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  • 1. Blogg, S. Lesley
    et al.
    Gennser, Mikael
    Swedish Defence Research Agency.
    Cerebral blood flow velocity and psychomotor performance during acute hypoxia2006Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 77, nr 2, s. 107-113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: The physiological effects of hypoxic environments can help determine safe limits for workers where cognitive and motor performance is important. We investigated the effects of a PIO2 of 15 kPa and 10 kPa on medial cerebral artery blood flow velocity (CBFV) and psychomotor performance.

    METHODS: Over 3 sessions, each involving 3 separate test batteries, 13 subjects breathed either 21 kPa PIO2 (control), 15 kPa PIO2, or 10 kPa PIO2. The tests measured reaction time, spatial orientation, voluntary repetitive movement, and fine manipulation. CBFV, PETCO2, PETO2, Sa02, and BP were recorded throughout.

    RESULTS: ANOVA analysis showed that 15 kPa PIO2 did not significantly change psychomotor test performance. The mean number of incorrect responses in the reaction time test significantly increased to 5.6 (SD - 4.0) while breathing 10 kPa PIO2, as did the mean number of errors (7.7 +/- 5.0) in the fine manipulation test. Only 10 kPa PIO2 affected CBFV, causing a significant increase in flow from 50 +/- 6.5 cm x s(-1) to 55 +/- 10.3 cm x s(-1). CBFV significantly increased during three psychomotor tests while breathing air; however, it did not increase further during psychomotor testing in hypoxia.

    DISCUSSION: A PIo2 of 15 kPa did not affect subject performance, and should not cause operational risk. At 10 kPa PIO2, accuracy and vigilance were slightly affected; however, the reduction in oxygenation was not great enough to cause major decrements. CBFV was not a good indicator of mental stress during hypoxia.

  • 2. 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.

  • 3.
    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.

  • 4.
    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.

  • 5.
    Eiken, Ola
    et al.
    Swedish Defence Research Agency.
    Kölegärd, Roger
    Swedish Defence Research Agency.
    Bergsten, Eddie
    Swedish Defence Research Agency.
    Grönkvist, Mikael
    Swedish Defence Research Agency.
    G protection: interaction of straining maneuvers and positive pressure breathing2007Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 78, nr 4, s. 392-398Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: G protection in the 39 Gripen aircraft is provided by a full coverage anti-G suit, a pressure-breathing system, and anti-G straining maneuvers (AGSM). The purpose was to study (1) the interaction of pressure breathing and AGSM while wearing an anti-G suit; and (2) the G-protective properties of the anti-G suit alone and in combination with the pressure-breathing system.

    METHODS: During rapid onset rate G-time profiles (< or =9 G), 10 subjects were investigated in 5 conditions: (I) sitting relaxed, without any G-protective garment; (II) sitting relaxed and wearing an anti-G suit; (III) sitting relaxed, wearing an anti-G suit, and pressure breathing; IV) wearing an anti-G suit and performing AGSM; and V) wearing an anti-G suit, pressure breathing, and performing AGSM. In supplementary experiments (n=9), the share of the anti-G suit protection afforded by the abdominal bladder was investigated.

    RESULTS: G tolerance was 3.4 Gz (range: 2.8-4.3) in condition I, > or = 6.5 Gz (4.5-9.0) in II, > or = 8.0 Gz (6.5-9.0) in III, > or = 8.9 Gz (8.5-9.0) in IV and > or = 9.0 Gz (8.5-9.0) in V. In the supplementary experiments, the anti-G suit afforded a 2.8-G protection, a third of which was contributed by the abdominal bladder. In the relaxed state, pressure applied to the airways was transmitted undistorted to the intrathoracic space. During AGSM, intrathoracic pressure rose to 10-14 kPa, regardless of whether AGSM was performed with or without pressure breathing.

    DISCUSSION AND CONCLUSIONS: The anti-G suit and the pressure breathing system provide G protection of > or = 4.6 G, of which the anti-G suit contributes about 3.0 G. The C-protective properties of the anti-G suit and those of pressure breathing appears to be additive, whereas the G protection afforded by pressure breathing does not add to that provided by AGSM.

  • 6.
    Eiken, Ola
    et al.
    Swedish Defence Research Agency.
    Kölegård, Roger
    Swedish Defence Research Agency.
    Relationship between arm pain and distension of arteries and veins caused by elevation of transmural pressure in local vascular segments2001Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 72, nr 5, s. 427-431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Exposure to high +Gz forces may induce arm pain, which has been hypothesized to be caused by pressure-induced overdistension of local blood vessels. The purpose of the present investigation was to study the pressure-distension relation of veins and arteries in the human arm and the relation between arm pain and distension of local vessels.

    METHODS: Increased distending pressures (DP) in the vasculature of the arm were accomplished by placing the subject (n = 8) in a pressure chamber with one arm positioned through a port in the chamber door, and increasing chamber pressure to +180 mm Hg in a stepwise manner. Diameters in the brachial artery and in the brachial, radial and cephalic veins were measured by ultrasonography. Changes in forearm volume were estimated from measurement of tissue impedance. Perceived pain was rated using a 10-point scale.

    RESULTS: Arm pain increased with pressure to a maximum rating of 8.5 (= median; range: 4-10). Increasing DP from 30 to 180 mm Hg resulted in a steady increase (p < 0.05) in venous diameter which varied from 12 +/- 8% (mean +/- SD) in the brachial vein to 23 +/- 14% in the radial vein. Inthe brachial vein diameter increases were most pronounced at the sites of the venous valves. Arterial diameter was unchanged up to a DP of about 200 mm Hg (calculated as diastolic arterial pressure + applied chamber pressure), but then increased by 32 +/- 9% (p < 0.001). Forearm impedance dropped with increasing pressure (delta = 23 +/- 5%; p < 0.01); the rate of change was non-linear with a faster change at the highest DP which may indicate pressure distension of precapillary resistance vessels.

    CONCLUSIONS: Elevation of pressure in arm vessels to levels that may occur in pilots flying high-performance aircraft results in distension not only of veins but also of arteries and probably of smaller precapillary vessels. Therefore, and because these changes coincide with the development of severe arm pain, local overdistension of blood vessels remains a plausible cause of G-induced arm pain.

