PlanHab: Hypoxia exaggerates the bedrest-induced reduction in peak oxygen uptake during upright cycle-ergometry
2016 (English)In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, E-ISSN 1522-1539Article in journal (Refereed) Published
The study examined the effects of hypoxia and horizontal bedrest, separately and in combination, on peak oxygen uptake (VO2peak) during upright cycle-ergometry. Ten male lowlanders underwent three 21-day confinement periods, in a counterbalanced order: i) normoxic bedrest (NBR; PIO2 = 133.1 ± 0.3 mmHg), ii) hypoxic bedrest (HBR; PIO2 = 90.0 ± 0.4 mmHg), and iii) 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 VO2peak 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 VO2peak was also reduced by HBR (-9.7%; p ≤ 0.001) and NBR (-6.1%; p ≤ 0.001). Peak CO was lower after both bedrest 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 bedrest confinements. No changes were observed in HAMB. Hence, the bedrest-induced decrease in VO2peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.
Place, publisher, year, edition, pages
American Physiological Society , 2016.
IdentifiersURN: urn:nbn:se:kth:diva-189194DOI: 10.1152/ajpheart.00304.2016OAI: oai:DiVA.org:kth-189194DiVA: diva2:944071
QC 201607132016-06-282016-06-282016-07-13Bibliographically approved