In vivo assessment of acute microvascular injury after reperfusion of ischemic tibialis anterior muscle of the hamster.

The purposes of this study were to develop an in vivo model of skeletal muscle ischemia--reperfusion to assess the patterns of microvascular injury, to evaluate a scoring system that permits quantitation of this injury, and to determine in vivo the extent of white blood cell adhesion within the microcirculation during the acute postreperfusion period. Syrian golden hamsters underwent 3.0 or 4.5 hr of lower extremity ischemia without anticoagulation. The microcirculation of the tibialis anterior muscle was visualized by fluorescent intravital microscopy (700X). During the first 1.5 hr of reperfusion the microvascular injury was scored by a grading system based upon the extent of extravasation of fluorescein-labeled albumin and the degree and level of microvessel obstruction. To correlate the observed changes in the microcirculation to changes in the whole muscle, in a separate group of animals, pH changes in the tibialis anterior muscle were measured at the same time intervals under identical experimental conditions as the microvascular measurements. White blood cells were transiently fluoresced at 1.5 hr after reperfusion by intravenous acridine red and the number of white blood cells rolling (rollers) or sticking (stickers) to the endothelium during a 30-sec observation period was recorded. Two distinct patterns of microvascular injury were seen: after 3.0 hr of ischemia there was a progressive extravasation, some capillary but no arteriolar or venular obstruction, flow velocities increased over time; after 4.5 hr of ischemia there was a greater heterogeneity of injury, primary "no reflow," extensive capillary, arteriolar, and venular obstruction, as well as a progressive decline in flow velocities. Thrombosis of microvessels was rare. There was no inflow vessel thrombosis.(ABSTRACT TRUNCATED AT 250 WORDS)