Autoregulation of Cerebral Blood Flow

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Abstract
Autoregulation of cerebral blood flow (constant perfusion despite variations in blood pressure) was studied in 15 control subjects and in 24 patients with cerebral vascular lesions. Thirteen patients were studied within the first 2 days of an episode of cerebral ischemia ("acute" group); 11 were studied from 15 days to several months after an ischemic episode ("chronic" group). Measurements of regional cerebral blood flow (rCBF) were made by recording extracranially in four to six locations the clearance of 85Kr dissolved in saline and injected into the internal carotid artery. Blood flow values were calculated with a digital computer, using a compartmental analysis of the clearance curves. After measuring rCBF in the resting state, the blood pressure was increased by 30 to 40 mm Hg by the intravenous infusion of angiotensin amide (Hypertensin, Ciba). While the blood pressure was kept constant at the new level, a second series of measurements was made. Autoregulation was present in all normal subjects: no significant differences were found in average or compartmental flow rates between values obtained at normal and at hypertensive levels of blood pressure. Loss of autoregulation was demonstrated in 10 of 13 patients of the "acute" group and in two of 11 patients of the "chronic" group. These data support previous observations that autoregulation is impaired during the first few days after an ischemic episode. The three patients of the "acute" group with a preserved autoregulatory response to hypertension had only transient ischemic attacks. In each of the other subjects of this group loss of autoregulation was found in one to three different regions of the brain. Our results suggest that regional loss of autoregulation is found frequently near the periphery of the ischemic brain. Impairment of autoregulation is one of the types of derangement of cerebral circulation that occurs after an ischemic episode.

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