Elevated CO2 Mitigates the Rise in CMRO2 During Acute Hypoxia & Improves Cerebral Tissue Oxygenation

Zachary Myles Smith¹, John S. Hunt, Jr. ¹, Ethan Li¹, Jia Guo¹, David D. Shin¹, Richard B. Buxton¹, David J. Dubowitz¹

We previously reported increased CMRO2 during sustained hypoxia, despite limited O2 availability. The biological rationale for this paradoxical response remains unclear. To investigate the possible influence of PaCO2 on CMRO2 and cerebral tissue oxygenation (PtO2), we made MRI measurements of CBF and oxygen extraction fraction during acute hypoxic conditions. Subjects CO2 levels were either unrestrained (low CO2), or clamped at normoxic levels (high CO2). Maintaining a high CO2 partially mitigated the paradoxical increase in CMRO2, and also improved cerebral tissue oxygentation during acute hypoxic conditions. CO2 is thus an important covariable in the cerebral response to hypoxia.