The paradoxical blood pressure-flow relationship in the brain with an arteriovenous malformation.

The responses of regional cerebral blood flow (CBF) to decrease in arterial blood pressure were studied in eight patients with arteriovenous malformations using the Xe-133 inhalation method. Measurements were performed twice for each study; before and during hypotension induced by trimethaphan camsylate (Arfonad). In all cases, there were regions where cerebral blood flow increased remarkably in response to hypotension. When the studies were repeated in five cases after total resection of the malformations, increase in the cerebral blood flow in response to hypotension was not observed. The underlying mechanisms that operate in such paradoxical blood pressure-flow relationship are discussed.