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  • 1. Amon, M
    et al.
    Keramidas, Michail E.
    Kounalakis, S
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Simpson, L
    MacDonald, I
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Mekjavic, IB
    Effect of hypoxia on postprandial blood glucose and insulin response2011Conference paper (Refereed)
  • 2. Arvedsen, SK
    et al.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Petersen, L. G.
    Damgaard, M.
    Body height and arterial pressure in seated and supine young males during +2 G centrifugation2015In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, E-ISSN 1522-1490, Vol. 309, no 9Article in journal (Refereed)
    Abstract [en]

    It is known that arterial pressure correlates positively with body height in males and it has been suggested that this is due to the increasing vertical hydrostatic gradient from the heart to the carotid baroreceptors. Therefore we tested the hypothesis that a higher gravitoinertial stress induced by the use of a human centrifuge would increase mean arterial pressure (MAP) more in tall than in short males in the seated position. In short (162-171cm, n=8) and tall (194-203cm, n=10) healthy males (18-41y), brachial arterial pressure, heart rate (HR) and cardiac output were measured during +2G centrifugation, while they were seated upright with the legs kept horizontal (+2Gz). In a separate experiment, the same measurements were done with the subjects supine (+2Gx). During +2Gz MAP increased in the short (22±2 mmHg, p<0.0001) and tall (23±2 mmHg, p<0.0001) males, with no significant difference between the groups. HR increased more (p<0.05) in the tall than in the short group (14±2 versus 7±2 bpm). Stroke volume (SV) decreased in the short group (26±4 mL, p=0.001) and more so in the tall group (39±5 mL, p<0.0001; short vs tall p=0.047). During +2GX, systolic arterial pressure increased (p<0.001) and SV (p=0.012) decreased in the tall group only. In conclusion, during +2Gz MAP increased in both short and tall males with no difference between the groups. However, in the tall group HR increased more during +2Gz which could be caused by a larger hydrostatic pressure gradient from heart to head leading to greater inhibition of the carotid baroreceptors.

  • 3. Bali, TC
    et al.
    Kounalakis, SN
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, IB
    PlanHab: The effects of 21-day hypoxic confinement and unloading/inactivity on regional body composition and muscle strength2015Conference paper (Refereed)
  • 4. Berg, Ulf
    et al.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Fysiska tester i samband med Grundläggande militär utbildning (GMU)2012Report (Other academic)
  • 5. Chowdhury, Helena H
    et al.
    Velebit, Jelena
    Mekjavic, Igor B
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Kreft, Marko
    Zorec, Robert
    Systemic Hypoxia Increases the Expression of DPP4 in Preadipocytes of Healthy Human Participants2017In: Experimental and clinical endocrinology & diabetes, ISSN 0947-7349, E-ISSN 1439-3646Article in journal (Refereed)
    Abstract [en]

    Dipeptidyl peptidase 4 (DPP4) is a transmembrane glycoprotein involved in protein degradation. Due to its action on incretins, which increase insulin secretion, DPP4 is considered a therapeutic target for type 2 diabetes. Here we have studied the role of single and combined effects of hypoxia and inactivity on the expression of DPP4 in human adipose tissue of 12 adult normal-weight males. Fat biopsies were obtained at baseline and after each of three experimental campaigns. The results revealed that in isolated human preadipocytes the expression of DPP4 was significantly increased by exposure of participants to hypoxia. Physical inactivity per se had no apparent effect on the DPP4 expression. It is concluded that DPP4 may be a marker to monitor indirectly tissue hypoxia, as occurs in obese subjects.

  • 6. Ciuha, U
    et al.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, IB
    PlanHab: Effects of normobaric hypoxic bed rest on behavioural temperature regulation2015Conference paper (Refereed)
  • 7. Ciuha, U
    et al.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, I.B.
    PlanHab: The effect of hypoxic bedrest on behavioural temperature regulation2014In: Proceedings from 35th Annual International Gravitational Physiology Meeting, 2014Conference paper (Other academic)
  • 8. Ciuha, U
    et al.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Strategies for increasing evaporative cooling during simulated desert patrol missions2014In: Proceedings from 3rd International Congress on Soldiers Physical Performance, 2014Conference paper (Other academic)
  • 9. Ciuha, U
    et al.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Strategies for increasing evaporative cooling during simulated desert patrol mission.2016In: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 59, no 2Article in journal (Refereed)
    Abstract [en]

    The study evaluated the efficiency of two heat dissipation strategies under simulated desert patrol missions. Ten men participated in four trials, during which they walked on a treadmill (45°C, 20% relative humidity), carrying a load of 35 kg; two 50-min walks were separated by a 20-min rest. Cooling strategies, provided by an ambient air-ventilated vest (active cooling condition, AC), or water spraying of the skin during the rest (passive cooling condition, PC), in addition to reduced clothing and open zippers, were compared to conditions with full protective (FP) clothing and naked condition (NC). Skin temperature was higher during NC (37.9 ± 0.4°C; p < 0.001), and rectal temperature and heart rate were higher during FP (38.6 ± 0.4°C, p < 0.001 and 145 ± 12, p < 0.001, respectively), compared to other conditions. Four subjects terminated the trial prematurely due to signs of heat exhaustion in FP. Both cooling strategies substantially improved evaporative cooling.

