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

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 (hct_body) is about 10% lower than the large vessel hematocrit (hct_l.v.).

The hematocrit of the leg (hct_leg) 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 hct_leg was 90.2% and hct_body 86.9% of hct_l.v.. Hct_leg was significantly higher than hct_body. During exercise hct_leg was also found to be significantly lower than hct_l.v. and higher than hct_body, but the ratio between hct_leg and hct_l.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.

Key Words:

• Blood circulation time
• erythrocyte circulation time
• exercise
• hematocrit
• plasma circulation time