title: Effect of acute hypoxia on muscle blood flow, VO₂p, and [HHb] kinetics during leg extension exercise in older men.
abstract: The adjustment of pulmonary oxygen uptake (VO2p), heart rate (HR), limb blood flow (LBF), and muscle deoxygenation [HHb] was examined during the transition to moderate-intensity, knee-extension exercise in six older adults (70 ± 4 years) under two conditions: normoxia (FIO₂ = 20.9 %) and hypoxia (FIO₂ = 15 %). The subjects performed repeated step transitions from an active baseline (3 W) to an absolute work rate (21 W) in both conditions. Phase 2 VO₂p, HR, LBF, and [HHb] data were fit with an exponential model. Under hypoxic conditions, no change was observed in HR kinetics, on the other hand, LBF kinetics was faster (normoxia 34 ± 3 s; hypoxia 28 ± 2), whereas the overall [HHb] adjustment (τ' = TD + τ) was slower (normoxia 28 ± 2; hypoxia 33 ± 4 s). Phase 2 VO₂p kinetics were unchanged (p < 0.05). The faster LBF kinetics and slower [HHb] kinetics reflect an improved matching between O₂ delivery and O₂ utilization at the microvascular level, preventing the phase 2 VO₂p kinetics from become slower in hypoxia. Moreover, the absolute blood flow values were higher in hypoxia (1.17 ± 0.2 L min(-1)) compared to normoxia (0.96 ± 0.2 L min(-1)) during the steady-state exercise at 21 W. These findings support the idea that, for older adults exercising at a low work rate, an increase of limb blood flow offsets the drop in arterial oxygen content (CaO₂) caused by breathing an hypoxic mixture.
authors: CeRiSM, Centre of Sport Health and Mountain, Rovereto, Italy.
authors: Livio
authors: L
authors: Zerbini
authors: Matthew D
authors: MD
authors: Spencer
authors: Tyler M
authors: TM
authors: Grey
authors: Juan M
authors: JM
authors: Murias
authors: John M
authors: JM
authors: Kowalchuk
authors: Federico
authors: F
authors: Schena
authors: Donald H
authors: DH
authors: Paterson
mesh_terms: D000367:Age Factors; D000368:Aged; D016022:Case-Control Studies; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology; D007700:Kinetics; D007866:Leg / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism* / Q000502:physiology; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation; D012039:Regional Blood Flow
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