Factors Influencing the Autoregulation of the Cerebral Blood Flow During Hypotension and Hypertension

GLENN W. KINDT, M.D., JULIAN R. YOUMANS, M.D., AND OTMAR ALBRAND, M.D. Medical College of South Carolina, Charleston, South Carolina

T IS well known that during ranges of ineffective. 2 The carotid arteries supply most hypotension and hypertension an auto- of the blood to the brain, and clamping theni I regulation of human cerebral blood flow above the mandibular and occipital arteries occurs, which keeps the cerebral perfusion causes almost immediate death. 31 Thus a relatively constant, s,19,32 This autoregulation nearly total blood supply to the brain is con- accompanies such diverse conditions as hy- tained within the easily-accessible carotid pertension due to toxemia of pregnancy, 2~ arteries, and makes theln a satisfactory essential hypertension, 9,t3 the adnlinistration channel for the study of changes in over-all of norepinephrine, '6,29 and moderate hypo- cerebral blood flow. tension due to spinal anesthesia '7 or arfonad Repeated observations were made on 18 administration. 25,~[~ In the intact cerebro- goats weighing 16 to 44 kg. After the animals vascular system, autoregulation fails only had been heparinized and anesthetized with with marked hypotension. 5,6 sodium seeobarbital, a traeheostomy was Despite the autoregulation phenomenon, performed and breathing was controlled with clinical observations have shown that it is a Bird respirator. The left femoral artery very important to nmintain an elevated sys- was cannulated for constant blood-pressure temic blood pressure in patients with certain recordings using a Statham strain gauge. The carotid and cerebral arterial diseases. 1 Far- right femoral artery and vein were also ean- hat 4 has reported cases in which the neuro- nulated so that blood could be removed or logical deficit developing after aneurysnml reinfused as needed during the hypotensive surgery, angiography, and craniotomy for study. Cisternal pressure measurements tumor was improved by elevating the sys- were made through an 18-gauge spinal needle temic blood pressures above normal. It is connected to a Statham strain guage. The reasonable to assume that these patients had carotid arteries were exposed from the bi- an altered and probably a compromised furcation of the braehioeephalie artery to cerebral circulation. Their improvement the base of the skull. The carotid sinuses with induced hypertension suggests that were denervated and all branches of the cerebral blood flow was increased. If this carotid arteries were ligated and divided. were true, it would appear that the autoreg- Statham Medicon flow probes were placed on ulation of cerebral blood flow, which has each carotid artery and connected to a dual- been proven so often in the normal situation, channel Medicon flow meter. All the mea- is not effective when the arterial tree is com- surements were recorded with a Honeywell promised. Our experiments have been di- eight-channel Visicorder. rected toward a study of this autoregulation During the first portion of the experiment phenomenon under conditions of a normal the animals were normotensive. One carotid and an impaired arterial tree. artery was occluded and the blood flow in the opposite carotid artery was recorded. This Materials and Methods was repeated with the occluded and moni- We chose goats as the experimental ani- tored vessels reversed. In the second part of nmls because their cerebrovascular system is the study, each animal was made hyper- favorable for the study of gross blood flow to tensive with norepinephrine, and hypoten- the brain with electromagnetic flow probes. sive by allowing it to bleed from the femoral The vertebral arteries are quite small and artery. Blood flow measurements were re- corded with both carotid arteries open and Received for publication July 29, 1966. with alternate occlusion of each carotid Revision received October 21, 1966. artery during the blood pressure alterations. 299 300 Glenn W. Kindt, Julian R. Youmans and Otmar Albrand

Two patients who were having carotid- minute. The average increase in blood flow in artery blood-flow studies were also observed the ipsilateral carotid artery following con- in a limited manner during hypotension and tralateral carotid occlusion was 48.4%. hypertension. Single carotid occlusion resulted in a ~6% re- duction in the total blood flow to the head as Results compared to that with both carotids open. Animal Studies. When one carotid artery The eisternal CSF pressure remained within was occluded, there was the expected prompt normal limits throughout the studies. increase in blood flow through the eontra- When hypertension was induced by in- lateral carotid artery (Fig. 1). There was fusion of norepinephrine, with both carotid little change in the systemic blood pressure. arteries open (Fig. ~), tile carotid artery The average flow rate in each carotid artery flow rate remained relatively constant or fell with both carotids open was 9~ ml per slightly, despite the marked increases in the

FIG. 1. A recording of the effect of unilateral occlusion of each carotid artery. A prompt increase in eontralateral flow occurs as the flow in the occluded carotid falls to its respective baseline. (BP--femoral artery blood pressure; LCF--left carotid blood flow; RCF--Right carotid blood flow.)

FIG. 2. A recording of the effect on rigilt (RCF) and left carotid artery flow (LCF) with blood pressure (BP) eleva- tion. In this instance there is a slight decrease in carotid flow as the blood pressure is elevated.