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  • 51.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Blogg, L
    Venous gas bubble load after trimix dives using electronic closed circuit rebreathers2014Conference paper (Refereed)
  • 52.
    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)
  • 53.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Blogg, SL
    Effekt av gasbyte på dekompressionshastighet efter korta trimix dykningar2015Conference paper (Refereed)
  • 54.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Blogg, SL
    Douglas, J
    Kvarnström, A
    Oscarsson, N
    Rosén, A
    Påverkar oxygenandning direkt efter dykning bubbelförekomst?2015Conference paper (Refereed)
  • 55.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Douglas, J
    High resolution chest CT: Findings with possible bearing on risk for pulmonary barotrauma2013Conference paper (Refereed)
  • 56.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Frånberg, Oskar
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Blogg, S. L
    Dekompressionsbelastning vid trimixdykning: Jämförelse mellan dykning med konstant fraktion och konstant partialtryck oxygen2014Conference paper (Refereed)
    Abstract [sv]

    Bakgrund: Användning av trimixgas (O2, N2, och He) tillåter dykning till större djup än med luft eller nitrox. Trots att den här dyktekniken blir alltmer populär bland sk ”tekniska dykare” så visar de få vetenskapliga rapporter som publicerats att trimixdykning ger upphov till rikligt med bubblor i den venösa cirkulationen (Ljubkovic et al 2010). Den här studien genomfördes för att undersöka venös bubbelförekomst efter dykning med konstant oxygenpartialtryck (PO2). Jämförelse gjordes med tidigare mätningar med konstant oxygenfraktion.

    Metoder: Sex försvarsmaktsdykare och en instruktör deltog i dykningar med sluten återandningsapparat där PO2 kontrollerades elektroniskt (eCCR). Dykningarna genomfördes med trimixgas till djup mellan 20 – 100 m. I de flesta fall hölls PO2 konstant vid 1,3 atm. Dekompressionsprofilerna beräknades med VPM-B algoritm. Förekomst av venösa gasbubblor detekterades med hjälp av ultraljuds-Doppler. Mängden bubblor skattades med Kisman-Masurel skalan (KM). Resultaten jämfördes med trimixdykningar (33 – 60 m) som genomförts i våt tryckkammare, men en halvsluten dykapparat som gav dykarna en konstant oxygenfraktion (FO2 27%). Dekompressionerna i dessa dykningar beräknades med en DCAP-algoritm.

     Resultat: Bubbelförekomst hos de 7 dykarna som använde eCCR undersöktes efter totalt 133 dykningar. Ingen bubbelpoäng över KM 3 uppmättes vid något dyk. Sammanlagt 92 dykningar genomfördes med den halvslutna apparaten. Bubbelpoängen i dessa dykningar varierade mellan 0 – 4 (16% av dykningarna >KM III). Efter upprepade dykningar till 70 m med eCCR var median bubbelpoängen KM 2 (n = 11).

    Slutsats: Djupa trimixdykningar med konstant PO2 och dekompressioner beräknade med VPM-B gav upphov till lägre maximal bubbelförekomst än dykningar med konstant oxygenfraktion.

  • 57.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Frånberg, Oskar
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Blogg, Samantha L.
    SLB Consulting, Cumbria, Storbritannien.
    Jämförelse mellan olika dekompressionstabeller med hjälp av ultraljudsdoppler2013In: Hygiea, 2013Conference paper (Refereed)
    Abstract [sv]

    Två dekompressionstabeller, en med sk djupa stopp, jämfördes avseende förekomst av bubblor i den centralvenösa cirkulationen. Tabellen med ortodox algoritm orsakade betydligt färre bubblor.

  • 58.
    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)
  • 59.
    Gennser, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Loveman, Geoff
    Seddon, Fiona
    Thacker, Julian
    Blogg, S. Lesley
    Oxygen and carbogen breathing following simulated submarine escape2014In: Undersea & Hyperbaric Medicine, ISSN 1066-2936, Vol. 41, no 5, p. 387-392Article in journal (Refereed)
    Abstract [en]

    Escape from a disabled submarine exposes escapers to a high risk of decompression sickness (DCS). The initial bubble load is thought to emanate from the fast tissues; it is this load that should be lowered to reduce risk of serious neurological DCS. The breathing of oxygen or carbogen (5% CO2, 95% O-2) post-surfacing was investigated with regard to its ability to reduce the initial bubble load in comparison to air breathing. Thirty-two goats were subject to a dry simulated submarine escape profile to and from 240 meters (2.5 MPa). On surfacing, they breathed air (control), oxygen or carbogen for 30 minutes. Regular Doppler audio bubble grading was carried out, using the Kisman Masurel (KM) scale. One suspected case of DCS was noted. No oxygen toxicity or arterial gas embolism occurred. No significant difference was found between the groups in terms of the median peak KM grade or the period before the KM grade dropped below III. Time to disappearance of bubbles was significantly different between groups; oxygen showed faster bubble resolution than carbogen and air. This reduction in time to bubble resolution may be beneficial in reducing decompression stress, but probably does not affect the risk of fast-tissue DCS.

