Factors influencing the autoregulation of the cerebral blood flow during hypotension and hypertension.

Abstract

T IS well known that during ranges of hypotension and hypertension an autoregulation of human cerebral blood flow occurs, which keeps the cerebral perfusion relatively constant, s,19,32 This autoregulation accompanies such diverse conditions as hypertension due to toxemia of pregnancy, 2~ essential hypertension, 9,t3 the adnlinistration of norepinephrine, '6,29 and moderate hypotension due to spinal anesthesia '7 or arfonad administration. 25,~[~ In the intact cerebrovascular system, autoregulation fails only with marked hypotension. 5,6 Despite the autoregulation phenomenon, clinical observations have shown that it is very important to nmintain an elevated systemic blood pressure in patients with certain carotid and cerebral arterial diseases. 1 Farhat 4 has reported cases in which the neurological deficit developing after aneurysnml surgery, angiography, and craniotomy for tumor was improved by elevating the systemic blood pressures above normal. It is reasonable to assume that these patients had an altered and probably a compromised cerebral circulation. Their improvement with induced hypertension suggests that cerebral blood flow was increased. If this were true, it would appear that the autoregulation of cerebral blood flow, which has been proven so often in the normal situation, is not effective when the arterial tree is compromised. Our experiments have been directed toward a study of this autoregulation phenomenon under conditions of a normal and an impaired arterial tree.