Does Global Cerebral Oxygen Metabolism Change During Hypercapnia and Hypocapnia in Awake Humans?

Jean J. Chen¹, G. Bruce Pike¹

The effect of CO₂ on cerebral metabolism is of great interest, since hypercapnia is routinely used in calibrated BOLD-based δCMRo₂ estimation and assumes that CMRo₂ remains unchanged during hypercapnia-induced blood flow increase. Certain anesthetized-animal studies, however, have put this claim under question, necessitating its verification in humans and under the conditions customary of calibrated BOLD. We report, for the first time, on steady-state global δCMRo₂ measurements in awake humans during graded hypercapnia and hypocapnia. Our results show that under the mild levels of end-tidal CO₂ changes commonly used in calibrated BOLD, there is negligible global δCMRo₂.