  • 10. Ciuha, U
    et al.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Mekjavic, I
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Pavlinič, D
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Thermal strain in soldiers performing patrol missions in a desert climate: effect of two different cooling strategies2011Conference paper (Refereed)
  • 11. Ciuha, Ursa
    et al.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, Igor B.
    Effects of normobaric hypoxic bed rest on the thermal comfort zone2015In: Journal of Thermal Biology, ISSN 0306-4565, E-ISSN 1879-0992, Vol. 49-50, 39-46 p.Article in journal (Refereed)
    Abstract [en]

    Future Lunar and Mars habitats will maintain a hypobaric hypoxic environment to minimise the risk of decompression sickness during the preparation for extra-vehicular activity. This study was part of a larger study investigating the separate and combined effects of inactivity associated with reduced gravity and hypoxia, on the cardiovascular, musculoskeletal, neurohumoural, and thermoregulatory systems. Eleven healthy normothermic young male subjects participated in three trials conducted on separate occasions: (1) Normobaric hypoxic ambulatory confinement, (2) Normobaric hypoxic bedrest and (3) Normobaric normoxic bedrest Normobaric hypoxia was achieved by reduction of the oxygen fraction in the air (FiO2=0.141 +/- 0.004) within the facility, while the effects of reduced gravity were simulated by confining the subjects to a horizontal position in bed, with all daily routines performed in this position for 21 days. The present study investigated the effect of the interventions on behavioural temperature regulation. The characteristics of the thermal comfort zone (TCZ) were assessed by a water-perfused suit, with the subjects instructed to regulate the sinusoidally varying temperature of the suit within a range considered as thermally comfortable. Measurements were performed 5 days prior to the intervention (D-5), and on days 10 (D10) and 20 (D20) of the intervention. no statistically significant differences were found in any of the characteristics of the TCZ between the interventions (HAMB, HBR and NBR), or between different measurement days (D-5, D10, D20) within each intervention. rectal temperature remained stable, whereas skin temperature (T-sk) increased during all interventions throughout the one hour trial, no difference in T-sk between 0-5, D10 and D20, and between HAMB, HBR and NBR were revealed, subjects perceived the regulated temperature as thermally comfortable, and neutral or warm, we conclude that regulation of thermal comfort is not compromised by hypoxic inactivity. (C) 2015 Elsevier Ltd. All rights reserved.

  • 12. De Boever, P
    et al.
    Louwies, T
    Kounalakis, S
    Cox, B
    Jaki Mekjavic, P
    Nawrot, T
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, I.B.
    PlanHab: In vivo retinal images for a non-invasive analysis of the microcirculation during hypoxia and unloading/inactivity2014In: Proceedings from 35th Annual International Gravitational Physiology Meeting, Waterloo, Canada, 2014Conference paper (Other academic)
  • 13. De Boever, P
    et al.
    Louwies, T
    Kounalakis, Stylianos
    Jaki Mekjavic, P
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    In vivo retinal images for a non-invasive analysis of the microcirculation during hypoxia and unloading/inactivity2013Conference paper (Refereed)
  • 14. Debevec, T
    et al.
    Bali, T
    Simpson, E.J.
    MacDonald, I.A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, I.B.
    PlanHab: Effects of simulated planetary habitation on body mass and whole body composition2014Conference paper (Other academic)
  • 15. Debevec, T
    et al.
    Ehrström, S
    Pialoux, V
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, IB
    Millet, GP
    FemHab: Prooxidant/antioxidant balance during and following a 10-day hypoxic bed rest2015Conference paper (Refereed)
    Abstract [en]

    Introduction:Inhabitants of the envisaged planetary habitats will be continuously exposed to reduced gravity and hypoxia. The combined effects of unloading and hypoxia on prooxidant/antioxidant balance are currently unknown.

    Methods:Healthy female participants underwent the following three, 10-day interventions: i) Normobaric normoxic bed-rest (NBR; n=11; FiO2=0.209) ii) Normobaric hypoxic ambulatory confinement (HAMB; n=9: FiO2~0.141), and iii) Normobaric hypoxic bed-rest (HBR; n=12; FiO2~0.141). Plasma oxidative stress [advanced oxidation protein products (AOPP) and nitrotyrosine], antioxidant markers [superoxide dismutase (SOD) and glutathione peroxidase (GPX)] and nitrites were determined before (Pre), during (Day 2, Day 6), immediately after (Post) and 24-hrs after (Post+1) each campaign.

    Results:Compared to Pre, the AOPP was only higher on Day 2, Day 6 and Post during the HBR and at Post during the NBR (P<0.05) while the nitrotyrosine was significantly reduced at Post+1 only during the HAMB (P<0.05). Higher levels of SOD were observed during the HAMB at Day 6 and Post+1whereas GPX was reduced at Day 6 and Post during the HBR. Nitrites were significantly higher at Post+1 in the HAMB both, compared to Pre and compared to HBR and NBR (P<0.05).

    Conclusion:These data suggest that the unloading-induced oxidative stress is exacerbated by exposure to simulated altitude of ~4000m. In addition, even habitual (low) physical activity, performed during hypoxic exposure, seems to blunt hypoxia-related oxidative stress via antioxidant system upregulation.

