CEREBRAL CONSTITUENTS IN RELATION TO BLOOD GASES

Abstract

Cerebral tissue from morphinized dogs was obtained for chemical analysis by freezing in situ with liquid air. The specimens were assayed for lactic acid, glucose, glycogen and acid-soluble P compounds. Blood samples obtained immediately prior to the freezing were analyzed for lactic acid, glucose, oxygen, CO2 and pH, and the tensions of oxygen and of CO2 we re calculated. The effects of variations in the respired gas mixtures were investigated. Variations of arterial CO2 tension in the presence of adequate O2 caused no significant changes in the cerebral constituents studied. Hypoxia induced an increase of lactic acid and a breakdown of phosphocreatine in the brain. These changes were diminished when the associated acapnia was counteracted by adding CO2 to the respired gas mixture. The effect of CO2 was due in large part to improved oxygenation of the arterial blood. Improved cerebral adenosine triphosphate was found to remain undecomposed during hypoxia until the extreme limit of tolerance was reached. At this point the phosphocreatine was almost completely decomposed and decomposition of adenosine triphosphate began. The cerebral glucose remained in the normal range during hypoxia. The glycogen values also were normal with the exception of one low result occurring in extreme hypoxia. In the morphinized dog, changes of CO2 tension did not play a major role in the regulation of the electrocortico-gram either in the presence or in the absence of adequate oxygen.