Autoregulation of cerebral blood flow: influence of the arterial blood pressure on the blood flow through the cerebral cortex.

Until fairly recently it 'was believed that cerebral blood flow followed more or less passively the mean arterial blood pressure, and the stability of the cerebral circulation under physiological conditions reflected only the relative constancy of the arterial pressure maintained by the homeostatic pressor reflex mechanism' (Sokoloff, 1959). That there might also be an intrinsic regulation of cerebrovascular tone was suggested by Fog (1934, 1938) and by Forbes, Nason, and Wortman (1937). These workers observed that the blood vessels of the pia mater constricted in response to a rise in arterial blood pressure and dilated in response to a fall in pressure. Although more recent studies in man (summarized by Lassen, 1959) seem to refute the idea of a passive pressure/flow relationship for the cerebral circulation, there is still conflict on the precise role of the arterial blood pressure in the control of the cerebral blood flow. The experiments reported in this paper were undertaken to measure the effect of gradual reduction of the mean arterial blood pressure on the blood flow through the cerebral cortex under 'normal' respiratory conditions (that is a PaCO2 of 40 mm. Hg) and under conditions of hypercapnia (CO2 being added to the respiratory mixture).