  • 16. Debevec, T.
    et al.
    Keramidas, Michail E.
    Norman, B
    Gustafsson, T
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Mekjavic, I
    No evidence for the “normobaric oxygen paradox”2011In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, Vol. 43, no S5, 151-151 p.Article in journal (Other academic)
  • 17. Debevec, T
    et al.
    McDonnell, A.C.
    MacDonald, I
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    Changes in body composition and dietary intake as a consequence of 10-day hypoxic confinement and unloading/inactivityIn: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5312, E-ISSN 1715-5320Article in journal (Refereed)
  • 18. Debevec, T.
    et al.
    Pialoux, V.
    Mekjavic, I.B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mury, P.
    Millet, G.P.
    Moderate exercise blunts oxidative stress induced by normobaric hypoxic confinement2014In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 46, no 1, 33-41 p.Article in journal (Refereed)
    Abstract [en]

    PURPOSE: Both acute hypoxia and physical exercise are known to increase oxidative stress. This randomized prospective trial investigated whether the addition of moderate exercise can alter oxidative stress induced by continuous hypoxic exposure. METHODS: Fourteen male participants were confined to 10-d continuous normobaric hypoxia (FIO2 = 0.139 ± 0.003, PIO2 = 88.2 ± 0.6 mm Hg, ∼4000-m simulated altitude) either with (HCE, n = 8, two training sessions per day at 50% of hypoxic maximal aerobic power) or without exercise (HCS, n = 6). Plasma levels of oxidative stress markers (advanced oxidation protein products [AOPP], nitrotyrosine, and malondialdehyde), antioxidant markers (ferric-reducing antioxidant power, superoxide dismutase, glutathione peroxidase, and catalase), nitric oxide end-products, and erythropoietin were measured before the exposure (Pre), after the first 24 h of exposure (D1), after the exposure (Post) and after the 24-h reoxygenation (Post + 1). In addition, graded exercise test in hypoxia was performed before and after the protocol. RESULTS: Maximal aerobic power increased after the protocol in HCE only (+6.8%, P < 0.05). Compared with baseline, AOPP was higher at Post + 1 (+28%, P < 0.05) and nitrotyrosine at Post (+81%, P < 0.05) in HCS only. Superoxide dismutase (+30%, P < 0.05) and catalase (+53%, P < 0.05) increased at Post in HCE only. Higher levels of ferric-reducing antioxidant power (+41%, P < 0.05) at Post and lower levels of AOPP (-47%, P < 0.01) at Post + 1 were measured in HCE versus HCS. Glutathione peroxidase (+31%, P < 0.01) increased in both groups at Post + 1. Similar erythropoietin kinetics was noted in both groups with an increase at D1 (+143%, P < 0.01), a return to baseline at Post, and a decrease at Post + 1 (-56%, P < 0.05). CONCLUSIONS: These data provide evidence that 2 h of moderate daily exercise training can attenuate the oxidative stress induced by continuous hypoxic exposure.

  • 19. Debevec, T.
    et al.
    Simpson, E. J.
    Mekjavic, I. B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Macdonald, I. A.
    Effects of prolonged hypoxia and bed rest on appetite and appetite-related hormones2016In: Appetite, ISSN 0195-6663, E-ISSN 1095-8304, Vol. 107, 28-37 p.Article in journal (Refereed)
    Abstract [en]

    Environmental hypoxia and inactivity have both been shown to modulate appetite. To elucidate the independent and combined effects of hypoxia and bed rest-induced inactivity on appetite-related hormones and subjective appetite, eleven healthy, non-obese males underwent three experimental interventions in a cross-over and randomized fashion: 1) Hypoxic confinement combined with daily moderate-intensity exercise (HAMB, FiO2 = 0.141 ± 0.004; PiO2 = 90.0 ± 0.4 mmHg) 2) Bed rest in normoxia (NBR, FiO2 = 0.209; PiO2 = 133.1 ± 0.3 mmHg) and 3) Bed rest in hypoxia (HBR, FiO2 = 0.141 ± 0.004; PiO2 = 90.0 ± 0.4 mmHg). A mixed-meal tolerance test (MTT), followed by an ad libitum meal were performed before (Pre) and after 16-days (Post) of each intervention. Composite satiety scores (CSS) during the MTT were calculated from visual analogue scores, while fasting and postprandial concentrations of total ghrelin, peptide YY (PYY), glucagon-like peptide-1 (GLP-1) and leptin were quantified from arterialized-venous samples. Postprandial CSS were significantly lower at Post compared to Pre in NBR only (P &lt; 0.05) with no differences observed in ad libitum meal intakes. Postprandial concentrations and incremental area under the curve (AUC) for total ghrelin and PYY were unchanged following all interventions. Postprandial GLP-1 concentrations were only reduced at Post following HBR (P &lt; 0.05) with resulting AUC changes being significantly lower compared to HAMB (P &lt; 0.01). Fasting leptin was reduced following HAMB (P &lt; 0.05) with no changes observed following NBR and HBR. These findings suggest that independently, 16-day of simulated altitude exposure (∼4000 m) and bed rest-induced inactivity do not significantly alter subjective appetite or ad libitum intakes. The measured appetite-related hormones following both HAMB and HBR point to a situation of hypoxia-induced appetite stimulation, although this did not reflect in higher ad libitum intakes. Clinical Trial Registration Number: NCT02293772.

  • 20. Debevec, T
    et al.
    Simpson, EJ
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, IB
    Macdonald, IA
    PlanHab: The individual and combined effects of inactivity and hypoxia on insulin resistance2015Conference paper (Refereed)
    Abstract [en]

    Inactivity is know to aggravate insulin resistance. The effects of hypoxia on insulin and glucose metabolism, on the other hand, are not completely understood.