  • 60. 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, p. 236-236Article in journal (Other academic)
  • 61.
    Grönkvist, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Bergsten, Eddie
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Skyddsdräkter för ytbärgare; Utvärdering under 2 timmars immersion i 6-gradigt vatten2015Report (Other academic)
  • 62.
    Grönkvist, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Cihua, U
    Mekjavic, I.B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Heat strain in a helicopter during a simulated desert mission2016Conference paper (Refereed)
  • 63.
    Grönkvist, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Ciuha, U
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    The effect of ambient humidity on performance during simulated desert patrols2014Conference paper (Refereed)
  • 64.
    Grönkvist, 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.
    Ciuha, U
    Mekjavic, IB
    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.
    Värmebelastning i helikopter vid simulerat ökenuppdrag2015Conference paper (Refereed)
  • 65.
    Grönkvist, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Effects of loss of pressure in the anti-G system during a simulated target chase2013Conference paper (Refereed)
  • 66.
    Grönkvist, Mikael
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Johannesson, Björn
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    KTH test report of CBRN equipment in the centrifuge2013Report (Other academic)
  • 67.
    Grönkvist, Mikael
    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.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Intraokulärt tryck och oxygenering av hjärnans frontallob under långvarig, måttlig G-belastning i huvud-fot-riktning2013In: Hygiea, 2013Conference paper (Refereed)
    Abstract [sv]

    Bakgrund: Under G-belastning i huvud-fot-riktning (+Gz) faller pilotens artärtryck mellan hjärt- och huvudnivå. Trots att avståndet - och därmed artärtrycksfallet - är större mellan hjärta och hjärnbark än mellan hjärta och ögon, är näthinnan vanligen det organ som tidigast drabbas av kritiskt ischemi vid +Gz-belastning, vilket huvudsakligen anses bero på att artärtrycket måste övervinna ögonbulbens övertryck om ca 10-15 mmHg för att genomblödning av näthinnan skall kunna ske. I en tidigare undersökning fann vi att den symptomsekvens som normalt uppträder efter 3-10 sekunders latensperiod vid förhöjning av G-belastningen från låg till övertrösklig nivå (d.v.s. perifer synfältsinskränkning - central synfältsinskränkning - grumlat medvetande - medvetandeförlust) ofta uteblir om exponeringen för övertrösklig G-nivå föregås av långvarig exponering för måttligt, men tolererbart, förhöjd belastning. Således, då trycket i G-dräkten fjärmades efter 2 minuter vid +Gz-belastning om 5-6 G var risken att drabbas av medvetslöshet mångfalt högre än då G-belastningen höjdes till motsvarande nivå utan trycksättning av G-dräkt. Föreliggande experimentserier genomfördes för att undersöka om den ändrade symptomsekvensen beror på successivt minskande syrereserver i frontalcortex eller på ökande genomblödning av retina (d.v.s. på minskande intraokulärt tryck (IOP)). Metoder: Friska försökspersoner (fp) exponerades för +Gz-belastning om 2 respektive 3 G, under det att IOP mättes (n= 10), samt för 2, 3, 4 och 5 G, under det att förändringar av frontalcortex syreinnehåll (total oxygen index; TOI) mättes (n=13). Under alla betingelser registrerades mättnadsgraden för oxyhemoglobin i kapillärblodet (SpO2). Samtliga mätningar genomfördes då fp använde G-dräkt och de vid 2 och 3 G även utan att fp använde G-dräkt Resultat: IOP påverkades ej nämnvärt av +Gz-belastning. Såväl SpO2 som TOI sjönk successivt under G-exponeringarna, i synnerhet vid 4- och 5-G-nivåerna, då fp bar G-dräkt. Slutsatser: Den successiva minskningen av TOI vid given belastning antas bero på en pulmonell höger-till-vänster shuntning av blod. Resultaten talar för att den ökade incidens G-betingade medvetslöshet då tryck i G-dräkt fjärmas efter långvarig, måttlig belastning beror på successivt minskande cerebral syrereserv, ledande till att medvetslöshet kan uppträda utan att föregås av varningssymtom i form av synfältsbortfall.

  • 68.
    Grönkvist, 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.
    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.
    Sundgren, Carl Johan
    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.
    Interaction of anti-G suit and airway pressures on cerebral oxygenation during prolonged headward acceleration.2015Conference paper (Refereed)
  • 69.
    Grönkvist, 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.
    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.
    Taylor, Nigel 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.
    Intraocular pressure and cerebral oxygenation during prolonged headward acceleration2014Conference paper (Refereed)
  • 70.
    Grönkvist, 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.
    Keramidas, Michail
    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.
    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.
    Samverkan mellan anti-G-dräkt och övertryck i luftvägarna på cerebral syresättning vid långvarig G-belastning i huvud-fot riktning2015Conference paper (Refereed)
  • 71. Helena, C. H.
    et al.
    Jelena, V. M.
    Nataša, R.
    Vito, F.
    Mekjavic, I. B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Robert, Z.
    A new approach to study properties of isolated preadipocytes following in vivo exposure to hypoxia2013In: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen, ESA Communications , 2013Conference paper (Refereed)
    Abstract [en]

    In the present study we developed a novel approach to study the properties of isolated human preadipocytes from subjects exposed to conditions of hypoxia equivalent to an altitude of 4000 m. By using confocal microscopy we studied the expression of dipeptidyl peptidase 4 (DPP4) in preadipocytes from adult normal-weight males. DPP4 is a transmembrane glycoprotein with enzymatic activity that cleaves Nterminal dipeptides from a diverse range of substrates. The activity of DPP4 is implicated in immune response as well as in glucose homeostasis. To gain insights into the pathophysiological role of DPP4 in insulin resistance we here explored DPP4 expression during prolonged exposure to hypoxia, an experimental model of obesity onset. We used here a rapid method to isolate cells from biopsies and immunolabelled them with antibodies. Then cells were prepared for the analysis with confocal microscopy. The results show that a prolonged exposure to hypoxic environment appears to increases the expression of DPP4 on preadipocytes.

