Effect of blood pressure on blood flow in ischemic and in nonischemic cerebral cortex

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Abstract
The right middle cerebral artery was occluded in 21 cats under halothane anesthesia. Simultaneous measurements of cerebral blood flow (CBF) were made from exposed cortex of ischemic and nonischemic hemispheres with krypton-85 (CBF = [lambda][H0-H10/A10]). Mean systemic arterial blood pressure (MABP) was varied, usually by the intravenous injection of phenylephrine or sodium nitroprusside. A total of 124 CBF measurements were made from nonischemic cortex and 88 from ischemic cortex, with MABP values ranging from 25-175 mm Hg. In nonischemic cortex, CBF remained relatively constant during changes in MABP. In ischemic cortex, CBF paralleled MABP at hypotensive and normotensive levels but not at hypertensive levels. This may have been due to an impairment of autoregulation. In 10 cats, red blood was seen in veins draining the ischemic cortex; CBF of ischemic cortex was greater when venous blood was red than when it was blue, but was still less than CBF of nonischemic cortex. Ischemia of cerebral cortex impairs vascular responsivity, probably as a result of accumulation of metabolites or damage to the vessel wall, with or without maximum vasodilatation. Treatment of patients with cerebral ischemia should include measures to maintain, but not increase, blood pressure.