Total and regional cerebral blood flow during hypotension, hypertension, and hypocapnia. Effect of sympathetic denervation in dogs.

SUMMARY This study was performed to determine whether acute or chronic sympathetic denervation increases or redistributes cerebral blood flow (CBF) during hypotension or during the action of vasoconstrictor stimuli (hypocapnia and hypertension). Left superior cervical and stellate ganglionectomy was performed in anesthetized dogs. Total and regional CBF were measured by using microspheres. In acute experiments, hemorrhagic hypotension produced a redistribution of CBF which tended to preserve blood flow to the brainstem and to cerebral gray matter. Hypertension and hypocapnia did not redistribute CBF. Blood flows were similar in the acutely denervated and nondenervated half of the brain during control conditions, hypotension, hypertension, and hypocapnia. Completeness of sympathetic denervation was demonstrated by large increases in blood flow to the masseter muscle on the denervated side. Similar studies were undertaken 6-7 days after sympathetic ganglionectomy, at which time cerebral vascular catecholamines were depleted on the denervated side: norepinephrine content in innervated and denervated middle cerebral arteries was 3.1 ± 0.5 and 0.1 ± 0.02 ng/g, respectively. Blood flows in the chronically denervated and nondenervated half of the brain were similar during control conditions and during interventions. The major new findings in this study are, first, that hypotension produces a redistribution of CBF which tends to preserve blood flow to brainstem and to cerebral gray matter, and second, that acute "or chronic sympathetic denervation does not alter distribution of CBF over a wide range of arterial pressure or during hypocapnia.