title: The effects of breathing a helium-oxygen gas mixture on maximal pulmonary ventilation and maximal oxygen consumption during exercise in acute moderate hypobaric hypoxia.
abstract: To test the hypothesis that maximal exercise pulmonary ventilation (VE max) is a limiting factor affecting maximal oxygen uptake (VO2 max) in moderate hypobaric hypoxia (H), we examined the effect of breathing a helium-oxygen gas mixture (He-O(2); 20.9% O(2)), which would reduce air density and would be expected to increase VE max. Fourteen healthy young male subjects performed incremental treadmill running tests to exhaustion in normobaric normoxia (N; sea level) and in H (atmospheric pressure equivalent to 2,500 m above sea level). These exercise tests were carried out under three conditions [H with He-O(2), H with normal air and N] in random order. VO2 max and arterial oxy-hemoglobin saturation (SaO(2)) were, respectively, 15.2, 7.5 and 4.0% higher (all p < 0.05) with He-O(2) than with normal air (VE max, 171.9 ± 16.1 vs. 150.1 ± 16.9 L/min; VO2 max, 52.50 ± 9.13 vs. 48.72 ± 5.35 mL/kg/min; arterial oxyhemoglobin saturation (SaO(2)), 79 ± 3 vs. 76 ± 3%). There was a linear relationship between the increment in VE max and the increment in VO2 max in H (r = 0.77; p < 0.05). When subjects were divided into two groups based on their VO2 max, both groups showed increased VE max and SaO(2) in H with He-O(2), but VO2 max was increased only in the high VO2 max group. These findings suggest that in acute moderate hypobaric hypoxia, air-flow resistance can be a limiting factor affecting VE max; consequently, VO2 max is limited in part by VE max especially in subjects with high VO2 max.
authors.affiliation: Institute of Health and Sports Science, University of Tsukuba, Tsukuba, Ibaraki, 305-8574, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ogawa
authors.forename: Jose A L
authors.initials: JA
authors.lastname: Calbet
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Honda
authors.forename: Naoto
authors.initials: N
authors.lastname: Fujii
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishiyasu
mesh_terms: D000006:Abdomen, Acute; D000328:Adult; D000531:Altitude; D001274:Atmospheric Pressure; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006371:Helium; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008954:Models, Biological; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010108:Oxyhemoglobins / Q000378:metabolism; D012123:Pulmonary Ventilation / Q000502:physiology*; D055815:Young Adult
chemical_list: D010108:Oxyhemoglobins; D006371:Helium; D010100:Oxygen