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- Kounalakis, S.N., et al.
(författare)
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Peak oxygen uptake and regional oxygenation in response to a 10-day confinement to normobaric hypoxia
- 2013
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 23:4, s. e233-e245
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effect of hypoxic acclimatization per se, without any concomitant influence of strenuous physical activity on muscle and cerebral oxygenation. Eight healthy male subjects participated in a crossover-designed study. In random order, they conducted a 10-day normoxic (CON) and a 10-day hypoxic (EXP) confinement. Pre and post both CON and EXP confinements, subjects conducted two incremental-load cycling exercises to exhaustion; one under normoxic, and the other under hypoxic (FIO2 = 0.154) conditions. Oxygen uptake ((V) over dotO(2)), ventilation ((V) over dot E), and relative changes in regional hemoglobin oxygenation (Delta([HbO(2)]) in the cerebral cortex and in the serratus anterior (SA) and vastus lateralis (VL) muscles were measured. No changes were observed in the CON confinement. Peak work rate and (V) over dotO(2peak) were similar pre and post in the EXP confinement, whereas (V) over dot(E) increased in the EXP post normoxic and hypoxic trials (P < 0.05). The exercise-induced drop in VL Delta[HbO(2)] was less in the post-than pre-EXP trial by 4.0 +/- 0.4 and 4.2 +/- 0.6 mMduring normoxic and hypoxic exercise, respectively. No major changes were observed in cerebral or SA oxygenation. These results demonstrate that a 10-day hypoxic exposure without any concomitant physical activity had no effect on normoxic or hypoxic (V) over dotO(2peak), despite the enhanced VL oxygenation.
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- Louwies, T., et al.
(författare)
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Separate and combined effects of hypoxia and horizontal bed rest on retinal blood vessel diameters
- 2016
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Ingår i: Investigative Ophthalmology and Visual Science. - : Association for Research in Vision and Ophthalmology Inc.. - 0146-0404 .- 1552-5783. ; 57:11, s. 4927-4932
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE. To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation. METHODS. Eleven healthy male subjects (mean 6 SD age = 27 ± 6 years; body mass index [BMI] = 23.7 ± 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 ± 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 6 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21- day intervention. RESULTS. Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (ΔDCRAE = -7.5 µm; 95% confidence interval [CI]: -10.8 to -4.2; P < 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (DCRAE = 9.4 µm; 95% CI: 6.0-12.7; P < 0.0001). During HBR, the increase in CRAE was highest on day 3 (ΔDCRAE = 4.5 µm; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (ΔDCRVE = -7.9 µm; 95 CI: -13.3 to -2.5), and the maximum ΔDCRVE during HAMB (24.6 µm; 95% CI: 18.9-30.3) and HBR (15.2 µm; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively. CONCLUSIONS. The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure.
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- McDonnell, A.C., et al.
(författare)
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Circadian rhythm of peripheral perfusion during 10-day hypoxic confinement and bed rest
- 2014
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 114:10, s. 2093-2104
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Tidskriftsartikel (refereegranskat)abstract
- Future planetary habitats will be hypobaric and hypoxic to reduce the risk of decompression sickness during preparation for extra-vehicular activities. This study was part of a research programme investigating the combined effects of hypoxia and microgravity on physiological systems. We tested the hypothesis that hypoxia-induced peripheral vasoconstriction persists at night and is aggravated by bed rest. Since sleep onset has been causally linked to nocturnal vasodilatation, we reasoned that hypoxia-induced vasoconstriction at night may explain sleep disturbances at altitude. Peripheral perfusion alterations as a consequence of bed rest may explain poor sleep quality reported during sojourns on the International Space Station. Eleven males underwent three 10-day interventions in a randomised order: (1) hypoxic ambulatory confinement; (2) hypoxic bed rest; (3) normoxic bed rest. During each intervention we conducted 22-h monitoring of peripheral perfusion, as reflected by the skin temperature gradient. Measurements were conducted on the first (D 1) and last day (D 10) of each intervention. All interventions resulted in a decrease in daytime toe perfusion from D 1 to D 10. There was no difference in the magnitude of the daytime reduction in toe perfusion between the three interventions. There was a significant vasodilatation of the toes in all interventions by 11 pm. The fingertips remained well perfused throughout. Daytime vasoconstriction induced by hypoxia and/or bed rest is abolished at night, lending further support to the theory that changes in peripheral skin temperature may be functionally linked to sleep onset.
