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- Karlsson, Lars L., et al.
(författare)
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Venous gas emboli and exhaled nitric oxide with simulated and actual extravehicular activity
- 2009
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Ingår i: Respiratory Physiology & Neurobiology. - : Elsevier BV. - 1569-9048 .- 1878-1519. ; 169, s. S59-S62
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Tidskriftsartikel (refereegranskat)abstract
- The decompression experienced due to the change in pressure from a space vehicle (1013hPa) to that in a suit for extravehicular activity (EVA) (386hPa) was simulated using a hypobaric chamber. Previous ground-based research has indicated around a 50% occurrence of both venous gas emboli (VGE) and symptoms of decompression illness (DCI) after similar decompressions. In contrast, no DCI symptoms have been reported from past or current space activities. Twenty subjects were studied using Doppler ultrasound to detect any VGE during decompression to 386hPa, where they remained for up to 6h. Subjects were supine to simulate weightlessness. A large number of VGE were found in one subject at rest, who had a recent arm fracture; a small number of VGE were found in another subject during provocation with calf contractions. No changes in exhaled nitric oxide were found that can be related to either simulated EVA or actual EVA (studied in a parallel study on four cosmonauts). We conclude that weightlessness appears to be protective against DCI and that exhaled NO is not likely to be useful to monitor VGE.
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- Linnarsson, Margareta, et al.
(författare)
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In-diffusion, trapping and out-diffusion of deuterium in 4H-SiC substrates
- 2006
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Ingår i: Silicon Carbide and Related Materials 2005, Pts 1 and 2. - 9780878494255 ; , s. 637-640
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Konferensbidrag (refereegranskat)abstract
- Incorporation of hydrogen/deuterium in n-, p-type, and semi-insulating 4H-SiC substrates during epitaxial growth at 1590 degrees C has been studied in detail by secondary ion mass spectrometry. Out-diffusion has been investigated in samples subsequently annealed at high temperatures. After the epitaxial growth, deuterium is detected throughout the entire substrates. Out-diffusion can be observed after anneals at 1300 degrees C, but traces of deuterium can still be found in samples annealed as high as 1700 degrees C. A trap limited diffusion mechanism is proposed with vacancy related hydrogen trapping centers in n-type and semi insulating 4H-SiC substrates.
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| 5. |
- Linnarsson, Margareta K., et al.
(författare)
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Formation of precipitates in heavily boron doped 4H-SiC
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:15, s. 5316-5320
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Tidskriftsartikel (refereegranskat)abstract
- Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000 degrees C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B4C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1 x 10(22) exp(-1.4 eV/k(B)T) cm(-3) over the studied temperature range.
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| 8. |
- Montmerle, S, et al.
(författare)
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Effects of gravity and blood volume shifts on cardiogenic oscillations in respired gas
- 2005
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Ingår i: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 99:3, s. 931-936
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Tidskriftsartikel (refereegranskat)abstract
- During the cardiac cycle, cardiogenic oscillations of expired gas ( x) concentrations (COS[ x]) are generated. At the same time, there are heart-synchronous cardiogenic oscillations of airway flow (COSflow), where inflow occurs during systole. We hypothesized that both phenomena, although primarily generated by the heartbeat, would react differently to the cephalad blood shift caused by inflation of an anti-gravity (anti-G) suit and to changes in gravity. Twelve seated subjects performed a rebreathing-breath-holding-expiration maneuver with a gas mixture containing O2 and He at normal (1 G) and moderately increased gravity (2 G); an anti-G suit was inflated to 85 mmHg in each condition. When the anti-G suit was inflated, COSflow amplitude increased ( P = 0.0028) at 1 G to 186% of the control value without inflation (1-G control) and at 2 G to 203% of the control value without inflation (2-G control). In contrast, the amplitude of COS of the concentration of the blood-soluble gas O2 (COS[O2/He]), an index of the differences in pulmonary perfusion between lung units, declined to 75% of the 1-G control value and to 74% of the 2-G control value ( P = 0.0030). There were no significant changes in COSflow or COS[O2/He] amplitudes with gravity. We conclude that the heart-synchronous mechanical agitation of the lungs, as expressed by COSflow, is highly dependent on peripheral-to-central blood shifts. In contrast, COS[blood-soluble gas] appears relatively independent of this mechanical agitation and seems to be determined mainly by differences in intrapulmonary perfusion.
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| 9. |
- Montmerle, S., et al.
(författare)
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Residual heterogeneity of intra- and interregional pulmonary perfusion in short-term microgravity
- 2005
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 98:6, s. 2268-2277
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Tidskriftsartikel (refereegranskat)abstract
- We hypothesized that the perfusion heterogeneity in the human, upright lung is determined by nongravitational more than gravitational factors. Twelve and six subjects were studied during two series of parabolic flights. We used cardiogenic oscillations of O(2)/SF(6) as an indirect estimate of intraregional perfusion heterogeneity (series 1) and phase IV amplitude (P(4)) as a indirect estimate of interregional perfusion heterogeneity (series 2). A rebreathing-breath holding-expiration maneuver was performed. In flight, breath holding and expiration were performed either in microgravity (0 G) or in hypergravity. Controls were performed at normal gravity (1 G). In series 1, expiration was performed at 0 G. Cardiogenic oscillations of O(2)/SF(6) were 19% lower when breath holding was performed at 0 G than when breath holding was performed at 1 G [means (SD): 1.7 (0.3) and 2.3 (0.6)% units] (P = 0.044). When breath holding was performed at 1.8 G, values did not differ from 1-G control [2.6 (0.8)% units, P = 0.15], but they were 17% larger at 1.8 G than at 1 G. In series 2, expiration was performed at 1.7 G. P(4) changed with gravity (P < 0.001). When breath holding was performed at 0 G, P(4) values were 45 (46)% of control. When breath holding was performed at 1.7 G, P(4) values were 183 (101)% of control. We conclude that more than one-half of indexes of perfusion heterogeneity at 1 G are caused by nongravitational mechanisms.
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| 10. |
- Petersson, J, et al.
(författare)
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Paradoxical redistribution of pulmonary blood flow in prone and supine humans exposed to hypergravity
- 2006
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Ingår i: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 100:1, s. 240-248
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Tidskriftsartikel (refereegranskat)abstract
- We hypothesized that exposure to hypergravity in the supine and prone postures causes a redistribution of pulmonary blood flow to dependent lung regions. Four normal subjects were exposed to hypergravity by use of a human centrifuge. Regional lung perfusion was estimated by single-photon-emission computed tomography (SPECT) after administration of 99mTc-labeled albumin macroaggregates during normal and three times normal gravity conditions in the supine and prone postures. All images were obtained during normal gravity. Exposure to hypergravity caused a redistribution of blood flow from dependent to nondependent lung regions in all subjects in both postures. We speculate that this unexpected and paradoxical redistribution is a consequence of airway closure in dependent lung regions causing alveolar hypoxia and hypoxic vasoconstriction. Alternatively, increased vascular resistance in dependent lung regions is caused by distortion of lung parenchyma. The redistribution of blood flow is likely to attenuate rather than contribute to the arterial desaturation caused by hypergravity.
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