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  • 1. Alkner, B.
    et al.
    Norrbrand, Lena
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Tesch, P.
    Neuromuscular adaptations following 90 days bed rest with or without resistance exercise.2016Inngår i: Aerospace Medicine and Human Performance, ISSN 2375-6322, Vol. 87, nr 7, s. 610-617Artikkel i tidsskrift (Fagfellevurdert)
  • 2. Arvedsen, SK
    et al.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Petersen, L. G.
    Damgaard, M.
    Body height and arterial pressure in seated and supine young males during +2 G centrifugation2015Inngår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, E-ISSN 1522-1490, Vol. 309, nr 9Artikkel i tidsskrift (Fagfellevurdert)
    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, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, IB
    PlanHab: The effects of 21-day hypoxic confinement and unloading/inactivity on regional body composition and muscle strength2015Konferansepaper (Fagfellevurdert)
  • 4. Bense, L
    et al.
    Jorulf, H
    Farkas, A
    Eden-Strindberg, J
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Jokay, A
    Krebsz, A
    Pulmonary gas conducting interstitial pathway2015Inngår i: Acta Radiologica Open, ISSN 2058-4601, Vol. 4, nr 10, s. 1-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In spite of the growing efforts oriented towards revealing different aspects of emphysema, the persistence of the emphysematous or emphysema-like changes (ELCs) is not explored yet in the open literature. In this study we demonstrate the persistence of an ELC for 22 years in a spontaneous pneumothorax (SP) patient which indicates a hitherto unknown gas supply to the ELC. For this purpose we used high resolution computed tomography (HRCT) images processed into three-dimensional (3D) geometry. By the same token, not only a long persistence but also the volume increase of this ELC between 2002 and 2010 was demonstrated. The 3D geometry visualized an aerated interstitial structure between the sites of supposed gas leakage at the wall of the third generation airways and the ELC. This potential gas conducting interstitial pathway is not a continuation and has neither the form nor the structure of a bronchus. The finding suggests that in this patient the intrabronchial gas passes through the bronchial wall and via a gas conducting interstitial pathway reaches the ELC. Despite the availability of the presently employed techniques for at least 15 years, such case and phenomenon have not been described previously. The retrieval of the patient suggests that the findings could be relevant for a considerable proportion of the population.

  • 5. Blogg, L
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Arterial bubbles following trimix dives2014Konferansepaper (Annet vitenskapelig)
  • 6. Blogg, L
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Predisponerar helium i dykgasen för arteriella bubblor?2014Konferansepaper (Annet vitenskapelig)
    Abstract [sv]

    Bakgrund: Bubblor i den arteriella cirkulationen observerades första gången vid 10 av 12 exkursioner från heliox- (O2/He) och trimix- (O2/He/N2) mättnad (1).  På senare tid har Ljukovic et al (2) redovisat resultat av trimixdykningar där 5 av 7 dykare uppvisade arteriella bubblor. Visserligen har arteriella bubblor observerats även i samband med nitrox- och luftdykningar men inte i så hög frekvens. Gör heliumgasen att bubblor lättare tar sig igenom lungfiltret?

    Metoder: Dykare undersöktes med kardiellt ekokardiografi efter 251 trimixdykningar och 37 nitroxdykningar med varierande dykprofiler. Dykdjupen varierade mellan 20 – 100 m för trimixdykningarna och 33 – 60 m för nitroxdykningarna. Totalt 43 dykare deltog i trimix- och 19 dykare i nitroxdykningarna. Dykarna undersöktes varje kvart i 2 timmar efter dykningarna. Förekomst av venösa och arteriella bubblor registrerades och skattades enligt Brubakk-Eftedal-skalan (EB).

    Resultat: Totalt observerades arteriella bubblor hos 3/43 dykare efter trimixdykning och hos 3/19 dykare efter nitroxdykning. En av dykarna med arteriella bubblor i nitroxgruppen behandlades för ledbends. Två av dykarna hade arteriella bubblor både efter trimix- och nitroxdykningar. I samtliga fall med artärbubblor observerades också venösa bubblor (EB 2 – 4c).