  • 72. Jacobs, Robert A.
    et al.
    Meinild Lundby, Anne-Kristine
    Fenk, Simone
    Gehrig, Saskia
    Christoph, Siebenmann
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. University of Zürich, Switzerland.
    Flück, Daniela
    Kirk, Niels
    Hilty, Matthias P.
    Lundby, Carsten
    Twenty-eight days of exposure to 3,454 m increases mitochondrial volume density in human skeletal muscle2015In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 594, no 5, p. 1151-1166Article in journal (Refereed)
    Abstract [en]

    The role of hypoxia on skeletal muscle mitochondria is controversial. Studies superimposing exercise training with hypoxic exposure demonstrate an increase in skeletal muscle mitochondrial volume density (MitoVD ) over equivalent normoxic training. In contrast, a reduction in both skeletal muscle mass and MitoVD have been reported following mountaineering expeditions. These observations may however be confounded by negative energy balance, which may obscure the results. Accordingly we sought to examine the effects of high altitude hypoxic exposure on mitochondrial characteristics, with emphasis on MitoVD , while minimizing changes in energy balance. For this purpose, skeletal muscle biopsies were obtained from 9 lowlanders at sea level (Pre) and following 7 (7 Days) and 28 (28 Days) days of exposure to 3454 m. Maximal ergometer power output, whole-body weight and composition, leg lean mass, and skeletal muscle fibre area all remained unchanged following the altitude exposure. Transmission electron microscopy determined intermyofibrillar (IMF) MitoVD was augmented (P = 0.028) by 11.5 ± 9.2% from Pre (5.05 ± 0.9%) to Day 28 (5.61 ± 0.04%). On the contrary, there was no change in subsarcolemmal (SS) MitoVD . As a result total MitoVD (IMF + SS) was increased (P = 0.031) from 6.20 ± 1.5% at Pre to 6.62 ± 1.4% on Day 28 (7.8 ± 9.3%). At the same time no changes in mass-specific respiratory capacities, mitochondrial protein or antioxidant content were found. This study demonstrates that skeletal muscle MitoVD may increase with 28 days acclimation to 3454 m.

  • 73. Jaki Mekjavic, P
    et al.
    Lenassi, E
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, IB
    Effect of acute hypercapnia during 10-day hypoxic bed rest on posterior eye structures.2016In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, no 10, p. 1241-1248Article in journal (Refereed)
  • 74. Jaki Mekjavic, P
    et al.
    Lenassi, E
    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
    FemHab: The effect of acute hypercapnia during hypoxic bedrest on posterior eye structures in females2015Conference paper (Refereed)
  • 75. Jaki Mekjavic, P.
    et al.
    Lenassi, E.
    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.
    The effect of acute hypercapnia during hypoxic bedrest and confinement on the retina2014Conference paper (Refereed)
  • 76. Keiser, Stefanie
    et al.
    Meinild-Lundby, Anne-Kristine
    Steiner, Thomas
    Trosch, Severin
    Rauber, Sven
    Krafft, Alexander
    Burkhardt, Tilo
    Hilty, Matthias Peter
    Siebenmann, Christoph
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Wehrlin, Jon Peter
    Lundby, Carsten
    Detection of blood volumes and haemoglobin mass by means of CO re-breathing and indocyanine green and sodium fluorescein injections2017In: Scandinavian Journal of Clinical and Laboratory Investigation, ISSN 0036-5513, E-ISSN 1502-7686, Vol. 77, no 3, p. 164-174Article in journal (Refereed)
    Abstract [en]

    The main aim of the present study was to quantify the magnitude of differences introduced when estimating a given blood volume compartment (e.g. plasma volume) through the direct determination of another compartment (e.g. red cell volume) by multiplication of venous haematocrit and/or haemoglobin concentration. However, since whole body haematocrit is higher than venous haematocrit such an approach might comprise certain errors. To test this experimentally, four different methods for detecting blood volumes and haemoglobin mass (Hb(mass)) were compared, namely the carbon monoxide (CO) re-breathing (for Hb(mass)), the indocyanine green (ICG; for plasma volume [PV]) and the sodium fluorescein (SoF; for red blood cell volume [RBCV]) methods. No difference between ICG and CO re-breathing derived PV could be established when a whole body/venous haematocrit correction factor of 0.91 was applied (p=0.11, r=0.43, mean difference -340 +/- 612mL). In contrast, when comparing RBCV derived by the CO re-breathing and the SoF method, the SoF method revealed lower RBCV values as compared to the CO re-breathing method (p<0.05, r=0.95, mean difference -728 +/- 184mL). However, compared to the ICG and the SoF methods, the typical error (%TE) and hence reliability of the CO re-breathing method was lower for all measured parameters. Therefore, estimating blood volume compartments by the direct assessment of another compartment can be considered a suitable approach. The CO re-breathing method proved accurate in determining the induced phlebotomy and is at the same time judged easier to perform than any of the other methods.

