^/2ttHb~- ftnJn inr nv RESPIRATION PHYSIOLOGY INDEXING PROBLEMS pflNtlllUMIIUlHllMF Index Section BSD 1968 RESPIRATION PHYSIOLOGY INDEXING PROBLEMS Prepared by David Millson National Lending Library of Science and Technology Boston Soa, Yorkshire A Index Section BSD lv6EN TO TISSUtS ^«b V is used by the tissue cells in their metabolic process (tissue respiration). The carbon dioxide produced in tissue respiration passes into the capillaries and is carried by the venous blood back to the lungs where it passes into the expired air. The main processes involved in respiration are listed in Figure 2\ The control of respiration by the central nervous system, the mechanics of breathing, gas exchange in the lung, and blood transport of gases are all considered from the MEDLARS point of view to be included in the field of respiratory physiology. For these the main heading RESPIRATION is used and not RESPIRATORY SYSTEM ^physiology. Tissue respiration, however, is considered to belong more to the field of biochemistry than to 2 Figure 2 inspiration Control of Respiraiion echourMCS of Brea+hincj Gas Exchange in. Lang Blood Transport of Oases] Considered as -field. of "Respiratory PKvjsiology." Use sub- Heading * physiology u^here appropriate. Ti ssue 3 ^^ p> rat ion. > Considered as a. biochemical concept- use ma\n heading OXY&EN CONSUMPTION not RESPIRAIION, and. ass subheading * metabolism u^Kere appropriate. physiology, and articles on it are indexed with the term OXYGEN CONSUMPTION rather than RESPIRATION, with the sub- heading *tnetabolism used where appropriate. Metabolism, Basal Metabolism and Calorimetry Gas exchange in the lungs and blood transport of oxygen and carbon dioxide are considered as physiological processes, and tissue respiration as metabolism, using metabolism in the sense of chemical changes occurring in the tissues. However, the term metabolism can also be used for the sum of chemical and energy transformations in the body as a whole: the metabolic rate is the rate of energy production of the whole body and is usually expressed in kilocalories per day; i.e., as heat energy. The metabolic rate can be measured by direct calorimetry The heat production of a human subject or animal is measured 3 directly while the subject is enclosed in a large calo- rimeter. However, metabolic rate is more frequently cal- culated in kilocalories by indirect calorimetry where the oxygen consumption of the subject is measured, and where, if the amount of energy released per liter of oxygen consumed is known, the metabolic rate in kilocalories can be estimated (Figure 3). To make accurate estimates, the Figure 3 DIRECT CALOPvimETRV INDIRECT CALORIMETRY "7777777777717% amount of carbon dioxide produced and the amount of nitrogen excreted need to be known so that the relative amounts of fat, protein and carbohydrates being oxidized in the body can be estimated. The MeSH headings available in this subject area are METABOLISM, BASAL METABOLISM, CALORIMETRY and OXYGEN CONSUMPTION, and sample titles might be "Resting metabolism in the aged," "Basal oxygen consumption in pregnancy," "Oxygen consumption in sleeping Eskimos," "Maximal oxygen consumption in exercise," "Energy expenditure in adolescents," "Energy metabolism of the chimpanzee," amd "Energy cost of walking." 4 The main difficulty in this area is that most studies of energy metabolism are carried out by using oxygen consump- tion; and that authors can treat the topic either in terms of energy expenditure or of oxygen consumption. Indexers will follow the usage of the author. Papers written in terms of energy metabolism will be indexed with METABOLISM or BASAL METABOLISM, and those written in terms of oxygen con- sumption with OXYGEN CONSUMPTION. (Figure 4) Figure 4 MeSH HEADINGS METABOLISM BASAL METABOLISM CALORIMETRY OXYGEN CONSUMPTION SAMPLE TITLES INDEXED -----Resting metabolism in the aged__________BASAL METABOLISM Basal oxygen consumption in pregnancy___ BASAL METABOLISM Je> OXYGEN CONSUMPTION Oxygen consumption in sleeping Eskimos___OXYGEN CONSUMPTION Maximal oxygen consumption in exercise___OXYGEN CONSUMPTION Energy expenditure of adolescents_______METABOLISM Energy metabolism of the chimpanzee_____METABOLISM Energy cost of walking________________METABOLISM TO SUMMARIZE A _TOW -----Index Energy Metabolism as METABOLISM or BASAL METABOLISM Index Oxygen Consumption as OXYGEN CONSUMPTION The MeSH heading BASAL METABOLISM should be used only for studies of the metabolism of subjects in the basal state, that is, in subjects who are awake but at rest and in a postabsorptive state (12 hours after eating and at a comfortable environmental temperature). The papers on "Resting metabolism in the aged" and "Basal oxygen consumption in pregnancy" fit this definition, and are indexed with BASAL METABOLISM. Since the second paper mentions oxygen consumption too, it is indexed with this term also. ^ The paper on "Oxygen consumption in sleeping Eskimos is indexed with OXYGEN CONSUMPTION, but not with BASAL METABOLISM for the subjects were not in the basal state. "Maximal oxygen consumption in exercise" is indexed with OXYGEN CONSUMPTION. 