  • 21. Debevec, T
    et al.
    Simpson, T
    MacDonald, I.A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, I.B.
    PlanHab: Energy expenditure and appetite sensation during hypoxic bedrest2014Conference paper (Other academic)
  • 22. Debevec, Tadej
    et al.
    Bali, Tarsi C.
    Simpson, Elizabeth J.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, Igor B.
    Separate and combined effects of 21-day bed rest and hypoxic confinement on body composition2014In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 114, no 11, 2411-2425 p.Article in journal (Refereed)
    Abstract [en]

    This study tested the hypothesis that hypoxia exacerbates reductions in body mass observed during unloading. To discern the separate and combined effects of simulated microgravity and hypoxia, 11 healthy males underwent three 21-day campaigns in a counterbalanced fashion: (1) normoxic bed rest (NBR; FiO2 = 0.209; PiO2 = 133.1 +/- A 0.3); (2) hypoxic ambulatory confinement (HAMB; FiO2 = 0.141 +/- A 0.004; PiO2 = 90.0 +/- A 0.4; similar to 4,000 m); and (3) hypoxic bed rest (HBR; FiO2 = 0.141 +/- A 0.004; PiO2 = 90.0 +/- A 0.4). The same dietary menu was applied in all campaigns. Targeted energy intakes were estimated individually using the Harris-Benedict equation taking into account whether the subjects were bedridden or ambulatory. Body mass and water balance were assessed throughout the campaigns. Whole body and regional body composition was determined before and after the campaigns using dual-energy X-ray absorptiometry. Before and during the campaigns, indirect calorimetry and visual analogue scores were employed to assess the resting energy expenditure (REE) and perceived appetite sensations, respectively. Energy intakes were lower than targeted in all campaigns (NBR: -5 %; HAMB: -14 %; HBR: -6 %; P < 0.01). Body mass significantly decreased following all campaigns (NBR: -3 %; HAMB: -4 %; HBR: -5 %; P < 0.01). While fat mass was not significantly altered, the whole body fat free mass was reduced (NBR: -4 %; HAMB: -5 %; HBR: -5 %; P < 0.01), secondary to lower limb fat-free mass reduction. Water balance was comparable between the campaigns. No changes were observed in REE and perceived appetite. Exposure to simulated altitude of similar to 4,000 m does not seem to worsen the whole body mass and fat-free mass reductions or alter resting energy expenditure and appetite during a 21-day simulated microgravity.

  • 23. Debevec, Tadej
    et al.
    Keramidas, Michail E.
    Norman, Barbara
    Gustafsson, Thomas
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Mekjavic, Igor B.
    Acute short-term hyperoxia followed by mild hypoxia does not increase EPO production: resolving the "normobaric oxygen paradox''2012In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 112, no 3, 1059-1065 p.Article in journal (Refereed)
    Abstract [en]

    Recent findings suggest that besides renal tissue hypoxia, relative decrements in tissue oxygenation, using a transition of the breathing mixture from hyperoxic to normoxic, can also stimulate erythropoietin (EPO) production. To further clarify the importance of the relative change in tissue oxygenation on plasma EPO concentration [EPO], we investigated the effect of a consecutive hyperoxic and hypoxic breathing intervention. Eighteen healthy male subjects were assigned to either IHH (N = 10) or CON (N = 8) group. The IHH group breathed pure oxygen (F(i)O(2) ~ 1.0) for 1 h, followed by a 1-h period of breathing a hypoxic gas mixture (F(i)O(2) ~ 0.15). The CON group breathed a normoxic gas mixture (F(i)O(2) ~ 0.21) for the same duration (2 h). Blood samples were taken just before, after 60 min, and immediately after the 2-h exposure period. Thereafter, samples were taken at 3, 5, 8, 24, 32, and 48 h after the exposure. During the breathing interventions, subjects remained in supine position. There were significant increases in absolute [EPO] within groups at 8 and 32 h in the CON and at 32 h only in the IHH group. No significant differences in absolute [EPO] were observed between groups following the intervention. Relative (∆[EPO]) levels were significantly lower in the IHH than in the CON group, 5 and 8 h following exposure. The tested protocol of consecutive hyperoxic-hypoxic gas mixture breathing did not induce [EPO] synthesis stimulation. Moreover, the transient attenuation in ∆[EPO] in the IHH group was most likely due to a hyperoxic suppression. Hence, our findings provide further evidence against the "normobaric O(2) paradox" theory.

  • 24. Debevec, Tadej
    et al.
    McDonnell, Adam C.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B.
    Whole body and regional body composition changes following 10-day hypoxic confinement and unloading-inactivity2014In: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5312, E-ISSN 1715-5320, Vol. 39, no 3, 386-395 p.Article in journal (Refereed)
    Abstract [en]

    Future planetary habitats will expose inhabitants to both reduced gravity and hypoxia. This study investigated the effects of short-term unloading and normobaric hypoxia on whole body and regional body composition (BC). Eleven healthy, recreationally active, male participants with a mean (SD) age of 24 (2) years and body mass index of 22.4 (3.2) kg.m(-2) completed the following 3 10-day campaigns in a randomised, cross-over designed protocol: (i) hypoxic ambulatory confinement (HAMB; FIO2 = 0.147 (0.008); PIO2 = 93.8 (0.9) mm Hg), (ii) hypoxic bed rest (HBR; FIO2 = 0.147 (0.008); PIO2 = 93.8 (0.9) mm Hg), and (iii) normoxic bed rest (NBR; FIO2 = 0.209; PIO2 = 133.5 (0.7) mmHg). Nutritional requirements were individually precalculated and the actual intake was monitored throughout the study protocol. Body mass, whole body, and regional BC were assessed before and after the campaigns using dual-energy X-ray absorptiometry. The calculated daily targeted energy intake values were 2071 (170) kcal for HBR and NBR and 2417 (200) kcal for HAMB. In both HBR and NBR campaigns the actual energy intake was within the targeted level, whereas in the HAMB the intake was lower than targeted (-8%, p < 0.05). Body mass significantly decreased in all 3 campaigns (-2.1%, -2.8%, and -2.0% for HAMB, HBR, and NBR, respectively; p < 0.05), secondary to a significant decrease in lean mass (-3.8%, -3.8%, -4.3% for HAMB, HBR, and NBR, respectively; p < 0.05) along with a slight, albeit not significant, increase in fat mass. The same trend was observed in the regional BC regardless of the region and the campaign. These results demonstrate that, hypoxia per se, does not seem to alter whole body and regional BC during short-term bed rest.

