title: Cardiac output, O2 delivery and VO2 kinetics during step exercise in acute normobaric hypoxia.
abstract: We hypothesised that phase II time constant (τ2) of alveolar O2 uptake ( [Formula: see text] ) is longer in hypoxia than in normoxia as a consequence of a parallel deceleration of the kinetics of O2 delivery ( [Formula: see text] ). To test this hypothesis, breath-by-breath [Formula: see text] and beat-by-beat [Formula: see text] were measured in eight male subjects (25.4±3.4yy, 1.81±0.05m, 78.8±5.7kg) at the onset of cycling exercise (100W) in normoxia and acute hypoxia ( [Formula: see text] ). Blood lactate ([La]b) accumulation during the exercise transient was also measured. The τ2 for [Formula: see text] was shorter than that for [Formula: see text] in normoxia (8.3±6.8s versus 17.8±3.1s), but not in hypoxia (31.5±21.7s versus 28.4 5.4±5.4s). [La]b was increased in the exercise transient in hypoxia (3.0±0.5mM at exercise versus 1.7±0.2mM at rest), but not in normoxia. We conclude that the slowing down of the [Formula: see text] kinetics generated the longer τ2 for [Formula: see text] in hypoxia, with consequent contribution of anaerobic lactic metabolism to the energy balance in exercise transient, witnessed by the increase in [La]b.
authors: Département des Neurosciences Fondamentales, Centre Médical Universitaire, Genève, 1 rue Michel Servet, 1211 Geneva 4, Switzerland. frederic.lador@hcuge.ch
authors: Frédéric
authors: F
authors: Lador
authors: Enrico
authors: E
authors: Tam
authors: Alessandra
authors: A
authors: Adami
authors: Marcel Azabji
authors: MA
authors: Kenfack
authors: Aurélien
authors: A
authors: Bringard
authors: Michela
authors: M
authors: Cautero
authors: Christian
authors: C
authors: Moia
authors: Denis R
authors: DR
authors: Morel
authors: Carlo
authors: C
authors: Capelli
authors: Guido
authors: G
authors: Ferretti
mesh_terms: D002302:Cardiac Output / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007700:Kinetics; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*
chemical_list: D010100:Oxygen