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When and Why

Lewis L. Levy, MD

JAMA. 1991;266(23):3332-3333.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

Many factors influence cerebral circulation in addition to carotid blood flow. The brain accounts for less than 2% of body weight but consumes 20% of the total circulation. Cerebral blood is not transported passively. Rather, complex control systems in the brain vasculature maintain almost constant total cerebral blood flow within a wide range of levels of systemic blood pressure and distribute circulation within the brain unevenly according to local metabolic needs. Signals that originate in pressure sensors in supply arteries initiate changes in systemic blood pressure and adjust resistance in cranial vasculature. These reflexes modify the direction of flow in extracranial arteries. Collateral channels bridge internal to external carotid and vertebral systems. Intracranial arteries link hemispheres, connect carotid and basilar artery territories, and—on the brain surface—join branches of middle cerebral, anterior cerebral, and posterior cerebral arteries. Within these vascular territories, blood flow is coupled to local brain metabolism. Parenchymal arteriolar . . . [Full Text PDF of this Article]

Author Affiliations
From the Department of Neurology, Yale University School of Medicine, New Haven, Conn.

Footnotes
Reprint requests to Prince Professional Center, 46 Prince St, Suite 201, New Haven, CT 06519 (Dr Levy).

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