Effects of changes in systemic hematocrit on the microcirculation in rat cremaster muscle.

This work aimed to establish how changes in systemic hematocrit ranging from 0.33 to 0.55, affect capillary red cell velocity (measured by the dual-slit correlator method), capillary volume flow, capillary density and arteriolar diameter. These microcirculatory parameters were determined on rat cremaster muscles surgically prepared for in vivo visualization and bathed with a modified Krebs-Henseleit solution. A significant rise in mean red cell velocity and mean volume flow rate in capillaries was found after hemodilution, and a significant drop after hemoconcentration. A large reduction in the number of capillaries with low flow rate was shown after hemodilution; an opposite effect was found after hemoconcentration. The number of capillaries containing erythrocytes did not change significantly in either state. However after hemoconcentration, the number of capillaries containing stationary erythrocytes was significantly larger. Arteriolar diameter did not alter significantly after either hemodilution or hemoconcentration. We conclude that, in the cremaster muscle, hematocrit is an important rheological factor that determines capillary flows without involving arteriolar regulation.