Haemodynamics of the circle of Willis and the leptomeningeal anastomoses: an electromagnetic flowmeter study of intracranial arterial occlusion in the monkey

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Abstract
The dynamic functions of the circle of Willis and leptomeningeal anastomoses in the monkey were quantitated with electromagnetic flowmeters. These were applied to the carotid and vertebral arteries while temporarily occluding the intracranial branches of these arteries. The experimental occlusion sites were as follows: the intracranial portion of the internal carotid artery proximal to the posterior communicating artery; the portion of the carotid distal to the posterior communicating artery; the proximal portions of the anterior cerebral artery; and the proximal portion of the middle cerebral artery. The various pathways of collateral circulations are described. The transitory hyperemia following release of an occluded middle cerebral artery supports the concept that cerebral vasodilata-tion is produced by an accumulation of metabolites which are produced by the preceding ischemia. Both metabolic and hydrostatic factors are important in maintaining an optimal level of systemic blood pressure which controls the cerebral collateral circulation.