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  • 51. Brantberg, Krister
    et al.
    Westin, Magnus
    Löfqvist, Lennart
    Verrecchia, Luca
    Tribukait, Arne
    Swedish Defence Research Agency.
    Vestibular evoked myogenic potentials in response to lateral skull taps are dependent on two different mechanisms2009Inngår i: Clinical Neurophysiology, ISSN 1388-2457, E-ISSN 1872-8952, Vol. 120, nr 5, s. 974-979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECTIVE: To explore the mechanisms for skull tap induced vestibular evoked myogenic potentials (VEMP).

    METHODS: The muscular responses were recorded over both sternocleidomastoid (SCM) muscles using skin electrodes. A skull tapper which provided a constant stimulus intensity was used to test cervical vestibular evoked myogenic potentials (VEMP) in response to lateral skull taps in healthy subjects (n=10) and in patients with severe unilateral loss of vestibular function (n=10).

    RESULTS: Skull taps applied approximately 2 cm above the outer ear canal caused highly reproducible VEMP. There were differences in VEMP in both normals and patients depending on side of tapping. In normals, there was a positive-negative ("normal") VEMP on the side contra-lateral to the skull tapping, but no significant VEMP ipsi-laterally. In patients, skull taps above the lesioned ear caused a contra-lateral positive-negative VEMP (as it did in the normals), in addition there was an ipsi-lateral negative-positive ("inverted") VEMP. When skull taps were presented above the healthy ear there was only a small contra-lateral positive-negative VEMP but, similar to the normals, no VEMP ipsi-laterally.

    CONCLUSIONS: The present data, in conjunction with earlier findings, support a theory that skull-tap VEMP responses are mediated by two different mechanisms. It is suggested that skull tapping causes both a purely ipsi-lateral stimulus side independent SCM response and a bilateral and of opposite polarity SCM response that is stimulus side dependent. Possibly, the skull tap induced VEMP responses are the sum of a stimulation of two species of vestibular receptors, one excited by vibration (which is rather stimulus site independent) and one excited by translation (which is more stimulus site dependent).

    SIGNIFICANCE: Skull-tap VEMP probably have two different mechanisms. Separation of the two components might reveal the status of different labyrinthine functions.

  • 52. Broman, Gi
    et al.
    Jonsson, Lena
    Stockholm University College of Physical Education and Sports.
    Kaijser, Lennart
    Golf: a high intensity interval activity ofor elderly men2004Inngår i: Aging Clinical and Experimental Research, ISSN 1594-0667, E-ISSN 1720-8319, Vol. 16, nr 5, s. 375-381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background and aims: The aim was to quantify the time spent at different exercise intensities for male golfers, in relation to age, while walking a "normal' 18-hole golf course. Methods: 19 healthy male golfers (six 27 (5) years old, seven of 50 (7) and six of 75 (4) years) performed a maximal exercise test on a treadmill (maximal oxygen uptake and maximal heart rate were measured). Within one week, they played an "average" 18-hole course starting at 7.00 a.m. During the round, their heart rate was monitored with a Polar Vantage heart rate monitor, which sampled the heart rate every 5 seconds. Body weight was measured before and after the round. Blood glucose was taken at rest before the round and after each 3rd hole. Perceived exertion and perceived pain in muscles and joints were rated using the CR 10 Borg scale just before reaching each green and after a few selected uphill parts of the course. Results: High intensity of exercise was reached during 6% of the total playing time for the young, 30% for the middle-aged and 70% for the elderly golfers, playing 18 holes (p<0.05). The golfers’ heart rate was below 50% of their individual maximal heart rate, 18% of total time for young golfers, 16% for the middle-aged, and not at all for the elderly. Perceived exertion, breathlessness and leg fatigue were rated in a similar manner for all three groups. Perceived pain in joints and muscles was rated extremely weak except in a few players who had some known joint or muscle problem. The mean blood glucose level fell by 20% for the young (p<0.05), 10% for the middle-aged and 30% for the elderly players (p<0.05) after 18 holes of play. Body weight was reduced 0.7% similarly for all three groups (p<0.05). Conclusions: Walking an 18-hole golf course corresponds to an exercise intensity which is moderate and high for the elderly, mainly low to moderate for the middle-aged, and low for young male golfers. All golfers, regardless of age, perceived their exertion similarly as weak to moderate.