5 The three papers in which the main theme is energy expenditure or energy metabolism are indexed with METABOLISM as a print heading. However, if in these papers the author states that the studies were made by measuring oxygen consumption, this term may also be used as a non-print heading. CALORIMETRY is defined by MeSH as "measurement of the amount of heat absorbed or given out." It is used only for descriptions of the technic of calorimetry where the heat output is actually measured directly, and never for theo- retical discussions of energy metabolism. Since indirect calorimetry involves measurement of oxygen consumption only, and not of actual heat production, the term CALORIMETRY cannot be used. Articles on indirect calorimetry are indexed with OXYGEN CONSUMPTION. OXYGEN CONSUMPTION can be used either for oxygen consumption of the cell or of the whole organism. An article on the effect of epinephrine on respiration in muscle tissue is indexed MUSCLES ^metabolism, EPINEPHRINE *pharmacodynamics, OXYGEN CONSUMPTION *drug effects and MUSCLES *drug effects (Figure 5). The terms marked with an X are print terms, i.e., the citation will appear under these headings in INDEX MEDICUS. Figure 5 title: The effect of epinephrine on respiration in muscle tissue index: X MUSCLES ^metabolism X EPINEPHRINE *pharmacodynamics X OXYGEN CONSUMPTION *drug effects MUSCLES *drug effects The combination MUSCLES *drug effects is indexed for computer storage for researchers interested in the effects of drugs on muscles, without reference specifically to respiration of muscle tissue. 6 Mechanics of Breathing: Respiratory Tract Anatomy In order to describe the mechanics of breathing, it is first necessary to discuss the anatomy of the lungs and respiratory airways. Figure 6 shows this arrangement. Figure 6 PHARYNX TRACHEA 3R0NCHI PLEURA CHEST WALL INTRAPLEURAL SPACE DIAPHRAGM The pharynx acts as a passage for both food and air. During swallowing the opening from the larynx into the pharynx is closed by the epiglottis which acts like a valve to prevent food from entering the airways. From the larynx, air passes down the trachea which forks to form the right and left primary bronchi supplying the right and left lungs. The primary bronchi subdivide into secondary and tertiary bronchi, and finally into 7 Figure 7 ALVEOLI ALVEOLAR SAC ALVEOLAE DUCT BRONCHIOLE BRONCHUS small tubes called bronchioles which finally communicate^ with alveolar sacs lined by minute pockets called alveoli (Figure 7). The walls of the alveoli are richly supplied with capillary blood vessels and it is here that the gas exchange between the air and the blood takes place. The MeSH terms available for the anatomy of the respiratory system are found in Category A4 (Figure 8). Figure 8 A4 RESPIRATORY SYSTEM NOSE * PARANASAL SINUSES * LARYNX * TRACHEA BRONCHI LUNG PLEURA PULMONARY ALVEOLI Respiratory Airways airways resistance airways obstruction RESPIRATORY TRACT DISEASES (IM) Bronchoconstriction BRONCHI ^'physiology (IM) CONSTRICTION (NIM) Bronchodilatation BRONCHI ^physiology (IM) DILATATION (NIM) Isolated Trachea or Bronchi TRACHEA or BRONCHI MUSCLE. SMOOTH 8 The terms marked with an asterisk are expanded further; for example, the individual paranasal sinuses are named. The main problem here is that it is not possible to specify respiratory airways, a concept commonly used, for instance, in papers on airways resistance or airways obstruction. Papers on airways obstruction should be indexed under RESPIRATORY TRACT DISEASES. The walls of the trachea, bronchi and bronchioles contain smooth muscle which can contract, narrowing the diameter of the airways. The terms bronchoconstrietion and bronchodilatation are frequently seen in the literature. They are indexed as BRONCHI ^physiology and the provisional heading CONSTRICTION, and BRONCHI ^physiology and the provisional heading DILATATION, respectively. Note, however, that bronchial constriction at a clinical level is sometimes the disease term BRONCHOSPASM. The isolated trachea or bronchus is sometimes used as a test preparation for studying tracheal or bronchial smooth muscle. Papers on this topic should be indexed with TRACHEA or BRONCHI and MUSCLE, SMOOTH. The slant of the article will determine which is IM and which NIM. The lungs are not connected with the chest wall. They lie in the pleural cavity. (Figure 9) Figure 9 WARYNX TRACHEA - BRONCHI - PLEURA - CHEST WALL - INTRA PLEURAL SPACE . .DIAPHRAGM 9 A serous membrane, the pleura, covers the surface of the lungs and lines the inside of the chest wall; the space it encloses is called the pleural cavity or intra- pleural space. A sheet of muscle, the diaphragm, separates the thorax and abdomen, and forms the lower boundary of the pleural cavity. The lungs under normal conditions practically fill the pleural cavity with only a thin layer of pleural fluid separating them from the chest wall. The lungs are elastic and exert an inward pull, so that there is a negative pressure in the pleural cavity. If the chest wall were perforated, the lung would collapse and the pleural cavity would fill with air, a condition called PNEUMOTHORAX. In normal conditions, however, air cannot enter the pleural space and the lungs follow the movements of the chest wall and diaphragm. Inspiration is brought about by the contraction of the inspiratory muscles ( the diaphragm and external intercostal muscles). The diaphragm, which is normally concave, flattens, increasing the volume of the thoracic cavity, and the external intercostal muscles lift the rib cage, a movement which increases the volume of the chest. Normal quiet expiration is a passive process: the lung and chest wall are elastic structures and their recoil is sufficient to drive air out of the lungs. The expiratory muscles (the internal intercostals and the abdominal muscles) come into action during vigourous breathing and force air out of the lungs. Mechanics of Breathing: Lung Elasticity, Compliance and Resistance Studies of the mechanics