A Study of Regional Autoregulation in the Cerebral Circulation to Increased Perfusion Pressure in Normocapnia and Hypercapnia

Catheterization of Labbe's vein and of a pial branch of the middle cerebral artery has been performed on anesthetized baboons. Closure of the skull has enabled the reaction of the venous outflow from Labbe's vein to be monitored in response to pressure step increases in the pial arterial pressure induced by gas compression of a perfusion mixture connected to the arterial line. Rapid changes in cerebrovascular resistance with swift emergence of regulatory constancy have been shown, and the time characteristics of the resistance changes strongly suggest that they are primarily myogenic in origin. Induction of hypercapnia did not interfere with this autoregulatory mechanism to increased perfusion pressure, which indeed appeared to be more effective at raised arterial P-CO2, but the mechanism was abolished by the induction of ischemia from middle cerebral occlusion.