operators must wear masks. 
19. Dust type respirators must be worn for chipping red 
lead, handling fibre glassy insulating materials, for dres- 
sing grinding wheels, and for other dusty work where ade- 
quate ventilation is lacking. 
20. Eye protectors(goggles or shields) 
must be worn when engaged in acid work- 
ing, babbitting, breaking metal (scrap 
work), cleaning overhead dril- 
ling, reaming, etc,, sawing (circular 
saw, large diameter, high speed), as- 
sisting welder, buffing, and in all work 
where flying particles are encountered, 
21. Rubber aprons, gloves, and rubber 
are to be worn when working in 
strong acids, alkali, etc, 
22. Breathing apparatus must be worn 
by sandblasters, acetylene welders, 
paint sprayers, when working in confined 
areas, and other occupations when necessary. 
23. All protectors, such as goggles, respirators, face 
shields, rubber gloves, and boots, shall be cleaned and 
sterilised once each quarter when used only by the same 
operator. 
24. Neve$ issue an employee a protector that has been 
used by another employee until it has been sterilised, 
25. Application of luminous paint is restricted to areas 
and enclosures specially provided for this purpose, 
26. Personnel assigned to this work must be familiar with 
safety precautions as outlined in the Navy Department Gene- 
ral Safety Rules, Section #9, Radioactive Luminous Compound. 
27. Working areas must be properly constructed, properly 
ventilated and approved with an approved type of ventilated 
hooded paint table. 
GoSClf ■ 
/«i OirtTOtf AMoTOPW 28. Operator* shall wear prescribed clothing respirators, 
and gloves, which shall be inspected in a dark room by ul- 
tra-violet lamp at the close of working hours. 
29. Operators must not point the brush with their lips or 
fingers.