MORPHOLOGIC ANALYSIS OF THE MICROCIRCULATION DURING REPERFUSION OF ISCHEMIC SKELETAL-MUSCLE AND THE EFFECT OF HYPERBARIC-OXYGEN

The morphologic events in the microcirculation that lead to reperfusio n injury of ischemic skeletal muscle remain incompletely understood. T he purpose of this experiment was to evaluate leukocyte endothelial ad herence characteristics and dynamic changes in microvessel caliber dur ing reperfusion of an in vivo skeletal muscle ischemia preparation. In addition, the effect of hyperbaric oxygen treatment on these microcir culatory changes also was studied. An intravital microscopy preparatio n of a transilluminated gracilis muscle in 27 rats was used to observe a total of 101 arterioles and 63 venules (13 to 73 mum diameter). Bas eline hemodynamics were videotaped for 30 minutes following muscle iso lation. The animals were divided into six groups: (1) sham, no ischemi a, (2) 4 hours of global ischemia only, (3) no ischemia plus hyperbari c oxygen (one 2.5 ATA/1 hour of treatment with 100% oxygen), (4) 4 hou rs of ischemia plus hyperbaric oxygen during ischemia, (5) 4 hours of ischemia plus hyperbaric oxygen immediately on reperfusion, and (6) 4 hours of ischemia plus hyperbaric oxygen 1 hour after reperfusion. Cha nges in arteriolar and venular diameters at specific times during 3 ho urs of reperfusion were recorded, and the number of adherent and slow- rolling leukocytes in 100-mum venular segments were counted and compar ed with baseline measurements. The proximity of arterioles to venules was classified as adjacent (< 1 5 mum) or distant (> 1 5 mum). No sign ificant changes in leukocyte endothelial adherence or arteriolar diame ter were noted in group 1 sham or group 3 nonischemic hyperbaric oxyge n-treated rats when compared with baseline measurements. A significant increase in adherent leukocytes was observed in group 2 ischemic venu les (+ 14.9 +/- 2.5) within 5 minutes of reperfusion, which was mainta ined for 3 hours. Reperfusion measurements of arteriolar diameter in g roup 2 ischemic muscle preparations demonstrated an initial vasodilati on that was followed at 1 hour by a progressive and severe vasoconstri ction (-46.9 +/- 11.3 percent at 3 hours) in arterioles adjacent to ve nules that was not seen in distant arterioles. The increase in adheren t leukocytes seen in group 2 ischemic venules was significantly reduce d by hyperbaric oxygen treatment given during ischemia (group 4) or up to 1 hour during reperfusion (groups 5 and 6). In addition, the progr essive ischemic arteriolar vasoconstriction was inhibited in all group s (4, 5, and 6) treated with hyperbaric oxygen. These results suggest that (1) leukocyte venular endothelial adherence and microarteriolar v asoconstriction are important morphologic events leading to reperfusio n injury of skeletal muscle, (2) this vasoconstriction is seen primari ly in arterioles that are in close proximity to venules, and (3) hyper baric oxygen treatment does not exacerbate reperfusion injury, but rat her appears to protect the microcirculation by reducing venular leukoc yte adherence and inhibiting progressive adjacent arteriolar vasoconst riction.