Assessing chemoreflexes and oxygenation in the context of acute hypoxia: Implications for field studies.

Carotid chemoreceptors detect changes in PO2 and elicit a peripheral respiratory chemoreflex (PCR). The PCR can be tested through a transient hypoxic ventilatory response test (TT-HVR), which may not be safe nor feasible at altitude. We characterized a transient hyperoxic ventilatory withdrawal test in the setting of steady-state normobaric hypoxia (13.5-14% FIO2) and compared it to a TT-HVR and a steady-state poikilocapnic hypoxia test, within-individuals. No PCR test magnitude was correlated with any other test, nor was any test magnitude correlated with oxygenation while in steady-state hypoxia. Due to the heterogeneity between the different PCR test procedures and magnitudes, and the confounding effects of alterations in CO2 acting on both central and peripheral chemoreceptors, we developed a novel method to assess prevailing steady-state chemoreflex drive in the context of hypoxia. Quantifying peak hypoxic/hyperoxic responses at low altitude may have minimal utility in predicting oxygenation during ascent to altitude, and here we advance a novel index of chemoreflex drive.