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- Ax, M, et al.
(author)
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The influence of gravity on regional lung blood flow in humans: SPECT in the upright and head-down posture
- 2017
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 122:6, s. 1445-1451
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Journal article (peer-reviewed)abstract
- Previous studies in humans have shown that gravity has little influence on the distribution of lung blood flow while changing posture from supine to prone. This study aimed to evaluate the maximal influence of posture by comparison of regional lung blood flow in the upright and head-down posture in 8 healthy volunteers, using a tilt table. Regional lung blood flow was marked by intravenous injection of macroaggregates of human albumin labeled with 99mTc or 113mIn, in the upright and head-down posture, respectively, during tidal breathing. Both radiotracers remain fixed in the lung after administration. The distribution of radioactivity was mapped using quantitative single photon emission computed tomography (SPECT) corrected for attenuation and scatter. All images were obtained supine during tidal breathing. A shift from upright to the head-down posture caused a clear redistribution of blood flow from basal to apical regions. We conclude that posture plays a role for the distribution of lung blood flow in upright humans, and that the influence of posture, and thereby gravity, is much greater in the upright and head-down posture than in horizontal postures. However, the results of the study demonstrate that lung structure is the main determinant of regional blood flow and gravity is a secondary contributor to the distribution of lung blood flow in the upright and head-down positions. NEW & NOTEWORTHY Using a dual-isotope quantitative SPECT method, we demonstrated that although a shift in posture redistributes blood flow in the direction of gravity, the results are also consistent with lung structure being a greater determinant of regional blood flow than gravity. To our knowledge, this is the first study to use modern imaging methods to quantify the shift in regional lung blood flow in humans at a change between the upright and head-down postures.
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- Crespo, AS, et al.
(author)
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Nasal nitric oxide and regulation of human pulmonary blood flow in the upright position
- 2010
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 108:1, s. 181-188
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Journal article (peer-reviewed)abstract
- There are a number of evidences suggesting that lung perfusion distribution is under active regulation and determined by several factors in addition to gravity. In this work, we hypothesised that autoinhalation of nitric oxide (NO), produced in the human nasal airways, may be one important factor regulating human lung perfusion distribution in the upright position. In 15 healthy volunteers, we used single-photon emission computed tomography technique and two tracers (99mTc and 113mIn) labeled with human macroaggregated albumin to assess pulmonary blood flow distribution. In the sitting upright position, subjects first breathed NO free air through the mouth followed by the administration of the first tracer. Subjects then switched to either nasal breathing or oral breathing with the addition of exogenous NO-enriched air followed by the administration of the second tracer. Compared with oral breathing, nasal breathing induced a blood flow redistribution of ∼4% of the total perfusion in the caudal to cranial and dorsal to ventral directions. For low perfused lung regions like the apical region, this represents a net increase of 24% in blood flow. Similar effects were obtained with the addition of exogenous NO during oral breathing, indicating that NO and not the breathing condition was responsible for the blood flow redistribution. In conclusion, these results provide evidence that autoinhalation of endogenous NO from the nasal airways may ameliorate the influence of gravity on pulmonary blood flow distribution in the upright position. The presence of nasal NO only in humans and higher primates suggest that it may be an important part of the adaptation to bipedalism.
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- Hedestig, T, et al.
(author)
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Validation of equilibration and chromium reduction methods for deuterium measurements of fluid volumes
- 2001
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 91:2, s. 733-736
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Journal article (peer-reviewed)abstract
- Determinations of fluid volumes are of importance for correct treatment of patients subjected to shock and trauma. Gas isotope ratio mass spectrometry (GIRMS) is an advanced method for analysis of stable isotopes. These can be used as tracers for measurement of various fluid volumes. In the current in vitro study, deuterium was used to determine different volumes of water simulating a range of body fluid volumes from neonates to adults. A high-precision scale gave control weights (i.e., volumes), and two methods, equilibration (EQ) and chromium reduction (CR), were compared by use of a GIRMS. The coefficient of variation was <1% when using both EQ (0.45%) and CR (0.79%). The variability was greater at small volumes, and, when regression equations for the relation between measured and calculated volumes were used as formulas, the deviation was 0.4% using EQ and 2.8% using CR at the volume of 1,000 ml. At larger volumes, the deviation when using CR approached 1%. These variations are better than previously published data using other methods. It was concluded that GIRMS is a suitable technique for fluid volume determinations in neonates as well as in adult patients, using deuterium as a tracer. EQ and CR methods were both regarded to give acceptable variabilities in this in vitro study. GIRMS may in the future increasingly be used clinically for accurate measurements of body fluid volumes.
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- Lindahl, SGE
(author)
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Perioperative management of children
- 1996
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In: Acta anaesthesiologica Scandinavica. - : Wiley. - 0001-5172. ; 40:88 Pt 2, s. 975-981
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Journal article (peer-reviewed)
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| 26. |
- Lindahl, SGE
(author)
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Sensing cold and producing heat
- 1997
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In: Anesthesiology. - : Ovid Technologies (Wolters Kluwer Health). - 0003-3022. ; 86:4, s. 758-759
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Journal article (other academic/artistic)
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- LINDAHL, SGE
(author)
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Thinner than blood
- 1995
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In: Anesthesia and analgesia. - : Ovid Technologies (Wolters Kluwer Health). - 0003-2999. ; 80:2, s. 217-218
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Journal article (other academic/artistic)
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- Mure, M, et al.