  • 7.
    Eiken, Ola
    et al.
    Swedish Defence Research Agency.
    Kölegård, Roger
    Swedish Defence Research Agency.
    Lindborg, B.
    Swedish Defence Research Agency.
    Mekjavic, I. B.
    Linder, J.
    The effect of straining maneuvers on G-protection during assisted pressure breathing2003Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 74, nr 8, s. 822-826Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: Pilots flying high-performance aircraft increase their acceleration tolerance by using straining maneuvers and anti-G suits. Recently, assisted positive pressure breathing has been added in some aircraft systems. This study assessed the effect of anti-G straining maneuvers on the G-protective properties of one such system, the AGE-39 anti-G ensemble used in the Swedish JAS 39 Gripen aircraft.

    METHODS: Ten subjects were studied in a centrifuge using each of the following: 1) the AGE-39 in combination with anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); 2) the AGE-39 in combination with AGSM only during the initial part of each high-G exposure (reduced maneuver; RM). G-tolerance was established during exposures to rapid onset rate (ROR) G profiles with plateau levels ranging from 6.5 to 9.0 G.

    RESULTS: Mean G-tolerance was > or = 8.8 G (range: 8.5 to > or = 9.0 G) in the RM condition and > or = 9.0 G in all subjects in the FM condition. Mean arterial pressure was 30-50 mm Hg higher (p < 0.001) in the FM than in the RM condition at any given ROR G-load.

    CONCLUSIONS: AGE-39 in combination with a brief period of straining provide efficient G-protection as illustrated by the finding that all subjects could tolerate 8.5 G while performing AGSM during the initial part of the high-G exposures. However, at 9.0 G, 40% of the subjects had to perform AGSM throughout the duration of the G-exposure. That arterial pressure was only 30-50 mm Hg higher in the FM than RM condition suggests that in the presence of straining maneuvers, pressure breathing makes only a minute contribution to the arterial-pressure response.

  • 8.
    Eiken, Ola
    et al.
    Swedish Defence Research Agency.
    Kölegård, Roger
    Swedish Defence Research Agency.
    Lindborg, Bertil
    Aldman, M.
    Karlmar, K. E.
    Linder, J.
    A new hydrostatic anti-G suit vs. a pneumatic anti-G system: preliminary comparison.2002Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 73, nr 7, s. 703-708Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    HYPOTHESIS: A newly developed hydrostatic anti-G suit is now commercially available. The suit is said to offer a high level of protection against +Gz acceleration. However, past experience shows that it is difficult to produce a hydrostatic suit with effective high-G protection. Careful testing is, therefore, needed to verify its efficacy.

    METHODS: The G-protective properties of the hydrostatic anti-G suit (Libelle; L) were compared with those of a pneumatic anti-G ensemble (AGE-39) used in the Swedish JAS 39 Cripen aircraft. Three pilots were studied during vertical (+Gz) acceleration in a centrifuge using the following: 1) the L-suit with varied straining maneuvers; 2) the AGE-39 in combination with full anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); and 3) the AGE-39 in combination with AGSM during the initial part of each high-G exposure (reduced maneuver; RM). G-intensity tolerance was established during exposures to rapid onset rate (ROR) profiles with G-plateau levels ranging from +6.0 to +9.0 Gz. G-endurance was studied during simulated aerial combat maneuvers (SACM) consisting of 10 cycles of 5.5 to 7.5 G.

    RESULTS: All three pilots tolerated 9.0 G with the pneumatic system both in the RM and FM conditions; their tolerances averaged 6.3 G (range 6.0 to 7.0 G) for the L suit. Thus, during the ROR exposures only the 6.0 G profile was completed by all subjects in all three conditions. At this G-load both muscle straining (as indicated by electromyographic activity in thigh and abdomen) and heart rate were higher in the L than in the RM condition. Mean arterial pressure at eye level was higher in the FM than in the L and RM conditions. Only one subject was able to complete the SACM profile in the L condition. In the RM condition all subjects completed the SACM profile and in the FM condition two subjects completed the SACM.

    CONCLUSIONS: Whether the AGE-39 was used in combination with maximal AGSM throughout the duration of each high-G exposure or with AGSM only during the initial part of the high-G exposure, G-intensity tolerance was 9.0 G. While wearing the L-suit, G-tolerance was 6.3 G. Thus, under the conditions tested, the G-protection afforded by the L-suit is not adequate for use in a 9-G aircraft.

  • 9.
    Eiken, Ola
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Mekjavic, Igor B.
    Kolegard, Roger
    Local Intravascular Pressure Habituation in Relation to G-Induced Arm Pain2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 7, s. 667-672Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 10.
    Eiken, Ola
    et al.
    Swedish Defence Research Agency.
    Tipton, Michael J.
    Kölegard, Roger
    Swedish Defence Research Agency.
    Lindborg, Bertil
    Swedish Defence Research Agency.
    Mekjavic, Igor B.
    Motion sickness decreases arterial pressure and therefore acceleration tolerance2005Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 76, nr 6, s. 541-546Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Motion sickness is a common aeromedical problem that may occur in pilots exposed to increased gravitoinertial load in the head-to-foot direction (+Gz). Since motion sickness may affect autonomic nervous functions including cardiovascular control, it was hypothesized that it might interfere with cardiovascular responses to high +Gz, thereby decreasing G tolerance.

    METHODS: G tolerance and cardiovascular responses to increased G load were studied in nine subjects in a centrifuge environment under two conditions. In the motion sickness condition, the subject was exposed to a motion sickness provocation (MSP) comprising repeated rapid changes in G load in combination with a regimen of head movements. In the control condition the subject was exposed to similar cumulative G-time stress, but without the MSP. Mean arterial pressure (MAP) was measured. An index of peripheral vascular resistance was achieved by measuring the difference in skin temperature between the forearm and fingertip (deltaT(forearm-fingertip)).