  • 53.
    Buendia, Rubén
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinska sensorer, signaler och system.
    Seoane, Fernando
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinska sensorer, signaler och system.
    Bosaeus, I.
    Gil-Pita, R.
    Johannsson, G.
    Ellegård, L.
    Lindecrantz, Kaj
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinska sensorer, signaler och system.
    Robustness study of the different immittance spectra and frequency ranges in bioimpedance spectroscopy analysis for assessment of total body composition2014Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 35, nr 7, s. 1373-1395Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The estimation of body fluids is a useful and common practice for assessment of disease status and therapy outcomes. Electrical bioimpedance spectroscopy (EBIS) methods are noninvasive, inexpensive and efficient alternatives for determination of body fluids. One of the main source of errors in EBIS measurements in the estimation of body fluids is capacitive coupling. In this paper an analysis of capacitive coupling in EBIS measurements was performed and the robustness of the different immittance spectra against it tested. On simulations the conductance (G) spectrum presented the smallest overall error, among all immittance spectra, in the estimation of the impedance parameters used to estimate body fluids. Afterwards the frequency range of 10-500 kHz showed to be the most robust band of the G spectrum. The accuracy of body fluid estimations from the resulting parameters that utilized G spectrum and parameters provided by the measuring device were tested on EBIS clinical measurements from growth hormone replacement therapy patients against estimations performed with dilution methods. Regarding extracellular fluid, the correlation between each EBIS method and dilution was 0.93 with limits of agreement of 1.06 +/- 2.95 l for the device, 1.10 +/- 2.94 l for G [10-500 kHz] and 1.04 +/- 2.94 l for G [5-1000 kHz]. Regarding intracellular fluid, the correlation between dilution and the device was 0.91, same as for G [10-500 kHz] and 0.92 for G [5- 1000 kHz]. Limits of agreement were 0.12 +/- 4.46 l for the device, 0.09 +/- 4.45 for G [10- 500 kHz] and 0.04 +/- 4.58 for G [5-1000 kHz]. Such close results between the EBIS methods validate the proposed approach of using G spectrum for initial Cole characterization and posterior clinical estimation of body fluids status.

  • 54.
    Castiglioni, Laura
    et al.
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Pignieri, Alice
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Fiasche, Melania
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Giudici, Marco
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Center for Protein Research. Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Crestani, Maurizio
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Mitro, Nico
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Abbate, Mauro
    IRCCS Ist Ric Farmacol Mario Negri, Ctr Anna Maria Astori, Sci & Technol Pk Kilometro Rosso, Bergamo, Italy..
    Zoja, Carlamaria
    IRCCS Ist Ric Farmacol Mario Negri, Ctr Anna Maria Astori, Sci & Technol Pk Kilometro Rosso, Bergamo, Italy..
    Rottoli, Daniela
    IRCCS Ist Ric Farmacol Mario Negri, Ctr Anna Maria Astori, Sci & Technol Pk Kilometro Rosso, Bergamo, Italy..
    Foray, Claudia
    IRCCS Ist Ric Farmacol Mario Negri, Dept Cardiovasc Res, Milan, Italy..
    Fiordaliso, Fabio
    IRCCS Ist Ric Farmacol Mario Negri, Dept Cardiovasc Res, Milan, Italy..
    Guerrini, Uliano
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy..
    Tremoli, Elena
    Ctr Cardiol Monzino, Milan, Italy..
    Sironi, Luigi
    Univ Milan, Dept Pharmacol & Biomol Sci, Via G Balzaretti 9, I-20133 Milan, Italy.;Ctr Cardiol Monzino, Milan, Italy..
    Gelosa, Paolo
    Ctr Cardiol Monzino, Milan, Italy..
    Fenofibrate attenuates cardiac and renal alterations in young salt-loaded spontaneously hypertensive stroke-prone rats through mitochondrial protection2018Inngår i: Journal of Hypertension, ISSN 0263-6352, E-ISSN 1473-5598, Vol. 36, nr 5, s. 1129-1146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives:The simultaneous presence of cardiac and renal diseases is a pathological condition that leads to increased morbidity and mortality. Several lines of evidence have suggested that lipid dysmetabolism and mitochondrial dysfunction are pathways involved in the pathological processes affecting the heart and kidney. In the salt-loaded spontaneously hypertensive stroke-prone rat (SHRSP), a model of cardiac hypertrophy and nephropathy that shows mitochondrial alterations in the myocardium, we evaluated the cardiorenal effects of fenofibrate, a peroxisome proliferator-activated receptor alpha (PPAR) agonist that acts by modulating mitochondrial and peroxisomal fatty acid oxidation.Methods:Male SHRSPs aged 6-7 weeks were divided in three groups: standard diet (n=6), Japanese diet with vehicle (n=6), and Japanese diet with fenofibrate 150mg/kg/day (n=6) for 5 weeks. Cardiac and renal functions were assessed in vivo by MRI, ultrasonography, and biochemical assays. Mitochondria were investigated by transmission electron microscopy, succinate dehydrogenase (SDH) activity, and gene expression analysis.Results:Fenofibrate attenuated cardiac hypertrophy, as evidenced by histological and MRI analyses, and protected the kidneys, preventing morphological alterations, changes in arterial blood flow velocity, and increases in 24-h proteinuria. Cardiorenal inflammation, oxidative stress, and cellular senescence were also inhibited by fenofibrate. In salt-loaded SHRSPs, we observed severe morphological mitochondrial alterations, reduced SDH activity, and down-regulation of genes regulating mitochondrial fatty-acid oxidation (i.e. PPAR, SIRT3, and Acadm). These changes were counteracted by fenofibrate. In vitro, a direct protective effect of fenofibrate on mitochondrial membrane potential was observed in albumin-stimulated NRK-52E renal tubular epithelial cells.Conclusion:The results suggest that the cardiorenal protective effects of fenofibrate in young male salt-loaded SHRSPs are explained by its capacity to preserve mitochondrial function.

