Cerebral Ischemia and Reactive Hyperemia

Correlative studies of cortical blood flow measured by the 85 Kr washout technique and observations of the cortical blood vessels of 10 squirrel monkeys subjected to temporary occlusion of the middle cerebral artery are described. During occlusion, cortical blood flow in core areas of ischemia decreased to 0.12 to 0.90 ml/g/min (20 to 50% of preocclusion values) and became pressure dependent with failure of autoregulation. After release of the occluding clip, cortical blood flow was restored. Correlation between degree of vascular reaction judged by observation of the cortex and degree of hyperemia as determined by cortical blood flow was poor. There was incomplete correlation between the degree of hyperemia and the degree of preceding ischemia. Hyperemia, or "luxury perfusion," manifested by red venous blood, appears to be related to failure of cerebral tissue to utilize available oxygen as well as to "reactive" hyperemia, or supernormal blood flow, in regions previously ischemic. There was no demonstrable gradual failure of collateral circulation during occlusion. Cerebral edema was progressive and even progressed after restoration of cortical blood flow; it was incompletely correlated with the degree of ischemia and degree of hyperemia.