Red cell perfusion in skeletal muscle at rest and after mild and severe contractions

The aim of this study was to evaluate the distribution of red cell perfusion in sartorius muscle of anesthetized frogs by analyzing simultaneously red cell velocity (VRBC), number of cells per unit capillary length (NRBC), and density of perfused capillaries (CD) in a 2.07 X 2.71-mm region of the muscle visualized microscopically at very low magnification. In the 16 muscles studied, a severe 1-min electrical stimulation induced statistically significant increases in the mean values, VRBC, NRBC, and CD, as well as significant decreases in heterogeneities (SD/mean) of these three parameters when going from rest to postcontraction hyperemia. A mild 3-s stimulation caused significant increases only in VRBC and NRBC. Red cell perfusion, computed as a product of the three parameters divided by the mean capillary length, increased significantly from 87.4 +/- 81.9 to 417.9 +/- 118.2 (SD) and from 96.9 +/- 75.7 to 192.5 +/- 190.2 (SD) cells X s-1 X mm-3, respectively. In both stimulations, the postcontraction increase of red cell supply to the muscle, expressed in cells per second per cubic millimeter, was larger than any individual increase in the three parameters. Based on pooled data from all muscles, both NRBC and CD were determined to be dependent on VRBC. The present study supports the view that VRBC, NRBC, CD, and heterogeneity of red cell distribution depend on vascular tone and demonstrates for the first time that these four dependencies can operate both concurrently and synergistically to increase O2 supply to muscle after contraction.