  • 55. Cervenka, Simon
    et al.
    Varrone, Andrea
    Fransén, Erik
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Halldin, Christer
    Farde, Lars
    PET Studies of D2-Receptor Binding in Striatal and Extrastriatal Brain Regions: Biochemical Support In Vivo for Separate Dopaminergic Systems in Humans2010Inngår i: Synapse, ISSN 0887-4476, E-ISSN 1098-2396, Vol. 64, nr 6, s. 478-485Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most molecular imaging studies of the dopamine (DA) system performed to date have focused on the striatum, a region receiving dense dopaminergic innervation. In clinical research on the DA D2-receptor, striatal binding has often been regarded as an index of global DA function, based on the underlying assumption of common regulatory mechanisms for receptor expression across brain regions. Recent data has challenged this view, suggesting differences in genetic regulation between striatal and extrastriatal brain regions. The relationship between binding levels in brain regions has, however, not been directly examined in the same sample. In this study, we searched for interregional correlations between DA D2-receptor availability as determined with Positron Emission Tomography in 16 control subjects. The radioligands [C-11]raclopride and [C-11]FLB 457 were used for measurements of D2-receptor binding in striatal and extrastriatal regions, respectively. No correlation was observed between D2-receptor availability in striatum and any of the extrastriatal regions, as assessed using both region of interest- and voxel-based analyses. Instead, the pattern of correlations was consistent with the model of separate dopaminergic systems as has been originally observed in rodents. These preliminary results encourage approaches searching for individual patterns of receptor binding across the whole brain volume in clinical studies on the dopamine system.

  • 56. 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)
  • 57. 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)
  • 58. 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)
  • 59. 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.

  • 60. Ciuha, U
    et al.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Mekjavic, I
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Pavlinič, D
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Thermal strain in soldiers performing patrol missions in a desert climate: effect of two different cooling strategies2011Konferansepaper (Fagfellevurdert)
  • 61. 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)
  • 62. 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)
  • 63. Debevec, T
    et al.
    Amon, M
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Kounalakis, S.N.
    Mekjavic, I.B.
    Hematological responses to two different intermittent hypoxic training regimens2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    "Hypoxic training has been reported to enhance athletes’ altitude and sea-level performance by augmenting oxygen carrying capacity of the blood, as a consequence of increases in hematocrit and hemoglobin concentrations. However the effect of intermittent hypoxic training on hematological responses remains unresolved."

    This study investigated the effect of two intermittent hypoxic training regimens on the response of hematological indices. Healthy male Ss (N = 27) were equally assigned to a control group, a live low-train high (LL-TH) group, or a intermittent hypoxic exposure group. Ss performed a one-hour submaximal endurance exercise on a cycle ergometer, five days per week for four weeks, at an intensity corresponding to 50% of normoxic peak power output for the control and intermittent hypoxic exposure groups, and to 50% of hypoxic peak power output for the LL-TH group. Thus, all groups trained at the same relative work rate. The absolute work rate during training was 18-20 W lower for the LL-TH group compared to the other two groups. All groups lived at an altitude of ~300 m above sea level. The control and intermittent hypoxic exposure groups also trained at this altitude, whereas the LL-TH group trained in a hypoxic chamber, breathing a hypoxic mixture (FIO2=12%). In addition to the daily exercise training, the intermittent hypoxic exposure group also inspired a hypoxic gas mixture at rest, and prior to the cycle ergometry. The intermittent hypoxic training comprised breathing a hypoxic mixture during seven phases. Each phase consisted of five minutes of breathing a hypoxic mixture, followed by three minutes of breathing a normoxic gas mixture. Prior to, during, at the end, and 10 days after the training period, blood samples were taken from all Ss in order to measure hemoglobin, hematocrit, erythrocytes, ferritin, and transferrin concentrations.