(author)
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Regional ventilation-perfusion distribution is more uniform in the prone position
- 2000
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 88:3, s. 1076-1083
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Journal article (peer-reviewed)abstract
- The arterial blood[Formula: see text] is increased in the prone position in animals and humans because of an improvement in ventilation (V˙a) and perfusion (Q˙) matching. However, the mechanism of improvedV˙a/Q˙ is unknown. This experiment measured regionalV˙a/Q˙ heterogeneity and the correlation between V˙a andQ˙ in supine and prone positions in pigs. Eight ketamine-diazepam-anesthetized, mechanically ventilated pigs were studied in supine and prone positions in random order. RegionalV˙a and Q˙ were measured using fluorescent-labeled aerosols and radioactive-labeled microspheres, respectively. The lungs were dried at total lung capacity and cubed into 603–967 small (∼1.7-cm3) pieces. In the prone position the homogeneity of the ventilation distribution increased ( P = 0.030) and the correlation betweenV˙a and Q˙ increased (correlation coefficient = 0.72 ± 0.08 and 0.82 ± 0.06 in supine and prone positions, respectively, P = 0.03). The homogeneity of the V˙a/Q˙distribution increased in the prone position ( P = 0.028). We conclude that the improvement inV˙a/Q˙ matching in the prone position is secondary to increased homogeneity of theV˙a distribution and increased correlation of regional V˙a andQ˙.
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| 45. |
- Nyren, S, et al.
(author)
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Pulmonary perfusion is more uniform in the prone than in the supine position: scintigraphy in healthy humans
- 1999
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 86:4, s. 1135-1141
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Journal article (peer-reviewed)abstract
- The main purpose of this study was to find out whether the dominant dorsal lung perfusion while supine changes to a dominant ventral lung perfusion while prone. Regional distribution of pulmonary blood flow was determined in 10 healthy volunteers. The subjects were studied in both prone and supine positions with and without lung distension caused by 10 cmH2O of continuous positive airway pressure (CPAP). Radiolabeled macroaggregates of albumin, rapidly trapped by pulmonary capillaries in proportion to blood flow, were injected intravenously. Tomographic gamma camera examinations (single-photon-emission computed tomography) were performed after injections in the different positions. All data acquisitions were made with the subject in the supine position. CPAP enhanced perfusion differences along the gravitational axis, which was more pronounced in the supine than prone position. Diaphragmatic sections of the lung had a more uniform pulmonary blood flow distribution in the prone than supine position during both normal and CPAP breathing. It was concluded that the dominant dorsal lung perfusion observed when the subjects were supine was not changed into a dominant ventral lung perfusion when the subjects were prone. Lung perfusion was more uniformly distributed in the prone compared with in the supine position, a difference that was more marked during total lung distension (CPAP) than during normal breathing.
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| 47. |
- Ohlson, Kerstin, et al.
(author)
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Inhibitory effects of halothane on the thermogenic pathway in brown adipocytes: localization to adenylyl cyclase and mitochondrial fatty acid oxidation
- 2004
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In: Biochemical Pharmacology. - : Elsevier BV. - 0006-2952. ; 68:3, s. 463-477
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Journal article (peer-reviewed)abstract
- Volatile anesthetics such as halothane efficiently inhibit nonshivering thermogenesis as well as the cellular manifestation of that phenomenon: norepinephrine-induced respiration in brown adipocytes. To identify the molecular site(s) of action of such anesthetics, we have examined the effect of halothane on the sequential intracellular steps from the interaction of norepinephrine with isolated brown adipocytes to the stimulation of mitochondrial respiration (=thermogenesis). We did not identify an inhibition at the level of the adrenergic receptors, but a first site of inhibition was identified as the generation of cAMP by adenylyl cyclase; this led to inhibition of norepinephrine-induced expression of the uncoupling protein-1 (UCP 1) gene and reduced norepinephrine-induced lipolysis as secondary effects. Although an inhibition of lipolysis in itself would inhibit thermogenesis, circumvention of this inhibition revealed that a second, postlipolytic, site of inhibition existed: halothane also inhibited the stimulatory effect of exogenous fatty acids on cellular respiration. This inhibition was independent of the presence of UCP1 in the mitochondria of the cells and was thus not directly on the thermogenic uncoupling mechanism. Since not only fatty acid oxidation but also pyruvate oxidation were inhibited by halothane in isolated mitochondria, whereas glycerol-3-phosphate oxidation was not, the second site of action of halothane, evident when cyclase/lipolytic inhibition was circumvented, was located to the respiratory chain, complex I. The results thus explain the inhibition of nonshivering thermogenesis by identifying two sites of action of halothane in brown adipocytes. In addition, the results may open for new formulations of the molecular background to anesthesia. (C) 2004 Elsevier Inc. All rights reserved.
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| 50. |
- Petersson, J, et al.
(author)
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Paradoxical redistribution of pulmonary blood flow in prone and supine humans exposed to hypergravity
- 2006
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 100:1, s. 240-248
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Journal article (peer-reviewed)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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