The Relation Between Cerebral Oxygen Consumption and Cerebral Vascular Reactivity to Carbon Dioxide

The mechanisms whereby CO 2 affects cerebral vessels are not as simple as once thought, 1, 2 and are probably both directly on cerebral vascular walls 3, 4 and indirectly by action on brain stem neurones. 5 Furthermore, cerebral vascular reactivity to CO 2 has been reported to be altered by a number of physiological and pathological circumstances. The capacity to dilate to increased Pa CO CO2 is decreased in cerebral vascular lesions, 6-8 and is affected by changes in cerebral perfusion pressure. 9 Cervical sympathectomy is said to increase CBF response to Pa CO CO2 changes, whereas sympathetic nerve stimulation abolishes reactivity to CO 2 . 10 Deep anesthesia, hypothermia, or trauma to brain reduces reactivity to cerebral vessels to CO 2 , the one common denominator for these states being reduced cerebral metabolism. This report demonstrates that the capacity of cerebral vessels to dilate or constrict in response to changes in Pa CO CO2 is influenced by cerebral oxygen consumption.