| 1. |
- Grönkvist, Mikael J, et al.
(författare)
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Contributions of lower limb and abdominal compression to ventilation inhomogeneity in hypergravity
- 2005
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Ingår i: Respir Physiol Neurobiol. - : Elsevier BV. - 1569-9048 .- 1878-1519. ; 148:1-2, s. 113-23
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Tidskriftsartikel (refereegranskat)abstract
- Gravito-inertial load in the head-to-foot direction (Gz) and compression of the lower body half by an anti-G suit (AGS) are both known to influence ventilation distribution in the lungs. To study the interaction of Gz and AGS and to asses the separate contributions from lower limbs and abdominal compressions to large and small-scale ventilation inhomogeneities nine males performed SF6/He vital capacity (VC) single-breath washouts at 1, 2, and 3 Gz in a centrifuge, with abdominal and/or lower limbs compressions. SF6/He and (SF6-He) phase III slopes were used for determination of overall and small-scale ventilation inhomogeneity. Closing volume and phase IV height were used as measures of large-scale inhomogeneity. VC decreased marginally with G-load but markedly with lower limbs compression. Small-scale ventilation inhomogeneity increased slightly with G-load, but substantially with AGS pressurization. Small-scale ventilation inhomogeneity increased with AGS pressurization. Large-scale inhomogeneity increased markedly with G-load. Translocation of blood to the lungs might be the key determinant for changes in small-scale ventilation inhomogeneity when pressurizing an AGS.
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| 2. |
- Debevec, Tadej, et al.
(författare)
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Whole body and regional body composition changes following 10-day hypoxic confinement and unloading-inactivity
- 2014
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Ingår i: Applied Physiology, Nutrition and Metabolism. - : Canadian Science Publishing. - 1715-5312 .- 1715-5320. ; 39:3, s. 386-395
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Holmström, Pontus
(författare)
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Protective Responses to Freediving Reveal High-Altitude Tolerance
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-altitude mountaineers - just as freedivers - are exposed to hypoxia. During freediving, the diving response leads to reduced oxygen consumption, and splenic contraction increases circulating hemoglobin concentration (Hb), which enhances freediving performance. It is unknown whether these responses relate with altitude-induced responses and what role the spleen has at high-altitude. My thesis aimed to explore whether associations exist between these apnea-induced responses and tolerance to high-altitude. In five studies, I investigated the diving response and splenic contraction during apnea in a range of groups, including recreational trekkers, elite climbers, indigenous Sherpa (living high and living low) and endurance athletes, at low-altitude and at high-altitude. My primary finding was striking: the diving response and splenic size were associated with tolerance to high-altitude; lowlanders with a strong diving response and large spleen showed less symptoms of acute mountain sickness at high-altitude. I also found that groups often exposed to high-altitude have larger spleens compared with groups who reside at sea-level. Interestingly, the Sherpa living high had larger spleens compared with Sherpa living low. Another important finding was that the spleen is reduced in size by ~14% per 1000 m of ascent in lowlanders, which was associated with enhanced baseline Hb. I also found that endurance athletes, who are dependent on efficient oxygen delivery, have larger spleens compared with untrained individuals. I conclude, that a strong diving response and a large spleen may be characteristics of high-altitude tolerant lowlanders, and could possibly be used to predict high-altitude sensitivity. Studies 1-4 suggest that a large spleen is a favourable trait in several groups to tolerate high-altitude hypoxia, likely by its ability to regulate circulating Hb. Sherpa had larger spleens compared with lowlanders, indicating that genetic factors influence splenic size, while the finding that Sherpa living high had larger spleens than Sherpa living low indicate that splenic size also is influenced by environmental exposure. Study 4 revealed a tonic splenic contraction in lowlanders at high-altitude, suggesting that the Hb regulating function may be important before EPO-induced red cell increase occurs, thereby aiding individual acclimatization.
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| 4. |
- Skoog, Johan
(författare)
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Cardiovascular regulation in women with vasovagal syncope : With special reference to the venous system
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although vasovagal syncope (VVS) is a common clinical condition the mechanisms behind VVS remain elusive. Upright posture is the major trigger of VVS and lower limb blood pooling affecting cardiac output has been proposed as a major determinant. The overall aim of this thesis was twofold. First, to develop new methodology for calculating limb venous compliance. Second, to study lower limb venous volume load and cardiovascular responses during hypovolemic circulatory stress caused by lower body negative pressure (LBNP) in healthy women and women with VVS, emphasizing compensatory mechanisms to maintain central blood volume.Net fluid filtration was associated with an underestimation ofvenous compliance. This could be accounted for with a correctionmodel. Further, a new venous wall model made it possible to adopt thevenous pressure-volume curve through the entire pressure range andthus provide a valid characterization of venous compliance.Calf blood pooling was similar between the groups and was not associated with tolerance to hypovolemic circulatory stress. Venous compliance was reduced at low venous pressures in VVS and correlated with decreased tolerance to circulatory stress. VVS women displayed attenuated sympathetic vasoconstrictor responses during graded circulatory stress, and mobilization of arm capacitance blood as well as capillary fluid absorption from extra- to intravascular space were reduced. Accordingly, more pronounced reductions in cardiac output were found in VVS. Thus, reduced compensatory mechanisms to maintain cardiac output could contribute to the pathogenesis oforthostatic VVS.In healthy women, rapid pooling in the lower limb was associated with higher tolerance to circulatory stress and more efficient cardiovascular responses, in part due to speed-dependent baroreflex-mediated sympathetic activation. In VVS however, rapid lower limb blood pooling was associated with lower tolerance and deficient cardiovascular responses. No speed-dependent baroreflexmediated sympathetic activation was found in VVS, indicating welldefined differences in cardiovascular regulation already in the initial responses to orthostatic stress.