    Slutsats: Jämfört med tidigare rapporterad incidens av artärbubblor i samband med trimixdykningar är de redovisade resultaten låga. Resultaten för nitroxdykningarna är också låga givet att ca 25% av normalpopulationen har öppetstående foramen ovale. Någon ökad incidens artärbubblor observerades inte med den heliuminnehållande gasen, utan det mest troliga är att förekomsten av artärbubblor beror på mängden venösa bubblor och individuell predisponering att ”läcka” bubblor från den venösa till den arteriella cirkulationen.

  • 7. Blogg, L
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Jurd, KM
    Møllerløkken, A
    Observed incidence of decompression sickness and venous gas bubbles following 18 M dives on RN table 11/Norwegian air diving table2015Konferansepaper (Fagfellevurdert)
  • 8. Blogg, S. Lesley
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Møllerløkken, Andreas
    Brubakk, Alf O.
    Ultrasound detection of vascular decompression bubbles: the influence of new technology and considerations on bubble load2014Inngår i: Diving and Hyperbaric Medicine, ISSN 1833-3516, Vol. 44, nr 1, s. 35-44Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Introduction: Diving often causes the formation of 'silent' bubbles upon decompression. If the bubble load is high, then the risk of decompression sickness (DCS) and the number of bubbles that could cross to the arterial circulation via a pulmonary shunt or patent foramen ovale increase. Bubbles can be monitored aurally, with Doppler ultrasound, or visually, with two-dimensional (2D) ultrasound imaging. Doppler grades and imaging grades can be compared with good agreement. Early 2D imaging units did not provide such comprehensive observations as Doppler, but advances in technology have allowed development of improved, portable, relatively inexpensive units. Most now employ harmonic technology; it was suggested that this could allow previously undetectable bubbles to be observed. Methods: This paper provides a review of current methods of bubble measurement and how new technology may be changing our perceptions of the potential relationship of these measurements to decompression illness. Secondly, 69 paired ultrasound images were made using conventional 2D ultrasound imaging and harmonic imaging. Images were graded on the Eftedal-Brubakk (EB) scale and the percentage agreement of the images calculated. The distribution of mismatched grades was analysed. Results: Fifty-four of the 69 paired images had matching grades. There was no significant difference in the distribution of high or low EB grades for the mismatched pairs. Conclusions: Given the good level of agreement between pairs observed, it seems unlikely that harmonic technology is responsible for any perceived increase in observed bubble loads, but it is probable that our increasing use of 2D ultrasound to assess dive profiles is changing our perception of 'normal' venous and arterial bubble loads. Methods to accurately investigate the load and size of bubbles developed will be helpful in the future in determining DCS risk.

  • 9. Blogg, S. Lesley
    et al.
    Mollerlokken, Andreas
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Observed decompression sickness and venous bubbles following 18-msw dive profiles using RN Table 112017Inngår i: Undersea & Hyperbaric Medicine, ISSN 1066-2936, Vol. 44, nr 3, s. 211-219Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The venous bubble load in the body after diving may be used to infer risk of decompression sickness (DCS). Retrospective analysis of post-dive bubbling and DCS was made on seven studies. Each of these investigated interventions, using an 18 meters of sea water (msw) air dive profile from Royal Navy Table 11 (Mod Air Table), equivalent to the Norwegian Air tables. A recent neurological DCS case suggested this table was not safe as thought. Two-hundred and twenty (220) man-dives were completed on this profile. Bubble measurements were made following 219 man-dives, using Doppler or 2D ultrasound measurements made on the Kisman-Masurel and Eftedal-Brubakk scales, respectively. The overall median grade was KM/EB 0.5 and the overall median maximum grade was KM/EB 2. Two cases of transient shoulder discomfort ("niggles") were observed (0.9% (95% CL 0.1% 3.3%)) and were treated with surface oxygen. One dive, for which no bubble measurements were made, resulted in a neurological DCS treated with hyperbaric oxygen. The DCS risk of this profile is below that predicted by models, and comparison of the cumulative incidence of DCS of these data to the large dataset compiled by DCIEM [1, 2], show that the incidence is lower than might be expected.