  • 25. Debevec, Tadej
    et al.
    Pialoux, Vincent
    Ehrström, Sabine
    Ribon, Alexandra
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B.
    Millet, Gregoire P.
    FemHab: The effects of bed rest and hypoxia on oxidative stress in healthy women2016In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, no 8, 930-938 p.Article in journal (Refereed)
    Abstract [en]

    Independently, both inactivity and hypoxia augment oxidative stress. This study, part of the FemHab project, investigated the combined effects of bed rest-induced unloading and hypoxic exposure on oxidative stress and antioxidant status. Healthy, eumenorrheic women were randomly assigned to the following three 10-day experimental interventions: normoxic bed rest (NBR; n = 11; PIO2 = 133 mmHg), normobaric hypoxic bed rest (HBR; n = 12; PIO2 = 90 mmHg), and ambulatory hypoxic confinement (HAMB; n = 8: PIO2 = 90 mmHg). Plasma samples, obtained before (Pre), during (D2, D6), immediately after (Post) and 24 h after (Post + 1) each intervention, were analyzed for oxidative stress markers [advanced oxidation protein products (AOPP), malondialdehyde (MDA), and nitrotyrosine], antioxidant status [ superoxide dismutase (SOD), catalase, ferric-reducing antioxidant power (FRAP), glutathione peroxidase (GPX), and uric acid (UA)], NO metabolism end-products (NOx), and nitrites. Compared with baseline, AOPP increased in NBR and HBR on D2 (+ 14%; + 12%; P < 0.05), D6 (+ 19%; + 15%; P < 0.05), and Post (+ 22%; + 21%; P < 0.05), respectively. MDA increased at Post + 1 in NBR (+ 116%; P < 0.01) and D2 in HBR (+114%; P < 0.01) and HAMB (+ 95%; P < 0.05). Nitrotyrosine decreased (-45%; P < 0.05) and nitrites increased (+46%; P < 0.05) at Post + 1 in HAMB only. Whereas SOD was higher at D6 (+ 82%) and Post + 1 (+ 67%) in HAMB only, the catalase activity increased on D6 (128%) and Post (146%) in HBR and HAMB, respectively (P < 0.05). GPX was only reduced on D6 (- 20%; P < 0.01) and Post (- 18%; P < 0.05) in HBR. No differences were observed in FRAP and NOx. UA was higher at Post in HBR compared with HAMB (P < 0.05). These data indicate that exposure to combined inactivity and hypoxia impairs prooxidant/antioxidant balance in healthy women. Moreover, habitual activity levels, as opposed to inactivity, seem to blunt hypoxia-related oxidative stress via antioxidant system upregulation.

  • 26. Debevec, Tadej
    et al.
    Simpson, Elizabeth J.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B.
    Exercise Training during Normobaric Hypoxic Confinement Does Not Alter Hormonal Appetite Regulation2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 6, e98874- p.Article in journal (Refereed)
    Abstract [en]

    Background: Both exposure to hypoxia and exercise training have the potential to modulate appetite and induce beneficial metabolic adaptations. The purpose of this study was to determine whether daily moderate exercise training performed during a 10-day exposure to normobaric hypoxia alters hormonal appetite regulation and augments metabolic health. Methods: Fourteen healthy, male participants underwent a 10-day hypoxic confinement at,4000 m simulated altitude (FIO2 = 0.139 +/- 0.003%) either combined with daily moderate intensity exercise (Exercise group; N = 8, Age = 25.8 +/- 2.4 yrs, BMI = 22.9 +/- 1.2 kg.m(-2)) or without any exercise (Sedentary group; N = 6 Age = 24.8 +/- 3.1 yrs, BMI = 22.3 +/- 2.5 kg.m(-2)). A meal tolerance test was performed before (Pre) and after the confinement (Post) to quantify fasting and postprandial concentrations of selected appetite-related hormones and metabolic risk markers. C-13-Glucose was dissolved in the test meal and (CO2)-C-13 determined in breath samples. Perceived appetite ratings were obtained throughout the meal tolerance tests. Results: While body mass decreased in both groups (-1.4 kg; p = 0.01) following the confinement, whole body fat mass was only reduced in the Exercise group (-1.5 kg; p = 0.01). At Post, postprandial serum insulin was reduced in the Sedentary group (-49%; p = 0.01) and postprandial plasma glucose in the Exercise group (-19%; p = 0.03). Fasting serum total cholesterol levels were reduced (-12%; p = 0.01) at Post in the Exercise group only, secondary to low-density lipoprotein cholesterol reduction (-16%; p = 0.01). No differences between groups or testing periods were noted in fasting and/or postprandial concentrations of total ghrelin, peptide YY, and glucagon-like peptide-1, leptin, adiponectin, expired (CO2)-C-13 as well as perceived appetite ratings (p>0.05). Conclusion: These findings suggest that performing daily moderate intensity exercise training during continuous hypoxic exposure does not alter hormonal appetite regulation but can improve the lipid profile in healthy young males.