of respiration can be divided into studies of the static properties of the respiratory system (i.e., the elasticity of the lungs and chest wall) and dynamic studies (i.e., resistance to air flow during respiration). The measure of lung elasticity most commonly used is COMPLIANCE, defined as the volume change of the lung per unit change of pressure \vvp- . The greater the compliance, the greater the "give" of the lung when air is pumped into it. The lung can be considered an elastic balloon 10 inside an elastic container, the chest wall. To study compliance and resistance (Figure 10), volume changes and pressure changes are measured. Figure 10 ( comPLiftNcs m\> Rfr&isTftNCE— X V , y S^ A ' ' /LUNGS \ \ y ) X---------- . MOUTH PRESSURE CHEST WALL INTRAPLEURAL PRESSURE ■ PRESSURE ^ ALVEOLt PRESSURE OUTSIDE CHEST Depending on the site chosen for pressure measurements, one can get figures relating to the airways only, or to the lung, or to the whole respiratory system. Pressure can be measured or estimated in the alveoli, in the pleural cavity, at the mouth or outside the chest. To measure lung compliance, it is necessary to see how the lung volume depends on the pressure difference between the inside and the outside of the lung. This can be measured in the isolated lung, but in the human subject it is necessary to measure the intrapleural pressure. This can be done by measuring the pressure of the esophageus or by introducing some air into the intrapleural space and measuring the pressure of the air. The compliance of the whole respiratory system is measured much more easily for the pressure difference between the inside of the lung and the outside air only is required. Resistance is measured as the pressure needed to produce a given rate of flow the greater the resistance to flow, the greater the pressure required. The airways resistance gives the relationship between the rate of flow of air from the lungs and the pressure difference between the alveoli and the mouth. One cannot measure the pressure in the alveoli directly, and the airway resistance 11 is usally determined using whole body plethysmography. The change in chest volume recorded by the plethysmograph indicates how much the air in the alveoli is compressed during expiration, and so its pressure can be calculated. The pulmonary resistance can be measured by recording the relationship between the rate of air flow from the lungs and the intrapleural pressure. It includes the resistance of the airways to air flow and the resistance of the lung tissue to change the shape. The respirator*"* resistance is the resistance of the whole respiratory system, and can be measured during passive inflation of the thorax. Figure 11 illustrates the principles of compliance and resistance. Figure 11 AY_ UANfr COMPLIANCE AP PRESSURE DIFFERENCE RESPIRATORY COMPLIANCE Complicxncc of Luvnj ancA Chest VUU PRESSURE DIFFERENCE AIRWAY RESISTANCE V PULMONARY RESISTANCE WteSSURt blPPERENCE .PRESSURE / DIFFERENCE fTfcSP) RATORY RESISTANCE, i PRESSURE » D\FFE.Stfi.NCE 12 The elasticity of the lung is due in large measure to the surface tension of the fluid lining the alveoli. The * alveoli behave like small bubbles, and the surface-tension effect tends to cause them to collapse. In fact, if it were not for the presence of a lipoprotein, the pulmonary surfactant.which reduces the surface tension of the alveolar fluids, the lungs would collapse under normal conditions. Spirometry Many studies of lung function, especially studies in disease states, fall under the heading spirometry. The spirometer is simply a device for measuring the volume of air inhaled or exhaled (Figure 12). It consists of an inverted bell floating on water and containing air breathed by the subject through a mouthpiece. Vertical movements of the bell are recorded on a rotating drum and can be read off as volumes of air inhaled or exhaled. Figure 12 SPIROMETER AIR IN ^t AIR NOUTH PIECE fQ= BELL o j\ J) '(■ 'A "Q U.W TV ftKOW*- 13 By means of spirometry the total lung volume can be divided into a number of components (Figure 13). i^ure SUBDIVISIONS ^ LUNC7 VOLUME . ERVa Expira+ory Reserve. Volume FRC- Func-Vtonal Residual Capacl+u IRV * Inspiratory Reserve Volume RV « Residual Volume TLC * TotaL Lung Capaa+u TV * Tidal Volume VC « Vi+al Capaci+ij -^ tiaal volume is the amount of air which moves in and out of the lungs during respiration under given conditions. The inspiratory reserve volume is the maximum amount which can be breathed in by making an effort, at the end of a normal inspiration. The expiratory reserve volume is the maximum amount of air that can be breathed out after making a normal expiration. The vital capacity is perhaps the most widely used of these measures of lung volume; it is the maximum amount of air which can be breathed in after forcibly emptying the lungs. The residual volume is the amount of air that is left in the lungs after a maximal expiration. A list of these subdivisions of lung volume and the abbreviations frequently used for them are given in the diagram. Alterations of these volumes are frequently used to diagnose respiratory diseases for in restrictive impair- ment of lung function the capacity of the lungs is decreased. 14 Besides these static volume measurements, dynamic studies can be made using spirometry, because the fastest rate at which a subject can breathe in or out depends on the resistance of the airways to the flow of air, and in disease where airway obstruction is present, the resistance is increased. A commonly used test is the timed vital capacity.