  • 10. Blogg, SL
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    The use of ultrasound bubble detection to develop the Swedish Navy trimix dive tables2015Konferansepaper (Fagfellevurdert)
  • 11. Ciuha, U
    et al.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, IB
    PlanHab: Effects of normobaric hypoxic bed rest on behavioural temperature regulation2015Konferansepaper (Fagfellevurdert)
  • 12. Ciuha, U
    et al.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, I.B.
    PlanHab: The effect of hypoxic bedrest on behavioural temperature regulation2014Inngår i: Proceedings from 35th Annual International Gravitational Physiology Meeting, 2014Konferansepaper (Annet vitenskapelig)
  • 13. Ciuha, U
    et al.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, I.B.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Strategies for increasing evaporative cooling during simulated desert patrol missions2014Inngår i: Proceedings from 3rd International Congress on Soldiers Physical Performance, 2014Konferansepaper (Annet vitenskapelig)
  • 14. Ciuha, U
    et al.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, B.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Strategies for increasing evaporative cooling during simulated desert patrol mission.2016Inngår i: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 59, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 15. De Boever, P
    et al.
    Louwies, T
    Kounalakis, S
    Cox, B
    Jaki Mekjavic, P
    Nawrot, T
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, I.B.
    PlanHab: In vivo retinal images for a non-invasive analysis of the microcirculation during hypoxia and unloading/inactivity2014Inngår i: Proceedings from 35th Annual International Gravitational Physiology Meeting, Waterloo, Canada, 2014Konferansepaper (Annet vitenskapelig)
  • 16. De Boever, P
    et al.
    Louwies, T
    Kounalakis, Stylianos
    Jaki Mekjavic, P
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, I.B.
    In vivo retinal images for a non-invasive analysis of the microcirculation during hypoxia and unloading/inactivity2013Konferansepaper (Fagfellevurdert)
  • 17. Debevec, T
    et al.
    Amon, Mojca
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Kounalakis, S.N.
    Pisot, R
    Mekjavic, I.B.
    Normoxic and hypoxic performance following four weeks of normobaric hypoxic training2010Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 81, nr 4, s. 387-393Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION:

    Although training in hypoxia has been suggested to improve sea level and altitude performance, most studies have only evaluated its effect on maximal aerobic capacity in either normoxia or hypoxia. The present study evaluated the effect of a live low-train high training regimen on both normoxic and hypoxic endurance performance and aerobic capacity.

    METHODS:

    There were 18 male subjects who performed 20 training sessions in either a normoxic (F(IO2) = 0.21) or hypoxic (F(IO2) = 0.12) environment. Both the Control (N = 9) and Hypoxic (N = 9) group subjects trained at an intensity that maintained their heart rate at a level corresponding to that elicited at 50% of peak power output attained in normoxia or hypoxia, respectively. Before, during, upon completion, and 10 d after the protocol, subjects' aerobic capacity (VO2 peak) and endurance performance (80% of VO2 peak) were determined under normoxic and hypoxic conditions.

    RESULTS:

    Mean +/- SD normoxic VO2 peak increased significantly only in the Control group from 45.7 +/- 6.1 to 53.9 +/- 3.9 (ml x kg(-1) x min(-1)), whereas hypoxic VO2 peak did not improve in either group. The Control group exhibited significant improvements in normoxic, but not hypoxic peak power output (PPO) and time to exhaustion, whereas the Hypoxic group only exhibited improvements in normoxic time to exhaustion. During each testing period, we also assessed pulmonary function, selected hematological variables, and anthropometry. There were no significant changes in these variables in either group after the training protocol.

    CONCLUSION:

    The hypoxic training regimen used in the present study had no significant effect on altitude and sea level performance.

