Cerebral oxidative metabolism and regional blood flow were studied, with changes in behavioral state over the immediate perinatal period, to determine the change in cerebral metabolism at birth and the relationship to behavioral activity. Nine unanesthetized fetal sheep (139-142 days gestation) were each studied during a period of high-voltage and low-voltage electrocorticogram (ECOG) activity and then again after cesarean delivery at 2 h of age while awake and at 24 h of age while awake and during a period of high-voltage ECOG sleep. Preductal arterial and sagittal vein blood samples were analyzed for O2 content, blood gases, and pH. Blood flow was measured with a radioactive microsphere technique. Cerebral oxidative metabolism showed no significant perinatal change, although a coupling to behavioral state was evident with significant increases during both the perinatal low-voltage ECOG state and the awake state at 24 h. Blood flow to the brain showed a significant perinatal decrease after birth and state-related increases during both the prenatal low-voltage ECOG state and the awake state at 24 h consistent with the tight coupling of flow and/or O2 delivery to metabolic needs reported for normal brain tissue. The cerebral metabolic rate of the prenatal low-voltage ECOG state suggested a level of functional excitation comparable with that of the awake state after birth, supporting the importance of the rapid-eye-movement (REM) state mechanism as a source of endogenous stimulation during the perinatal period of brain growth and development.
Cerebral oxidative metabolism is decreased with extreme apnoea in humans; impact of hypercapnia
