Carbon Dioxide and Cerebral Circulatory Control

IN A series of papers in this journal last year Shalit and his co-workers discussed "Carbon Dioxide and Cerebral Circulatory Control." From three series of experiments on anesthetized dogs they concluded that the well-known CO₂effect on the cerebral blood flow (CBF increases when the arterial CO₂pressure [Pco₂] increases) was due to receptors sensitive to CO₂and not to pH,₁that changes in the arterial Pco₂had no direct effect on the cerebral vessels,²and that destruction in the upper part of the medulla, pons, and the lower part of mesencephalon abolished the CBF response to changes in the arterial Pco₂.³These experiments suggest the existence of a CO₂-sensitive center in the brain stem regulating the cerebral vascular resistance in the hemispheres via a neurogenic mechanism. Two different problems are involved in this hypothesis: is the CO