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Relationship between resting ventilatory chemosensitivity and maximal oxygen uptake in moderate hypobaric hypoxia

¹Institute of Health and Sports Science, University of Tsukuba, Tsukuba City, Japan

Submitted 6 February 2007 ; accepted in final form 20 July 2007

This study tested the hypothesis that the extent of the decrement in O_2max and the respiratory response seen during maximal exercise in moderate hypobaric hypoxia (H; simulated 2,500 m) is affected by the hypoxia ventilatory and hypercapnia ventilatory responses (HVR and HCVR, respectively). Twenty men (5 untrained subjects, 7 long distance runners, 8 middle distance runners) performed incremental exhaustive running tests in H and normobaric normoxia (N) condition. During the running test, O₂, pulmonary ventilation (E) and arterial oxyhemoglobin saturation (Sa_O2) were measured, and in two ventilatory response tests performed during N, a rebreathing method was used to evaluate HVR and HCVR. Mean HVR and HCVR were 0.36 ± 0.04 and 2.11 ± 0.2 l·min^–1·mmHg^–1, respectively. HVR correlated significantly with the percent decrements in O_2max (%dO_2max), Sa_O2 [%dSa_O2 = (N–H)·N^–1·100], and E/O₂ seen during H condition. By contrast, HCVR did not correlate with any of the variables tested. The increment in maximal E between H and N significantly correlated with %dO_2max. Our findings suggest that O₂ chemosensitivity plays a significant role in determining the level of exercise hyperventilation during moderate hypoxia; thus, a higher O₂ chemosensitivity was associated with a smaller drop in O_2max and Sa_O2 under those conditions.

ventilation; hypoxia ventilatory response; moderate altitude