title: Pulmonary gas exchange during exercise in highly trained cyclists with arterial hypoxemia.
abstract: The causes of exercise-induced hypoxemia (EIH) remain unclear. We studied the mechanisms of EIH in highly trained cyclists. Five subjects had no significant change from resting arterial PO(2) (Pa(O(2)); 92.1 +/- 2.6 Torr) during maximal exercise (C), and seven subjects (E) had a >10-Torr reduction in Pa(O(2)) (81.7 +/- 4.5 Torr). Later, they were studied at rest and during various exercise intensities by using the multiple inert gas elimination technique in normoxia and hypoxia (13.2% O(2)). During normoxia at 90% peak O(2) consumption, Pa(O(2)) was lower in E compared with C (87 +/- 4 vs. 97 +/- 6 Torr, P < 0.001) and alveolar-to-arterial O(2) tension difference (A-aDO(2)) was greater (33 +/- 4 vs. 23 +/- 1 Torr, P < 0. 001). Diffusion limitation accounted for 23 (E) and 13 Torr (C) of the A-aDO(2) (P < 0.01). There were no significant differences between groups in arterial PCO(2) (Pa(CO(2))) or ventilation-perfusion (VA/Q) inequality as measured by the log SD of the perfusion distribution (logSD(Q)). Stepwise multiple linear regression revealed that lung O(2) diffusing capacity (DL(O(2))), logSD(Q), and Pa(CO(2)) each accounted for approximately 30% of the variance in Pa(O(2)) (r = 0.95, P < 0.001). These data suggest that EIH has a multifactorial etiology related to DL(O(2)), VA/Q inequality, and ventilation.
authors.affiliation: Department of Thoracic Medicine, Royal Adelaide Hospital, Adelaide, South Australia 5000. arice@earthling.net
authors.forename: A J
authors.initials: AJ
authors.lastname: Rice
authors.forename: A T
authors.initials: AT
authors.lastname: Thornton
authors.forename: C J
authors.initials: CJ
authors.lastname: Gore
authors.forename: G C
authors.initials: GC
authors.lastname: Scroop
authors.forename: H W
authors.initials: HW
authors.lastname: Greville
authors.forename: H
authors.initials: H
authors.lastname: Wagner
authors.forename: P D
authors.initials: PD
authors.lastname: Wagner
authors.forename: S R
authors.initials: SR
authors.lastname: Hopkins
mesh_terms: D000328:Adult; D000465:Algorithms; D001642:Bicycling / Q000502:physiology*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood; D004058:Diffusion; D015444:Exercise / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D005741:Noble Gases; D010101:Oxygen Consumption / Q000502:physiology; D010108:Oxyhemoglobins / Q000378:metabolism; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012044:Regression Analysis; D014692:Ventilation-Perfusion Ratio / Q000502:physiology
chemical_list: D005741:Noble Gases; D010108:Oxyhemoglobins; D002245:Carbon Dioxide