[Wonder Engine of the Body(The Human Heart)] [Produced with the cooperation of the American Heart Association by The Bray Studios, Inc.] [Narrator:] The heart is a pumping engine which, from its earliest appearance in the embryo to the end of our life, keeps our blood in circulation so that all our organs may grow and perform their appointed tasks. Few people realize the amount of work required of this small mass of muscle no larger than a man's fist. Considered an engine, the heart is rated as having only about 1/240th of a horsepower, but it is an engine which sometimes remains in motion for 60, 80, or more years without layups, repairs, or replacements. You will say that a motor of only 1/240th horsepower is not very strong. But the work done by the heart beating 70 times per minute could in one hour raise the weight of four tons over a distance of one foot. The energy expended by the heart in the course of a whole day could, if he were not in a hurry, lift a person weighing 150 pounds to the very top of the Empire State Building. Or it could, in one day, fill a tank holding 2,500 gallons or about ten tons of fluid. The heart beats by contracting rhythmically. Normally, it contracts about 70 times per minute. This amounts to about 100,000 beats in the course of 24 hours and nearly 36 million times in a year. Could you, without tiring, perform a similar task with your hands more than 100,000 times in one day? How then can the heart, without ceasing and without fatigue, perform its big task over the years of a lifetime? The answer is that the heart takes a short rest between each beat, and the rest amounts to about 12 hours in the course of 24. During these rest periods, the heart recovers for the next beat. It teaches the lesson that periods of rest are necessary for sustained efficiency. Without these rest periods, the heart could not execute the 36 million pump strokes which are required to keep us alive for one year. [...] The whole amount of blood in the body is from 5 to 6 quarts, and the heart is the circulating pump which keeps these five to six quarts constantly coursing through the body by way of two circuits of blood vessels: a larger one, which leaves the left half of the heart by way of the aorta and passes to every part of the body, [...] returning to the right half of the heart by way of the superior and the inferior vena cava, and a smaller circuit, which leaves the right half of the heart by way of the pulmonary arteries, to enter the lungs, where the blood takes up oxygen, [...] and then flows back to the left half of the heart, which it enters by way of the pulmonary veins. Both of these circuits are working simultaneously. In their course, the vessels of both circuits divide into smaller and smaller branches. The smallest branches are called capillaries and are of microscopic size, so small that the tiny blood corpuscles must pass through them single file. [...] So enormous is their number that if all the blood vessels of the body were laid end to end, they would encircle the globe four times. But their enormous number also accounts for the fact that it takes about a half a minute for a givenportion of the blood to complete its course through the two circuits. Thus, a single blood cell may make almost 3,000 round trips in the course of a single day. [...] The normal heart beats 70 times per minute on the average. The physician, feeling the pulse, can count its frequency and, within limits, can draw some conclusions as to the state of the heart. Normally also, the pulse rate varies within fairly large limits. It may drop to 60 or even lower during sleep, may rise to 90 during the morning shower, remain near 70 during the larger part of the day, go up above 100 while taking some recreational exercise, and drop back to below 70 while relaxing therefrom. Such temporary variations are perfectly normaland to be expected. Temporary variations of the heartbeat may also be due to other causes, such as various forms of excitement, pleasant or unpleasant. Such variations may be very noticeable and even alarming, but they do not indicate an unhealthy condition of the heart, nor need they be a cause for worry. Yet, if such occurrences are too frequent or too persistent, a physical examination is called for. [...] One of the methods available to the physician for judging the condition of the heart is by listening to its rhythmic movements by means of the stethoscope. The sounds are representedby a subdued lub-dub, with a pause of about a half a second between each double sound. [...] Another method of envisioning the condition of this hidden motor is by the use of the electrocardiogram, a sensitive instrument which records the electrical changes which occur in the heart muscle during each beat. These records are called electrocardiograms. By a knowledge of the records of normal hearts, a physician draws useful information as to the condition of the heart muscle and the rhythm of the beat. [...] This is a record of a normal heartbeat. [...] This is one of an abnormal beat. [...] Every time the heart contracts, it forces a volume of blood into the elastic arteries. The increased pressure causes their brief distension. This is noticed as the pulse, as you have seen. Between heart contractions and its rest periods, the arteries relax and blood pressure within decreases. The blood pressure is measured by means of an apparatus known as the sphygmomanometer. It is recorded in two phases of the heartcycle: one when the heart is contracted, systole, and one when the heart is relaxed, diastole. Normal limits of pressure have been established for both phases. But, like the pulse rate, blood pressure may vary without indicating a condition dangerous to health. The heart is the strongest organ of our body. Yet, statistics show that heart disease has become the most frequent cause of death. One reason for this is that more people live to an age where the effects of wear and tear on the heart is one of the natural incidents of life. [...] A normal artery, when cut in half lengthwise, shows the normal thickness of its walls. In arteriosclerosis, there occurs a gradual thickening of the walls, narrowing the channel of the flow. The narrowing of the channels may extend to the blood vessels supplying the heart itself. The heart does not lie free in the chest cavity but is enclosed within a sac-like covering, the pericardium. If this sac is removed, we see the heart itself and the blood vessels that enter and emerge from it. This large vessel is called the aorta. Branching from the aorta, where it emerges from the heart, are two vessels call the coronary arteries because of their fancied resemblance to a crown. In a sectional view of the heart wall, the coronary arteries are seen branching into many thousands of small vessels. They supply the heart muscle with its necessary food, for, strange to say, the blood passing through the chambers of the heart does not enter the surrounding muscular structure. A sclerotic narrowing may occur progressively in the arteries of any area of the heart. Here, the coronary arteries are seen in an enlarged sectional view. These vessels show coronary sclerosis. This heart area supplied by these blood vessels may not receive enough nourishment, and this may result in a heart attack so-called. In this greatly enlarged cross-section of the heart muscle, we see a part of the affected area. The lessening of the blood supply caused by coronary sclerosis causes the muscle to weaken and, by a gradual process, to be replaced by scar tissue. [...] Through a number of causes, unforeseen or due to some disease condition, a blood clot within a coronary artery may cause a complete and sudden stoppage of the blood supply, causing a sudden and complete stoppage of function in this part of the heart muscle. This is called coronary thrombosis. While it may kill the patient suddenly, like the blow of an ax, more frequently he recovers. Recovery from coronary thrombosis is enhanced by a period of complete rest, the chief treatment, during which absence of strain permits the healing process to proceed. This healing process consists in the establishment of so-called collateral circulation. [...] Here we see a section of the heart muscle which has been incapacitated. During the rest period, branches from adjoining unaffected arteries become larger, and spreading through the affected area, restore it to a greater or lesser degreeof functional capacity. There are other general facts to be considered. Overweight, for instance, definitely throws additional work upon the heart. Its cure and prevention are possible. An excessive secretion of the thyroid gland overstimulates the heart and the circulation. This is called hypothyroidism and may be cured or its progress at least controlled. [...] Syphilis is avoidable, preventable, and curable. It affects the cardiovascular system years after the onset, causing a disease condition of the wall of the aorta. Infections in any part of the body, such as the kidneys, the lungs, the nose and throat, throw additional work upon the heart. While all of these are not preventable or curable, prompt and adequate treatment will diminish their effects on the heart. Luckily, your heart is the strongest organ of your body. It has a tremendous task to perform. It daily pumps nine to ten tons of blood through miles of blood vessels to keep your body functioning. Help it function properly by following the rules of good health and the advice of your family doctor. [The End][A Bray Studios Production] [from the film library of The American Medical Association]