Localized heterogeneity of red cell velocity in skeletal muscle at rest and after contraction

Using intravital video microscopy, the present study focussed on a detailed analysis of Vrbc heterogeneity in a 2.4 x 1.8 x 0.15 surface volume of a frog sartorius muscle, before and after supramaximal contraction. Heterogeneity of Vrbc was evaluated (1) for an entire population of capillaries seen in this volume, (2) for a series of optical cross-sections, (3) along a series of longitudinal muscle strips, and (4) in terms of an asymmetry ratio for pairs of concurrent capillaries surrounding a muscle fibre. All four types of analysis showed an increased Vrbc homogeneity after contraction. Velocities became more homogeneous along rather than across muscle fibres. The mean asymmetry ratio became significantly larger during post-contraction hyperemia suggesting that each fibre receives a more uniform blood supply that will contribute to an improved exchange of materials across the capillary wall. The analysis of localized Vrbc heterogeneity provides new means of pinpointing the sources of perfusion heterogeneity. It enables, therefore, a specific experimental intervention that is aimed at an improved perfusion under both normal and abnormal conditions.