Effect of Hematocrit on Venous Return

In 18 dogs, the major factors besides blood hematocrit that are known to affect venous return were exactly controlled, while the hematocrit itself was varied from 9.5 up to 65. In general, the changes in venous return in these experiments were approximately the reciprocal of the changes in blood viscosity, as estimated from standard blood viscosity curves. An interesting sidelight of these studies was the fact that the minute volume of red blood cells transported by the arterial blood to the tissues, as calculated by multiplying the hematocrit times the venous return, reached a maximum at a hematocrit of 40. The minute volume of red blood cells fell drastically in anemia because of decreased hematocrit and in polycythemia because of greatly reduced venous return.