  • 27. Dolenc Grošelj, L
    et al.
    Morrisson, SA
    Mirnik, D
    Korsic, S
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, IB
    PlanHab: Periodic breathing during hypoxic bedrest2015Conference paper (Refereed)
  • 28.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Militär verksamhet på höga höjder2011Report (Other academic)
  • 29.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Bergsten, Eddie
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Environmental Physiology.
    G-protection mechanisms afforded by the anti-G suit abdominal bladder with and without pressure breathing.2011In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 82, no 10, 972-7 p.Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: G protection afforded by the abdominal bladder of a pneumatic anti-G suit is usually attributed to counteraction of G-induced caudad displacement of the heart and pooling of blood in the abdominal veins. The study examined whether the abdominal bladder might provide G protection also via other mechanisms.

    METHODS: Each subject was exposed to +Gz loads while sitting relaxed, wearing a full-coverage anti-G suit modified to permit separate pressurization of the abdominal and leg bladders. In two experimental series (N = 8, N = 14), subjects were breathing at positive airway pressure (PPB); in a third series, five subjects were breathing at atmospheric airway pressure. Intrathoracic pressures were estimated by use of esophageal catheters.

    RESULTS: During PPB at high G loads, intrathoracic pressure was higher with than without the pressurized abdominal bladder. In 7 of the 14 subjects, basilar intrathoracic pressure exceeded airway pressure during PPB when the abdominal bladder was pressurized. The mean arterial pressure response at high G loads was higher in this subset of subjects (55 +/- 23 mmHg) than in the subjects in whom airway pressure exceeded intrathoracic pressure (41 +/- 27 mmHg). Without PPB at increased G load, the intrathoracic pressure gradient was higher with than without the pressurized abdominal bladder.

    DISCUSSION: During PPB, the abdominal bladder acts as an airway counterpressure, thereby facilitating pressure transmission from the airways to the thorax and hence improving G protection. It also appears that in several individuals, pressure may be transmitted from the abdominal bladder to the thorax and heart.

  • 30.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Danielsson, Ulf
    Hallberg, M.
    Mekjavic, I.
    Kounalakis, S.N.
    Energiomsättning vid simulerad patrullering i mörker2010Report (Other academic)
  • 31.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Danielsson, Ulf
    Hallberg, M
    Mekjavic, IB
    Babic, J
    Kounalakis, S
    Energy expenditure during simulated patrol in darkness2011Conference paper (Refereed)
  • 32.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Signs and symptoms during supra-tolerance +Gz exposures, with reference to G-garment failure.2013In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 84, no 3, 196-205 p.Article in journal (Refereed)
    Abstract [en]

    Introduction: +Gz exposure above the tolerance threshold typically induces a sequence of symptoms/signs, with loss of: peripheral vision, central vision (black out), and consciousness (G-LOC). The aims of this study were to investigate: 1) whether G history influences latent time to, or sequence of, symptoms/signs upon G exposures exceeding the tolerance threshold; and 2) how pilots respond to a sudden loss of pressure in the anti-G garment (AGG) in flight-like scenarios. Methods: There were 14 subjects who were exposed to rapid onset rate +Gz-time profiles, with plateaus 1 and 2 G above the relaxed tolerance level, without initial pressurization of the AGG (NoAGG) and when losing AGG pressure after 10 (AGG_10) and 120 (AGG_120) s at the plateau. Simulated target-chase flights during which AGG pressure was released were performed by seven pilots; the pilot was instructed to behave as during real flight. Results: Latent time to symptoms was shorter at +2 G than at +1 G, and shorter in AGG_10 and AGG_120 than in NoAGG. In AGG_120, 43 and 64% of the subjects experienced serious symptoms (black out, Almost LOC, G-LOC) at +1 and +2 G, respectively, compared to 21 and 54% in AGG_10 and 7 and 29% in NoAGG. The incidence of A-LOC/G-LOC was higher in AGG_10 and especially in AGG_120 than in NoAGG. During the target chase, one pilot did not notice the pressure loss, one experienced G-LOC, and two A-LOC. Discussion: The risk of serious consequences of G exposure exceeding the tolerance level appears to be greater when G-garment failure occurs after a prolonged than after a brief exposure.

  • 33.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Gennser, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Kabintryck och risk för barotrauma vid explosiv decompression I fpl 392015Report (Other academic)
  • 34.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Danielsson, Ulf
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Zavec, D.
    Kounalakis, S.N.
    Mekjavic, I.
    Termisk belastning hos soldater som bär svensk stridsutrustning2010Report (Other academic)
  • 35.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Zavec, D.
    Ciuha, U.
    Mekjavic, I.
    Termisk belastning hos markstridssoldater vid patrullering i ökenklimat: effekter av två olika ballistiska kroppsskydd samt av två olika strategier för nedkylning2011Report (Other academic)
  • 36.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Keramidas, Michail E.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Taylor, Nigel A S
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Intraocular pressure and cerebral oxygenation during prolonged headward acceleration2017In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 117, no 1, 61-72 p.Article in journal (Refereed)
    Abstract [en]