    No significant differences were observed between groups in any measured hematological variables. Similarly, no significant differences were found within groups at the different testing periods.

    Implication. Although it has been reported that both LL-TH and intermittent hypoxic exposure protocols provide hematological benefits, that was not confirmed by this study. The tested protocols did not induce any changes in the measured hematological variables; therefore no improvements of the oxygen carrying capacity of the blood should be expected following this type of hypoxic training.

  • 64. Debevec, T
    et al.
    Amon, M
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Kounalakis, S.N.
    Mekjavic, I.B.
    The use of live low – train high protocol for the enhancement of endurance performance and aerobic capacity.2009Konferansepaper (Annet vitenskapelig)
  • 65. Debevec, T.
    et al.
    Amon, M.
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Simunic, B.
    Pisot, R.
    Kounalakis, S.N.
    Eiken, O.
    Mekjavic, I.B.
    “Sleep high – train low” altitude training2008Konferansepaper (Annet vitenskapelig)
  • 66. 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.

  • 67. 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)
  • 68. 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.

  • 69. Debevec, T.
    et al.
    Ganse, B.
    Mittag, U.
    Eiken, Ola
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Omgivningsfysiologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Centrum för flyg- och rymdfysiologi, SAPC.
    Mekjavic, I. B.
    Rittweger, J.
    Hypoxia aggravates inactivity-Related muscle wasting2018Inngår i: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, nr May, artikkel-id 494Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poor musculoskeletal state is commonly observed in numerous clinical populations such as chronic obstructive pulmonary disease (COPD) and heart failure patients. It, however, remains unresolved whether systemic hypoxemia, typically associated with such clinical conditions, directly contributes to muscle deterioration. We aimed to experimentally elucidate the effects of systemic environmental hypoxia upon inactivity-related muscle wasting. For this purpose, fourteen healthy, male participants underwent three 21-day long interventions in a randomized, cross-over designed manner: (i) bed rest in normoxia (NBR; PiO2 = 133.1 ± 0.3 mmHg), (ii) bed rest in normobaric hypoxia (HBR; PiO2 = 90.0 ± 0.4 mmHg) and ambulatory confinement in normobaric hypoxia (HAmb; PiO2 = 90.0 ± 0.4 mmHg). Peripheral quantitative computed tomography and vastus lateralis muscle biopsies were performed before and after the interventions to obtain thigh and calf muscle cross-sectional areas and muscle fiber phenotype changes, respectively. A significant reduction of thigh muscle size following NBR (-6.9%, SE 0.8%; P &lt; 0.001) was further aggravated following HBR (-9.7%, SE 1.2%; P = 0.027). Bed rest-induced muscle wasting in the calf was, by contrast, not exacerbated by hypoxic conditions (P = 0.47). Reductions in both thigh (-2.7%, SE 1.1%, P = 0.017) and calf (-3.3%, SE 0.7%, P &lt; 0.001) muscle size were noted following HAmb. A significant and comparable increase in type 2× fiber percentage of the vastus lateralis muscle was noted following both bed rest interventions (NBR = +3.1%, SE 2.6%, HBR = +3.9%, SE 2.7%, P &lt; 0.05). Collectively, these data indicate that hypoxia can exacerbate inactivity-related muscle wasting in healthy active participants and moreover suggest that the combination of both, hypoxemia and lack of activity, as seen in COPD patients, might be particularly harmful for muscle tissue.

  • 70. Debevec, T
    et al.
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Amon, M
    Kounalakis, S.N.
    Mekjavic, I.B.
    Evaluation of training protocols for the improvement of altitude and sea level performance2009Konferansepaper (Annet vitenskapelig)
  • 71. Debevec, T.
    et al.
    Keramidas, Michail E.
    Norman, B
    Gustafsson, T
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Mekjavic, I
    No evidence for the “normobaric oxygen paradox”2011Inngår i: Medicine & Science in Sports & Exercise, ISSN 0195-9131, Vol. 43, nr S5, s. 151-151Artikkel i tidsskrift (Annet vitenskapelig)
  • 72. 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)
  • 73. 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.