    RESULTS: MSP decreased gradual-onset rate G tolerance from 5.1 +/- 1.0 G (mean +/- SD) to 4.6 +/- 0.9 G. There was no change in gradual-onset rate G tolerance in the control condition. Rapid-onset rate G tolerance was lower in the motion sickness (2.9 +/- 0.5 G) than in the control (3.4 +/- 0.3 G) condition. MSP reduced MAP by 11 mmHg and deltaT(forearm-fingertip) by 4.2 +/- 4.1 degrees C. In the control condition MAP and deltaT(forearm-fingertip) were unaffected.

    CONCLUSIONS: Motion sickness may reduce the arterial pressure response to the extent that the capacity of an individual to withstand increased G loads in the head-to-foot direction is significantly diminished.

  • 11.
    Eriksson, Lars
    et al.
    Swedish Defence Research Agency.
    von Hofsten, Claes
    Swedish Defence Research Agency.
    Tribukait, Arne
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Andersson, Peter
    Swedish Defence Research Agency.
    Hedström, Johan
    Swedish Defence Research Agency.
    Visual flow scene effects on the somatogravic illusion in non-pilots2008Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 79, nr 9, s. 860-866Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: The somatogravic illusion (SGI) is easily broken when the pilot looks out the aircraft window during daylight flight, but it has proven difficult to break or even reduce the SGI in non-pilots in simulators using synthetic visual scenes. Could visual-flow scenes that accommodate compensatory head movement reduce the SGI in naive subjects?

    METHODS: We investigated the effects of visual cues on the SGI induced by a human centrifuge. The subject was equipped with a head-tracked, head-mounted display (HMD) and was seated in a fixed gondola facing the center of rotation. The angular velocity of the centrifuge increased from near zero until a 0.57-G centripetal acceleration was attained, resulting in a tilt of the gravitoinertial force vector, corresponding to a pitch-up of 30 degrees. The subject indicated perceived horizontal continuously by means of a manual adjustable-plate system. We performed two experiments with within-subjects designs. In Experiment 1, the subjects (N = 13) viewed a darkened HMD and a presentation of simple visual flow beneath a horizon. In Experiment 2, the subjects (N = 12) viewed a darkened HMD, a scene including symbology superimposed on simple visual flow and horizon, and this scene without visual flow (static).

    RESULTS: In Experiment 1, visual flow reduced the SGI from 12.4 +/- 1.4 degrees (mean +/- SE) to 8.7 +/- 1.5 degrees. In Experiment 2, the SGI was smaller in the visual flow condition (9.3 +/- 1.8 degrees) than with the static scene (13.3 +/- 1.7 degrees) and without HMD presentation (14.5 +/- 2.3 degrees), respectively.

    CONCLUSION: It is possible to reduce the SGI in non-pilots by means of a synthetic horizon and simple visual flow conveyed by a head-tracked HMD. This may reflect the power of a more intuitive display for reducing the SGI.

  • 12.
    Frånberg, Oskar
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Loncar, Mario
    Larsson, Ake
    Örnhagen, Hans
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    A Metabolic Simulator for Unmanned Testing of Breathing Apparatuses in Hyperbaric Conditions2014Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 85, nr 11, s. 1139-1144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 13.
    Gennser, Mikael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Blogg, Samantha L.
    Venous Gas Emboli in Goats After Simulated Submarine Escape from 290 msw Breathing Air or Hyperoxic Gas2009Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 80, nr 11, s. 927-932Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    GENNSER M, BLOGG. SL. Venous gas emboli in goats after simulated submarine escape from 290 msw breathing air or hyperoxic gas. Aviat Space Environ Med 2009; 80:927-32. Introduction: Escape from a disabled submarine has many inherent risks. Including the development of venous gas emboli (VGE) Breathing hyperoxic gas during rapid ascent from 2500 kPa (240 msw) reduces VGE, we Investigated whether it would also be beneficial during all escape from 3000 kPa (290 msw), thought to be at the limit of escape from a sunk sub Methods: Adult castrated male or female goats (45-85 kg, N = 35) Underwent dry chamber compression to 3000 kPa in 28 s, then decompressed at a rate of 2 75 m . s(-1) while breathing either air or hyperoxic gas (60/40%. O-2/N-2) Postsurfacing, precordial Doppler measurements were made using the Kisman Masurel (KM) scoring system, the animals were observed for signs of decompression illness (DCI) and/or oxygen toxicity Results: Six animals in the air group (N = 19) and two in the hyperoxic group (N = 10) suffered from severe I)pulmonary barotrauma on surfacing and were euthanized No cases of DO arose later than 5 min postsurfacing. Oxygen toxicity was not observed Although initial bobble Scores (median KM score 4) were the same in both groups, the time taken for the median KM score to reach 3 or less was significantly faster in the hyperoxic group (20 min vs 120 min) Disappearance of VGE was faster in the hyperoxic group Conclusion: Breathing hyperoxic gas during escape from 3000 kPa reduces the overall time. With circulating VGE and, despite exposure to a maximum inspired partial pressure, of oxygen of 1 8 MPa, symptoms of oxygen toxicity were not observed

  • 14.
    Gennser, Mikael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Blogg, S.L.
    Jurd, K.
    Pre-dive exercise and post-dive evolution of gas emboli2011Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448Artikkel i tidsskrift (Annet vitenskapelig)
  • 15.
    Gennser, Mikael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Jurd, Karen M.
    Blogg, S. Lesley
    Pre-Dive Exercise and Post-Dive Evolution of Venous Gas Emboli2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 1, s. 30-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Recent studies have indicated that exercise before diving significantly reduces the number of circulating bubbles and the risk of decompression sickness. However, the most effective time delay between exercise and dive is not clear; the present aim was to resolve this. Methods: In a hyperbaric chamber, 10 men were compressed to 18 m for 100 min, then decompressed as per Royal Navy Table 11. Each subject performed three dives: a control dive and two after exercise performed either 24 h or 2 h before diving. Exercise consisted of 40 min submaximal work on a cycle ergometer. Venous gas emboli (VGE) were evaluated using precordial Doppler ultrasound immediately on surfacing, with measurements made at 5-min intervals for 30 min, and at 15-min intervals for at least 2.5 h total using the Kisman Masurel (KM) scale. Results: Exercise either 24 or 2 h prior to a dive did not reduce the median number of circulating VGE (median maximum KM grade: control, 2+; for both exercise dives, 3). Bubbles disappeared from the circulation faster after the control dive than the exercise dives. Time to median KM Doppler scores of zero were: control:120 min; 2-h group: 225 min; 24-h group: 165 min. Conclusion: Cycling exercise prior to diving did not reduce the number of circulating VGE in comparison to control, in contrast to recent studies. A number of factors may be responsible for these findings, including type of exercise performed, wet diving experience, and disparity in Doppler measurement techniques.

