The rate and distribution of muscle blood flow after prolonged ischemia

Abstract

The magnitude and distribution of muscle blood flow in the lower extremity after relief of an acute arterial occlusion may influence the extent of the resulting necrosis. The object of this study was to document the distribution of blood flow in the resting state and after prolonged periods of complete ischemia, and to assess the relationship between the degree of reactive hyperemia and subsequent necrosis. The isolated bilateral canine gracilis muscle preparation that we have previously characterized was used for microsphere studies. Total blood flow was measured by means of timed venous collections, and the distribution of flow was determined by means of a multiple microsphere injection technique. Measurements of microsphere distribution and blood flow were made before ischemia and during the initial 48 minutes of reperfusion after both 4 and 5 hours of normothermic ischemia, which resulted in 46.7% ± 6% and 71.2% ± 7% necrosis, respectively. The muscle was harvested and sectioned transversely into six slices approximately 1.5 cm thick, and the extent of necrosis was quantified by means of nitroblue tetrazolium staining 48 hours after reperfusion. Blood flow distribution during the early reperfusion phase was determined in each muscle slice and in both the alive and dead portions of each slice by use of the microsphere injection technique. Preischemic blood flow was distributed homogeneously throughout the muscle and was 4.5 ± 0.8 ml/100 gm/min (mean ± SEM, n = 8). On reperfusion total flow was 6 to 10 times higher than it was before ischemia and was distributed predominantly to the middle slices (p < 0.05, n = 12). In both the 4- and 5-hour ischemia groups there was no correlation between blood flow in each slice and the extent of necrosis (p > 0.1). The degree of reactive hyperemia was greater after 4 hours of ischemia than after 5 hours (20.3 ± 2.5 ml/100 gm/min vs 12.5 ± 1.6 ml/100 gm/min, p < 0.05). On reperfusion, blood flow is not distributed homogeneously throughout the muscle and the extent of reactive hyperemia is inversely related to the length of ischemia. Hyperemic blood flow reaches the maximum rate in the center portions of the muscle belly closest to the inflow and does not seem to be related to the distribution of necrosis.