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| 5. |
- Eriksson, Lars, 1963-, et al.
(författare)
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Visual flow scene effects on the somatogravic illusion in non-pilots
- 2008
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Ingår i: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 79:9, s. 860-866
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Tidskriftsartikel (refereegranskat)abstract
- 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 TIMID 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.
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| 6. |
- Grönkvist, Mikael, et al.
(författare)
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Inter- and intraregional ventilation inhomogeneity in hypergravity and after pressurization of an anti-G suit
- 2003
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 94:4, s. 1353-1364
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Tidskriftsartikel (refereegranskat)abstract
- This study assessed the effects of increased gravity in the head-to-foot direction (+G(z)) and anti-G suit (AGS) pressurization on functional residual capacity (FRC), the volume of trapped gas (V(TG)), and ventilation distribution by using inert- gas washout. Normalized phase III slope (Sn(III)) analysis was used to determine the effects on inter- and intraregional ventilation inhomogeneity. Twelve men performed multiple-breath washouts of SF(6) and He in a human centrifuge at +1 to +3 G(z) wearing an AGS pressurized to 0, 6, or 12 kPa. Hypergravity produced moderately increased FRC, V(TG), and overall and inter- and intraregional inhomogeneities. In normogravity, AGS pressurization resulted in reduced FRC and increased V(TG), overall, and inter- and intraregional inhomogeneities. Inflation of the AGS to 12 kPa at +3 G(z) reduced FRC markedly and caused marked gas trapping and intraregional inhomogeneity, whereas interregional inhomogeneity decreased. In conclusion, increased +G(z) impairs ventilation distribution not only between widely separated lung regions, but also within small lung units. Pressurizing an AGS in hypergravity causes extensive gas trapping accompanied by reduced interregional inhomogeneity and, apparently, results in greater intraregional inhomogeneity.
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| 7. |
- McDonnell, A. C., et al.
(författare)
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Effect of hypoxia and bedrest on peripheral vasoconstriction
- 2013
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Ingår i: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen. - : ESA Communications. - 9789290922704 ; , s. 1-2
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Konferensbidrag (refereegranskat)abstract
- Future planetary habitats may expose astronauts to both microgravity and hypobaric hypoxia, both inducing a reduction in peripheral perfusion. Peripheral temperature changes have been linked to sleep onset and quality [5]. However, it is still unknown what effect combining hypoxia and bedrest has on this relationship. Eleven male participants underwent three 10-day campaigns in a randomized manner: 1) normobaric hypoxic ambulatory confinement (HAmb); 2) normobaric hypoxic bed rest (HBR); 3) normobaric normoxic bed rest (NBR). There was no change in skin temperature gradient between the calf and toes, an index of peripheral perfusion (ΔTc-t), over the 10-d period in the HAmb trial. However, there was a significant increase (p< 0.001) in daytime (9am-9pm) ΔTc-t on day 10 of the inactivity/unloading periods (HBR and NBR trials). This reduction in the perfusion of the toes during the daytime was augmented during the HBR trial compared to NBR (p< 0.001). Before and on day 10 of the interventions we conducted polysomnographic assessment, which revealed no changes in sleep onset and/or architecture. These data support the theory that circadian changes in temperature are functionally linked to sleepiness [1].
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| 8. |
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| 9. |
- Keramidas, Michail E., et al.
(författare)
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Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males : evidence against the 'normobaric oxygen paradox' theory
- 2011
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Ingår i: Acta Physiologica. - : Wiley-Blackwell. - 1748-1708 .- 1748-1716. ; 202:1, s. 91-98
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO). Methods: Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration. Results: The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P < 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P < 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P < 0.05). Conclusion: In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.
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| 10. |
- Keramidas, Michail E., et al.
(författare)
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Muscle and cerebral oxygenation during exercise performance after short-term respiratory work
- 2011
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Ingår i: Respiratory Physiology & Neurobiology. - : Elsevier BV. - 1569-9048 .- 1878-1519. ; 175:2, s. 247-254
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the study was to investigate the effect of 30-min voluntary hyperpnoea on cerebral, respiratory and leg muscle balance between 02 delivery and utilization during a subsequent constant-power test. Eight males performed a VO2max test, and two exercise tests at 85% of peak power output: (a) a control constant-power test (CPT), and (b) a constant-power test after a respiratory maneuver (CPTRM). Oxygenated (Delta[O(2)Hb]), deoxygenated (Delta[HHb]) and total (Delta[tHb]) hemoglobin in cerebral, intercostal and vastus lateralis were monitored with near-infrared spectroscopy. The performance time dropped similar to 15% in CPTRM (6:55 +/- 2:52 min) compared to CPT (8:03 +/- 2:33 min), but the difference was not statistically significant. The vastus lateral's and intercostal Delta[tHb] and Delta[HHb] were lower in CPTRM than in CPT (P <= 0.05). There were no differences in cerebral oxygenation between the trials. Thus, respiratory work prior to an exercise test influences the oxygenation during exercise in the leg and respiratory muscles, but not in the frontal cortex. (C) 2010 Elsevier B.V. All rights reserved.
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