Autoregulatory responses of cerebral blood vessels in hypercapnia

Simultaneous determinations of cerebral blood flow, measured by 85Kr clearance, and of intracranial pressure, measured in the cisterna magna, were made in anesthetized normocapnic and hypercapnic vagotomized cats. All animals were tested at their normal arterial pressure and at elevated arterial pressure induced by angiotensin infusion. Autoregulatory responses of cerebral blood vessels to the elevation of blood pressure were quantitatively characterized by a pressure-flow function. In 10 of 12 animals, hypercapnia interfered with the autoregulatory responses of the cerebral vasculature. Analysis of the simultaneous behavior of intracranial pressure and cerebral vascular resistance did not indicate that changes in intracranial pressure affected the autoregulatory responses. The results of this study support the view that CO2 interferes with the basic reaction of vascular smooth muscle to contract after distension by increased transmural pressure.