  • 77.
    Keramidas, Michail E.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Effects of acute and long-term hypoxia on local cold tolerance2016Conference paper (Refereed)
    Abstract [en]

    Exposure to high altitude is commonly considered a predisposing factor for local cold injury. A number of field studies have indeed confirmed that local cold tolerance is impaired in low-oxygen environments, presumably due to hypoxia-induced cutaneous vasoconstriction. However, during acute and long-term high-altitude exposure, the hypoxic stressor typically co-exists with other environmental and behavioral components, viz. hypothermia, malnutrition and physical fatigue, which independently or interactively may affect peripheral blood-flow responses. Laboratory-based, control studies have demonstrated that acute exposure to hypoxia, isolated from other confounding factors, does not potentiate vasoconstriction during local cold stress, but delays spontaneous rewarming following such cold stress. Conversely, it appears that long-term exposure to hypoxia elicits adaptive processes, in particular when the high-altitude acclimatization regimen is combined with physical exercise, that reverse the hypoxia-induced vasoconstriction after local limb cooling. Such adaptive responses do, however, not seem to be transferable to sea-level conditions, i.e. they do not reduce vasoconstriction during normoxic conditions, nor to be homogeneous across the limbs.

  • 78.
    Keramidas, Michail E.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Local cold tolerance: acute hypoxia and hypoxic acclimation2014Conference paper (Refereed)
  • 79.
    Keramidas, Michail E.
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Amon, M.
    Debevec, T.
    Simunic, B.
    Pisot, R.
    Di Prampero, PE
    Mekjavic, I.B.
    Endurance respiratory muscle training: Does it affect performance in normoxia and hypoxia?2007Conference paper (Refereed)
  • 80. Keramidas, Michail E.
    et al.
    Kounalakis, S. N.
    Debevec, T.
    Norman, B.
    Gustafsson, T.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I. B.
    Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory2011In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 202, no 1, p. 91-98Article in journal (Refereed)
    Abstract [en]

    Aim: The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO). Methods: Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration. Results: The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P < 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P < 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P < 0.05). Conclusion: In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.

  • 81.
    Keramidas, Michail E.
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Kounalakis, Stylianos N.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B
    Effects of two short-term, intermittent hypoxic training protocols on the finger temperature response to local cold stress2015In: High Altitude Medicine & Biology, ISSN 1527-0297, E-ISSN 1557-8682, Vol. 16, no 3, p. 251-260Article in journal (Refereed)
    Abstract [en]

    Keramidas, Michail E., Stylianos N. Kounalakis, Ola Eiken, and Igor B. Mekjavic. Effects of two short-Term, intermittent hypoxic training protocols on the finger temperature response to local cold stress. High Alt Med Biol 16:251-260, 2015.-The study examined the effects of two short-Term, intermittent hypoxic training protocols, namely exercising in hypoxia and living in normoxia (LL-TH; n=8), and exercising in normoxia preceded by a series of brief intermittent hypoxic exposures at rest (IHE+NOR; n=8), on the finger temperature response during a sea-level local cold test. In addition, a normoxic group was assigned as a control group (NOR; n=8). All groups trained on a cycle-ergometer 1h/day, 5 days/week for 4 weeks at 50% of peak power output. Pre, post, and 11 days after the last training session, subjects immersed their right hand for 30min in 8°C water. In the NOR group, the average finger temperature was higher in the post (+2.1°C) and 11-day after (+2.6°C) tests than in the pre-Test (p≤0.001). Conversely, the fingers were significantly colder immediately after both hypoxic protocols (LL-TH:-1.1°C, IHE+NOR:-1.8°C; p=0.01). The temperature responses returned to the pre-Training level 11 days after the hypoxic interventions. Ergo, present findings suggest that short-Term intermittent hypoxic training impairs sea-level local cold tolerance; yet, the hypoxic-induced adverse responses seem to be reversible within a period of 11 days.

  • 82.
    Keramidas, Michail E.
    et al.
    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.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    Prolonged physical inactivity leads to a drop in toe skin temperature during local cold stress2014In: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5312, E-ISSN 1715-5320, Vol. 39, no 3, p. 369-374Article in journal (Refereed)
    Abstract [en]

    The purpose was to examine the effects of a prolonged period of recumbency on the toe temperature responses during cold-water foot immersion. Ten healthy males underwent 35 days of horizontal bed rest. The right foot of the subjects was assigned as the experimental (EXP) foot. To prevent bed rest-induced vascular deconditioning in the left control foot (CON), a sub-atmospheric vascular pressure countermeasure regimen was applied on the left lower leg for 4 x 10 min every second day. On the first (BR-1) and the last (BR-35) day of the bed rest, subjects performed two 30 min foot immersion tests in 8 degrees C water, one with the EXP foot and the other with the CON foot. The tests were conducted in counter-balanced order and separated by at least a 15 min interval. At BR-35, the average skin temperature of the EXP foot was lower than at BR-1 (-0.8 degrees C; P = 0.05), a drop that was especially pronounced in the big toe (-1.6 degrees C; P = 0.05). In the CON foot, the average skin temperature decreased by 0.6 degrees C in BR-35, albeit the reduction was not statistically significant (P = 0.16). Moreover, the pressure countermeasure regimen ameliorated immersion-induced thermal discomfort for the CON foot (P = 0.05). Present findings suggest that severe physical inactivity exaggerates the drop in toe skin temperature during local cold stress, and thus might constitute a potential risk factor for local cold injury.

