Evaluation of Cerebral Energy Demand During Graded Hypercapnia

Stefan Alexandru Carp¹, Maria Angela Franceschini¹, David Alan Boas¹, Young Ro Kim¹

The cerebral metabolic rate of oxygen (CMRO₂) is a physiological parameter closely linked to neural activation as well as to various disease states. Hypercapnic calibration is used to calibrate the BOLD-CBF-CBV relationship under the assumption of iso-metabolic blood flow increase during CO₂ inhalation. Simultaneous near infrared optical measurements of cerebral blood volume, blood flow and oxygen extraction can also be used to monitor CMRO₂ changes, albeit at low spatial resolution. We use these optical measurements during graded hypercapnia to test the iso-metabolic assumption, and demonstrate an apparent increase in brain metabolism at higher inhaled CO₂ levels.