Reperfusion after cerebral ischemia: influence of duration of ischemia.

The influence of the duration of ischemia on the pattern of cerebral blood flow in recirculation was studied in anesthetised rats. Severe incomplete cerebral ischemia (mean ischemic flow = 5.8 +/- 0.4 ml/100 g/min) was produced by four-vessel occlusion and recirculation permitted after 15, 30 or 60 minutes ischemia. All three groups showed an immediate hyperemia followed by hypoperfusion. Hyperemia was maximal following 15 minutes ischemia and least pronounced following 60 minutes ischemia (p = 0.0249). Hypoperfusion started most quickly following 15 minutes ischemia and was delayed following 60 minutes ischemia (p less than 0.001). In established hypoperfusion there was no difference in flow between the three groups. The possible mechanisms of these changes in flow are discussed.