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- Johansson, Mats, 1958-, et al.
(författare)
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Inhibition of constitutive nitric oxide synthase does not influence ventilation : matching in normal prone adult sheep with mechanical ventilation
- 2016
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Ingår i: Anesthesia and Analgesia. - : Lippincott Williams & Wilkins. - 0003-2999 .- 1526-7598. ; 123:6, s. 1492-1499
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundLocal formation of nitric oxide (NO) in the lung in proportion to ventilation, leading to vasodilation, is a putative mechanism behind ventilation- perfusion matching. We examined the role of local constitutive NO formation on regional distributions of ventilation (V) and perfusion (Q) and ventilation-perfusion matching (V/Q) in mechanically ventilated adult sheep with normal gas exchange.MethodsV and Q were analyzed in lung regions (≈1.5 cm3) before and after inhibition of constitutive nitric oxide synthase (cNOS) with Nω-nitro-L-arginine methyl ester (L-NAME) (25 mg/kg) in seven prone sheep ventilated with PEEP. V and Q were measured using aerosolized fluorescent and infused radiolabeled microspheres, respectively. The animals were exsanguinated while deeply anaesthetized; lungs were excised, dried at total lung capacity and divided into cube units. The spatial location for each cube was tracked and fluorescence and radioactivity per unit weight determined.ResultsPulmonary artery pressure increased significantly after L-NAME (from mean 16.6 to 23.6 mmHg, P<0.01) while there were no significant changes in PaO2, PaCO2 or SD log(V/Q). Distribution of V was not influenced by L-NAME but a small redistribution of Q from ventral to dorsal lung regions resulting in less heterogeneity in Q along the gravitational axis was seen (p<0.01). Perfusion to regions with the highest ventilation (5th quintile of the V distribution) remained unchanged with L-NAME.ConclusionsThere was minimal or no influence of cNOS inhibition by L-NAME on the distributions of V and Q, and V/Q in prone anesthetized and ventilated adult sheep with normal gas exchange.
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- Johansson, Mats, 1958-, et al.
(författare)
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Minimal redistribution of regional ventilation-perfusion ratios by 10 and 20 cmH2O positive end-expiratory pressure in prone sheep
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundPositive end-expiratory pressure (PEEP) has posture dependent effects on the distributions of ventilation (V) and perfusion (Q). We examined if redistribution of regional ventilation-perfusion ratios (V/Q) by PEEP was identical in prone and supine.MethodsMechanically ventilated sheep (n=16) were studied in prone or supine with 0, 10 and 20 cmH2O PEEP. V and Q were measured with a fluorescent microsphere aerosol and an intravenous infusion of microspheres, respectively. The right lung was dried at total lung capacity and diced into approx. 1000 regions tracking the spatial location of each region.ResultsIn prone V/Q was close to unity in all horizontal planes with 0 PEEP and remained so with 10 and 20 PEEP. In supine V/Q was imperfect in the most dependent planes with 0 and 10 PEEP. V/Q approached unity in these planes when 20 PEEP was applied, but V/Q in non-dependent planes increased. The slope of the linear relationship between vertical height and V/Q was not different from zero at any PEEP in prone, but was larger than zero with all PEEP levels in supine. Mean V/Q heterogeneity (SDlogV/Q) was lower in prone at all PEEP levels (0 PEEP: 0.22 vs. 0.37, 10 PEEP: 0.21 vs. and 0.32 and 20 PEEP: 0.19 vs. 0.39, P<0.01).ConclusionsRedistribution of regional V/Q was minimal in prone with PEEP and remained close to ideal in all horizontal planes. The absence of high V/Q with PEEP in prone may be clinically important when recruitment fails in the supine posture.
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- Johansson, Mats, 1958-, et al.
(författare)
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Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep
- 2004
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Ingår i: Critical Care Medicine. - 0090-3493 .- 1530-0293. ; 32:10, s. 2039-2044
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To examine interactions between positive end-expiratory pressure (PEEP) and posture on regional distribution of ventilation and to compare measurements of regional ventilation with two aerosols: a wet fluorescent microsphere aerosol (FMS, median mass aerodynamic diameter 1.1 μm) and a dry 99mTc-labeled carbon particle aerosol (Technegas, TG, median mass aerodynamic diameter ≈0.1 μm). Design: Experimental study. Setting. Academic laboratory. Subjects: Anesthetized and mechanically ventilated sheep (n = 16). Interventions: Four conditions were studied: prone or supine posture with of without 10 cm H2O PEEP. Measurements and Main results: Comparisons of FMS and TG were made in five animals. The median correlation coefficient of the two ventilation tracers was .95 (range, .91-.96). The mean ventilation per unit weight of dry lung for horizontal planes was almost identical whether measured with TG or FMS. The distribution of ventilation was assessed by analyzing deposition of aerosol in about 1,000 lung regions per animal. Distribution of ventilation down the vertical axis was linear in prone (the slope indicated a dorsal-to-ventral three-fold difference in ventilation) but unimodal in supine animals with the mode in the center of the lung. Redistribution of ventilation with 10 PEEP differed between posture, shifting the mode in supine toward dependent lung regions while eliminating the dorsal-to-ventral gradient in prone. The regional heterogeneity in ventilation was greater in supine sheep at both levels of PEEP, and this was due mostly to greater isogravitational heterogeneity in supine than in prone position. Conclusions: The wet fluorescent microsphere aerosol was as reliable as Technegas for high-resolution measurements of regional ventilation. The markedly different effects of 10 PEEP in supine and prone sheep may have important implications for gas exchange both in noninjured and injured lungs.
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- Walther, Sten M, et al.
(författare)
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Marked differences between prone and supine sheep in effect of PEEP on perfusion distribution in zone II lung
- 2005
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 99:3, s. 909-914
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Tidskriftsartikel (refereegranskat)abstract
- The classic four-zone model of lung blood flow distribution has been questioned. We asked whether the effect of positive end-expiratory pressure (PEEP) is different between the prone and supine position for lung tissue in the same zonal condition. Anesthetized and mechanically ventilated prone (n = 6) and supine (n = 5) sheep were studied at 0, 10, and 20 cmH2O PEEP. Perfusion was measured with intravenous infusion of radiolabeled 15-μm microspheres. The right lung was dried at total lung capacity and diced into pieces (≈1.5 cm3), keeping track of the spatial location of each piece. Radioactivity per unit weight was determined and normalized to the mean value for each condition and animal. In the supine posture, perfusion to nondependent lung regions decreased with little relative perfusion in nondependent horizontal lung planes at 10 and 20 cmH2O PEEP. In the prone position, the effect of PEEP was markedly different with substantial perfusion remaining in nondependent lung regions and even increasing in these regions with 20 cmH2O PEEP. Vertical blood flow gradients in zone II lung were large in supine, but surprisingly absent in prone, animals. Isogravitational perfusion heterogeneity was smaller in prone than in supine animals at all PEEP levels. Redistribution of pulmonary perfusion by PEEP ventilation in supine was largely as predicted by the zonal model in marked contrast to the findings in prone. The differences between postures in blood flow distribution within zone II strongly indicate that factors in addition to pulmonary arterial, venous, and alveolar pressure play important roles in determining perfusion distribution in the in situ lung. We suggest that regional variation in lung volume through the effect on vascular resistance is one such factor and that chest wall conformation and thoracic contents determine regional lung volume. Copyright © 2005 the American Physiological Society.
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