(Figure 14) Figure 14 TIMED VITAL CAPACITY VOLUME t s*x AIRWAY OBSTRUCTION s. NORMAL 1 S£C ASSC i SEC T\ra-c The subject takes a maximal inspiration and then breathes out as rapidly as possible into a spirometer. The most commonly used measure is the FEV-|_ q (one-second forced expiratory volume). The dotted line on the diagram represents the curve for a patient with airway obstruction and it can be seen that the FEV is much reduced. Other parameters*of this same curve can also be used as a measure of respiratory resistance, for example, the midexpiratory time (MET) and the maximal mid expiratory flow (MMEF). 15 A spirometer can also be used to record the maximum voluntary ventilation (MW) (Figure 15), also called the maximal breathing copacity (MBC). K?>~\T^F\ VOLUNTARY VENTILATION Figure 15 vommfc T «- NORMAL A\RWAY OBSTRUCTION —^ TltAfc This is the largest volume of air which can be breathed in and out in one minute. This quantity is reduced in obstructive lung diseases. Bronchospirometry Brochospirometry is a special technic in which the volume of air breathed by the right and left lung is recorded separately. A special double-lumen catheter is 16 passed down the trachea and inflatable cuffs are used to separate the air flow from the right and left lungs (Fig- Figure 16 BftOfYCHQS?')RornETKY DOUBLE- LUHEtf CATHETEPs L£PT BRONCHUS RIOHT BRONCHUS Gas Exchange in the Lungs As we have seen, gas exchange in the lungs take* •JS* sr-Ai-ssm^m€ 17 of the alveolar air, therefore, remains fairly constant; the partial pressure of oxygen in the alveolar air is about lOOcim Hg and the partial pressure of carbon dioxide about 40mm Hg. To get a sample of alveoli air, one has only to breathe out into a long tube. (Figure 17) Figure 17 __ ALVEOLAR Al D-ADSPACE AIR ALVfcOLAR ..A\R _DEADSPACE At ft P^zzmhMmml -ALVfcOLAR AIR The first air to emerge comes from the trachea and the bronchi—the so-called deadspace air. Deadspace air is similar to room air in composition, but the later fractions of the air breathed out come from the alveoli and reach a fairly uniform composition, that of alveolar air. In Figure 18, the curve shows the percentage of carbon dioxide in the expired air during the course of 18 a single expiration. It can be seen that during the later part of the expiration the carbon dioxide content reaches a steady level equal to that in alveolar air. t Figure 18 COMPOSITION OF ALVEOLAR -----*" AiR .VOLUME EXPIRED Devices which automatically sample the last few milli- liters of each breath—the end tidal air sampie—can be used to follow changes in the composition of alveolar air. Gas exchange takes place between the alveolar air and the capillaries by diffusion. The venous blood which arrives at the lung contains much carbon dioxide and little oxygen. The alveolar air contains much oxygen and little carbon dioxide. The gases diffuse across the 19 Figure 19 GAS EXCHANGE in ALVEOLI VENOUS BLOOD BLOOD FLOW ALVEOLUS pO* * *00 mm Ha ARTERIAL BLOOD .Pojt * ^ mm Ho PULMONARY pulmonary membrane from regions of high concentration to regions of low concentrations (Figure 19). Venous blood arriving in the alveolar capillaries has a Pq2 (partial pressure of oxygen) of 40mm Hg. The Pq? of alveolar air is 100mm Hg. Oxygen diffuses across the pulmonary membrane from the alveolus to the capillary until the blood leaving the alveolus is nearly equilibrated with alveolar air (the partial pressure of oxygen in this "arterial blood" is about 97mm Hg, in comparison with 100mm Hg in the alveolus). Quantitative measures of this diffusion process are frequently used. The pulmonary diffusing capacity (Dl) is the quantity of gas diffusing across the pulmonary membrane per minute per millimeter of partial pressure difference between the alveolar air and the inside of the erythrocytes in pulmonary capillary blood. The membrane diffusing capacity (D*^) is the quantity of gas diffusing across the pulmonary membrane per minute 20 per milliliter of partial pressure difference between the alveolar air and the plasma in the pulmonary capillaries. The Dt is a measure of diffusion across both the pul- monary membrane and the red cell membrane; the DM, across the pulmonary membrane alone. The "pulmonary membrane" is composed of the wall of the alveolus and the wall of the capillary, plus any interstitial tissue between. The pulmonary diffusing capacity is most easily measured for carbon monoxide. If a snail amount of carbon monoxide is breathed, the hemoglobin in the pulmonary capillaries combines with it all, so that the partial pressure dif- ference between the alveoli and the capillaries is thus very easily measured. The pulmonary diffusing capacity for carbon monoxide (Dlco) Is often used as a diagnostic test. In disease, pulmonary diffusion is often impaired due to fibrosis of the alveolar wall or destruction of the alveoli, and the D*Lco S^ves a measure of this. The lung diffusing capacity of other gases (for example, oxygen) can also be measured, but with less cer- tainty owing to difficulties in calculating the partial pressure difference across the pulmonary membrane. Figure 20 .DISTRIBUTION of VENTILATION !l : f The term ventilation is used for the process of the removal of air in the lungs during breathing. Pulmonary ventilation is simply the amount of air breathed per minute (Figure 20). Alveolar ventilation is simply the amount reaching the alveoli per minute.Not all the air breathed reaches the alveoli: some remains in the airways (this is called deadspace air). Many recent papers deal with 21 the concept of uneven distribution