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Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep
Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Anaesthesiology. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
Department of Anaesthesia and Intensive Care, Karolinska Hospital, Stockholm, Sweden.
Institute of Basic Medical Sciences, Department of Physiology, University of Oslo, Norway..
Institute of Basic Medical Sciences, Department of Physiology, University of Oslo, Norway.
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2004 (English)In: Critical Care Medicine, ISSN 0090-3493, E-ISSN 1530-0293, Vol. 32, no 10, 2039-2044 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2004. Vol. 32, no 10, 2039-2044 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-24429DOI: 10.1097/01.CCM.0000142395.82277.6FLocal ID: 6535OAI: diva2:244747
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2014-11-24
In thesis
1. Gas Exchange in the Normal Lung: Experimental studies on the effects of positive end-expiratory pressure and body position
Open this publication in new window or tab >>Gas Exchange in the Normal Lung: Experimental studies on the effects of positive end-expiratory pressure and body position
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

BACKGROUND: The principal function of the lung is gas exchange requiring adequate ventilation and perfusion at the level of the alveoli. The efficiency of gas exchange is depending on the distributions of regional ventilation (V) and pulmonary blood flow (Q) and their correlation.

AIMS: To validate a high-resolution method to quantify regional V and to investigate the combined effect of positive end-expiratory pressure (PEEP) and body position on distributions of regional V and Q in the normal lung with mechanical ventilation. To assess the matching of V and Q by calculating ventilation-perfusion ratio (V/Q) heterogeneity, determining the spatial distribution of V/Q and to investigate the role of nitric oxide (NO) in regional V/Q matching.

METHODS: Anesthetized mechanically ventilated sheep were studied in prone or supine position with different levels of PEEP (0, 10 and 20 cmH2O). Measurements of regional V were done by determining the deposition of a wet aerosol of fluorescent microspheres (FMS) with a median mass aerodynamic diameter of 1.1 μm, and validated against Technegas. Radioactive microspheres, 15 μm in diameter, were used for determining regional Q. Nitric oxide synthase (NOS) was inhibited with Nω-nitro-L-arginine methyl ester (L-NAME) to evaluate the role of NO on regional V/Q matching. The right lung was dried at total lung capacity and diced in approx. 1000 regions tracking the spatial location of each region.

RESULTS: The deposition of FMS mirrored regional deposition of Technegas and thus regional ventilation well. In prone, with PEEP, only a small dorsal redistribution of V but not of Q was observed. The vertical Q gradient was abolished with PEEP in prone position in conflict with the classical zonal model. In supine position both V and Q were distributed with a unimodal gradient and PEEP displaced the mode further dorsally. V/Q heterogeneity was greater in supine than in prone position with and without PEEP. Furthermore, PEEP generated regions with high V/Q in supine but not in prone position. Inhibition of NOS did not change the V/Q distribution in prone position.

CONCLUSION: There were marked differences in redistribution of regional ventilation and regional pulmonary blood flow between prone and supine position when PEEP was applied. NO was not an active mechanism for V/Q matching in normal sheep lungs.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 74 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1425
National Category
Anesthesiology and Intensive Care
urn:nbn:se:liu:diva-112364 (URN)10.3384/diss.diva-112364 (DOI)978-91-7519-219-2 (print) (ISBN)
Public defence
2014-12-12, Berzeliussalen, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2014-11-24Bibliographically approved

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Johansson, MatsWalther, Sten
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