Cardiovascular and splenic responses to exercise in humans

Abstract

To investigate splenic erythrocyte volume after exerciseand the effect on hematocrit- and hemoglobin-basedplasma volume equations, nine men cycled at an intensity of60% maximal O2 uptake for 5-, 10-, or 15-min duration,followed by an incremental ride to exhaustion. The reductionin spleen volume, calculated using 99mTc-labeled erythrocytes,was not significantly different among the three submaximalrides (5 min 28%, 10 min 30%, 15 min 36%;P 0.26). The incremental ride to exhaustion resulted in a56% reduction in spleen volume, which recovered to baselinelevels within 20 min. Plasma catecholamines were inverselyrelated to spleen volume after exercise (r 0.70–0.84; P 0.0001). There were no differences in red cell or total blood volume pre- to postexercise; however, a significant reduction in plasma volume was observed (18.9%; P 0.01). There was no difference between the iodinated albumin and the hematocritand hemoglobin methods of assessing plasma volume changes. These results suggest that the spleen regulates its volume in response to an intensity-dependent signal, andplasma catecholamines appear partially responsible. Splenic release of erythrocytes has no effect on indirect measures of plasma volume.