Heterogeneity of microvascular response to ischemia in skeletal muscle

The aim of this study was to use the video-microscopic approach to analyze simultaneously, at very low magnification, red cell velocity (VRBC) and density of perfused capillaries (CD) in an entire capillary network of a frog sartorius muscle before and after 3 s, 1 min and 30 min arterial occlusions. In 11 muscles studied, the 3 s occlusion caused a significant increase in the overall peak hyperemic VRBC and CD (from 0.14 +/- 0.08 to 0.28 +/- 0.16 S.D. mm/s, and from 104 +/- 41 to 126 +/- 42 S.D. cap/mm2). All muscles participated in this overall response. On average, 71% of capillaries per network showed hyperemia. The 1 min occlusion also caused significant increases in overall VRBC and CD (from 0.14 +/- 0.08 to 0.34 +/- 0.17 S.D. mm/s, and from 94 +/- 44 to 123 +/- 44 S.D. cal/mm2). In contrast to the 3 s response, only 9 out of 11 muscles participated in this response, with an average capillary participation of 80%. The 30 min occlusion caused a significant increase in overall VRBC (from 0.13 +/- 0.07 to 0.24 +/- 0.17 S.D. mm/s) but no change in CD. Only 6 out of 11 muscles participated in this response, with an average capillary participation of 56%. In terms of these microvascular data, the present study demonstrate for the first time ever (1) an appreciable spatial heterogeneity of responses within the capillary network in a single muscle following all three types of occlusions, and (2) a progressively larger muscle-to-muscle heterogeneity of responses with longer duration of occlusion. Since the spatial heterogeneity (i.e. increase, no change or even decrease in flow) was associated with groups of similarly behaving capillaries supplied by a common arteriole, the existence of a flow-suppressing arteriolar mechanism (in addition to metabolic and myogenic vasodilating mechanisms) is postulated to explain the dramatic heterogeneity of response to ischemia in this muscle.