  • 74. 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.

  • 75. 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)
  • 76. 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.

  • 77. Debevec, Tadej
    et al.
    Keramidas, Michail E.
    Norman, Barbara
    Gustafsson, Thomas
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Mekjavic, Igor B.
    Acute short-term hyperoxia followed by mild hypoxia does not increase EPO production: resolving the "normobaric oxygen paradox''2012Inngår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 112, nr 3, s. 1059-1065Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 78. 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.

  • 79. 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.

  • 80.
    Dillon-Murphy, Desmond
    et al.
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Marlevi, David
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Ruijsink, Bram
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Qureshi, Ahmed
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Chubb, Henry
    Stanford Univ, Dept Cardiothorac Surg, Palo Alto, CA 94304 USA..
    Kerfoot, Eric
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    O'Neill, Mark
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Nordsleffen, David
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Aslanidi, Oleg
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    de Vecchi, Adelaide
    Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England..
    Modeling Left Atrial Flow, Energy, Blood Heating Distribution in Response to Catheter Ablation Therapy2018Inngår i: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, artikkel-id 1757Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introduction: Atrial fibrillation (AF) is a widespread cardiac arrhythmia that commonly affects the left atrium (LA), causing it to quiver instead of contracting effectively. This behavior is triggered by abnormal electrical impulses at a specific site in the atrial wall. Catheter ablation (CA) treatment consists of isolating this driver site by burning the surrounding tissue to restore sinus rhythm (SR). However, evidence suggests that CA can concur to the formation of blood clots by promoting coagulation near the heat source and in regions with low flow velocity and blood stagnation. Methods: A patient-specific modeling workflow was created and applied to simulate thermal-fluid dynamics in two patients pre- and post-CA. Each model was personalized based on pre- and post-CA imaging datasets. The wall motion and anatomy were derived from SSFP Cine MRI data, while the trans-valvular flow was based on Doppler ultrasound data. The temperature distribution in the blood was modeled using a modified Pennes bioheat equation implemented in a finite-element based Navier-Stokes solver. Blood particles were also classified based on their residence time in the LA using a particle-tracking algorithm. Results: SR simulations showed multiple short-lived vortices with an average blood velocity of 0.2-0.22 m/s. In contrast, AF patients presented a slower vortex and stagnant flow in the LA appendage, with the average blood velocity reduced to 0.08-0.14 m/s. Restoration of SR also increased the blood kinetic energy and the viscous dissipation due to the presence of multiple vortices. Particle tracking showed a dramatic decrease in the percentage of blood remaining in the LA for longer than one cycle after CA (65.9 vs. 43.3% in patient A and 62.2 vs. 54.8% in patient B). Maximum temperatures of 76 degrees and 58 degrees C were observed when CA was performed near the appendage and in a pulmonary vein, respectively. Conclusion: This computational study presents novel models to elucidate relations between catheter temperature, patient-specific atrial anatomy and blood velocity, and predict how they change from SR to AF. The models can quantify blood flow in critical regions, including residence times and temperature distribution for different catheter positions, providing a basis for quantifying stroke risks.

  • 81. 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)
  • 82.
    Domkin, Dmitry
    et al.
    Univ Gavle, Fac Hlth & Occupat Studies, Dept Occupat & Publ Hlth Sci, Ctr Musculoskeletal Res, S-80176 Gavle, Sweden..
    Forsman, Mikael
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Ergonomi.
    Richter, Hans O.
    Univ Gavle, Fac Hlth & Occupat Studies, Dept Occupat & Publ Hlth Sci, Ctr Musculoskeletal Res, S-80176 Gavle, Sweden..
    Effect of ciliary-muscle contraction force on trapezius muscle activity during computer mouse work2019Inngår i: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 119, nr 2, s. 389-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study aimed to identify whether or not an increase in ciliary-muscle contraction force, when the eye-lens is adjusted for viewing at a near distance, results in an increase in trapezius muscle activity, while performing a natural work task. Twelve participants, ranging in age from 21 to 32years, performed a computer-mouse work task during free gaze conditions. A moving visual target was tracked with a computer mouse on a screen placed at two different distances from the eyes, 25cm and 50cm. Tracking performance, eye accommodation, and bilateral trapezius muscle activity were measured continuously. Ciliary-muscle contraction force was computed according to a formula which takes into account the age-dependent, non-linear relationship between the contraction force of the ciliary muscle and the produced level of eye accommodation. Generalized estimating equations analyses were performed. On the dominant hand side and for the nearest screen distance, there was a significant effect of ciliary-muscle contraction force on the trapezius muscle activity (p<0.001). No other effects were significant (p>0.05). The results support the hypothesis that high visual demands, during computer mouse work, increase ciliary muscle contraction force and contribute to a raise of the sustained level of trapezius muscle activity. The current study specifically clarifies the validity of the relationship between ciliary-muscle contraction force and trapezius muscle activity and demonstrates that this relationship is not due to a general personality trait. We conclude that a high level of ciliary muscle contraction force can contribute to a development of musculoskeletal complaints in the neck-shoulder area.