  • 18. Debevec, T
    et al.
    Bali, T
    Simpson, E.J.
    MacDonald, I.A.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, I.B.
    PlanHab: Effects of simulated planetary habitation on body mass and whole body composition2014Konferansepaper (Annet vitenskapelig)
  • 19. Debevec, T
    et al.
    Ehrström, S
    Pialoux, V
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, IB
    Millet, GP
    FemHab: Prooxidant/antioxidant balance during and following a 10-day hypoxic bed rest2015Konferansepaper (Fagfellevurdert)
    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.

  • 20. Debevec, T
    et al.
    McDonnell, A.C.
    MacDonald, I
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, I.B.
    Changes in body composition and dietary intake as a consequence of 10-day hypoxic confinement and unloading/inactivityInngår i: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5312, E-ISSN 1715-5320Artikkel i tidsskrift (Fagfellevurdert)
  • 21. Debevec, T.
    et al.
    Pialoux, V.
    Mekjavic, I.B.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mury, P.
    Millet, G.P.
    Moderate exercise blunts oxidative stress induced by normobaric hypoxic confinement2014Inngår i: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 46, nr 1, s. 33-41Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22. Debevec, T.
    et al.
    Simpson, E. J.
    Mekjavic, I. B.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Macdonald, I. A.
    Effects of prolonged hypoxia and bed rest on appetite and appetite-related hormones2016Inngår i: Appetite, ISSN 0195-6663, E-ISSN 1095-8304, Vol. 107, s. 28-37Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 23. Debevec, T
    et al.
    Simpson, EJ
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, IB
    Macdonald, IA
    PlanHab: The individual and combined effects of inactivity and hypoxia on insulin resistance2015Konferansepaper (Fagfellevurdert)
    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.

  • 24. Debevec, T
    et al.
    Simpson, T
    MacDonald, I.A.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, I.B.
    PlanHab: Energy expenditure and appetite sensation during hypoxic bedrest2014Konferansepaper (Annet vitenskapelig)
  • 25. Debevec, Tadej
    et al.
    Bali, Tarsi C.
    Simpson, Elizabeth J.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, Igor B.
    Separate and combined effects of 21-day bed rest and hypoxic confinement on body composition2014Inngår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 114, nr 11, s. 2411-2425Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 26. Debevec, Tadej
    et al.
    McDonnell, Adam C.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, Igor B.
    Whole body and regional body composition changes following 10-day hypoxic confinement and unloading-inactivity2014Inngår i: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5312, E-ISSN 1715-5320, Vol. 39, nr 3, s. 386-395Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 27. Debevec, Tadej
    et al.
    Pialoux, Vincent
    Ehrström, Sabine
    Ribon, Alexandra
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, Igor B.
    Millet, Gregoire P.
    FemHab: The effects of bed rest and hypoxia on oxidative stress in healthy women2016Inngår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, nr 8, s. 930-938Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 28. Debevec, Tadej
    et al.
    Simpson, Elizabeth J.
    Macdonald, Ian A.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, Igor B.
    Exercise Training during Normobaric Hypoxic Confinement Does Not Alter Hormonal Appetite Regulation2014Inngår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, nr 6, s. e98874-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 29. Dolenc Grošelj, L
    et al.
    Morrisson, SA
    Mirnik, D
    Korsic, S
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, IB
    PlanHab: Periodic breathing during hypoxic bedrest2015Konferansepaper (Fagfellevurdert)
  • 30.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Kabintryck och risk för barotrauma vid explosiv decompression I fpl 392015Rapport (Annet vitenskapelig)
  • 31.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Taylor, Nigel A S
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Intraocular pressure and cerebral oxygenation during prolonged headward acceleration2017Inngår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 117, nr 1, s. 61-72Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 32.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, Igor, B
    Keramidas, Michail E
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    PlanHab: Normobaric hypoxia may exaggerate bedrest-induced reductions in peak oxygen uptake2015Inngår i: International Society for Gravitational Physiology, 2015Konferansepaper (Fagfellevurdert)
  • 33.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    McDonnell, Adam C.
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Lind, Britta
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning.
    Mekjavic, Igor B.
    Lunar habitat simulation2013Konferansepaper (Annet vitenskapelig)
  • 34.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, I.B.
    The hypoxic bedrest research programme2013Konferansepaper (Fagfellevurdert)
  • 35.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Mekjavic, I.B.
    Kounalakis, S.N.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Pressure distension in leg vessels as influenced by prolonged bed rest and a pressure habituation regimen2016Inngår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, nr 12, s. 1458-1465Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 36.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, Igor B.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi. KTH, Skolan för teknik och hälsa (STH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Blood pressure regulation V: in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading2014Inngår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 114, nr 3, s. 499-509Artikkel, forskningsoversikt (Fagfellevurdert)
    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.

