The Hematocrit of the Lower Extremity in Man at Rest and during Exercise

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Abstract
The aim of the present work was to study to what extent the vascular area of the leg contributes to the body hematocrit phenomenon, i.e. the fact that the total body hematocrit (hctbody) is about 10% lower than the large vessel hematocrit (hctl.v.). The hematocrit of the leg (hctleg) was calculated from the mean circulation times of plasma and red cells through the vascular bed of the lower extremity. These values were determined at rest and during exercise by the arteriovenous equilibration technique after injection of 125I-labelled albumin and 51Cr-labelled red cells into an antecubital vein and sampling from a peripheral artery and the femoral vein. In 14 normal resting subjects the average hctleg was 90.2% and hctbody 86.9% of hctl.v.. Hctleg was significantly higher than hctbody. During exercise hctleg was also found to be significantly lower than hctl.v. and higher than hctbody, but the ratio between hctleg and hctl.v. was not significantly lower during exercise than during rest. It is concluded that the body hematocrit phenomenon is to a major part due to a larger intravascular volume of distribution for plasma than for red cells, and that rapidly exchangeable extravascular plasma pools only exist in special vascular areas, e.g. the liver.