Capillary network geometry and red cell distribution in hamster cremaster muscle.

Vascular geometry and red cell distribution were examined in 133 capillaries by means of intravital microscopy in the cremaster muscle of the pentobarbital-anesthetized hamster. Significant correlations (P less than 0.01) were found between diameter and flow, length and resistance, red cell transit time and flow, and red cell flux and hematocrit. Most unexpected was the lack of correlation (P greater than 0.2) between flow and resistance, length, or hematocrit. In addition, we analyzed the relation between blood flow and red cell flux at capillary bifurcations. The red blood cells had a slight (7%), but significant (P less than 0.025), tendency to enter the branch having either higher flow, red cell velocity, or pseudoshear rate (velocity/diameter). The net effect of the preferential red cell flow was to reduce mean capillary hematocrit from 13.7% prior to the bifurcation to 13.3% in the two branches. Finally, increasing the oxygen level of the superfusate above the muscle caused vasoconstriction and an increased heterogeneity of capillary red cell flux and hematocrit, decreasing the capacity for oxygen transport to the tissue.