Electric activity and oxygen tension of the brain during ischaemic anoxia and reperfusion

Electric activity of the cerebral cortex and the mesencephalon and pO2 of the brain surface were analysed in 47 dogs after serial periods of cerebral anoxia induced by clamping of the aorta for less than 3 minutes and subsequent reperfusion. After restoring the circulation, characteristic stages were observed in the normalization of cortical electric activity and pO2. Improvement in cortical oxygen utilization progressed parallel to the return of rapid activity, though normalization of the EEG preceded that of oxygen utilization. The relative duration of the stages determined from the pO2 curve and from the parameters of electric activity allowed conclusions concerning the injury of the brain tissue. It is assumed that [1] after ischaemic anoxia an excess perfusion develops in the brain; [2] during anoxia, autoregulation of the cerebral vascular system ceases simultaneously with the disintegration of the oxidative metabolic processes of the brain; [3] restitution of the cortex is indicated more reliably by its oxygen consumption rate than by the normalization of EEG activity.