Marked regional heterogeneity in blood flow within a single skeletal muscle at rest and during exercise hyperaemia in the rabbit

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Abstract
In 1985 both Pendergast et al. and Piiper et al. described a major regional heterogeneity in blood flow within single skeletal muscles both at rest and during exercise. Based on the microsphere method they described large variations in blood flow between muscle samples as large as 1 g each.The aims of the present study were: To test this notion of regional heterogeneity in microsphere deposition within single skeletal muscles both at rest and during exercise. To compare the distribution of microspheres with other blood flow tracers. To test whether or not any heterogeneity was due to vasomotion in small arteries or arterioles. Microspheres were infused into anaesthetized rabbits over either 10, 30 or 120 s, or 10 min. Exercise was mimicked by tetanic contractions obtained by electrical stimulation of the motor nerves. Three hindleg muscles were divided into samples of 0.25 g each. Regional heterogeneity was expressed as the coefficient of variation corrected for statistical distribution of microspheres (CVc). The CVc at rest was about 0.34. The CVc was unaffected by the various infusion periods and did not change during exercise. Simultaneous infusions of microspheres and 86Rb+ or antipyrine gave high correlations between the two blood flow tracers, with all r values exceeding 0.83 (n= 18).We conclude that the microsphere method provides reliable estimates for regional blood flow within single skeletal muscles. The distribution of blood flow was markedly heterogeneous both at rest and during exercise. The heterogeneity in blood flow was apparently not a result of vasomotion.