Autoregulation of Cerebral Blood Flow

Abstract

Changes in blood flow through the internal carotid, vertebral and external carotid arteries were measured by electromagnetic flowmeters during and after acute hypertension induced by closing a clamp around the thoracic aorta in anesthetized monkeys.The internal carotid and vertebral arterial system showed both rapid and delayed autoregulatory responses to rapid increases in blood pressure; the rapid (primary) responses occurred within seconds, the progressive (delayed) within 3 to 4 minutes. In contrast, the flow response within the external carotid system appeared to be passive. Cervical sympathetic innervation and myogenic reflexes (Bayliss reflex) both appear to play a part in the rapidly occurring (primary) regulation of cerebral blood flow. The mechanism responsible for delayed and progressive (secondary) autoregulation in the cerebral vasculature appeared to be metabolic, since it was predominantly influenced by changes in blood Pco 2 . Changes in intracranial pressure did not seem to be involved in autoregulation. ADDITIONAL KEY WORDS vertebral blood flow carotid blood flow intracranial pressure cerebral vascular resistance baroreceptor denervation• In a previous study, autoregulation of internal carotid artery flow was demonstrated when the blood pressure was reduced by fractional withdrawal of venous blood (1). Cerebral arterial blood flow showed little or no decrease until a critical blood pressure was reached, then a sharp drop in cerebral blood flow accompanied any further fall in blood pressure. Some data from studies in man suggest that there is autoregulation of cerebral blood flow during hypertension. In essential hypertension (2), toxemia of pregnancy with hypertension, and during drug-induced hypertension, cerebral blood flow was within normal limits. These data and the whole question of autoregulation of cerebral blood flow are summarized in Lassen's excellent review and are often quoted to support the concept that autoregulation also exists in man, although effects of age and the level of carbon dioxide tension in arterial blood were not considered (3). We are unaware of quantitative studies of autoregulation of cerebral blood flow during nonpharmacologically induced hypertension, although there are the qualitative observations that pial vessels constrict during elevation of the blood pressure (5-7). The present study was designed to measure blood flow through the major cerebral arteries in the necks of monkeys, by means of electromagnetic flowmeters before and after induction of acute hypertension without the use of drugs. From quantitative data on pressure, flow, and resistance, the existence of autoregulation within the cerebral arterial system was determined and its mechanisms were investigated. 727Methods Twenty-two monkeys (6 Macacus rhesus and 16 Anubis baboons) weighing 3 to 4 kg were used. Results obtained from the two species were not significantly different. Each animal was anesthetized with pentobarbital sodium (initially 35 to 40 mg/kg, intravenously), with supplements g...

MRI study of cerebral, retinal and choroidal blood flow responses to acute hypertension

“…Similar non-passive CBF responses to BP elevation by aortic occlusion have been observed in cats, dogs (Busija et al, 1980) and monkeys (Yoshida et al, 1966) suggesting that the choice of species was reasonable. Similar non-passive CBF responses to BP have also been reported in studies using different anesthetics (Busija et al, 1980) and a variety of different BF measuring techniques (Busija et al, 1980; Yoshida et al, 1966). Different anesthetics have different effects on baroregulation.…”

Cerebral Autoregulation in Middle Cerebral Artery Territory Precedes That of Posterior Cerebral Artery in Human Cortex

“…Whereas this mechanism was described first in animals [1, 2, 3], introduction of transcranial Doppler (TCD) allowed investigations of CA in man usign the non-invasive leg cuff test (LCT) [4]. Doppler sonography investigations helped in differentiating between static and dynamic CA measurements.…”

The Role of the Peripheral Sympathetic Nervous System in Cerebral Blood Flow Autoregulation

“…Both fluorescence histochemical 9 and electron microscopy studies 10 n have revealed rich sympathetic innervation on the extraparenchymal cerebral arteries. Physiological observations in man 12 " 16 as well as laboratory animals 17 ' 23 have produced conflicting results about the role of these nerves in CBFA. Unfor-tunately, in no instance has the degree of sympathetic innervation been verified histologically and compared with the state of CBFA either in patients with acquired autonomic insufficiency or in sympathectomized animals.…”