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THE HEART ACTION
If this exchange of gases is to function smoothly, the two atria and the two ventricles must work in close harmony. This harmony is achieved by the coordinated action of the-atria and ventricles: the two atria release their blood simultaneously into the adjacent ventricles, and these in turn simultaneously pump the blood into both the pulmonary and systemic arteries. The system controlling this coordinated action operates like an electrical generator and distributor. The generator, located in the region of the atria, sends forth rhythmical electrical impulses which cause the atria to contract and release the blood into the ventricles. Then, with only a minimum delay, the distributor sends these impulses to the blood-filled ventricles, whereupon they release the blood into the circulation. This electrical "conduction system" is the most sensitive part of the heart pump. That is why irregular heart beat—arrhythmia—is often the first indication of a possible circulatory disturbance or a malfunctioning heart muscle.
In order to gain an idea of the tremendous work done by the heart let us try to visualize its operation. The volume of blood released by the ventricles with each thrust of the pump—the heart beat—is a measurable quantity. The heart-beat frequency, the number of heart beats per minute, normally ranges between 60 and 80. Under conditions of stress or physical exertion this rate can double. One measure of the work performed by the heart is the per minute volume, i.e., the amount of blood pumped out per minute. While resting, this volume ranges between 3 and 5 quarts, an amount large enough to fill an 80 by 165 foot pool in about one year, and can increase from 3 to 5 times this amount with physical work or exercise depending on the individual condition.
The heart is a pump with the strength of 0.1 horsepower. It does not only perform strenuous labor but, unlike other muscles, it must do so throughout life. This makes it utterly dependent on a constant adequate supply of oxygen and necessary fuels. The job of assuring this flow falls to the coronary arteries surrounding the heart. They branch out from the aorta, immediately behind the exit from the left heart, into the muscles of both the left and the right heart. As mentioned earlier, the coronary vessel system is a danger zone for people with risk factors—particularly for those with high blood pressure.
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Cardio & Blood |
