Effects of hemorrhagic shock on the microvasculature of skeletal muscle

The relationship between arteriolar and venular dimensions and the progressive failure of the homeostatic mechanisms leading to irreversibility in hemorrhagic shock was evaluated in mammalian skeletal muscle (rat cremaster). The small distribution arterioles (diameter = 17 μm) were observed to lose their tone and vasomotion at irreversibility although at 15 min after hemorrhage they exhibited enhanced vascular activity. Slowing of flow was seen to occur in the large venules (100 μm) and late in shock in smaller venules (25 μm). Venular dilatation was adjudged to be the vascular defect associated with the onset of irreversibility. Muscle surface pH and PO 2 followed a course similar to that seen in unanesthetized subjects. The red cell aggregation seen in the venules during the low flow state was generally reversed after reinfusion of the shed blood and restoration of arterial pressure.