Evidence that capillary perfusion heterogeneity is not controlled in striated muscle.

We tested the hypothesis that the heterogeneity of capillary blood flow distribution in striated muscle is inversely proportional to tissue blood flow by examining the patterns of red blood cell flow in the capillaries of hamster tibialis anterior muscles. Capillary red blood cell velocities and capillary red blood cell fluxes were measured as indexes of blood flow and red blood cell distribution in vasoconstricted and vasodilated vascular beds of resting and working striated muscle. Standard statistical parameters describing dispersion of data (standard deviation and coefficient of variation) in addition to measured and normalized histograms were compared across treatments. With vasodilation the standard deviations of both variables increased linearly with the means, and measured distributions became broader. The coefficients of variation and normalized distributions of both variables did not differ across treatments. These observations do not support the idea that the heterogeneity of capillary perfusion is controlled. Rather they suggest that fractional flow dispersion among capillaries is constant and independent of muscle blood flow and/or O2 demand.