  • 83.
    Keramidas, Michail E.
    et al.
    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.
    Mekjavic, I.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Acute effects of normobaric hypoxia on hand-temperature responses during and after local cold stress2014In: High Altitude Medicine & Biology, ISSN 1527-0297, E-ISSN 1557-8682, Vol. 15, no 2, p. 183-191Article in journal (Refereed)
    Abstract [en]

    The purpose was to investigate acute effects of normobaric hypoxia on hand-temperature responses during and after a cold-water hand immersion test. Fifteen males performed two right-hand immersion tests in 8 degrees C water, during which they were inspiring either room air (Fio(2): 0.21; AIR), or a hypoxic gas mixture (Fio(2): 0.14; HYPO). The tests were conducted in a counterbalanced order and separated by a 1-hour interval. Throughout the 30-min cold-water immersion (CWI) and the 15-min spontaneous rewarming (RW) phases, finger-skin temperatures were measured continuously with thermocouple probes; infrared thermography was also employed during the RW phase to map all segments of the hand. During the CWI phase, the average skin temperature (Tavg) of the fingers did not differ between the conditions (AIR: 10.2 +/- 0.5 degrees C, HYPO: 10.0 +/- 0.5 degrees C; p = 0.67). However, Tavg was lower in the HYPO than the AIR RW phase (AIR: 24.5 +/- 3.4 degrees C; HYPO: 22.0 +/- 3.8 degrees C; p = 0.002); a response that was alike in all regions of the immersed hand. Accordingly, present findings suggest that acute exposure to normobaric hypoxia does not aggravate the cold-induced drop in hand temperature of normothermic males. Still, hypoxia markedly impairs the rewarming responses of the hand.

  • 84.
    Keramidas, Michail E.
    et al.
    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.
    Mekjavic, Igor B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Hand temperature responses to local cooling after a 10-day confinement to normobaric hypoxia with and without exercise2015In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 25, no 5, p. 650-660Article in journal (Refereed)
    Abstract [en]

    The study examined the effects of a 10-day normobaric hypoxic confinement (FiO2: 0.14), with (HT; n = 8) or without (HA; n = 6) exercise, on the hand-temperature responses during and after local cold stress. Before and after the confinement, subjects immersed their right hand for 30 min in 8°C water (CWI), followed by a 15-min spontaneous rewarming (RW), while breathing either room air (AIR), or a hypoxic gas mixture (HYPO). The hand-temperature responses were monitored with thermocouples and infrared-thermography. The confinement did not influence the hand-temperature responses of the HA group during the AIR and HYPO CWI and the HYPO RW phases; but it impaired the AIR RW response (-1.3°C; P = 0.05). After the confinement, the hand-temperature responses were unaltered in the HT group throughout the AIR trial. However, the average hand-temperature was increased during the HYPO CWI (+0.5°C; P ≤ 0.05) and RW (+2.4°C; P ≤ 0.001) phases. Accordingly, present findings suggest that prolonged exposure to normobaric hypoxia per se does not alter the hand-temperature responses to local cooling; yet, it impairs the normoxic rewarming response. Conversely, the combined stimuli of continuous hypoxia and exercise enhance the finger cold-induced vasodilatation and hand-rewarming responses, specifically, under hypoxic conditions.

  • 85.
    Keramidas, Michail E.
    et al.
    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.
    Mekjavic, Igor B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    PlanHab: Hypoxia exaggerates the bedrest-induced reduction in peak oxygen uptake during upright cycle-ergometry2016In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, E-ISSN 1522-1539Article in journal (Refereed)
    Abstract [en]

    The study examined the effects of hypoxia and horizontal bedrest, separately and in combination, on peak oxygen uptake (VO2peak) during upright cycle-ergometry. Ten male lowlanders underwent three 21-day confinement periods, in a counterbalanced order: i) normoxic bedrest (NBR; PIO2 = 133.1 ± 0.3 mmHg), ii) hypoxic bedrest (HBR; PIO2 = 90.0 ± 0.4 mmHg), and iii) hypoxic ambulation (HAMB; PIO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room-air (AIR), or a hypoxic gas (HYPO; PIO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR VO2peak was decreased by both HBR (~13.5%; p ≤ 0.001) and NBR (~8.6%; p ≤ 0.001), with greater drop after HBR (p = 0.01). The HYPO VO2peak was also reduced by HBR (-9.7%; p ≤ 0.001) and NBR (-6.1%; p ≤ 0.001). Peak CO was lower after both bedrest interventions, and especially after HBR (HBR: ~13%, NBR: ~7%; p ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bedrest confinements. No changes were observed in HAMB. Hence, the bedrest-induced decrease in VO2peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.

  • 86.
    Keramidas, Michail E.
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    LunHab: interactive effects of a 10 day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders2017In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 102, no 6, p. 694-710Article in journal (Refereed)
    Abstract [en]

