Heterogeneous blood flow distribution within single skeletal muscles in the rabbit: role of vasomotion, sympathetic nerve activity and effect of vasodilation.

A major heterogeneous distribution of blood flow has been described on a non-microvascular level within single skeletal muscles at rest and during exercise hyperaemia both in the dog and in the rabbit. The heterogeneity in blood flow distribution could be composed of both a steady-state region-to-region variability (spatial) and a time-dependent variability (temporal) in blood flow to each region. In the present study we estimated their relative contributions to the variations in blood flow within the muscles. Furthermore, we determined whether sympathetic nerve activity contributed to and whether pharmacologically induced vasodilation affected the heterogeneous blood flow pattern. Regional blood flow measurements were based on microsphere infusions into anaesthetized rabbits. Blood flow was determined under both resting conditions and during exercise hyperaemia in regions weighing 0.25 g each within hind leg muscles. The coefficient of variation for the spatial variability was twice that of the temporal one: 0.32 and 0.16 (mean) respectively. Neither stimulation of the sympathetic nerves, sympathectomy nor vasodilation affected the heterogeneity in blood flow. When exercise hyperaemia was induced, blood flow increased in all regions so that a positive (P less than 0.05) correlation was present between resting and exercising blood flow values in the individual regions. Although regional variation in vascularization could explain the observations during exercise hyperaemia, we have at present no fully satisfying explanation for the observed regional heterogeneity in blood flow.