Normal and Epileptic EEG Patterns Related to Cortical Oxygen Tension in the Cat

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Abstract
The oxygen tension of the cerebral cortex was measured in relative terms with a polaro‐graphic technique (membrane covered platinum electrode of the Clarktype; Lübbers1960) in lightly, or non‐anaesthetized cat preparations of theencéphaleorcerveau isolétype. In steady states with controlled systemic circulation and respiration, the cortical pO2measured was found to be stable. Only small changes in cortical pO2were seen during periods of slowly changing EEG patterns. Acute EEG changes, on the other hand, induced by electrical stimulation, or chemically, were accompanied by regular, reproducible changes in cortical pO2, indicating – under these conditions — a correlation between EEG pattern and cortical oxygen consumption. The arousal reaction of the EEG elicited by electrical stimulation of the meso‐diencephalic brain stem was studied especially. It was accompanied by a biphasic change in cortical pO2with a small initial decrease and a more constant subsequent large increase, proportional to stimulus strength and of duration about equal to the EEG change. The pO2change during arousal was interpreted as due to an acute increase of the cortical oxygen consumption, which was secondarily modified by concomitant local cortical vasomotor reactions. The results support the view that the cortical oxygen tension is stabilized by homeostatic mechanisms which adapt the blood flow to the functional demands. When the functional demands are greater than the supply, the pO2level falls. This was especially evident during epileptic seizures, when the pO2level fell markedly and pathologic patterns appeared in the EEG.