The pressure-flow relations of the canine brain in acute mechanically induced arterial hypertension at different levels of cerebral blood flow.

Cerebral pressure-flow relations were studied in anaesthetized dogs during acute arterial hypertension, induced by compression of the thoracic aorta. In one group of animals steady state measurements were made with the radioactive gas elimination method. In another group the immediate changes of blood flow at a blood pressure change, as indicated by variations in the cerebral venous oxygen saturation, were studied with continuous oximetric analyses of the superior sagittal sinus blood. The initial blood flow was varied by variations of the arterial carbon dioxide tension of injections of papaverine. At low or normal blood flows autoregulation was efficient up to pressures around 180-200 mmHg, while at higher flows the upper autoregulatory pressure limit was found at lower blood pressures. Above the autoregulatory limit-irrespective of the control flow level-there was a rise in blood flow and a decrease in cerebrovascular resistance.