title: Regulation of VO₂ kinetics by O₂ delivery: insights from acute hypoxia and heavy-intensity priming exercise in young men.
abstract: This study examined the separate and combined effects of acute hypoxia (Hypo) and heavy-intensity "priming" exercise (Hvy) on pulmonary O(2) uptake (Vo(2p)) kinetics during moderate-intensity exercise (Mod). Breath-by-breath Vo(2p) and near-infrared spectroscopy-derived muscle deoxygenation {deoxyhemoglobin concentration [HHb]} were monitored continuously in 10 men (23 ± 4 yr) during repetitions of a Mod 1-Hvy-Mod 2 protocol, where each of the 6-min (Mod or Hvy) leg-cycling bouts was separated by 6 min at 20 W. Subjects were exposed to Hypo [fraction of inspired O(2) (Fi(O(2))) = 15%, Mod 2 + Hypo] or "sham" (Fi(O(2)) = 20.9%, Mod 2-N) 2 min following Hvy in half of these repetitions; Mod was also performed in Hypo without Hvy (Mod 1 + Hypo). On-transient Vo(2p) and [HHb] responses were modeled as a monoexponential. Data were scaled to a relative percentage of the response (0-100%), the signals were time-aligned, and the individual [HHb]-to-Vo(2) ratio was calculated. Compared with control (Mod 1), τVo(2p) and the O(2) deficit (26 ± 7 s and 638 ± 144 ml, respectively) were reduced (P < 0.05) in Mod 2-N (20 ± 5 s and 529 ± 196 ml) and increased (P < 0.05) in Mod 1 + Hypo (34 ± 14 s and 783 ± 184 ml); in Mod 2 + Hypo, τVo(2p) was increased (30 ± 8 s, P < 0.05), yet O(2) deficit was unaffected (643 ± 193 ml, P > 0.05). The modest "overshoot" in the [HHb]-to-Vo(2) ratio (reflecting an O(2) delivery-to-utilization mismatch) in Mod 1 (1.06 ± 0.04) was abolished in Mod 2-N (1.00 ± 0.05), persisted in Mod 2 + Hypo (1.09 ± 0.07), and tended to increase in Mod 1 + Hypo (1.10 ± 0.09, P = 0.13). The present data do not support an "O(2) delivery-independent" speeding of τVo(2p) following Hvy (or Hvy + Hypo); rather, this study suggests that local muscle O(2) delivery likely governs the rate of adjustment of Vo(2) at τVo(2p) greater than ∼20 s.
authors.affiliation: Canadian Centre for Activity and Aging, University of Western Ontario, London, Ontario, Canada.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Spencer
authors.forename: Juan M
authors.initials: JM
authors.lastname: Murias
authors.forename: Tyler M
authors.initials: TM
authors.lastname: Grey
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007700:Kinetics; D007866:Leg / Q000502:physiology / Q000503:physiopathology; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D010100:Oxygen / Q000008:administration & dosage* / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D055815:Young Adult
chemical_list: D006454:Hemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen