Local cerebral blood flow in experimental middle cerebral artery vasospasm

Abstract

✓ The authors report a study of the effect of middle cerebral artery spasm on cerebral blood flow, its autoregulation, and the subsequent development of ischemic infarction in the rhesus monkey. Spasm induced by puncturing the middle cerebral artery was followed by serial angiography and the determination of “local” cerebral blood flow (1CBF). Xenon133 washout was measured by a collimator whose isoresponse characteristics allowed exclusive sampling from the middle cerebral territory. Before the development of ischemic necrosis, 1CBF varied indirectly with the severity of spasm. The onset of infarction was marked by permanent depression of 1CBF despite recovery of arterial caliber. Despite wide changes in blood pressure, autoregulation of 1CBF was maintained in the normal rhesus monkey. However, soon after the onset of spasm, the 1CBF was constant only during hypotensive periods, and flow values increased significantly during hypertensive periods. When prolonged spasm (22 hrs) caused ischemic infarction, a reversal of the autoregulatory pattern occurred; the 1CBF was constant in the hypertensive period and decreased during the hypotensive period. Although the constancy of the relationship of 1CBF to hypotension in the absence of infarction might indicate a degree of reflex vasodilatation, this could not be substantiated on serial angiography. The therapeutic implications of these findings are discussed.