    NEW FINDINGS: What is the central question of this study? What are the distinct and interactive effects of a 10 day exposure to hypoxia and horizontal bedrest on the whole-body peak oxygen uptake and on the regional cerebral and skeletal muscle tissue oxygenation during upright cycle ergometry in male lowlanders? What is the main finding and its importance? A 10 day sustained exposure to hypoxia aggravates the bedrest-induced reduction in peak oxygen uptake during dynamic exercise engaging large muscle groups, but mitigates the skeletal muscle oxidative capacity impairment elicited by bedrest. The study examined the interactive effects of a 10 day exposure to hypoxia and bedrest on the whole-body peak oxygen uptake (V̇O2 peak ) during maximal exercise and on skeletal muscle and cerebral oxygenation during submaximal exercise. Nine males underwent three 10 day confinements, in a Latin-square order, as follows: (i) a normoxic bedrest [NBR; partial pressure of inspired O2 (PI,O2) = 134.2 ± 0.7 mmHg]; (ii) a hypoxic bedrest (HBR; PI,O2 = 102.9 ± 0.1 mmHg at day 1, 91.5 ± 1.2 mmHg at days 3-10); and (iii) a hypoxic ambulation (HAMB; PI,O2 as in HBR). Before, 1 (R+1) and 3 days (R+3) after each confinement, subjects performed exhaustive, incremental-load and moderate-intensity constant-load (CLTs) cycle-ergometry trials, while breathing either room air or a hypoxic gas mixture. During the CLTs, changes in the regional oxygenation of the cerebral frontal cortex and the vastus lateralis and intercostal muscles were monitored with near-infrared spectroscopy. At R+1, the confinement-related impairment in V̇O2 peak was greater after HBR than after NBR or HAMB, regardless of whether the trial was performed in room air or hypoxia (HBR, -16.2%; NBR, -8.3%; HAMB, -4.1%; P = 0.001). During the CLTs, bedrest aggravated the exercise-induced reduction in locomotor and respiratory muscle oxygenation (P ≤ 0.05); an effect that was less after HBR than after NBR (P ≤ 0.05). The hypoxic exercise-induced cerebral vasodilatory response was blunted by HBR, probably because of the marked hyperventilation-dependent hypocapnia, attendant to the sustained hypoxic stimulus. Hence, short-term exposure to hypoxia potentiates the reduction in V̇O2 peak , but it mitigates the impairment in skeletal muscle oxidative capacity induced by bedrest.

  • 87.
    Keramidas, Michail E.
    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.
    Chouker, Alexander
    Strewe, Claudia
    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.
    PlanHab: Hypoxia counteracts the erythropoietin suppression, but seems to exaggerate the plasma volume reduction induced by 3 weeks of bed rest2016In: Physiological Reports, E-ISSN 2051-817X, Vol. 4, no 3Article in journal (Refereed)
    Abstract [en]

    The study examined the distinct and synergistic effects of hypoxia and bed rest on the erythropoietin (EPO) concentration and relative changes in plasma volume (PV). Eleven healthy male lowlanders underwent three 21‐day confinement periods, in a counterbalanced order: (1) normoxic bed rest (NBR; PIO2: 133.1 ± 0.3 mmHg); (2) hypoxic bed rest (HBR; PIO2: 90.0 ± 0.4 mmHg, ambient simulated altitude of ~4000 m); and (3) hypoxic ambulation (HAMB; PIO2: 90.0 ± 0.4 mmHg). Blood samples were collected before, during (days 2, 5, 14, and 21) and 2 days after each confinement to determine EPO concentration. Qualitative differences in PV changes were also estimated by changes in hematocrit and hemoglobin concentration along with concomitant changes in plasma renin concentration. NBR caused an initial reduction in EPO by ~39% (= 0.04). By contrast, HBR enhanced EPO (= 0.001), but the increase was less than that induced by HAMB (< 0.01). All three confinements caused a significant reduction in PV (< 0.05), with a substantially greater drop in HBR than in the other conditions (< 0.001). Thus, present results suggest that hypoxia prevents the EPO suppression, whereas it seems to exaggerate the PV reduction induced by bed rest.

  • 88.
    Keramidas, Michail E.
    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. Jozef Stefan Institute, Slovenia.
    Stavrou, Nektarios A.M.
    Kounalakis, Stylianos D.
    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.
    Igor B., Mekjavic
    Severe hypoxia during incremental exercise to exhaustion provokes negative post-exercise affects2016In: Physiology and Behavior, ISSN 0031-9384, E-ISSN 1873-507X, Vol. 156Article in journal (Refereed)
    Abstract [en]

    The post-exercise emotional response is mainly dependent on the intensity of the exercise performed; moderate exercise causes positive feelings, whereas maximal exercise may prompt negative affects. Acute hypoxia impairs peak O2 uptake (VO2peak), resulting in a shift to a lower absolute intensity at the point of exhaustion. Hence, the purpose of the study was to examine whether a severe hypoxic stimulus would influence the post-exercise affective state in healthy lowlanders performing an incremental exercise to exhaustion. Thirty-six male lowlanders performed, in a counter-balanced order and separated by a 48-h interval, two incremental exercise trials to exhaustion to determine their VO2peak, while they were breathing either room air (AIR; FiO2: 0.21), or a hypoxic gas mixture (HYPO; FiO2: 0.12). Before and immediately after each trial, subjects were requested to complete two questionnaires, based on how they felt at that particular moment: (i) the Profile of Mood States-Short Form, and (ii) the Activation Deactivation Adjective Check List. During the post-exercise phase, they also completed the Multidimensional Fatigue Inventory. VO2peak was significantly lower in the HYPO than the AIR trial (~15%; p<0.001). Still, after the HYPO trial, energy, calmness and motivation were markedly impaired, whereas tension, confusion, and perception of physical and general fatigue were exaggerated (p≤0.05). Accordingly, present findings suggest that an incremental exercise to exhaustion performed in severe hypoxia provokes negative post-exercise emotions, induces higher levels of perceived fatigue and decreases motivation; the affective responses coincide with the comparatively lower VO2peak than that achieved in normoxic conditions.

