Lower limit of cerebral blood flow autoregulation in experimental renovascular hypertension in the baboon.

The effect of chronic renovascular hypertension on the autoregulation of cerebral blood flow was studied in anesthetized baboons. Cerebral blood flow was measured by the intracarotid 133Xe clearance method. Six baboons with renal hypertension of 8-12 weeks' duration were compared with six normotensive controls. The lower limit of autoregulation was determined following controlled hemorrhage. In the initially normotensive baboons, cerebral blood flow remained constant until mean arterial pressure had decreased to the range of 45-59 mm Hg. Thereafter, cerebral blood flow decreased with each further decrease in mean arterial pressure. In the chronically hypertensive baboons cerebral blood flow autoregulated until the mean arterial pressure had decreased to the range of 75-89 mm Hg. Therefore, the lower limit of autoregulation of cerebral blood flow was shifted to higher absolute levels of mean arterial pressure in baboons with chronic renovascular hypertension presumably due to adaptive changes in the cerebral circulation.