of ventilation in the lungs. That is, some alveoli are well-ventilated, while the air in others is not renewed very efficiently. Other studies deal with the uneven distribution of blood flow in the lungs. Note that in Figure 21 the lower part of the lung receives more blood than the upper part. The term ven- tilation-perfusion ratio is much used for the study of the ratio of ventilation of the alveolus to the blood flow through its capillaries. This subject area can be studied with the aid of radioactive gases, with radioactive carbon dioxide, oxygen and xenon being frequently used. Figure 21 DISTRIBUTION of BLOOD fLOW VENTILATION — PERFUSION VENTILATION //// v' PERFUSION 22 If a subject takes a breath of radioactive carbon dioxide, scanning of the lungs shows most radioactivity in the well-ventilated parts of the lung. The rate-of disappearance of the carbon dioxide from different parts of the lung while the subject holds his breath reflects the distribution of blood flow in the lung. It will be carried away more rapidly in regions with a large blood supply. A simple method of study is to switch a subject from breathing air to breathing oxygen, and to follow the rate of washout of nitrogen from the lung. The nitrogen is cleared rapidly from well-ventilated areas, but not from the poorly ventilated parts of the lung. If some of the blood flowing through the lung passes through alveoli which are not ventilated at all, it is as though venous blood had been mixed with arterial blood. This is referred to as venous admixture or pulmonary arteriovenous shunt (Figure 22). Figure 22 PULMONARY ARTERIOVENOUS SHUNT VENOUS BLOOD WZ7777, NOT 0XY&ERA1ED OX>f&ErfATE.b 23 The difference between the po2 in arterial blood and that in the alveoli gives a measure of the amount of blood passing through the bung vmbthout being oxygenated. This is called the alveolar-arterial oxygen gradient. Symbols in Respiration Physiology In much of the work on gas exchange, authors use an internationally accepted set of symbols. Thus, "V" stands for gas volume, "p" for gas pressure, "Q" for volume flow of blood, and so on. The subscript "I" means inspired gas and "A," alveolar gas, while the subscript "a" means arterial blood and "b," venous blood. These symbols can be combined to express many different concepts. Thus Aq2 is alveolar partial pressure of oxygen, while O2 is the partial pressure of oxygen in arterial blood. Vq2 is volume of oxygen per unit time and can be used to mean the rate of oxygen consumption FEC0 is the fraction of carbon monoxide in the expired air, while A is the ventilation perfusion ratio. Since these symbols^are often used by authors without being defined in the text, indexers should be familiar with them (Figure 23) . Figure 23 GENERAL VARIABLES V Gas volume V Gas volume per unit time P Gas pressure F Fractional concentration Q Volume flow of blood C Concentration f Respiratory frequency R Respiratory exchange ratio D Diffusing capacity p A°2 partial pressure of oxygen in alveolar air 02 partial pressure of oxygen in arterial blood Vq2 oxygen consumption fEqo fraction of CO2 in the expired air ^a ventilation-perfusion ratio Q SUBSCRIPTS I Inspired gas ! E Expired gas A Alveolar gas t T Tidal gas D. Deadspace air B Barometric b Blood :io a Arterial V Venous c Capillary 24 Transport of Gases in the Blood Oxygen and carbon dioxide are transported in the blood from the lungs to the tissues, the oxygen in combination with hemoglobin in the erythrocytes and the carbon dioxide mainly as bicarbonate in the plasma but also partly in combination with blood proteins, including hemoglobin. Hemoglobin, therefore, plays a part in the transport of both oxygen and carbon dioxide. When the partial pressure of oxygen is high (as it is in the lungs), four molecules of oxygen can combine with one molecule of hemoglobin to form oxyhemoglobin. When the partial pressure of oxygen is low (as it is in the tissues) the oxyhemoglobin gives up its oxygen. The curve relation, the percent oxygen saturation of hemoglobin with the partial pressure of oxygen in the blood, is called the oxygen dissociation curve of hemoglobin (Figure 24) Figure 24 OXYOEN D\SSOCIM\ON CURVE OF KEM0O>LOB\N ARTERIAL BLOOD Percent saturation of oxyc^an 70%--------- ~> . r— =~-m "m \QQ mmY\? PRESSURE <£ 0XYOEN 25 The diagram shows that the percentage saturation of hemoglobin with oxygen is nearly 100% at the partial pressure of oxygen found in arterial blood, and is about 70% at the partial pressure found in venous blood at rest. Thus in a subject at rest about \ of the oxygen carried by hemoglobin in arterial blood is given up to the tissues. This fraction, which is termed the coefficient of oxygen utllizationT may be much greater in exercise, when the concentration of oxygen in the tissues is very low. The oxygen dissociation curve shifts to the right when blood is acidified or when CO2 is added as it is in the tissues. This shift helps the hemoglobin to give up its oxygen, and is called the Bohr effect. Carbon dioxide transport in the blood is closely linked with the ACID-BASE EQUILIBRIUM of the body. Carbon dioxide reacts with water to produce carbonic acid, and if it was not for the buffering action of the plasma proteins and of bicarbonate present in the blood, the pH of the blood would not remain as stable as it does at pH 7.3-7.6. In respiratory alkalosis, hyperventilation lowers the blood CO2 below normal. Blood gas analysis used to be carried out by laborious chemical methods, but it is now usually done polarogra- phically using membrane-covered