title: Hyperventilation-induced hypocapnic alkalosis slows the adaptation of pulmonary O2 uptake during the transition to moderate-intensity exercise.
abstract: The effect of voluntary hyperventilation-induced hypocapnic alkalosis (RALK) on pulmonary O2 uptake (VO2) kinetics and muscle deoxygenation was examined in young male adults (n=8) during moderate-intensity exercise. Subjects performed five repetitions of a step-transition in work rate from 20 W cycling to a work rate corresponding to 90% of the estimated lactate threshold during control (CON; PET,CO2, approximately 40 mmHg) and during hyperventilation (RALK; PET,CO2, approximately 20 mmHg). was measured breath-by-breath and relative concentration changes in muscle deoxy- (DeltaHHb), oxy- (DeltaO2Hb) and total (DeltaHbtot) haemoglobin were measured continuously using near-infrared (NIR) spectroscopy (Hamamatsu, NIRO 300). The time constant for the fundamental, phase 2, VO2 response (tau VO2) was greater (P<0.05) in RALK (48+/-11 s) than CON (31+/-9 s), while tauHHb was similar between conditions (RALK, 12+/-4 s; CON, 11+/-4 s). The DeltaHb(tot) was lower (P<0.05) in RALK than CON, prior to (RALK, -3+/-5 micromol l(-1); CON, -1+/-4 micromol l(-1)) and at the end (RALK, 1+/-6 micromol l(-1); CON, 5+/-5 micromol l(-1)) of moderate-intensity exercise. Although slower adaptation of during RALK may be related to an attenuated activation of PDH (and other enzymes) and provision of oxidizable substrate to the mitochondria (i.e. metabolic inertia), the present findings also suggest a role for a reduction in local muscle perfusion and O2 delivery.
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, Department of Physiology and Pharmacology, HSB 411C, University of Western Ontario, London, Ontario, Canada N6A 5B9.
authors.forename: Lisa M K
authors.initials: LM
authors.lastname: Chin
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Leigh
authors.forename: George J F
authors.initials: GJ
authors.lastname: Heigenhauser
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000472:Alkalosis, Respiratory / Q000209:etiology / Q000503:physiopathology*; D001784:Blood Gas Analysis; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006985:Hyperventilation / Q000150:complications / Q000503:physiopathology*; D016857:Hypocapnia / Q000209:etiology / Q000503:physiopathology*; D007773:Lactates / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D007773:Lactates