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- McDonnell, A. C., et al.
(författare)
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Effect of hypoxia and bedrest on peripheral vasoconstriction
- 2013
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Ingår i: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen. - : ESA Communications. - 9789290922704 ; , s. 1-2
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Konferensbidrag (refereegranskat)abstract
- Future planetary habitats may expose astronauts to both microgravity and hypobaric hypoxia, both inducing a reduction in peripheral perfusion. Peripheral temperature changes have been linked to sleep onset and quality [5]. However, it is still unknown what effect combining hypoxia and bedrest has on this relationship. Eleven male participants underwent three 10-day campaigns in a randomized manner: 1) normobaric hypoxic ambulatory confinement (HAmb); 2) normobaric hypoxic bed rest (HBR); 3) normobaric normoxic bed rest (NBR). There was no change in skin temperature gradient between the calf and toes, an index of peripheral perfusion (ΔTc-t), over the 10-d period in the HAmb trial. However, there was a significant increase (p< 0.001) in daytime (9am-9pm) ΔTc-t on day 10 of the inactivity/unloading periods (HBR and NBR trials). This reduction in the perfusion of the toes during the daytime was augmented during the HBR trial compared to NBR (p< 0.001). Before and on day 10 of the interventions we conducted polysomnographic assessment, which revealed no changes in sleep onset and/or architecture. These data support the theory that circadian changes in temperature are functionally linked to sleepiness [1].
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- Mekjavic, I. B., et al.
(författare)
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Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest?
- 2020
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Ingår i: Experimental Physiology. - : Blackwell Publishing Ltd. - 0958-0670 .- 1469-445X.
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Tidskriftsartikel (refereegranskat)abstract
- New Findings: What is the central question of this study? Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest? What is the main finding and its importance? During 10-day bed rest, exposure to a simulated (normobaric hypoxia) altitude of ∼4000 m does not exert additional significant structural or functional effect on the weight-bearing muscles in females compared to those noted under normoxic conditions. Whereas males and females exhibit decrements in muscle cross-sectional area and mass during normoxic and hypoxic bed rest, a concomitant strength decrement was only observed in males. Abstract: This study investigated the effects of hypoxia on the known processes of adaptation of body composition and muscle function to normoxic inactivity. Females (n = 12) and males (n = 11) took part in the following interventions: hypoxic ambulation (HAMB; ∼4000 m); hypoxic bed rest (HBR; ∼4000 m) and normoxic bed rest (NBR). Prior to and immediately following each intervention, body composition, thigh and lower leg cross-sectional area (CSA) and isometric muscular strength were recorded. Participants lost body mass (HAMB: male −1.5 ± 0.9 kg, female −1.9 ± 0.7 kg; HBR: male −2.0 ± 1.8 kg, female −2.4 ± 0.8 kg; NBR: male −1.4 ± 1.3 kg, female −1.4 ± 0.9 kg) and lean mass (HAMB: male −3.9 ± 3.0%, female −3.4 ± 2.0%; HBR: male −4.0 ± 4.4%, female −4.1 ± 2.0%; NBR: male −4.0 ± 3.4%, female −2.2 ± 2.7%) with no between-condition or sex differences. Knee extension decreased for males in NBR compared to HAMB (HAMB: male −0.2 ± 9.1%, female 1.3 ± 4.9%; HBR: male −7.8 ± 10.3%, female −3.3 ± 10.9%; NBR: male −14.5 ± 11%, female −3.4 ± 6.9%). Loss of force during maximal voluntary contraction (MVC) in the knee extensors was significantly different between males and females following NBR. There were no other significant changes noted following the experimental interventions. There were no differences recorded between sexes in maximal MVC for elbow or ankle joints. Female lower leg CSA decreased following bed rest (HAMB: -4.5 ± 2.0%; HBR: -9.9 ± 2.6%; NBR: -8.0 ± 1.6%). These findings indicate that a 10-day hypoxic bed rest does not exert any significant additional effect on muscle atrophy when compared to NBR, except for female thigh CSA. In contrast to males, who exhibited a significant loss of muscle strength, no such decrement in strength was observed in the female participants.
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