Microcirculation in striated muscle after acute reduction in systemic hematocrit

Capillary blood flow variables were measured in cremaster muscles of anesthetized Golden hamsters after isovolemic hemodilution with donor hamster plasma to mean systemic hematocrits of 49% of normal (Group 1) and 32% of normal (Group 2). Despite their different systemic hematocrits, Groups 1 and 2 showed no significant differences in any measured capillary variable. Capillary cell content decreased significantly after hemodilution from 9.4 +/- 0.8 (SE) in controls to 5.8 +/- 0.7 (Group 1) and 5.0 +/- 0.5 cells/100 microns (Group 2). Hemodilution did not change resting capillary cell velocity or capillary cell flux. Velocities were 115 +/- 14, 186 +/- 25 and 203 +/- 23 microns/sec in controls. Group 1 and Group 2, respectively, while the corresponding mean values for cell flux were 9.8 +/- 2.0, 11.5 +/- 2.1 and 11.9 +/- 2.4 cells/sec. Functional capillary density was unchanged after hemodilution, but tissue cell capacity (estimated from cell content and capillary density) attained only 50% of the expected value, being 26% (Group 1) and 16% (Group 2) of control. Thus, none of the changes in indices of capillary cell flow, capillary cell content or tissue cell capacity were directly proportional to the changes in systemic hematocrit. This suggests that tissue oxygen delivery from capillaries cannot be predicted from measured changes in systemic oxygen transport capacity.