Volume and Distribution of Blood and Their Significance in Regulating the Circulation

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Abstract
The following theses, elucidated by recent investigations, primarily on human beings, are presented: Blood volume varies with physical activity and with the distribution and avg. oxygen saturation of the blood. In the human being, when resting in the lying position, an appreciable protion of total blood in the body may be regarded as a hemodynamic reserve. This reserve blood is rather uniformly distributed between the thorax and rest of the body. That in the thorax is apportioned between the heart and lungs according to a definite ratio. The reserve blood contained in the heart and in the lungs has a regulative effect which, through the vascular pressor reflexes, influences vasomotor tone in the greater circuit (and probably also in the pulmonary) and the frequency and stroke volume of the heart. The reserve blood in the heart is utilized during physical work to increase the stroke volume of the right and left ventricles. That in the venous side of the lesser circuit functions as the fluid in an air chamber to determine the maximal filling rate of the left side of the heart. The volume of blood in the body is an important factor in establishing autonomic equilibrium. The blood volume is a decisive factor in determining maximal physical working capacity. The blood volume is regulated by vasomotor tone, which affects the balance between water diffusion and reabsorption in peripheral portions of the vascular system, and by the rate of destruction of erythrocytes or hemoglobin which, in some unknown way, influences hematopoiesis. It is not justifiable to draw conclusions regarding the general regulation of the circulation in human beings from results obtained in experiments on isolated organ preparations or on animals under anesthesia and after surgical procedures.

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