  • 37.
    Frånberg, Oskar
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Oxygen content in semi-closed rebreathing apparatuses for underwater use: Measurements and modeling2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The present series of unmanned hyperbaric tests were conducted in order to investigate the oxygen fraction variability in semi-closed underwater rebreathing apparatuses. The tested rebreathers were RB80 (Halcyon dive systems, High springs, FL, USA), IS-Mix (Interspiro AB, Stockholm, Sweden), CRABE (Aqua Lung, Carros Cedex, France), and Viper+ (Cobham plc, Davenport, IA, USA). The tests were conducted using a catalytically based propene combusting metabolic simulator. The metabolic simulator connected to a breathing simulator, both placed inside a hyperbaric pressure chamber, was first tested to demonstrate its usefulness to simulate human respiration in a hyperbaric situation. Following this the metabolic simulator was shown to be a useful tool in accident investigations as well as to assess the impact of different engineering designs and physiological variables on the oxygen content in the gas delivered to the diver by the rebreathing apparatuses. A multi-compartment model of the oxygen fractions was developed and compared to the previously published single-compartment models. The root mean squared error (RMSE) of the multi-compartment model was smaller than the RMSE for the single-compartment model, showing its usefulness to estimate the impact of different designs and physiological variables on the inspired oxygen fraction.

  • 38.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Dödsfall i samband med dykning med återandningsapparater: ett människa–maskin interaktionsproblem2013Inngår i: Hygiea, 2013Konferansepaper (Fagfellevurdert)
    Abstract [sv]

    Huvuddelen av de rapporterade och undersökta olyckorna med återandningsapparater utlöstes av felaktigt handhavande, eller bristande människa–maskininteraktion.

  • 39.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Measurement and modeling of oxygen content in a demand mass ratio injection rebreather2015Inngår i: Undersea & Hyperbaric Medicine, ISSN 1066-2936, Vol. 42, nr 6, s. 573-592Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanical semi-closed rebreathers do not need oxygen sensors for their functions, thereby reducing the complexity of the system. However, testing and modeling are necessary in order to determine operational limits as well as the decompression obligation and to avoid hyperoxia and hypoxia. Two models for predicting the oxygen fraction in a demand constant mass ratio injection (DCMRI) rebreather for underwater use were compiled and compared. The model validity was tested with an IS-MIX, Interspiro AB rebreather using a metabolic simulator connected to a breathing machine inside a water-filled pressure chamber. The testing schedule ranged from 0.5-liter (L) to 3-liter tidal volumes, breathing frequencies from five to 25 breaths/minute and oxygen consumptions from 0.5 L/minute to 4 L/minute. Tests were carried out at surface and pressure profiles ranging to 920 kPa(a) (81 meters of sea water, 266 feet of sea water). The root mean squared error (RMSE) of the single-compartment model was 2.4 percent-units of oxygen for the surface test with the 30% dosage setting but was otherwise below 1% unit. For the multicompartment model the RMSE was below 1% unit of oxygen for all tests. It is believed that these models will aid divers in operational settings and may constitute a helpful tool when developing semi-closed rebreathing apparatuses.