    Supra-tolerance head-to-foot directed gravitoinertial load (+Gz) typically induces a sequence of symptoms/signs, including loss of: peripheral vision-central vision-consciousness. The risk of unconsciousness is greater when anti-G-garment failure occurs after prolonged rather than brief exposures, presumably because, in the former condition, mental signs are not consistently preceded by impaired vision. The aims were to investigate if prolonged exposure to moderately elevated +Gz reduces intraocular pressure (IOP; i.e., improves provisions for retinal perfusion), or the cerebral anoxia reserve. Subjects were exposed to 4-min +Gz plateaux either at 2 and 3 G (n = 10), or at 4 and 5 G (n = 12). Measurements included eye-level mean arterial pressure (MAP), oxygenation of the cerebral frontal cortex, and at 2 and 3 G, IOP. IOP was similar at 1 (14.1 +/- 1.6 mmHg), 2 (14.0 +/- 1.6 mmHg), and 3 G (14.0 +/- 1.6 mmHg). During the G exposures, MAP exhibited an initial prompt drop followed by a partial recovery, end-exposure values being reduced by ae<currency>30 mmHg. Cerebral oxygenation showed a similar initial drop, but without recovery, and was followed by either a plateau or a further slight decrement to a minimum of about -14 mu M. Gz loading did not affect IOP. That cerebral oxygenation remained suppressed throughout these G exposures, despite a concomitant partial recovery of MAP, suggests that the increased risk of unconsciousness upon G-garment failure after prolonged +Gz exposure is due to reduced cerebral anoxia reserve.

  • 37.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Repeated exposures to moderately increased intravascular pressure increases stiffness in human arteries and arterioles2011In: Journal of Hypertension, ISSN 0263-6352, E-ISSN 1473-5598, Vol. 29, no 10, 1963-1971 p.Article in journal (Refereed)
    Abstract [en]

    The aim was to investigate whether repeated exposures to moderate pressure elevations in the blood vessels of the arms (pressure training; PT) affect pressure distension in arteries/arterioles of healthy subjects (n=11). PT and vascular pressure-distension determinations were conducted with the subject seated in a pressure chamber with one arm slipped through a hole in the chamber door. Increased intravascular pressure was accomplished by increasing chamber pressure. Before PT, one arm was investigated (control arm) during stepwise increases in chamber pressure to 180 mmHg. Artery diameter and flow were measured in the brachial artery using ultrasonography/Doppler techniques. Thereafter, the contralateral arm underwent a PT regimen consisting of three 40 min sessions/ week during 5 weeks. Chamber pressure was increased during PT from 65 mmHg during the first week to 105 mmHg during the last week. After PT, pressure-distension relationships were examined in both the trained arm and the control arm. Prior to and following PT, endothelium-dependent and endothelium-independent dilatations of the brachial artery were studied. PT reduced (p<0.01) arterial pressure distension by 46 ± 18%. Likewise, the pressure-induced increase in arterial flow was less pronounced after (350 ± 249%) compared with before (685 ± 216 %) PT. The PT-induced reductions in arterial/arteriolar pressure distension were reversed 5 weeks post-PT. Neither endothelium-dependent nor endothelium-independent arterial dilatation were affected by PT. It thus appears that the in vivo wall stiffness in arteries and arterioles increases markedly in response to intermittent, moderate increments of transmural pressure during 5 weeks. The increases in arterial/arteriolar stiffness are reversible and do not reflect a reduced capacity to dilate the vessels. The findings are compatible with the notion that local load serves as “ a prime mover” in the development of vascular changes in hypertension.

  • 38.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, Igor, B
    Keramidas, Michail E
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    PlanHab: Normobaric hypoxia may exaggerate bedrest-induced reductions in peak oxygen uptake2015In: International Society for Gravitational Physiology, 2015Conference paper (Refereed)
  • 39.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    McDonnell, Adam C.
    Keramidas, Michail E.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Mekjavic, Igor B.
    Lunar habitat simulation2013Conference paper (Other academic)
  • 40.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Mekjavic, I.
    Sundblad, Patrik
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology (Closed 20130701).
    G tolerance vis-à-vis pressure-distension and pressure-flow relationships of leg arteries2012In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 112, no 10, 3619-3627 p.Article in journal (Refereed)
    Abstract [en]

    During increased gravitoinertial (G) load in the head-to-foot direction, pressures in dependent vascular beds are commonly raised to levels capable of distending precapillary vessels, which, in turn, may reduce arterial pressure, and hence compromise the capacity to withstand G load (G tolerance). We hypothesized that distensibility in precapillary leg vessels would be lower in a group of subjects possessing high G tolerance (H; n = 7; relaxed G tolerance = 6.6 ± 0.8 G) than in a group with low G tolerance (L; n = 8; G tolerance = 3.9 ± 0.3 G). The groups were matched with regard to gender, age, weight, height, and resting arterial pressure. Arterial pressure-distension and pressure-flow experiments were performed with the subject supine in a pressure chamber with a lower leg protruding to the outside. Increased intravascular pressure in the blood vessels of the outside leg was accomplished by stepwise increasing chamber pressure to 240 mmHg. Diameter and flow in the posterior tibial artery were measured by ultrasonographic/Doppler techniques. Pressure-induced increments in arterial diameter and flow were more pronounced (p < 0.03) in the L (14.1 ± 4.2% and 32 ± 21 ml/min respectively) than in the H (1.7 ± 5.0% and 1.6 ± 25 ml/min) group, and the pressure thresholds at which these increments commenced were lower (by 52 and 48 mmHg, respectively) in the L than in the H group (p < 0.04). Negative correlations were observed between G tolerance and the increments in diameter and flow (p < 0.02). Thus, the wall stiffness of precapillary leg vessels is greater in individuals with high relaxed G tolerance; whether a causal relationship exists remains to be established.

