Toward Reliable Quantification of Global Cerebrovascular Reactivity to Hypoxic Hypoxia

Motivation: The cerebrovascular response to mild hypoxia has not been well-characterized, but hypoxic cerebrovascular reactivity (CVR) may be an important metric that could complement hypercapnic CVR in clinical applications, giving distinct information about cerebrovascular health. Goal(s): We aimed to increase reliability of hypoxic CVR and modulate the effects of concurrent CO2 changes. Approach: Using phase-contrast MRI, we measured cerebral blood flow during baseline, hypoxic, and hypercapnic respiratory states, induced with a computer-controlled gas blender. We used hypercapnic CVR to implement a simple correction for changes in PETCO2 that occurred during hypoxia. Results: While substantial inter-subject variability remained, PETCO2 correction reduced variability and improved reliability. Impact: Minimizing and correcting for concurrent changes in PETCO2 during a mild inhaled hypoxic stimulus improves the reliability of hypoxic cerebrovascular reactivity, but normal inter-subject variability and the utility of hypoxic cerebrovascular reactivity in clinical populations have yet to be determined.