  • 40.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Modeling a demand constant volume ratio exhaust and a self-mixing constant oxygen injection semi-closed rebreatherManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Unmanned tests of two types of gas dosage techniques for semi-closed underwater rebreathing apparatuses were carried out with a metabolic simulator in a water filled pressure chamber. Tests were conducted over a wide range of tidal volumes (0.5-3 L), respiratory frequencies (5-25 min-1), and oxygen consumptions (0.5-4 L/min), as well as with changing chamber pressures from 100 kPa to 920 kPa. Two models were set up, one single compartment model and one model assuming multiple serial compartments. Both models seem to have about the same level of accuracy at predicting the inspired oxygen levels at pressure, but the surface tests seem to favor the serial compartments model.

  • 41.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Loncar, Mario
    Larsson, Ake
    Örnhagen, Hans
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    A Metabolic Simulator for Unmanned Testing of Breathing Apparatuses in Hyperbaric Conditions2014Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 85, nr 11, s. 1139-1144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: A major part of testing of rebreather apparatuses for underwater diving focuses on the oxygen dosage system. Methods: A metabolic simulator for testing breathing apparatuses was built and evaluated. Oxygen consumption was achieved through catalytic combustion of propene. With an admixture of carbon dioxide in the propene fuel, the system allowed the respiratory exchange ratio to be set freely within human variability and also made it possible to increase test pressures above the condensation pressure of propene. The system was tested by breathing ambient air in a pressure chamber with oxygen uptake (VO2) ranging from 1-4 L.min(-1), tidal volume (V-T) from 1-3 L, breathing frequency (f) of 20 and 25 breaths/min, and chamber pressures from 100 to 670 kPa. Results: The measured end-tidal oxygen concentration (FO2) was compared to calculated end-tidal FO2. The largest average difference in end-tidal FO2 during atmospheric pressure conditions was 0.63%-points with a 0.28%-point average difference during the whole test. During hyperbaric conditions with pressures ranging from 100 to 670 kPa, the largest average difference in FO2 was 1.68%-points seen during compression from 100 kPa to 400 kPa and the average difference in FO2 during the whole test was 0.29%-points. Conclusion: In combination with a breathing simulator simulating tidal breathing, the system can be used for dynamic continuous testing of breathing equipment with changes in V-T, f, VO2, and pressure.

  • 42.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Loncar, Mario
    Larsson, Åke
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Örnhagen, Hans
    Metsim, ett hjälpmedel för att testa slutna andningsapparater på ett fysiologiskt sätt2013Inngår i: Hygiea, 2013Konferansepaper (Fagfellevurdert)
    Abstract [sv]

    Valet av propen som bränsle och de tekniska svårigheter som övervanns för att skapa en säker ämnesomsättningssimulator som kan användas vid tester i tryck motsvarande 100 m dykdjup.

  • 43.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Silvanus, M
    Rebreather technology and practical tests2014Konferansepaper (Fagfellevurdert)
  • 44.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Application of ultrasound techniques in diving research: Use of bubble detection to develop trimix tables for Swedish mine-clearance divers and evaluating trimix decompressions2015Konferansepaper (Fagfellevurdert)
  • 45.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    PM avseende resultat av provdykningar med OMD10 (IS-MIX) vid DN under våren 2016.2016Rapport (Annet vitenskapelig)
  • 46.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Problems with introducing the new USN air diving tables for the Swedish Navy.2016Konferansepaper (Fagfellevurdert)
  • 47.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Submarine escape physiology2013Konferansepaper (Fagfellevurdert)
  • 48.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Testing of decompression tables and use of decompression algorithms: a pragmatic view2014Konferansepaper (Fagfellevurdert)
  • 49.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Trimix tables for semi-closed mechanical rebreather: IS-Mix2013Konferansepaper (Fagfellevurdert)
  • 50.
    Gennser, Mikael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Blogg, L
    Effect of gas switch on decompression from trimix dives2015Konferansepaper (Fagfellevurdert)
1234 1 - 50 of 171
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