  • 89. Kirbis, M.
    et al.
    Morrison, S.
    Rojc, B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Igor, M.
    Groselj, L. Dolenc
    Hypoxia and bedrest progressively attenuate parasympathetic activity during sleep2016In: Journal of Sleep Research, ISSN 0962-1105, E-ISSN 1365-2869, Vol. 25, p. 236-237Article in journal (Other academic)
  • 90. Kounalakis, Stylianos N.
    et al.
    Keramidas, Michail E.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Amon, Mojca
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B.
    A 10-day confinement to normobaric hypoxia impairs toe, but not finger temperature response during local cold stress2017In: Journal of Thermal Biology, ISSN 0306-4565, E-ISSN 1879-0992, Vol. 64, p. 109-115Article in journal (Refereed)
    Abstract [en]

    The study examined the effects of a 10-day normobaric hypoxic confinement on the finger and toe temperature responses to local cooling. Eight male lowlanders underwent a normoxic (NC) and, in a separate occasion, a normobaric hypoxic confinement (HC; FO2: 0.154; simulated altitude ~3400 m). Before and after each confinement, subjects immersed for 30 min their right hand and, in a different session, their right foot in 8 °C water, while breathing either room air (AIR) or a hypoxic gas mixture (HYPO). Throughout the cold-water immersion tests, thermal responses were monitored with thermocouples on fingers and toes. Neither confinement influenced thermal responses in the fingers during the AIR or HYPO test. In the foot, by contrast, HC, but not NC, reduced the average toe temperature by ~1.5 °C (p=0.03), both during the AIR and HYPO test. We therefore conclude that a 10-day confinement to normobaric hypoxia per se augments cold-induced vasoconstriction in the toes, but not in the fingers. The mechanism underlying this dissimilarity remains to be established.

  • 91.
    Kölegard, Roger
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, Igor B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Effects of physical fitness on relaxed G-tolerance and the exercise pressor response2013In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 113, no 11, p. 2749-2759Article in journal (Refereed)
    Abstract [en]

    Fighter pilots are commonly recommended strength training as a means of improving the tolerance to withstand high gravitoinertial (G) loads. Previous studies on the effect of short-term strength-training regimens on G-endurance show equivocal results, with a majority of the studies suggesting improved G-endurance. The mechanisms underlying such improvement are unknown. Presumably, any change in G-tolerance induced by physical training habits should be manifest following long-term training. We also reasoned that during repeated straining maneuvers-as during certain G-endurance protocols-the relaxed G-tolerance and the exercise pressure response may play a significant role in maintaining adequate arterial pressure, and hence that different training modalities might alter G-endurance, by altering the exercise pressor response. Three groups of males were studied, long-term (>6 months) endurance-trained (E; n = 17), strength-trained (S; n = 16) and untrained (U; n = 17) individuals. The pressor response was studied during sustained (40 s) isometric knee extensions at 50 % of the maximal contraction level. Relaxed gradual onset-rate G-tolerance was determined. G-tolerance was similar in the E (4.6 +/- 0.5 G), S (4.9 +/- 0.8 G) and U (4.6 +/- 0.8 G) groups. The mean arterial pressure increase during isometric exercise was higher in the S (36 +/- 7 mmHg = mean +/- SD) and U (35 +/- 16 mmHg) groups than in the E group (28 +/- 8 mmHg). The results suggest that relaxed G-tolerance is unaffected by physical training habits, and that the training modality affects the magnitude of the exercise pressor response. However, it seems that the response is blunted by endurance training rather than enhanced by strength training.

  • 92.
    Kölegård, Roger
    et al.
    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.
    Grönkvist, Mikael
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Är det möjligt att uppskatta Gz-tolerans medelst ortostatisk prov?2015Conference paper (Refereed)
  • 93.
    Linnarsson, D
    et al.
    Karolinska Institutet.
    Spaak, J
    Karolinska Institutet.
    Sundblad, Patrik
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology. Karolinska Institutet.
    Baroreflex impairment during rapid posture changes at rest and exercise after 120 days of bed rest.2006In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 96, no 1, p. 37-45Article in journal (Refereed)
    Abstract [en]

    Orthostatic intolerance is common after space flight and head-down tilt (HDT) bed rest. We hypothesized that HDT-induced impairments of arterial blood pressure (AP) control would be more marked during exercise and that recovery of baroreflex function after very long-term HDT would be delayed. Six subjects were studied before (BDC) during (day 60, D60; D113) and after (recovery day 0, R0; R3; R15) 120 days of HDT. Supine resting subjects were exposed to repeated 1 min passive tilts to upright at 3-min interval. During 50 W steady-state exercise corresponding tilt had a 2-min duration at 4-min interval. The amplitudes of the tilt-induced transient beat-by-beat deviations in AP and rate (HR) were determined during the gravity transients. At rest these deviations did not change over time, but during exercise the total peak-to-nadir range of deviations in systolic AP (SAP) at up-tilt and down-tilt increased to 168+/-16% (mean+/-SEM) of BDC at D113 with no clear recovery upto and including R15. Counter-regulatory HR responses were not increased proportionally and especially not tachycardic responses to up-tilt, resulting in a reduction of baroreflex sensitivity (deltaRR-interval/deltaSAP) by 55+/-9% of BDC at D113 with no recovery upto and including R15. We conclude that prolonged bed rest cause long-lasting impairments in AP control and baroreflex function in exercising humans.

