THE EFFICIENCY OF THE HEART, AND THE SIGNIFICANCE OF RAPID AND SLOW PULSE RATES

Abstract

The efficiency of the heart is defined as the volume of blood that it can pump in relation to the O requirement of the body; and the index of efficiency is the arterio-venous O difference during rest and exercise. The correlations of the circulation, stroke volume, and pulse rate, with body weight, surface, and respiratory metabolism are here briefly defined. Data from 50 healthy young men are summarized. Those habitually taking only moderate exercise had the same stroke volume during rest and exercise, so that the volume of the circulation during exercise is merely double that during rest. But athletes have supernormal hearts; the stroke volume increases during exercise, and not merely the pulse rate, so that the circulation is tripled. For any given exertion therefore the arterio-venous O difference in the athlete is less than in the untrained man. Exact coordination of heart action and venous return results in a uniform stroke volume. This may be regarded as the normal condition, but one from which deviations frequently occur. This normal relation exists only when the pulse rate varies in precise proportion to the volume of the venous return. Athletes have much slower pulses than non-athletes; the advantage of this condition for the circulation under muscular exertion is that it permits a larger circulation and a smaller arterio-venous O difference. The ill effects of tobacco on "wind" are explained as due to the chronic acceleration of the pulse; consequently the ventricles make small strokes. The heart is thus rendered unable to increase the circulation during muscular exercise to the same extent that is afforded by a heart with large strokes and a slow rate during rest.