Cardiac Output During Muscular Work and Its Regulation

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Abstract
The circulatory changes that occur at the transition from rest to work may be thought to proceed as follows a stimulus closely correlated to the intensity of work and possibly of peripheral nervous origin influences the circulatory centers in such a way that a relative increase in sympathetic tone is produced. As a result the heart frequency is increased and the emptying of the heart becomes more complete. The hereby produced increase in blood flow from the heart will return to the heart through the dilated vessels of the working muscles, assisted only by the venous pump. From the experimental data, available only for light and moderate work, it seems that an emptying of venous blood depots is not necessary in order to obtain the increase in cardiac output. The vasocon-striction in resting organs observed in heavy work is presumably elicited by the above-mentioned stimulus, possibly from special receptors in the working muscles. The physiological significance of this vasoconstriction is to secure that an adequate blood flow through the working muscles is obtained. The role of the arterial pressoreceptors during work is presumably to counteract and thus moderate the increase in the arterial blood pressure.