The relative flow rates of red cells and plasma—peripheral and central circulation studies in the dog

Abstract

The relative flow rates of I 131-labeled plasma and Cr 51-labeled red cells injected as a mixture were studied in the pulmonary and peripheral (leg and head) circulations of the dog. The red cells traversed the pulmonary circulation an average of 3·7 per cent (S.D. ± 2·2) faster than the plasma. The red cells traversed the peripheral capillaries of the leg circulation 10·7 per cent (S.D. ± 5·9) faster than the plasma. In the head circulation the red cells flowed 12·8 per cent (S.D. ± 5·5) faster than the associated plasma. The differences between the flow rates of the two phases were significant ( P < 0·01) in all three vascular beds. Also, the difference between the mean transit times of the two phases was significantly shorter ( P < 0·01) in the lung circulation than it was in either of the peripheral beds tested. The calculated hematocrit of all three vascular beds tested was significantly lower ( P < 0·01) than the simultaneously obtained large vessel hematocrit. These findings can be partially explained by the hydrodynamic laws of Poisseuille and Bernoulli, but the vascular beds are too complex considering the perfusing liquid to allow full quantitation by the existing formulas.