Comparison of 85 Krypton and 133 Xenon Cerebral Blood Flow Measurements before , during , and following Focal , Incomplete Ischemia in the Squirrel

A comparison of regional cerebral blood flow measurements made with betaand gamma-emitting isotopes revealed good correspondence in areas of normal perfusion and reactive hyperemia but poor correspondence in areas of focal ischemia. After middle cerebral artery occlusion at normocapnia, there was a 65% reduction in regional cerebral blood flow from 1.40 ± 0.27 ml/g min~' to 0.49 ± 0.10 ml/g min~' in monkeys studied with Kr but only a 27% reduction in regional cerebral blood flow from 0.84 ± 0.09 ml/g min-' to 0.61 ± 0.08 ml/g min~' in monkeys studied with Xe. The lack of correlation within areas of focal, incomplete ischemia was attributed to an impairment of isotope delivery to the area of ischemia coupled with the inherent lack of spatial resolution of determinations made with Xe. This finding may partly explain the numerous discrepancies in experimental and clinical studies of the effects of alterations in the arterial partial pressure of C(X on regional cerebral blood flow in areas of ischemia; it may also explain the failure of such studies to reflect the true severity of focal ischemia.