  • 16.
    Grönkvist, Mikael
    et al.
    Swedish Defence Research Agency.
    Bergsten, Eddie
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Lung mechanics and transpulmonary pressures during unassisted pressure breathing at high Gz loads2008Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 79, nr 11, s. 1041-1046Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Positive pressure breathing (PPB) is commonly used in modern fighter aircraft as part of the anti-G ensemble. PPB is combined with a chest counterpressure bladder which is pressurized to the same magnitude as the breathing mask (balanced PPB). The chest counterpressure is expected to reduce the expiratory work of breathing, reduce the risk for lung rupture, and increase G tolerance. In a previous study we did not find any effect from chest counterpressure on G tolerance or G endurance. The aim of this study was to investigate the effects of chest counterpressure on the work of breathing and the risk for lung rupture.

    METHODS: Eight male test subjects were exposed to 20-s periods of PPB at +1.0, 5.0, 6.0, 7.0, and 8.0 Gz. Each Gz level was accomplished twice, with and without pressurization of the chest bladder. Inspiratory and expiratory flows were measured and esophageal pressures were measured in the lower and upper third of the thorax. Subsequently, work and power of breathing and apical transpulmonary pressure were estimated.

    RESULTS: The apical transpulmonary pressure was slightly larger without than with chest counterpressure at 1.0 Gz, while chest counterpressure did not affect apical transpulmonary pressure at increased Gz load. Nor did the chest counterpressure affect work or power of breathing at any Gz load.

    CONCLUSION: Inflation of the chest bladder does not seem to have any effects on work or power of breathing or risk for lung rupture during PPB at high Gz loads.

  • 17.
    Grönkvist, Mikael
    et al.
    Swedish Defence Research Agency.
    Bergsten, Eddie
    Swedish Defence Research Agency.
    Kölegård, Roger
    Swedish Defence Research Agency.
    Linder, Jan
    Eiken, Ola
    Swedish Defence Research Agency.
    G tolerance and pulmonary effects of removing chest counterpressure during pressure breathing2005Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 76, nr 9, s. 833-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: In agile fighter aircraft positive pressure breathing is commonly used as part of the anti-G ensemble. To optimize G protection and prevent over-distention of the lungs, increased airway pressure is balanced by applying a counterpressure to the chest. The aim was to investigate the efficacy of chest counterpressure.

    METHODS: Three series of experiments were performed using the anti-G ensemble of the 39 Gripen aircraft (AGE-39) and exposing the subjects to 20-s G time profiles; in the first (n = 12) up to +8.0 Gz, in the second (n = 9) up to + 9.0 Gz, and also to simulated aerial combat maneuvers (SACM). Central and peripheral vision, arterial and airway pressures, pressure in the lower portion of the esophagus, and chest wall distension were measured. In the third series, six subjects were exposed to up to +7.0 Gz and esophageal pressure was measured in the upper thorax. In all series, two conditions were compared: with and without pressurized chest bladder.

    RESULTS: During the 20-s profiles arterial and esophageal pressures, chest wall distension, and visual impairment were similar with and without pressurized chest bladder. Upper esophageal pressure was slightly higher by 10-24% with than without chest bladder (p = 0.03). During SACM, time to exhaustion and the level of perceived exertion were similar with and without pressurized chest bladder.

    SUMMARY: The results suggest that the chest counterpressure can be removed from the AGE-39 without diminishing G tolerance or G endurance or significantly increasing the risk of lung parenchyma disruption.

  • 18. Gustafsson, C
    et al.
    Gennser, Mikael
    Swedish Defence Research Agency.
    Örnhagen, H
    Derefeldt, G
    Effects of normobaric hypoxic confinement on visual and motor performance1997Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 68, nr 11, s. 985-992Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: The use of reduced oxygen levels has been suggested for fire prevention in closed spaces, such as submarines. However, if humans are to work and live in environments with reduced oxygen levels, the effect of hypoxia on human performance must be further assessed.

    METHODS: In 3, 11- to 14-d confinements a total of 22 subjects were exposed to different levels of normobaric hypoxia (13, 14, and 15 kPa O2), for up to 10 d, with intervening periods of normoxia. In each experiment eight subjects were divided into two teams, working in 6-h shifts around the clock. Subjects performed tests of spatial orientation, visual reaction time, parallel processing and motor skills. Performance tests and questionnaires were administered once or twice in every 24-h period.

    RESULTS: All of the subjects appeared to tolerate the acute reduction in oxygen partial pressure well. In many of the tests performance improved with time as a result of learning, despite reductions in the oxygen level. No reduction in performance or decrease in rate of learning was observed at any of the oxygen levels tested.

    CONCLUSIONS: Oxygen levels down to 14 kPa appear not to impair visual and motor performance during rest.

  • 19. Lindholm, Peter
    et al.
    Blogg, S. Lesley
    Gennser, Mikael
    Swedish Defence Research Agency.
    Pulse oximetry to detect hypoxemia during apnea: comparison of finger and ear probes2007Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 78, nr 8, s. 770-773Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    INTRODUCTION: When investigating apnea, for example in diving or altitude studies, hypoxemia is a variable that must be monitored to reduce the risk of hypoxic syncope. Pulse oximetry is a simple technique that measures arterial oxygen saturation (SpO2). As apnea induces a peripheral vasoconstriction, we hypothesized that it would be better to measure hypoxia using more centrally placed ear lobe oximetry probes rather than peripheral finger probes.

    METHODS: Seven men were studied, ages 18-35. Two pulse oximeters were used, a Satlite Trans (Ox-1) and Ohmeda Biox (Ox-2), both with ear and finger probes. Subjects carried out a sub-maximal breath hold for 60 s while performing dynamic leg exercise on a cycle ergometer at 50 W. Subjects performed the maneuver six times in total, in a crossover design.

