Elimination by hypoxia cerebral blood flow autoregulation and EEG relationship.

Abstract

1. The relationship between cortical blood flow and the frequency content of the EEG was studied in a circumscribed area of the exposed cerebral cortex in cats under nitrous oxide-oxygen anaesthesia. Autoregulation of the cortical blood flow was also tested during step-changes of the arterial blood pressure. Observations were made before and after an episode of severe hypoxia. 2. An episode of systemic hypoxia disrupted the normal high correlation between cortical blood flow and EEG frequency content. In the post-hypoxic period cortical flows of up to about three times normal values were recorded together with brain swelling and a slow wave EEG. The hyperemia and swelling subsided during 1–2 h after the hypoxic episode, and were accompanied by partial or complete recovery of the EEG. In the post-hypoxic period a defective autoregulation of the cortical blood flow to changes in the systemic blood pressure was demonstrated. 3. The cerebral post-hypoxic state with hyperaemia, brain swelling, EEG depression, and loss of autoregulation of blood flow, is probably caused by an accumulation of anaerobic metabolites which lead to cerebral tissue acidosis.