  • 83.
    Eiken, Ola
    Karolinska Institutet.
    Effects of increased muscle perfusion pressure on responses to dynamic leg exercise in man1988Inngår i: European Journal of Applied Physiology and Occupational Physiology, ISSN 0301-5548, E-ISSN 1432-1025, Vol. 57, nr 6, s. 772-776Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ventilatory, cardiovascular and metabolic functions and work performance were studied in men performing incremental-load dynamic leg exercise until exhaustion. Part I: Responses to supine exercise were investigated in 8 subjects during exposure of the lower body to subatmospheric pressure at -6.67 kPa (-50 mm Hg) (Lower Body Negative Pressure, LBNP). Due to curtailment of stroke volume, cardiac output was reduced by LBNP over a wide range of work intensities, including heavy loads: ventilation, oxygen uptake and blood lactate concentrations increased with work load, but at lower rates than in the control condition. Part II: In 9 subjects, work performance was compared in three conditions: supine exercise with and without LBNP, and upright exercise. Performance in supine exercise was enhanced by LBNP, and was further improved in upright exercise. In supine exercise, the LBNP-induced reduction in blood lactate and enhancement of work performance are attributed to a more efficient muscle blood flow resulting from increased local perfusion pressure. This strongly suggests that the primary limitation of work performance was set by the peripheral circulation in working muscles rather than by cardiac performance. A similar mechanism may, in part, explain why work performance in dynamic leg exercise was greater in the upright than in the supine posture. It is also concluded that supine leg exercise during LBNP is a useful model of upright exercise, with regard to the central circulation and the circulation in working muscles.

  • 84.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Militär verksamhet på höga höjder2011Rapport (Annet vitenskapelig)
  • 85.
    Eiken, Ola
    Karolinska Institutet.
    Responses to changed perfusion pressure in working muscles--factors to be considered in exercise testing in space flights?1989Inngår i: The Physiologist, ISSN 0031-9376, E-ISSN 1522-1202, Vol. 32, nr 1 Suppl, s. S12-15Artikkel i tidsskrift (Fagfellevurdert)
  • 86.
    Eiken, Ola
    Karolinska Institutet.
    Responses to dynamic leg exercise in man as influenced by changes in muscle perfusion pressure1987Inngår i: Acta Physiologica Scandinavica Supplementum, ISSN 0302-2994, Vol. 566, s. 1-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influences of induced alterations in muscle perfusion pressure on the physiological responses to rhythmic exercise in man were investigated. The experiments were carried out in healthy subjects performing leg exercise on a cycle ergometer at light to exhaustive work intensities. Increased muscle perfusion pressure was brought about by exposing the working legs of the supine subject to a subatmospheric pressure of -50 mm Hg (Lower Body Negative Pressure, LBNP), decreased perfusion pressure by instead applying a supraatmospheric pressure of 50 mm Hg (Leg Positive Pressure, LPP). In this way, the perfusion pressure in dynamically exercising large muscle groups could be altered in a controlled fashion. The influences of such manipulation of the perfusion pressure on the physiological adjustments to incremental-load exercise were studied and analysed. The main results and conclusions were as follows: (1) Exercise-induced increases in cardiac output were attenuated by LBNP, an effect caused by curtailment of stroke volume secondary to suction-induced sequestration of blood volume in capacitance vessels not affected by the action of the leg muscle pump. This situation resembles that of dynamic leg exercise in the upright body position. Thus, supine exercise with LBNP at -50 mm Hg seems to be a valid model of upright leg exercise, not only in that it increases perfusion pressure in working muscles but also by causing similar changes in the central circulation as a shift from supine to upright leg exercise. (2) Exercise-induced increases in systolic arterial pressure were markedly exaggerated by LPP, an effect attributable to increased exercise responses in both cardiac output and total peripheral resistance. The exaggerated pressor response supports the notion of a muscle chemoreflex drive in response to flow-restricted exercise tending to reduce the existing flow error. (3) Exercise-induced increases in O2 uptake and blood lactate concentration were both attenuated by LBNP and exaggerated by LPP. The changes in blood lactate levels are attributable to perfusion-pressure dependent variations in muscle blood flow, resulting in opposite changes in the share contributed by anaerobic metabolism to the energy release. Possible explanations for the fact that impaired muscle perfusion was associated with increased O2 uptake at given external work loads are discussed. (4) Exercise-induced responses of the pulmonary ventilation were attenuated by LBNP and markedly exaggerated by LPP.(ABSTRACT TRUNCATED AT 400 WORDS)