  • 41.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    The hypoxic bedrest research programme2013Conference paper (Refereed)
  • 42.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Mekjavic, IB
    Kounalakis, S
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Stiffness in leg arteries/arterioles is reduced by prolonged bedrest.2011Conference paper (Refereed)
  • 43.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, IB
    Kounalakis, SN
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Pressure distension in leg vessels as influenced by prolonged bed rest and a pressure habituation regimen2016In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, no 12, 1458-1465 p.Article in journal (Refereed)
    Abstract [en]

    Bed rest increases pressure distension in arteries, arterioles, and veins of the leg. We hypothesized that bed-rest-induced deconditioning of leg vessels is governed by the removal of the local increments in transmural pressure induced by assuming erect posture and, therefore, can be counteracted by intermittently increasing local transmural pressure during the bed rest. Ten men underwent 5 wk of horizontal bed rest. A subatmospheric pressure (-90 mmHg) was intermittently applied to one lower leg [pressure habituation (PH) leg]. Vascular pressure distension was investigated before and after the bed rest, both in the PH and control (CN) leg by increasing local distending pressure, stepwise up to +200 mmHg. Vessel diameter and blood flow were measured in the posterior tibial artery and vessel diameter in the posterior tibial vein. In the CN leg, bed rest led to 5-fold and 2.7-fold increments (P < 0.01) in tibial artery pressure-distension and flow responses, respectively, and to a 2-fold increase in tibial vein pressure distension. In the PH leg, arterial pressure-distension and flow responses were unaffected by bed rest, whereas bed rest led to a 1.5-fold increase in venous pressure distension. It thus appears that bed-rest-induced deconditioning of leg arteries, arterioles, and veins is caused by removal of gravity-dependent local pressure loads and may be abolished or alleviated by a local pressure-habituation regimen.

  • 44.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Mekjavic, Igor B.
    Kolegard, Roger
    Local Intravascular Pressure Habituation in Relation to G-Induced Arm Pain2012In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, no 7, 667-672 p.Article in journal (Refereed)
    Abstract [en]

    EIKEN O, MEKJAVIC IB, KOLEGARD R. Local intravascular pressure habituation in relation to G-induced arm pain. Aviat Space Environ Med 2012; 83:667-72. Background: During high +G(z) loads, pilots may experience arm pain. It is commonly assumed that such pain is caused by distension of blood vessels and that vascular distensibility adapts to the prevailing transmural pressure. The aim was to investigate whether vascular pressure habituation (PH) is as efficient in alleviating G-induced arm pain as using counterpressure/support garments. Methods: In Series I, 7 subjects underwent a 5-wk PH regimen, consisting of 15 40-min sessions, during which intravascular pressures in one arm were elevated by 65-105 mmHg. Before and after PH, arm pain was determined during incremental +G(z)-exposures in a centrifuge. In Series II, the effect on G-induced arm pain of wearing protective garments around the lower part of the upper arm was investigated in 10 subjects in 4 conditions: 1) counterpressure; 2) rigid support; 3) sham support; and 4) no support (control). Pain was rated using a 10-point graded scale. Results: PH reduced arm pain at 7.5 G from [median (range)] 4 (2-9) to 2 (0-5) in the pressure-habituated arm. The sham support did not affect pain compared to in the control condition (5.2; 3.0-10.0), whereas pain was reduced by both the rigid support (3.7; 1.0-8.0) and the counterpressure (2.5; 0.0-5.5). PH was as efficient in alleviating pain as the counterpressure and more efficient than the rigid support. Discussion: The results support the notion that G-induced arm pain is caused by vascular overdistension. Repeated moderate elevations of local intravascular pressure reduce G-induced arm pain, presumably because such PH reduces vascular distensibility.

  • 45.
    Eiken, Ola
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Mekjavic, Igor B.
    Kölegård, Roger
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Blood pressure regulation V: in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading2014In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 114, no 3, 499-509 p.Article, review/survey (Refereed)
    Abstract [en]

    Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness were determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressure-induced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5-wk period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressure-induced flow in the brachial artery by about 50%. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 wks of sustained horizontal bedrest, induced three-fold increases of the pressure-distension and pressure-flow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.

  • 46.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Blogg, L
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. KTH, School of Technology and Health (STH), Centres, Swedish Aerospace Physiology Centre, SAPC.
    Jaki Mekjavic, P
    Mekjavic, IB
    Comparison of venous bubbles and tear film bubbles after decompression during a five week 6° head-down tilt bed rest2015Conference paper (Refereed)
  • 47.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Blogg, L.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Mekjavic, I.
    Comparison between mild dehydration and body temperature on decompression bubble formation2010Conference paper (Refereed)
  • 48.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Environmental Physiology.
    Effekter av exponering för måttlig hypoxi vid vistelse i brandsäkrat arbetsutrymme.2011Report (Other academic)
  • 49.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Norrbrand, Lena
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Sundblad, Patrik
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Effekt av gasdensitet på ventilation och arteriell oxygenmättnad vid normobar och hypobar hypoxi2016Conference paper (Refereed)
  • 50. Groselj, L. Dolenc
    et al.
    Morrison, S. A.
    Rojc, B.
    Mirnik, D.
    Korsic, S.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I. B.
    Hypoxic bedrest and sleep architecture: effect of initial hypoxic exposure and total stimulus duration2016In: Journal of Sleep Research, ISSN 0962-1105, E-ISSN 1365-2869, Vol. 25, 236-236 p.Article in journal (Other academic)
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