Submitted on February 6, 2007
Accepted on July 20, 2007
Relationship between resting ventilatory chemosensitivity and maximal oxygen uptake in moderate hypobaric hypoxia
Takeshi Ogawa1, Keiji Hayashi1, Masashi Ichinose1, and Takeshi Nishiyasu1*
1 Inst Health & Sports Sci, Univ Tsukuba, Tsukuba, Ibaraki, Japan
* To whom correspondence should be addressed. E-mail: nisiyasu{at}taiiku.tsukuba.ac.jp.
This study tested the hypothesis that the extent of the decrement in VO2max 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, VO2, pulmonary ventilation (VE) and arterial oxyhemoglobin saturation (SaO2) 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 l·min-1·%-1 and 2.11 ± 0.2 l·min-1·mmHg-1, respectively. HVR correlated significantly with the percent decrements in VO2max (%dVO2max), SaO2 (%dSaO2 = (H-N)·N-1·100), and VE·VO2-1 seen during H condition. By contrast, HCVR did not correlate with any of the variables tested. The increment in maximal VE between H and N significantly correlated with %dVO2max. 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 VO2max and SaO2 under those conditions.