    RESULTS: The Ox-1 finger probe showed 6.0 +/- 3.7% higher values than the ear-lobe probe at their respective nadirs. The Ox-2 probes differed in the same manner by 6.5 +/- 4.2%. The average delay between the nadir shown by the ear and finger probes was 15 s (+/- 3.5). When the ear-probes were at their nadir (SpO2 78 +/- 3.5%), the finger probes had considerably higher SpO2 levels (94.6 +/- 3.5%).

    DISCUSSION: Apneic induced hypoxemia was monitored poorly by finger probe pulse oximetry. The delay in response may jeopardize safety, for example in breath-hold diving studies. Hypoxemia does not seem to be accurately reflected by finger measurements in situations where peripheral vasoconstriction may occur.

  • 20. Mekjavic, I.
    et al.
    Keramidas, Michail E.
    Kounalakis, S.
    Pisot, R.
    DiPrampero, P.
    Narici, M.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Heat Production and Heat Loss Responses to Cold Water Immersion After 35 Days Horizontal Bed Rest2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 5, s. 472-476Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introduction: Bed rest is a terrestrial experimental analogue of unloading experienced during exposure to microgravity. Such unloading causes atrophy predominantly of the postural muscles, especially those of the lower limbs. Methods: We tested the hypothesis that 35 cl horizontal bed rest alters thermoregulatory responses of subjects (N = 10) immersed in 15 C water, particularly the heat produced by the shivering tremor of the skeletal muscles. Before and after bed rest we measured the thickness of the gastrocnemius medialis (GM), vastus lateralis (VL), tibialis anterior (TA), and biceps brachii (BB) muscles by ultrasonography. During the immersions, we monitored rectal and skin temperatures, heat flux, heart rate, and oxygen uptake. Results: After bed rest, muscle thickness decreased significantly by 12.2 +/- 8.8% and 8.0 +/- 9.1% in the GM and VL, respectively. No changes were observed in the TA and BB muscles. The 35-d bed rest caused a significant reduction in aerobic power, as reflected in maximal oxygen uptake. There were no significant differences in any of the observed thermoregulatory responses between the pre- and post-bed rest immersions. Conclusions: Cardiovascular and muscular deconditioning had no effect on the heat production and heat loss responses. Due to the significant reduction in the mass of the muscles in the lower limbs, concomitant with no change in heat production, we conclude that leg muscles do not play a significant role in shivering thermogenesis.

  • 21. Mekjavic, I.B.
    et al.
    Kounalakis, S.N.
    Keramidas, Michail E.
    Amon, M
    Debevec, T
    Simunic, B
    Pisot, R
    Eiken, Ola
    FOI, Swedish Defence Research Agency,Sweden.
    Evaluation of hypoxic training protocols2009Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 80, nr 3, s. 289-289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Acute exposure to high altitude impairs performance, both aerobic and psychomotor. Consequently preparation of personnel to be deployed to high attitude regions should incorporate a programme of altitude acclimatisation.  The aim of the present study was to evaluate the effect of several training programmes on sea level and altitude performance: Live low-Train High (LL-TH), Intermittent Hypoxic Training (IHT), Respiratory Muscle Training (RMT), and Sleep High-Train Low (SH-TL).

  • 22. Mekjavic, Igor B.
    et al.
    Debevec, Tadej
    Amon, Mojca
    Keramidas, Michail E.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi (Stängd 20130701).
    Kounalakis, Stylianos N.
    Intermittent Normobaric Hypoxic Exposures at Rest: Effects on Performance in Normoxia and Hypoxia2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 10, s. 942-950Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     Introduction: It has been speculated that short (similar to 1-h) exposures to intermittent normobaric hypoxia at rest can enhance subsequent exercise performance. Thus, the present study investigated the effect of daily resting intermittent hypoxic exposures (IHE) on peak aerobic capacity and performance under both normoxic and hypoxic conditions. Methods: Eighteen subjects were equally assigned to either a control (CON) or IHE group and performed a 4-wk moderate intensity cycling exercise training (1 h . d(-1), 5 d . wk(-1)). The IHE group additionally performed IHE (60 min) prior to exercise training. IHE consisted of seven cycles alternating between breathing a hypoxic gas mixture (5 min; FlO2 = 0.12-0.09) and room air (3 min; FlO2, = 0.21). Normoxic and hypoxic peak aerobic capacity ((V) over dotO(2peak)) and endurance performance were evaluated before (PRE), during (MID), upon completion (POST), and 10 d after (AFTER) the training period. Results: Similar improvements were observed in normoxic (V) over dotO(2peak) tests in both groups [IHE: Delta(POST-PRE) = +10%; CON: Delta(POST-PRE) = +14%], with no changes in the hypoxic condition. Both groups increased performance time in the normoxic constant power test only [IHE: Delta(POST-PRE) = +108%; CON: Delta(POST-PRE) = +114%], whereas only the IHE group retained this improvement in the AFTER test. Higher levels of minute ventilation were noted in the IHE compared to the CON group at the POST and AFTER tests. Conclusion: Based on the results of this study, the IHE does not seem to be beneficial for normoxic and hypoxic performance enhancement.

  • 23. Mekjavić, I. B.
    et al.
    Eiken, Ola
    Karolinska Institutet.
    Inhalation rewarming from hypothermia: an evaluation in -20 degrees C simulated field conditions1995Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 66, nr 5, s. 424-429Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study evaluates the efficacy of inhaling warm moist air as a method of rewarming from hypothermia in -20 degrees C field conditions. The method of inhalation rewarming is compared to two other methods of rewarming: a) passive rewarming; and b) passive rewarming, with a respiratory heat exchanger designed to minimize respiratory heat loss. Eight male subjects were rendered hypothermic by immersion in 15 degrees C water for 1 h. They were withdrawn from the tank earlier, in the event that their rectal temperature (Tre) decreased to 35 degrees C, or by 1.5 degrees C from the pre-immersion value. Upon completion of the immersion, they were placed in a well-insulated sleeping bag assembly and transferred to a cold room maintained at -20 degrees C for a 2 h rewarming period. They participated in 3 trials: Control-passive rewarming; Heat Treat-inhalation rewarming with the Heat Treat; HME-passive rewarming in conjunction with a respiratory heat and moisture exchanger (HME). During the rewarming period, inspired air temperature was -19.4 +/- 1.1 degrees C in the control trial. In the HME and Heat Treat trials subjects breathed via an oro-nasal mask. The inspired air temperature was +20.5 +/- 1.2 degrees C in the HME and +36.2 +/- 2.9 degrees C in the Heat Treat trial. The post-immersion drop in Tre was significant in all conditions. The reduction in the post-exposure drop in Tre observed with the Heat Treat may be attributed to the minimization of respiratory heat loss, since the magnitude of the reduction was similar to that observed with the HME. (ABSTRACT TRUNCATED AT 250 WORDS)

