Short intermittent hypoxic exposures augment ventilation but do not alter regional cerebral and muscle oxygenation during hypoxic exercise.

This study investigated the effects of four exposures to normobaric hypoxia (SIH group; FIO₂ = 0.120, N=10) or placebo-control normoxia (Control group; FIO₂ = 0.209, N=9) on cardio-respiratory responses to hypoxic exercise. Before and after the exposures all subjects performed a constant power test (CP) to exhaustion in hypoxia FIO₂ = 0.120 at a work load corresponding to 75% of previously determined normoxic VO₂ peak. Arterial oxygen saturation (SPO₂) and minute ventilation (V(E)) were measured continuously. NIRS was used to monitor regional changes in oxygenated, de-oxygenated and total hemoglobin concentrations of the frontal cortex, vastus lateralis and serratus anterior. Although neither group improved CP time, the SIH group exhibited increases in both V(E) (+15%; P<0.05) and SPO₂ (+4%; P<0.05) after intermittent hypoxia. No physiologically significant differences were observed during exercise in vastus lateralis, serratus anterior and cerebral oxygenation between groups and testing periods. These data suggest that normobaric SIH enhances hypoxic exercise V(E) and SPO₂ without affecting regional oxygenation or time to exhaustion.