  • 87.
    Eiken, Ola
    Karolinska Inst, Swedish Def Res Agcy.
    Simulation of Lunar habitats2009Rapport (Annet vitenskapelig)
  • 88.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Bergsten, Eddie
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    G-protection mechanisms afforded by the anti-G suit abdominal bladder with and without pressure breathing.2011Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 82, nr 10, s. 972-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

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

  • 89.
    Eiken, Ola
    et al.
    Karolinska Institutet.
    Bjurstedt, H.
    Cardiac responses to lower body negative pressure and dynamic leg exercise1985Inngår i: European Journal of Applied Physiology and Occupational Physiology, ISSN 0301-5548, E-ISSN 1432-1025, Vol. 54, nr 5, s. 451-455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cardiac responses to dynamic leg exercise at 0, 50, and 100 W in the supine position were investigated with and without the lower portion of the body exposed to a pressure of -6.6 kPa (Lower Body Negative Pressure, LBNP). Resting values for heart rate (HR) and stroke volume (SV) were considerably higher and lower, respectively, during LBNP than in the control condition. At the transition from rest to the mildest exercise during LBNP SV showed a prompt increase by about 40%, but no significant change in the control condition. HR, which increased by 17 beats X min-1 in the control condition, showed during LBNP no change initially and subsequently a small but significant drop below its resting value. Steady-state values for HR at the various levels of exercise were not significantly affected by LBNP, whereas corresponding values for SV were considerably lowered, so that exercise values for cardiac output were about 3 l X min-1 less during LBNP than in the control condition. The reductions in SV and cardiac output indicate residual pooling of blood in intra- and extramuscular capacitance vessels of the legs. With a change from rest to exercise at 100 W during LBNP mean systolic ejection rate (MSER) increased by 67%, the relations between SV and MSER suggesting that ventricular performance was maintained by a combination of the Frank-Starling mechanism and enhanced contractile strength.

  • 90.
    Eiken, Ola
    et al.
    Karolinska Institutet.
    Bjurstedt, H.
    Cardiorespiratory responses to supine leg exercise during lower body negative pressure (LBNP)1987Inngår i: The Physiologist, ISSN 0031-9376, E-ISSN 1522-1202, Vol. 30, nr 1 Suppl, s. S70-71Artikkel i tidsskrift (Fagfellevurdert)
  • 91.
    Eiken, Ola
    et al.
    Karolinska Institutet.
    Bjurstedt, H.
    Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles1987Inngår i: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 131, nr 3, s. 339-345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra-atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O2 at a given work load was markedly higher in the LPP than in the control condition, while exercise-induced decreases in end-tidal PCO2 were considerably exaggerated by LPP. The augmented pressor response during flow-restricted exercise, together with the strong ventilatory response which was out of proportion to overall O2 uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working muscles.