  • 24.
    Norrbrand, Lena
    et al.
    Karolinska Institutet, Department of Physiology and Phamacology.
    Tous-Fajardo, Julio
    Vargas, Roberto
    Tesch, Per A.
    Quadriceps muscle use in the flywheel and barbell squat2011Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 82, nr 1, s. 13-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Resistance exercise has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in Orbit. While space authorities have advocated the squat exercise should be prescribed, no exercise system suitable for in-flight use has been validated with regard to quadriceps muscle use. We compared muscle involvement in the terrestrial “gold standard” squat using free weights and a non-gravity dependent flywheel resistance exercise device aimed at use in space. Methods: Ten strength-trained men performed five sets of 10 repetitions using the Barbell Squat (BS; 10 repetition maximum) or Flywheel Squat (FS; each repetition maximal), respectively. Functional magnetic resonance imaging (MRI) and surface electromyography (EMG) techniques assessed quadriceps muscle use. Exercise-induced contrast shift of MR images was measured by means of transverse relaxation time (T2). EMG root mean square (RMS) was measured during concentric (CON) and eccentric (ECC) actions and normalized to EMG RMS determined during maximal voluntary contraction. Results: The quadriceps muscle group showed greater exercise-induced T2 increase following FS compared with BS. Among individual muscles, the rectus femoris displayed greater T2 increase with FS (+24±14%) than BS (+8±4%). Normalized quadriceps EMG showed no difference across exercise modes. Discussion: Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free weight resistance exercise. Data appears to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.

  • 25.
    Tribukait, Arne
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Bergsten, Eddie
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Variability in Perceived Tilt During a Roll Plane Canal-Otolith Conflict in a Gondola Centrifuge2013Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 84, nr 11, s. 1131-1139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: During a simulated coordinated turn in a gondola centrifuge, the perceived roll-tilt, quantified as the subjective visual horizontal (SVH), may differ tenfold between individuals. One aim of this study was to discern whether this variability reflects real individual characteristics or is due to noise or day-to-day variation. We also wanted to establish whether there are any habituation or learning effects of the centrifuge test. Methods: In nine nonpilots (NP) and nine student pilots (SP), with a flight experience of 150 h, the SVH was measured using an adjustable luminous line in darkness. At two test occasions (T1, T2) (interval 5-14 d) subjects underwent two runs (R1, R2; acceleration to 2 G in 10 s, gondola inclination 60 degrees, 5 min at 2 G, deceleration to 1 g in 10 s, interval between runs 5 min) in a centrifuge (r = 9.1 m). Initial and final SVH was determined for each individual run. Results: Acceleration of the centrifuge induced a tilt of the SVH. At T1R1, this SVH tilt was, in NP, initially 24 +/- 18 degrees and finally 8 +/- 10 degrees. The corresponding values for SP were 28 +/- 18 degrees and 31 +/- 33 degrees. The SVH tilt was slightly larger at R2 than at R1. There was no difference between T1 and T2. Reliability coefficients ranged between 0.86 and 0.98 for NP and between 0.78 and 0.99 for SR. Conclusion: The large interindividual variability combined with a very high reproducibility suggests the existence of persistent individual characteristics in the perception of complex vestibular stimuli. Habituation or learning effects of gondola centrifugation appears to be small.

  • 26.
    Tribukait, Arne
    et al.
    Swedish Defence Research Agency.
    Bergsten, Eddie
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Visual sensations of roll rotation during complex vestibular stimulation2008Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 79, nr 5, s. 479-487Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: In aviation, vestibular-induced spatial disorientation is a significant cause of accidents. Recreating flight-like vestibular stimuli in simulators might be a means for training pilots to respond adequately in disorienting situations. Due to the physical constraints of land-based simulators, the question arises whether a given illusion may be created in different ways. For instance, is it possible to induce sensations of tilt by rotary stimuli? The present study concerns the relationship between sensations of rotation and tilt during complex vestibular stimulation.

    METHODS: The visual sensation of roll rotation was quantified by means of a velocity-matching procedure. In a large gondola centrifuge eight subjects underwent four runs (2 G, 2 min) with different heading positions (forward, backward, centripetally, and centrifugally). The inclination of the gondola persistently corresponded with the vector sum of the Earth gravity force and the centrifugal force (60 degrees at 2 G). Thus, the semicircular canal stimulus in roll was combined in different ways with stimuli in yaw and pitch, as well as with an increasing or decreasing G vector.

    RESULTS: The magnitude of the responses was only dependent on the roll component of the stimulus. The gain, defined as the ratio between the response and the roll stimulus, was 7-10%. The responses decayed with a time constant ranging from 4 to 5.5 s.

    CONCLUSION: The visual sensation of roll rotation reflects the roll plane canal velocity stimulus independently of other stimulus components. This is in contrast to earlier findings on the sensation of changes in position (roll tilt).