electrodes such as the Clark oxygen electrode, which can give a continous record of blood gas composition. The degree of oxygen saturation of the blood can be recorded continuously using an oximeter. This is a photoelectric colorimeter which can sense the difference between the colors of oxygenated and deoxygenated hemoglobin. In indexing this subject area, studies of the oxygen dissociation curve or gas transport by hemoglobin should be indexed with HEMOGLOBIN and OXYGEN *blood, both print. The term BLOOD GAS ANALYSIS is used only for studies of the technic of blood gas analysis, and not as a synonym for analysis of oxygen. Studies of blood pH should be indexed with HYDROGEN-ION CONCENTRATION and with the term BLOOD, both print (the sub- heading *blood cannot be used with HYDROGEN-ION CONCENTRATION which is in Category H of MeSH). Thus an article on the effect of hyperventilation on blood Pq2 , FC02 > an<^ P^ 26 should be indexed with HYPERVENTILATION, OXYGEN *b!ood, CARBON DIOXIDE *blood, HYDROGEN-ION CONCENTRATION and BLOOD. Subheadings with OXYGEN and CARBON DIOXIDE The use of some subheadings available to Category D (Chemicals and Drugs) with OXYGEN and CARBON DIOXIDE can give misleading results. In the MEDLARS system the sub- heading ^pharmacodynamics used with names of drugs and chemicals is used in the sense of "the effect of an exogenously administered drug or chemical." -pharmaco- dynamics should not be used with respect to OXYGEN and CARBON DIOXIDE. Thus, a paper on the effect of breathing oxygen in the heart rate should be indexed not with OXYGEN *pha*rmacodynamics and HEART RATE *drug effects but simply as with OXYGEN and HEART RATE. The combination OXYGEN "^metabolism should not be used; the term OXYGEN CONSUMPTION is preferred. CARBON DI- OXIDE ^metabolism may be used for the production of carbon dioxide in cellular respiration or for quantitative studies of the amount of carbon dioxide produced by the entire organism, but not for gas exchange in the lung or for blood transport of carbon dioxide.. The subheading "^physiology should not be used with either OXYGEN or CARBON DIOXIDE. Articles on the physio- logical role or OXYGEN in breathing should be indexed with the term OXYGEN without any subheadings. It would be logical to use OXYGEN ^physiology for studies of oxygen exchange in the- lungs or the effects of breathing oxygen, but the subheading -physiology cannot be used in the system for an exogenous chemical. Carbon dioxide may be endogenous, but to avoid treating the two gases in different ways, the same rule will apply here: omit the subheading ^physiology. 27 GLOSSARY AND INDEXING INSTRUCTIONS This glossary lists terms commonly seen in articles on respiratory physiology. Official definitions supplied by Medical Subject Headings (MeSH) are printed here as given. It was not felt necessary to define such terms as THORAX, LUNG, etc. ACIDOSIS, RESPIRATORY bronchocilatation ACIDOSIS, RESPIRATORY (C5) 1968 an abnormal condition due to excess retention of carbon dioxide in the body and resulting in an increase in hydrogen ion concentration in the body fluids; the retention in this case is the result of the failure to adequately clear the blood of carbon dioxide by reason of pulmonary disease.(MeSH definition) airways obstruction mechanical blockage of airways Index RESPIRATORY TRACT DISEASES (68) airways resistance relationship between the rate of flow of air from the lungs and the pressure difference between the pulumonary alveoli and the mouth Index RESPIRATORY SYSTEM *physiology(68) alkalosis, respiratory blood carbon dioxide below normal because of hyperventilation Index ALKALOSIS (IM) (68) HYPERVENTILATION (IM) (68) . alveolar air air in the pulmonary alveoli Index RESPIRATION (IM) (68) PULMONARY ALVEOLI (IM) (68) alveolar-arterial oxygen gradient amount of blood passing through the lung without being oxygenated alveolar capillaries the capillaries of the pulmonary alveoli Index PULMONARY ALVEOLI (IM) (68) CAPILLARIES (IM) (68) alveoli, pulmonary the air cells In the lung Index PULMONARY ALVEOLI (68) alveolar duct passageway in air cells Index PULMONARY ALVEOLI (68) alveolar sac the covering around the air cells Index PULMONARY ALVEOLI (68) alveolar ventilation amount of air reaching alveoli per minute Index PULMONARY ALVEOLI (IM) (68) RESPIRATION (IM) (68) METABOLISM (Gl) turnover of energy in a fasting and resting organism to maintain cellular activity; determined with subjects in a basal state (awake, after eating, and at rest at a comfortable environmental temperature) ' basal oxygen consumption respiration in a resting organism Index BASAL METABOLISM (68) basal state awake but at rest; in reference to conditions under which basal -metabolism is measured; see BASAL METABOLISM Index BASAL METABOLISM' (68) bLOOD GAS ANALYSIS (El) blood pH measure of acidity or basicity of the blood Index HYDROGEN-ION CONCENTRATION (IM)(68) BLOOD (IM) (68) Bohr effect shift of the oxygen dissociation curve to the right when the blood is acidified, thus helping hemoglobin to give up oxygen Index HEMOGLOBIN (IM) (68) OXYGEN *blood (IM) (68) HYDROGEN-ION CONCENTRATION (NIM) (68) BRONCHI (A4) 1963 bronchiole a branch of the bronchus Index BRONCHI (68) bronchoconstriction Index BRONCHI ^physiology (IM) (68) CONSTblCTION (Prov) (NIM) (68) bronchodilatation Index BRONCHI ^physiology (IM) (68) DILATATION (Prov) (NIM) (68) i BRONCKOSPIRCMETRY BRONCi-CSPIROMETRY (El) spirometric technic in which the volume of air breathed in the ri3ht and left lung is recorded separately buffering action action