  • 92.
    Eiken, Ola
    et al.
    Simon Fraser University.
    Convertino, V. A.
    Doerr, D. F.
    Dudley, G. A.
    Morariu, G.
    Mekjavic, I. B.
    Characteristics of the carotid baroreflex in man during normal and flow-restricted exercise1992Inngår i: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 144, nr 3, s. 325-331Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Eight subjects were studied in the supine position at rest, during normal dynamic leg exercise (control exercise) and with blood-flow restriction in the working legs (flow-restricted exercise). Graded muscle blood-flow restriction was accomplished by applying a supra-atmospheric pressure of 50 mmHg to the working legs. During incremental-load exercise, flow restriction reduced exercise performance and peak heart rate by 36% and 13%, respectively. The function of the cardiac branch of the carotid baroreflex was studied over its full operational range, at rest and during constant-load control and flow-restricted exercise, by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Heart rate and arterial pressure were higher during flow-restricted than control exercise, indicating that the flow restriction activated the muscle chemoreflex. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) was accompanied by increasing R-R intervals in all conditions. The set point (point of baseline carotid transmural pressure and R-R interval) coincided with the midportion of the pressure-response curve at rest and with the threshold point of the curve during exercise. The maximal rate of change in relative R-R intervals and the corresponding carotid transmural pressure range were higher during control exercise than at rest and highest during flow-restricted exercise, indicating that exercise and especially flow-restricted exercise increased carotid baroflex sensitivity, and shifted the carotid baroreflex optimal buffering range to higher pressures. The results suggest that the carotid baroflex attenuates exercise heart rate increases mediated by the muscle chemoreflex and/or by central command.

  • 93.
    Eiken, Ola
    et al.
    Simon Fraser University.
    Convertino, V.A.
    Doerr, D.F.
    Dudley, G.A.
    Morariu, G.
    Mekjavic, I.B.
    Interaction of the carotid baroreflex, the muscle chemoreflex and the cardiopulmonary baroreflex in man during exercise1991Inngår i: The Physiologist, ISSN 0031-9376, E-ISSN 1522-1202, Vol. 34, nr 1 Suppl, s. S118-120Artikkel i tidsskrift (Fagfellevurdert)
  • 94.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Danielsson, Ulf
    Hallberg, M.
    Mekjavic, I.
    Kounalakis, S.N.
    Energiomsättning vid simulerad patrullering i mörker2010Rapport (Annet vitenskapelig)
  • 95.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Danielsson, Ulf
    Hallberg, M
    Mekjavic, IB
    Babic, J
    Kounalakis, S
    Energy expenditure during simulated patrol in darkness2011Konferansepaper (Fagfellevurdert)
  • 96.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Signs and symptoms during supra-tolerance +Gz exposures, with reference to G-garment failure.2013Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 84, nr 3, s. 196-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 97.
    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)
  • 98.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Danielsson, Ulf
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Zavec, D.
    Kounalakis, S.N.
    Mekjavic, I.
    Termisk belastning hos soldater som bär svensk stridsutrustning2010Rapport (Annet vitenskapelig)
  • 99.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Kölegård, Roger
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Zavec, D.
    Ciuha, U.
    Mekjavic, I.
    Termisk belastning hos markstridssoldater vid patrullering i ökenklimat: effekter av två olika ballistiska kroppsskydd samt av två olika strategier för nedkylning2011Rapport (Annet vitenskapelig)
  • 100.
    Eiken, Ola
    et al.
    Karolinska Institutet.
    Hesser, C.M.
    Lind, F.
    Thorsson, A.
    Tesch, P.A.
    Human skeletal muscle function and metabolism during intense exercise at high O2 and N2 pressures1987Inngår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 63, nr 2, s. 571-575Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The maximal contractile force (peak torque) of the quadriceps femoris was studied during 60 repeated unilateral dynamic knee extensions in nine subjects under three different conditions, viz., during air breathing at normal (1 ATA) and raised (6 ATA) ambient pressures and during O2 breathing at 1.3 ATA. In six subjects the electromyographic (EMG) activity of the working muscle was recorded. Muscle biopsies were obtained from the vastus lateralis before, immediately after, and 1 min after exercise. Tissue specimens were subsequently assayed for various muscle metabolites. Peak torque, as an average of the 60 knee extensions, was higher (P less than 0.05) at 1.3 ATA than at 6 or 1 ATA. Peak torque of the exercising muscle declined more rapidly at 1 ATA than at 1.3 ATA, differing in the final 24 contractions by 14%. At 6 ATA peak torque of the initial 12 contractions was 6% lower (P less than 0.05) than at 1 ATA but equaled 1-ATA values in the latter third of the exercise bout. Although the EMG activity at 1 ATA increased relative to that at 6 ATA as exercise proceeded, the rate of force decline was greater at 1 ATA. Despite greater total work produced at 1.3 ATA than at 1 ATA, the metabolic response to exercise was not substantially altered at increased O2 pressure. However, the restitution rate of energy-rich phosphagens and the elimination of lactate during recovery were greater (P less than 0.05) at 1.3 ATA. These results suggest that hyperoxia may enhance the rate of energy release, whereas high N2 pressure and/or high hydrostatic pressure seem to interfere with neuromuscular activity.

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