  • 94. Linnarsson, D
    et al.
    Zou, L
    Chuang, C.C.
    Li, G
    Gao, F
    Mekjavic, P.J.
    Dua, H
    Amoaku, W
    Macdonald, I.A.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I.B.
    Commentaries on Viewpoint: Standardization of bed rest studies in the spaceflight context.2016In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 121, no 1, p. 350-351Article in journal (Refereed)
  • 95. Louwies, T.
    et al.
    Mekjavic, P. J.
    Cox, B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Mekjavic, I. B.
    Kounalakis, S.
    De Boever, P.
    Separate and combined effects of hypoxia and horizontal bed rest on retinal blood vessel diameters2016In: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 57, no 11, p. 4927-4932Article in journal (Refereed)
    Abstract [en]

    PURPOSE. To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation. METHODS. Eleven healthy male subjects (mean 6 SD age = 27 ± 6 years; body mass index [BMI] = 23.7 ± 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 ± 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 6 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21- day intervention. RESULTS. Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (ΔDCRAE = -7.5 µm; 95% confidence interval [CI]: -10.8 to -4.2; P &lt; 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (DCRAE = 9.4 µm; 95% CI: 6.0-12.7; P &lt; 0.0001). During HBR, the increase in CRAE was highest on day 3 (ΔDCRAE = 4.5 µm; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (ΔDCRVE = -7.9 µm; 95 CI: -13.3 to -2.5), and the maximum ΔDCRVE during HAMB (24.6 µm; 95% CI: 18.9-30.3) and HBR (15.2 µm; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively. CONCLUSIONS. The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure.

  • 96. Mazzucco, S
    et al.
    Agostini, F
    Tence, M
    Baglio, V
    Mekjavic, I. B.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Biolo, G
    Physical inactivity blunted the protein anticatabolic effects of hypoxia in healthy volunteers – the PlanHab study.2013In: Clinical Nutrition, ISSN 0261-5614, E-ISSN 1532-1983, Vol. 32, no Supplement 1, p. S8-S9Article in journal (Refereed)
  • 97. McDonnell, A. C.
    et al.
    Mekjavic, I. B.
    Dolenc-Grošelj, L.
    Mekjavic, P. J.
    Eiken, Ola
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.
    Effect of hypoxia and bedrest on peripheral vasoconstriction2013In: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen, ESA Communications , 2013, p. 1-2Conference paper (Refereed)
    Abstract [en]

    Future planetary habitats may expose astronauts to both microgravity and hypobaric hypoxia, both inducing a reduction in peripheral perfusion. Peripheral temperature changes have been linked to sleep onset and quality [5]. However, it is still unknown what effect combining hypoxia and bedrest has on this relationship. Eleven male participants underwent three 10-day campaigns in a randomized manner: 1) normobaric hypoxic ambulatory confinement (HAmb); 2) normobaric hypoxic bed rest (HBR); 3) normobaric normoxic bed rest (NBR). There was no change in skin temperature gradient between the calf and toes, an index of peripheral perfusion (ΔTc-t), over the 10-d period in the HAmb trial. However, there was a significant increase (p< 0.001) in daytime (9am-9pm) ΔTc-t on day 10 of the inactivity/unloading periods (HBR and NBR trials). This reduction in the perfusion of the toes during the daytime was augmented during the HBR trial compared to NBR (p< 0.001). Before and on day 10 of the interventions we conducted polysomnographic assessment, which revealed no changes in sleep onset and/or architecture. These data support the theory that circadian changes in temperature are functionally linked to sleepiness [1].

  • 98. McDonnell, A
    et al.
    Stavrou, N
    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 effect of activity during hypoxic confinement on emotional state2015Conference paper (Refereed)
  • 99. McDonnell, AC
    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
    Peripheral Perfusion and Acute Mountain Sickness: Is There a Link?2015Conference paper (Refereed)
  • 100. McDonnell, A.C.
    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, P.J.
    Mekjavic, I.B.
    Circadian rhythm of peripheral perfusion during 10-day hypoxic confinement and bed rest2014In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 114, no 10, p. 2093-2104Article in journal (Refereed)
    Abstract [en]

    Future planetary habitats will be hypobaric and hypoxic to reduce the risk of decompression sickness during preparation for extra-vehicular activities. This study was part of a research programme investigating the combined effects of hypoxia and microgravity on physiological systems. We tested the hypothesis that hypoxia-induced peripheral vasoconstriction persists at night and is aggravated by bed rest. Since sleep onset has been causally linked to nocturnal vasodilatation, we reasoned that hypoxia-induced vasoconstriction at night may explain sleep disturbances at altitude. Peripheral perfusion alterations as a consequence of bed rest may explain poor sleep quality reported during sojourns on the International Space Station. Eleven males underwent three 10-day interventions in a randomised order: (1) hypoxic ambulatory confinement; (2) hypoxic bed rest; (3) normoxic bed rest. During each intervention we conducted 22-h monitoring of peripheral perfusion, as reflected by the skin temperature gradient. Measurements were conducted on the first (D 1) and last day (D 10) of each intervention. All interventions resulted in a decrease in daytime toe perfusion from D 1 to D 10. There was no difference in the magnitude of the daytime reduction in toe perfusion between the three interventions. There was a significant vasodilatation of the toes in all interventions by 11 pm. The fingertips remained well perfused throughout. Daytime vasoconstriction induced by hypoxia and/or bed rest is abolished at night, lending further support to the theory that changes in peripheral skin temperature may be functionally linked to sleep onset.

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