title: PlanHab: hypoxia exaggerates the bed-rest-induced reduction in peak oxygen uptake during upright cycle ergometry.
abstract: The study examined the effects of hypoxia and horizontal bed rest, separately and in combination, on peak oxygen uptake (V̇o2 peak) during upright cycle ergometry. Ten male lowlanders underwent three 21-day confinement periods in a counterbalanced order: 1) normoxic bed rest [NBR; partial pressure of inspired O2 (PiO2 ) = 133.1 ± 0.3 mmHg]; 2) hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mmHg), and 3) hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room air (AIR), or a hypoxic gas (HYPO; PiO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR V̇o2 peak was decreased by both HBR (∼13.5%; P ≤ 0.001) and NBR (∼8.6%; P ≤ 0.001), with greater drop after HBR (P = 0.01). The HYPO V̇o2 peak was also reduced by HBR (-9.7%; P ≤ 0.001) and NBR (-6.1%; P ≤ 0.001). Peak CO was lower after both bed-rest interventions, and especially after HBR (HBR: ∼13%, NBR: ∼7%; P ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bed-rest confinements. No changes were observed in HAMB. Hence, the bed-rest-induced decrease in V̇o2 peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.
authors.affiliation: Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden; michail.keramidas@sth.kth.se.
authors.forename: Michail E
authors.initials: ME
authors.lastname: Keramidas
authors.affiliation: Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden;
authors.forename: Roger
authors.initials: R
authors.lastname: Kölegård
authors.affiliation: Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia; and Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Igor B
authors.initials: IB
authors.lastname: Mekjavic
authors.affiliation: Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden;
authors.forename: Ola
authors.initials: O
authors.lastname: Eiken
mesh_terms: D000328:Adult; D001510:Bed Rest; D002302:Cardiac Output / Q000502:physiology*; D002540:Cerebral Cortex / Q000098:blood supply / Q000378:metabolism*; D005080:Exercise Test; D064368:Healthy Volunteers; D006339:Heart Rate; D006801:Humans; D020896:Hypovolemia / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D010092:Oximetry; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D052097:Quadriceps Muscle / Q000098:blood supply / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared; D013318:Stroke Volume / Q000502:physiology*; D055815:Young Adult
keywords: cardiac output; high altitude; hypovolemia; inactivity; microgravity