OPTIMAL HEMATOCRIT - THEORY, REGULATION AND IMPLICATIONS

Hematocrit is likely to be optimized because of its influences on oxyg en transport. However, optimal hematocrit must also change because she ar rates and blood vessel radii within circulations change temporally. Blood vessel endothelia regulate shear stress on their walls by chang ing their radius. Wall shear stress is dependent on shear rate and vis cosity. Because there is regulation of vessel radius by the endotheliu m it is hypothesized that hematocrit may be regulated near optimal by changes in plasma volume. The implication of such regulation is that c hanges in vascular volume (blood volume) would occur with alterations in red blood cell mass. Data are presented which indicate that regulat ion of optimal hematocrit normally occurs through changes in plasma vo lume. The regulation of optimal hematocrit has significant implication s for processes that depend on oxygen transport (e.g., exercise) becau se of the effect of blood volume on cardiac output.