that keeps the pH stable Index BUFFERS (68) CALORIMETRY (H) 1968 measurement of the amounts of heat absorbed ot given out, also the technic for determining specific heats (MeSH definition) calorimetry, direct direct measure of heat production of a subject with the subject in a calorimeter; does not refer to theo- retical aspects of energy metabolism Index CALORIMETRY (68) calorimetry, indirect measure of oxygen consumption; does not measure actual heat production Index OXYGEN CONSUMPTION (68) cell respiration Index OXYGEN CONSUMPTION "(68) chest wall the limiting structure of the chest Index THORAX (68) coefficient of oxygen utilization the fraction of oxygen carried by hemoglobin in arterial blood that is given up to the tissues Index OXYGEN CONSUMPTION (68) compliance (Gl) (Prov) (68) the capacity of an organ or tissue to resist change in size or shape and to return to its orginal state following removal of the stress See also LUNG COMPLIANCE (Prov) Index appropriate main heading *physiology or *physiopathology ELASTICITY (68) constriction (C17,E4,G1)(Prov) (68) narrowing or reducing in size; in medicine it usually refers to the narrowing of the lumen of an organ producing increased resistance to flow Index appropriate main heading (IM) (68) CONSTaICTICN (Prov) (NIM) (68) ii energy metabolism deadspace air first air to emerge from the trachea and bronchi during respiration Index RESPIRATION (68) deoxygenated hemoglobin hemoglobin with oxygen removed Index HEMOGLOBIN (68) DIAPHRAGM (A 2) diffusion (G1,H) (Prov) (68) the spontaneous mixing of one sub- stance with another; usually refers to the passage of substances from regions of high concentration to low without significant energy requirement Index BIOPHYSICS (IM) (68) CHEMISTRY, PHYSICAL (IM) (68) dilatation (C17,E4,G1) (Prov) (68) increase in size by stretching or expansion; usually refers to in- crease In diameter of the lumen of an organ Index appropriate main heading and subheading \ ' see pulmonary diffusing capacity >M see membrane diffusing capacity end tidal air sample sample of the last few milliliters of each breath Index SPIROMETRY (68) energy cost Index METABOLISM (68) or BASAL METABOLISM (68) clergy expenditure Index METABOLISM (68) or EASAL METABOLISM (68) or OXYGEN CONSUMPTION (68) energy metabolism Index METABOLISM (68) or BASAL METABOLISM (68) or OXYGEN CONSUMPTION (68) ERV ERV see expiratory reserve volume esophageal pressure pressure in the esophagus Index ESOPHAGUS (IM) (68) PRESSURE (NIM) (68) ESOPHAGUS (A3) 1966 expiration breathing carbon dioxide out of the lungs Index RESPIRATION (68) expiratory reserve volume . maximum amount of air that can be breathed out after making a normal expiration Index SPIROMETRY (68) external intercostal muscles inspiratory muscles index INTERCOSTAL MUSCLES (68) ' Fev 1.0 see forced expiratory volume forced expiratory volume maximal inspiration breathed out as rapidly as possible; FEV Index SPIROMETRY (68) FRC see functional residual capacity functional residual capacity Index SPIROMETRY (68) gas exchange, respiratory Index RESPIRATION (68) HEMOGLOBIN (D10) HYDROGEN-ION CONCENTRATION (H) concentration of hydrogen ions as a measure of alkalinity and acidity HYPERVENTILATION (C5,C17) 1968 increased amount of air entering the pulmonary alveoli, resulting b in reduction of carbon dioxide tension inspiration breathing of air Into the lungs Index RESPIRATION (68) MBC inspiratory reserve volume maximum amount of air that can be breathed in by making an effort, at the end of a normal inspiration Index SPIROMETRY (68) internal intercostal muscles expiratory muscles Index INTERCOSTAL MUSCLES (68) intrapleural pressure pressure inside the pleura Index PLEURA (IM) (68) PRESSURE (NIM) (68) intrapleural space see pleural cavity IRV see inspiratory reserve volume b.iljcalories beat energy units Index CALORIMETRY (68) LUNG (A4) lung compliance (Prov) (E1,G1) (68) elastic properties of the lung measured by the relation between volume changes of the lung and the pressure required to Inflate the lung Index LUNG *physiology (IM) (68) LUNG COMPLIANCE (Prov) (NIM) ((38) maximal breathing capacity see maximum voluntary ventilation maximal midexpiratory flow spirometric technic for measurement of respiratory resistance Index SPIROMETRY (IM) (68) RESPIRATORY SYSTEM ^physiology (LM) (68) maximum voluntary ventilation syn. maximal breathing capacity; MBC; MVV largest volume of air which can be breathed in and out in one minute Index SPIROMETRY (68) MBC maximal breathing capacity; see immcimum voluntary ventilation membrane diffusing capacity membrane diffusing capacity quantity of gas diffusing across the pulmonary membrane per minute per milliliter of partial pressure difference between the alveolar air and the plasma in the pulmonary capillaries; D>j Index RESPIRATION (IM) (68) PULMONARY ALVEOLI ^physiology (IM) (68) DIFFUSION (Prov) (NIM) (68) MET see midexpiratory time metabolic rate rate of energy production of the whole body; usually expressed in kilocalories per day Index METABOLISM (68) METABOLISM (Gl) chemical and energy changes in the organism or specified parts midexpiratory time spirometric technic for measurement of respiratory resistance Index SPIROMETRY (IM) (68) RESPIRATORY SYSTEM *physiology (IM) (68) MMEF see maximal midexpiratory flow MW see maximum voluntary ventilation OXIMETRY (El) measurement of oxygen saturation of blood; a specific technic, not a synonym for the determination of blood oxygen OXYGEN CONSUMPTION (Gl) syn. Qo2, rate of respiration the volume of oxygen consumed by a cell (at