INTERPRETATION OF CHANGES IN “CENTRAL” BLOOD VOLUME AND SLOPE VOLUME DURING EXERCISE IN MAN*

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Abstract
The "central" blood volume (CBV) was measured in 4 subjects at rest supine, standing and during exercise on inclined treadmill. Injections of indicator were made into the superior vena cava, and dilution curves were obtained from the radial artery. Mean values for the CBV were 1034 ml/m2 at rest supine, 722 ml/m2 while standing and 1652 ml/m2 during walking at 3.5 miles per hour. In 4 further subjects, the CBV was increased during the performance of leg exercise in the supine position. Such exercise is associated with an increased flow of blood to the lower limbs. When the rate of blood flow to the arm used for sampling also was increased by sudden release of pressure from an arterial-occlusion cuff, a great decrease in the CBV occurred, the values approaching, or even falling below, those obtained under the initial resting conditions. Thus, the increase in the CBV during exercise is partly or wholly caused by an increase in its systemic "arterial" component, in consequence of relative changes in the rates of blood flow to different regions. Evidence has been obtained that the "slope volume" is influenced by linear dispersal of indicator in peripheral arteries. Thus, this volume no longer can be held to reflect either quantitatively or qualitatively the volume of any single component of the central circulation, such as the lungs.