The effect of gradual or acute arterial occlusion on skeletal muscle blood flow, arteriogenesis, and inflammation in rat hindlimb ischemia

Current experimental models of critical limb ischemia are based on acute ischemia rather than on chronic ischemia. Human peripheral vascular disease is largely a result of chromic ischemia. We hypothesized that a model of chronic hindlimb ischemia would develop more collateral arteries, more blood flow, and less necrosis and inflammation than would acute hindlimb ischemia. We therefore developed a rat model of chronic hindlimb ischemia and compared the effects of chronic ischemia with those of acute ischemia on hindlimb skeletal muscle. Acute or chronic ischemia was induced in 36 male Sprague-Dawley rats. Chronic ischemia caused blood flow, as measured by laser Doppler scanning and confirmed by muscle oxygen tension measurements, to gradually decrease over 1 to 2 weeks after operation. Histologic analysis showed chronic hindlimb ischemia better preserved muscle mass and architecture and stimulated capillary angiogenesis, while lacking the muscle necrosis and inflammatory cell infiltrate seen after acute ischemia. Surprisingly, the chronic ischemia group recovered dermal blood flow more slowly and less completely than did the acute ischemia group, as measured by laser Doppler (0.66 ± 0.02 vs 0.76 ± 0.04, P < .05) and tissue oxygen tension (0.61 ± 0.06 vs 0.81 ± 0.05, P < .05) at 40 days postoperatively. Consistent with poorer blood flow recovery, chronic ischemia resulted in smaller diameter collateral arteries (average diameter of the five largest collaterals on angiogram was 0.01 ± 0.0003 mm vs 0.013 ± 0.0007 mm for acute, P < .005 at 40 days postoperatively). Acute ischemia resulted in decreased tissue concentrations of vascular endothelial growth factor (VEGF) (0.96 ± 0.23 pg/mg of muscle for acute vs 4.4 ± 0.75 and 4.8 ± 0.75 pg/mg of muscle for unoperated and chronic, respectively, P < .05 acute vs unoperated), and in increased tissue concentrations of interleukin (IL)-1β (7.3 ± 4.0 pg/mg of muscle for acute vs undetectable and 1.7 ± 1.6pg/mg of muscle for unoperated and chronic, respectively, P < 0.05 acute vs unoperated). We describe here the first model of chronic hindlimb ischemia in the rat. Restoration of blood flow after induction of hindlimb ischemia is dependent on the rate of arterial occlusion. This difference in blood flow recovery correlates with distinct patterns of muscle necrosis, inflammatory cell infiltration, and cytokine induction in the ischemic muscle. Differences between models of acute and chronic hindlimb ischemia may have imp