Carbon Dioxide and Cerebral Circulatory Control

IN a previous report¹we demonstrated that carbon dioxide (CO₂) may increase cerebral blood flow (CBF) when supplied to the brain via the subarachnoid space (SAS) while the arterial carbon dioxide tension (Paco₂) is kept at a low level, suggesting that the effect of CO₂on CBF may not necessarily be mediated by its effect on the smooth muscle of the cerebral arterial wall, but perhaps by another mechanism, such as mediation through a chemoreceptor reflex mechanism. Reviewing previous pertinent work, it was somewhat surprising to discover that no direct demonstration of the effect of CO₂on the smooth muscle of the cerebral arterial wall had been described. The only direct investigation, frequently quoted in various reviews dealing with this subject, is the work of Cow²in 1911 who observed that isolated segments of the carotid artery dilate when CO₂is added