  • 27.
    Tribukait, Arne
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Flight Experience and the Perception of Pitch Angular Displacements in a Gondola Centrifuge2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 5, s. 496-503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: It has been shown that flight experience may induce an adaptation of the vestibular system. The aim of the present work was to elucidate whether pilots, in comparison with non-pilots, have an increased responsiveness to angular displacement canal stimuli in the pitch plane during a conflict between the otolith organs and the semicircular canals. Methods: In a large swing-out gondola centrifuge, eight non-pilots, eight fighter pilots, and eight helicopter pilots underwent three runs (2 G, 5 min) heading forward, centripetally, and centrifugally. The direction of the gravitoinertial force was constant with respect to the subject. The visually perceived eye level (VPEL.) was measured in darkness by means of an adjustable luminous dot. Results: In the forward position the three groups produced similar results. After acceleration there was a sensation of backward tilt and an increasing depression of VPEL. This effect was smaller in the centripetal position and larger in the centrifugal position. The difference in VPEL between the opposite positions constitutes a measure of the ability to sense the pitch angular displacement canal stimulus related to the swing out of the gondola (600). This difference was most pronounced initially at the 2-G plateau (mean +/- SD): 13.5 +/- 12.9 degrees (non-pilots), 41.6 +/- 21.10 degrees (fighter pilots), and 19.5 +/- 14.0 degrees (helicopter pilots). There was no significant difference between non-pilots and helicopter pilots. Fighter pilots differed significantly from both non-pilots and helicopter pilots. Conclusion: Vestibular learning effects of flying may be revealed in a centrifuge. Fighter pilots had an increased ability, as compared to non-pilots and helicopter pilots, to perceive pitch angular displacements.

  • 28.
    Tribukait, Arne
    et al.
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Roll-tilt perception during gondola centrifugation: influence of steady-state acceleration (G) level.2006Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 77, nr 7, s. 695-703Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Spatial disorientation is an important problem in aviation. The significance of the C level for illusions elicited from the semicircular canals is not clear. The aim of the present investigation was to elucidate how a gravitoinertial force, acting in parallel with the subject's long (z) axis, may influence the magnitude and persistence of canal-induced tilts of the subjective visual horizontal (SVH) present after acceleration in a gondola centrifuge.

    METHODS: The SVH was measured by means of an adjustable luminous line in darkness. Two series of experiments were performed. In series 1, the SVH was measured in 13 subjects at 1.1 G, 1.7 G, and 2.5 G. In series 2, it was measured in 8 subjects at 2.5 G and 4.5 G.

    RESULTS: After acceleration of the centrifuge the SVH was tilted relative to the gravitoinertial horizontal. The direction of tilt was compensatory to the gondola inclination. In series 1 the initial SVH tilt was: 16.2 +/- 7.0 degrees (1.1 G), 24.2 +/- 10.2 degrees (1.7 G), and 27.1 +/- 13.9 degrees (2.5 G). In series 2 it was: 27.6 +/- 14.6 degrees (2.5 G), and 31.2 +/- 18.8 degrees (4.5 G). The gain for this response, defined as the ratio between the initial tilt and the inclination of the gondola, was: 0.65 +/- 0.28 (1.1 G), 0.45 +/- 0.19(1.7 G), 0.41 +/- 0.21 (2.5 G) (series 1); and 0.42 +/- 0.22 (2.5 G), and 0.40 +/- 0.24 (4.5 G) (series 2). Thus, an increase from 1.1 G to 1.7 G caused a reduction in the gain, but at G levels beyond 1.7 G there was no further decrease. The time constant for exponential decay tended to increase with the G level. It was: 61 +/- 31 s (1.1 G), 84 +/- 36 s (1.7 G), 89 +/- 42 s (2.5 G) (series 1); and 67 +/- 49 s (2.5 G), and 101 +/- 73 s (4.5 G) (series 2).

    CONCLUSION: It appears that otolithic stimulation via an increased gravitoinertial force vector, acting in parallel with the head and body long axis, does not substantially influence the magnitude of the canal-mediated sensation of roll-tilt after acceleration in a swing-out gondola centrifuge. Nor does it reduce the duration of this sensation.

  • 29.
    Tribukait, Arne
    et al.
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Semicircular canal contribution to the perception of roll tilt during gondola centrifugation2005Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 76, nr 10, s. 940-946Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Spatial disorientation is an important problem in aviation. The mechanisms behind the sensation of roll tilt during coordinated turns are not well known. The present study aimed at elucidating what kind of semicircular canal information might cause tilts of the subjective horizontal during gondola centrifugation.

    METHODS: The subjective visual horizontal (SVH) was measured by means of an adjustable visual line in darkness. Subjects (n = 8) underwent four centrifuge runs (2 G, 5 min), sitting in different positions, i.e., heading forwards, backwards, centripetally, and centrifugally. The roll position of the gondola (60 degrees at 2 G) was controlled so that the subject was always upright with respect to the resultant gravitoinertial force vector. Thus, the semicircular-canal stimulus components in yaw, pitch, and roll were varied to some extent independently of each other.

    RESULTS: For the forward position the SVH was substantially tilted in a direction compensatory with respect to the inclination of the gondola. For the backward position there was also a tendency to a compensatory SVH tilt. In all subjects the magnitude of tilt was larger for the forward position than for the backward. The group means were +20.9 +/- 8.4 degrees and -6.9 +/- 10.5 degrees (positive sign designates a clockwise deviation of the SVH), p < 0.001, n = 8. There were no significant SVH tilts for the centripetal (+6.4 +/- 10.7 degrees) and centrifugal (+2.1 +/- 4.8 degrees) positions. The effects of deceleration of the centrifuge were very small for all positions.

    CONCLUSION: These findings suggest that the substantial SVH tilt after acceleration heading forwards is not directly related to any single component of semicircular canal stimulation but depends on the ability of the brain to expediently process complex stimulus patterns.

  • 30.
    Tribukait, Arne
    et al.
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Semicircular canal influence on the visually perceived eye level during gondola centrifugation2006Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 77, nr 5, s. 500-508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: When exposed to an increased gravitoinertial force, a subject, sitting upright, experiences an illusion of being tilted backwards. This so-called "G-excess illusion" is generally ascribed to the otolith organs. The present study aimed at elucidating how stimulation of the semicircular canals may influence the development of the G-excess illusion.

    METHODS: The visually perceived eye level (VPEL) was measured by means of a visual indicator in a large swing-out gondola centrifuge. The roll position of the gondola was controlled so that the subject was always upright with respect to the resultant vector of the Earth gravity force and the centrifugal force. Subjects (n = 8) underwent four centrifuge runs (2 G, 5 min), sitting in different positions, i.e., heading forwards, backwards, centripetally, and centrifugally.

