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Marked differences between prone and supine sheep in effect of PEEP on perfusion distribution in zone II lung
Department of Intensive Care, Ulleva°l University Hospital, Oslo, Norway.
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 Physiology, University of Oslo, Oslo, Norway.
Department of Physiology, University of Oslo, Oslo, Norway.
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2005 (English)In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 99, no 3, 909-914 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2005. Vol. 99, no 3, 909-914 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-29636DOI: 10.1152/japplphysiol.01388.2004Local ID: 15015OAI: diva2:250453
Available from: 2009-10-09 Created: 2009-10-09 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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Walther, Sten MJohansson, Mats
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Faculty of Health SciencesAnaesthesiologyDepartment of Thoracic and Vascular Surgery
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