The Influence of Anaesthesia and of Arterial Hypocapnia on Regional Blood Flow in the Normal Human Cerebral Hemisphere

Wilkinson, Iain; Browne, D.R.G.

doi:10.1093/bja/42.6.472-a

Cited by 29 publications

(12 citation statements)

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“…Anesthetic agents that have been reported to have little influence on cerebral blood flow were used. Cerebral blood flow values for patients anesthetized with N 2 O and O 2 supplemented with neuroleptic drugs are on the same order as those for conscious patients (10); N 2 O anesthesia does not influence the autoregulatory response to an angiotensin-induced blood pressure increase in normal man (11).…”

Section: Discussionmentioning

confidence: 73%

Upper Limit of Autoregulation of Cerebral Blood Flow in the Baboon

Strandgaard

MacKenzie

Sengupta

et al. 1974

Circulation Research

165

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The upper limit of autoregulation of cerebral blood flow was studied in ten young baboons. Blood pressure was increased by infusing angiotensin, and cerebral blood flow was measured by the intracarotid 133 xenon injection method. Autoregulation was maintained until blood pressure was 30-40% above resting values. At this blood pressure level, cerebrovascular resistance reached a maximum. Any additional increase in blood pressure resulted in an increase in cerebral blood flow and a decrease in cerebrovascular resistance; this situation is designated the "breakthrough of autoregulation." In four baboons subjected to unilateral sympathetic denervation, autoregulation of cerebral blood flow was studied bilaterally; no difference in the upper limit of autoregulation was found between the intact and the sympathectomized hemisphere. The breakthrough of autoregulation supposedly plays an important role in the pathogenesis of acute hypertensive encephalopathy. The old concept of hypertensive cerebral vasospasm has been revised in recent years, and it is now generally recognized that acute hypertensive encephalopathy is caused by focal overdistention of brain arterioles with lesions of the blood-brain barrier. However, whether this condition is associated with a high cerebral blood flow in the clinical syndrome has not been investigated. KEY WORDSinduced hypertension breakthrough of autoregulation hypertensive encephalopathy cerebrovascular resistance angiotensin 133 xenon clearance• When blood pressure rises, cerebral blood flow is held constant by autoregulatory constriction of the cerebral resistance vessels. Some recent communications have described the existence of an upper limit of autoregulation. When blood pressure rises beyond this limit, autoregulation is exhausted; a forced arteriolar dilation and an increase in cerebral blood flow occur. This situation is called the "breakthrough of autoregulation" (l) and has been observed in hypercapnic dogs (2), in man by the arteriovenous oxygen difference method (3), and, in a limited study, in man by the intracarotid criticism because of the unphysiological experimental conditions (2), the use of an indirect method for assessment of cerebral blood flow (3), and the limited number of experiments performed (4). The present study was undertaken to obtain conclusive evidence on the upper limit of autoregulation. Normocapnic baboons were used, and cerebral blood flow was measured by the intracarotid 133 Xe injection method. The involvement of sympathetic nerves in the regulation of cerebral blood flow during acutely induced hypertension was also evaluated. MethodsThe study was carried out in ten young adult baboons {Papio cynocephalus or Papio anubis) weighing 10-14 kg. Three of the baboons were studied 2 weeks after a unilateral cervical sympathectomy, and one baboon was studied immediately after an acute cervical sympathetic block. The baboons were anesthetized with phencyclidine (12 mg, im) and sodium thiopental (7.5 mg/kg, iv). They were intubated and connected to ...

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Section: Discussionmentioning

confidence: 73%

Upper Limit of Autoregulation of Cerebral Blood Flow in the Baboon

Strandgaard

MacKenzie

Sengupta

et al. 1974

Circulation Research

165

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“…The current demonstration, for example, that flow under basal conditions in these experimental animals was not homogenous, has a parallel in the demonstration by Wilkinson et al 13 and by Herrschaft and his colleagues 23 of inhomogeneity of regional cerebral blood flow over the surface of the primate hemisphere. This, most evident in Wilkinson's work in unanesthetized patients, also was evident 24 to a lesser extent in studies under anesthesia. It is by no means clear why experimental baboons anesthetized with alpha chloralose should show a significantly lower blood flow in the parieto-occipital association areas than in the remainder of the hemispheral surface, and it would be particularly interesting to study the distribution of these inhomogeneities in animals under different types of anesthesia.…”

Section: Discussionmentioning

confidence: 79%

The Distribution and Density of Reduced Cerebral Blood Flow Following Acute Middle Cerebral Artery Occlusion: An Experimental Study by the Technique of Hydrogen Clearance in Baboons

Symon

Pásztor

Branston

1974

Stroke

209

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“…The present observations may fit in with that observation. CO 2 reactivity measured in terms of change in 2 drops, progressively diminishing blood flow by constricting the resistance vessels, a second mechanism gradually comes into play which tends to counteract the "direct" vasoconstrictive action of lowered Paco 2 on the larger vessels.…”

Section: Discussionmentioning

confidence: 99%

Paradoxical dilation of the large cerebral arteries in hypocapnia in man.

Radü¹,

Boulay²

1976

Stroke

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SUMMARY By grouping patients who had carotid angiograms under unusually carefully monitored conditions it has been shown that hypocapnia is associated with vasodilatation at low blood pressure but not at high blood pressure. The mechanism is discussed in general terms and it is suggested that the hypocapnic vasodilatation may be a response to cerebral hypoxia and may be transmitted via an intracerebral autonomic pathway. Clinical and angiographical diagnoses are given for SO patients.IN THE BABOON there is angiographical evidence that during hypocapnia the response of the larger cerebral arteries to a further drop in Paco 2 is vasodilatation. 1 This paradoxical reactivity was also observed in man, but the conditions under which diagnostic angiography had to be performed in the hospital could not be as carefully controlled as in the experiments with baboons, so that in man the effects of concomitant blood pressures (BP) were unknown.To investigate the phenomenon further we have measured the internal diameters of the intracranial carotid, the middle and the anterior cerebral arteries in a series of angiograms which were all carried out under unusually carefully monitored conditions. The arterial diameters have been related both to blood pressure and Paco 2 . The findings indicated that though paradoxical CO 2 reactivity is generally seen at low blood pressure in hypocapnic patients, it is not seen if a normal blood pressure is maintained. MethodsFrom patients at The National Hospital, Queen Square, London (England) who were anesthetized using a short-acting barbiturate for inductions and who were maintained on nitrous oxide and oxygen, supplemented by neuroleptanalgesia 2 in order to carry out intracarotid U3 Xe cerebral blood flow (CBF) studies and carotid angiography, 40 were chosen because their blood pressure levels fitted into our predetermined grouping. Ten further patients had had angiography at St. Bartholomew's Hospital also under very carefully monitored conditions, but anesthetized (after in-

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The Influence of Anaesthesia and of Arterial Hypocapnia on Regional Blood Flow in the Normal Human Cerebral Hemisphere

Cited by 29 publications

References 0 publications

Upper Limit of Autoregulation of Cerebral Blood Flow in the Baboon

Upper Limit of Autoregulation of Cerebral Blood Flow in the Baboon

The Distribution and Density of Reduced Cerebral Blood Flow Following Acute Middle Cerebral Artery Occlusion: An Experimental Study by the Technique of Hydrogen Clearance in Baboons

Paradoxical dilation of the large cerebral arteries in hypocapnia in man.

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