STP) per unit weight of organism, per unit time (MeSH definition: Geise Cell Physi- ology, 1962, p. 370; Davson: Text- book of Physiology, 1964, p. 186) oxygen dissociation curve percent of oxygen saturation of hemoglobin with partial pressure of oxygen in the blood Index HEMOGLOBIN (IM) (68) OXYGEN *blood (IM) (68) iv pulmonary arteriovenous shunt oxygen saturation of blood amount of oxygen contained in the blood Index OXYGEN *blood (68) oxygenated hemoglobin hemoglobin of arterial blood, com- bined with oxygen Index HEMOGLOBIN (68) oxyhemoglobin a compound formed from hemoglobin on exposure to air, with formation of a covalent bond with oxygen and without change of the charge of the ferrous state Index HEMOGLOBIN (68) PARTIAL PRESSURE (H) the pressure exerted by an indi- vidual gas in a mixture of gases; the sum of the partial pressures of individual gases is equal to the total pressure (MeSH definition; Fulton: Textbook of Physiology) pH of the blood measure of acidity of basicity of the blood Index HYDROGEN-ION CONCENTRATION (IM)(68' BLOOD (IM) (68) PHARYNX (A3) 1964 plethysmography, whole body a method for measuring alveolar pressure indirectly; based on changes in chest volume to show how much air in alveoli is com- pressed during expiration Index PLETHYSMOGRAPHY (68) PLEURA (A4) pleural cavity Index PLEURA (68) PNEUMOTHORAX (C5) condition occurring if chest wall is perforated, causing the lung to collapse and the pleural cavity to fill with air pulmonary arteriovenous shunt see venous admixture % pulmonary diffusing capacity pulmonary diffusing capacity quantity of gas diffusing across the pulmonary membrane per minute per milliliter of partial pressure (difference between the alveolar air and the Inside of the erythrocytes in pulmonary capillary blood; Dl- Index RESPIRATION (IM) (68) PULMONARY ALVEOLI ^physiology (IM) (68) DIFFUSION (NIM) (68) pulmonary membrane includes the wall of the alveolus, the wall of the capillary and any interstitial tissue between Index PULMONARY ALVEOLI (IM) (68) CAPILLARIES (NIM) (68) pulmonary resistance includes the resistance of airways to air flow and the resistance of lung tissue to change shape Index LUNG ^physiology (68) pulmonary surfactant lipoprotein that reduces tension of the pulmonary alveolar fluids Index LUNG *physiology (IM) (68) SURFACE-ACTIVE AGENTS (IM) (68) SURFACE PROPERTIES (Prov)(NIM)(6G) LIPOPROTEINS (IM) (68) pulmonary ventilation Index RESPIRATION (68) residual volume amount of air left in the lungs after forced expiration Index SPIROMETRY (68) RESPIRATION (Gl) gas exchange between an organism and the environment, an essential feature of most living systems; intake of air through the lungs, gills, air tubes, etc. respiratory acidosis see ACIDOSIS, RESPIRATORY respiratory airways Index RESPIRATORY SYSTEM (68) tidal volume respiratory alkalosis see alkalosis, respiratory respiratory compliance compliance of lung and chest wall Index RESPIRATORY SYSTEM *physiology (IM) (68) COMPLIANCE (Prov) (NIM) (68) respiratory physiology includes the mechanics of respiration and activities involved in gas exchange and oxygen consumption Index RESPIRATION without the subheading *physiology (68) respiratory resistance resistance of the whole respiratory system Index RESPIRATORY SYSTEM ^physiology (IM) (68) RESISTANCE (Prov) (NIM) (68) resting metabolism chemical changes in a quiet or resting organism or organ Index BASAL METABOLISM (68) RV see residual volume SPIROMETRY (El) measurement of volume of air inhaled or exhaled by the lung; applicable to various degrees of the respiratory process SURFACE TENSION (H) a resistance that acts to preserve the integrity of a surface thoracic cavity space in which heart and lungs lie Index THORAX (68) THORAX (A, A2, A4) uidal volume amount of air which moves in and out of the lungs during respiration under given conditions Index SPIROMETRY (68) v lmeu vita! capam ty whole body plethysmography tinmJ vital capacity spirometric technic in which the subject takes a maximal inspiration, then breathes out as rapidly as possible into a spirometer. The mea- sure is the FEVj^q (one-second forced expiratory volume) Index SPIROMETRY (IM) (53) TIME FACTORS (NIM) (68) tissue metabolism see tissue respiration tissue respiration use of oxygen by tissue cells for their metabolic processess Index OXYGEN CONSUMPTION (68) TLC see total lung capacity total lung capacity syn. TLC Index SPIROMETRY (A4) (68) TRACHEA TV see tidal volume uneven distribution of blood flow some parts of the lungs receive more blood than the other parts Index PULMONARY CIRCULATION (68) VC see vital capacity ' venous admixture the flowing of blood through the lung, passing through alveoli which have not been ventilated; comparable to the mixing of venous blood with arterial blood Index PULMONARY CIRCULATION (IM) (68) RESPIRATION (IM) (68) PULMONARY ALVEOLI (NIM) (68) venous blood blood arriving at the lung; coau^na much C02 and little 02 Index BLOOD (IM) (68) VEINS (NIM) (68) ventilation flushing of air in lungs during breathing Index RESPIRATION (63) VENTILATION-PERFUSION RATIO (El)(Prov) (68) the ratio between the total air entering the lung to the blood flow through the lung during a specified time period; usually measured as a function of oxygen exchange Index RESPIRATORY FUNCTION TESTS (IM)(68) PULMONARY CIRCULATION (IM) (68) ventilation, pulmonary see pulmonary ventilation vital capacity syn. VC maximum amount of air that can be breathed in after forcibly emptying the lungs Index SPIROMETRY (68) whole body plethysmography see plethysmography, whole body VI