title: Changes in ventilatory responses to hypercapnia and hypoxia after intermittent hypoxia in humans.
abstract: The purpose of this study was to clarify the changes in hypercapnic and hypoxic ventilatory responses (HCVR and HVR) after intermittent hypoxia and following the cessation of hypoxic exposure. Twenty-nine males were assigned to one of four groups, i.e., a hypoxic (EX1-H, n=7) or a control (EX1-C, n=7) group in Experiment 1, and a hypoxic (EX2-H, n=8) or a control (EX2-C, n=7) group in Experiment 2. In each experiment, the hypoxic tent system was utilized for intermittent hypoxia, and the oxygen levels in the tent were maintained at 12.3+/-0.2%. In Experiment 1, the EX1-H group spent 3 h/day in the hypoxic tent for 1 week. HCVR and HVR were determined before and after 1 week of intermittent hypoxia, and again 1 and 2 week after the cessation of hypoxic exposure. In Experiment 2, the subjects in the EX2-H group performed 3 h/day for 2 weeks in intermittent hypoxia. HCVR and HVR tests were carried out before and after intermittent hypoxia, and were repeated again after 2 weeks of the cessation of hypoxic exposure. The slope of the HCVR in the EX1-H group did not show a significant increase after 1 week of intermittent hypoxia, while HCVR in the EX2-H group increased significantly after 2 weeks of intermittent hypoxia. The HCVR intercept was unchanged following 1 or 2 weeks of intermittent hypoxia. There was a significant increase in the slope of the HVR after 1 and 2 weeks of intermittent hypoxia. The increased HCVR and HVR returned to pre-hypoxic levels after 2 weeks of the cessation of hypoxia. These results suggest that 3 h/day for 2 weeks of intermittent hypoxia leads to an increase in central hypercapnic ventilatory chemosensitivity, which is not accompanied by a re-setting of the central chemoreceptors, and that the increased hypercapnic and hypoxic chemosensitivities are restored within 2 weeks after the cessation of hypoxia.
authors.affiliation: Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya 464-8601, Japan. katayama@htc.nagoya-u.ac.jp
authors.forename: Keisho
authors.initials: K
authors.lastname: Katayama
authors.forename: Kohei
authors.initials: K
authors.lastname: Sato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsuo
authors.forename: Norio
authors.initials: N
authors.lastname: Hotta
authors.forename: Zhihu
authors.initials: Z
authors.lastname: Sun
authors.forename: Koji
authors.initials: K
authors.lastname: Ishida
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Miharu
authors.initials: M
authors.lastname: Miyamura
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D015444:Exercise / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D012119:Respiration; D012129:Respiratory Function Tests / Q000379:methods; D013997:Time Factors