    RESULTS: At the 2-G plateau there was a depression of the VPEL which was initially small but increased with a time constant of 90 +/- 30 s toward an asymptote of -22.0 +/- 6.9 degrees (mean and 1 SD for all positions). The initial depression was significantly smaller for the centripetal (+2.0 +/- 14.6 degrees) than for the centrifugal position (-14.5 +/- 10.4 degrees). However, there was no difference between the forward (-5.6 +/- 4.8 degrees) and backward (-4.0 +/- 4.5 degrees) positions. Initially after deceleration of the centrifuge to 1 G there was still a significant depression of the VPEL (-13.5 +/- 7.9 degrees), decreasing with a time constant of 100 +/- 46 s.

    CONCLUSIONS: The considerable delay in the otolith-mediated changes in the VPEL is interpreted as due to the absence of adequate canal information for a change in head position. The difference in VPEL between the centripetal and centrifugal positions suggests an influence of canal change-in-position information. However, pitch-plane angular velocity, being of considerable magnitude but of opposite sign for the forward and backward positions, did not influence the VPEL.

  • 31.
    Tribukait, Arne
    et al.
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Naturvetenskap och biomedicin, Omgivningsfysiologi.
    Lemming, D.
    Levin, B.
    Use of an adjustable hand plate in studying the perceived horizontal plane during simulated flight2013Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 84, nr 7, s. 739-745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Quantitative data on spatial orientation would be valuable not only in assessing the fidelity of flight simulators, but also in evaluation of spatial orientation training. In this study a manual indicator was used for recording the subjective horizontal plane during simulated flight. Methods: In a six-degrees-of-freedom hexapod hydraulic motion platform simulator, simulating an F-16 aircraft, seven fixed-wing student pilots were passively exposed to two flight sequences. The first consisted in a number of coordinated turns with visual contact with the landscape below. The visually presented roll tilt was up to a maximum 67. The second was a takeoff with a cabin pitch up of 10, whereupon external visual references were lost. The subjects continuously indicated, with the left hand on an adjustable plate, what they perceived as horizontal in roll and pitch. There were two test occasions separated by a 3-d course on spatial disorientation. Results: Responses to changes in simulated roll were, in general, instantaneous. The indicated roll tilt was approximately 30% of the visually presented roll. There was a considerable interindividual variability. However, for the roll response there was a correlation between the two occasions. The amplitude of the response to the pitch up of the cabin was approximately 75%; the response decayed much more slowly than the stimulus. Discussion: With a manual indicator for recording the subjective horizontal plane, individual characteristics in the response to visual tilt stimuli may be detected, suggesting a potential for evaluation of simulation algorithms or training programs.

  • 32.
    Tribukait, Arne
    et al.
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Grönkvist, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Eiken, Ola
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    The perception of roll tilt in pilots during a simulated coordinated turn in a gondola centrifuge.2011Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 82, nr 5, s. 523-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: It has previously been reported that nonpilots underestimate the roll tilt angle after acceleration in a gondola centrifuge. The aim of the present work was to elucidate the significance of flight experience for roll tilt perception based on vestibular information.

    METHODS: The subjective visual horizontal (SVH) was measured by means of an adjustable luminous line in darkness. Eight nonpilots (N), nine fighter pilots (F), and eight helicopter pilots (H) underwent two centrifuge runs (2 G, 5 min) heading forward and backward, respectively. The roll position of the gondola (60 degrees at 2 G) was controlled so that the subject was always upright with respect to the gravitoinertial force.

    RESULTS: Upon acceleration of the centrifuge there was a tilt of the SVH in a direction compensatory to the inclination of the gondola. This tilt was larger in the forward position [N: 17.2 +/- 6.4 degrees, F: 31.2 +/- 16.4 degrees, H: 33.6 +/- 18.2 degrees (means +/- SD)] than in the backward position (N: -5.0 +/- 6.8 degrees, F: -12.2 +/- 17.4 degrees, H: -10.4 +/- 15.4 degrees). In N the tilt declined with time, approaching zero by the end of the 2-G plateau. In the pilots it was significantly larger and did not decline.

    CONCLUSION: Flight experience results in an increased ability to perceive the roll tilt during movement along a curved path. That this can be revealed in a centrifuge might suggest that acceleration of the centrifuge constitutes a movement pattern which is similar, from a vestibular point of view, to that of an airplane entering a coordinated turn.

  • 33. Verrecchia, Luca
    et al.
    Gennser, Mikael
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Tribukait, Arne
    KTH, Skolan för teknik och hälsa (STH), Omgivningsfysiologi.
    Brantberg, Krister
    Superior Vestibular Dysfunction in Severe Decompression Sickness Suggests an Embolic Mechanism2012Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 83, nr 11, s. 1097-1100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    VERRECCHIA L, GENNSER M, TRIBUKAIT A, BRANTBERG K. Superior vestibular dysfunction in severe decompression sickness suggests an embolic mechanism. Aviat Space Environ Med 2012; 83:1097-1100. Background: Both nitrogen bubble embolism and the difficulty of inner ear tissues to wash out nitrogen have been discussed as possible reasons for the selective vulnerability of the inner ear to decompression illness. This case report suggests that nitrogen bubble embolism plays a crucial role in the pathogenesis of inner ear lesions in decompression accidents. Case Report: The current patient, a 48-yr-old male dive master, suffered a severe decompression illness with vertigo as the only residual symptom. At the 1-mo follow-up, neuro-otological evaluation revealed a selective lesion of the superior vestibular division of the left labyrinth with normal functioning inferior vestibular division. At vestibular testing, there was no caloric response from the affected left ear, and the head impulse tests for the lateral and anterior semicircular canal were also impaired. Tests of vestibular evoked myogenic potentials (VEMP) showed divergent results. Ocular VEMP in response to left ear stimulation were absent, whereas the cervical VEMP were completely symmetrical and normal. Thus, the lesion profile implies a partial vestibular loss selectively affecting the superior vestibular division of the inner ear. Discussion: The most likely explanation for such a selective injury seems to be bubble microembolism coupled with both the specific anatomy of this terminally supplied subunit, and with the slow nitrogen wash-out of the vestibular organ.

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