title: Effects of acute hypoxia at moderate altitude on stroke volume and cardiac output during exercise.
abstract: It has been unclear how acute hypoxia at moderate altitude affects stroke volume (SV), an index of cardiac function, during exercise. The present study was conducted to reveal whether acute normobaric hypoxia might alter SV during exercise.Nine healthy male subjects performed maximal exercise testing under normobaric normoxic, and normobaric hypoxic conditions (O(2): 14.4%) in a randomized order. A novel thoracic impedance method was used to continuously measure SV and cardiac output (CO) during exercise. Acute hypoxia decreased maximal work rate (hypoxia; 247 + or - 6 [SE] versus normoxia; 267 + or - 8 W, P < 0.005) and VO(2) max (hypoxia; 2761 + or - 99 versus normoxia; 3039 + or - 133 mL/min, P < 0.005). Under hypoxic conditions, SV and CO at maximal exercise decreased (SV: hypoxia; 145 + or - 11 versus normoxia; 163 + or - 11 mL, P < 0.05, CO: hypoxia; 26.7 + or - 2.1 versus normoxia; 30.2 + or - 1.8 L/min, P < 0.05). In acute hypoxia, SV during submaximal exercise at identical work rate decreased. Furthermore, in hypoxia, 4 of 9 subjects attained their highest SV at maximal exercise, while in normoxia, 8 of 9 subjects did.Acute normobaric hypoxia attenuated the increment of SV and CO during exercise, and SV reached a plateau earlier under hypoxia than in normoxia. Cardiac function during exercise at this level of acute normobaric hypoxia might be attenuated.
authors.affiliation: Department of Cardiovascular Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
authors.forename: Taira
authors.initials: T
authors.lastname: Fukuda
authors.forename: Taketeru
authors.initials: T
authors.lastname: Maegawa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Matsumoto
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Komatsu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Nakajima
authors.forename: Ryozo
authors.initials: R
authors.lastname: Nagai
authors.forename: Takashi
authors.initials: T
authors.lastname: Kawahara
mesh_terms: D000208:Acute Disease; D000328:Adult; D000531:Altitude; D001794:Blood Pressure / Q000502:physiology; D002307:Cardiography, Impedance; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D015203:Reproducibility of Results; D013318:Stroke Volume / Q000502:physiology*