The effect of prolonged total ischemia on the ultrastructure of human skeletal muscle capillaries. A morphometric analysis.

Human skeletal muscle shows reflow impairment after prolonged tourniquet ischemia of 1-3 hours, increasing with the duration of ischemia. A sample of 275 cross-sectioned capillary profiles from muscle biopsies of human m. quadriceps femoris made totally ischemic by tourniquet for 90-180 minutes (mean 110 min.) from 5 patients during surgery, show frequent evidence of ultrastructural damage to microvascular membranes and organelles. Frequency analyses demonstrate a significant increase in damage during ischemia (p = 0.03), but not increasing further following 5 min of reperfusion. One of the signs of ischemic damage was endothelial swelling, found in some endothelial cells, lying next to ultrastructurally intact ones. The swelling found cannot be explained by a general loss of volume control of the microvascular endothelium during ischemia, since a computerized morphometry on the entire sample shows a preserved capillary wall thickness during ischemia and following reperfusion. During reperfusion the capillaries dilate with an increase in median max. diameter from 3.4 micron (4.7 micron shrinkage-corrected) to 3.9 micron (5.4 corr.) (p less than 0.001), despite reported reperfusion impairment. However, since capillaries in skeletal muscle consist of 20-40 endothelial cells, a distribution of such localized endothelial swelling or luminal membrane changes in a few percent of the microvascular endothelial population after ischemia, trapping leucocytes, would affect microvascular hydraulic conductance to reperfusion.