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Minimal redistribution of regional ventilation-perfusion ratios by 10 and 20 cmH2O positive end-expiratory pressure in prone sheep
Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Thoracic and Vascular Surgery.
Department of Physiology, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Norway.
Department of Physiology, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Norway.
Department of Physiology, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Norway.
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Background

Positive 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.

Methods

Mechanically 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.

Results

In 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).

Conclusions

Redistribution 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.

Place, publisher, year, edition, pages
2014.
National Category
Surgery
Identifiers
URN: urn:nbn:se:liu:diva-112360OAI: oai:DiVA.org:liu-112360DiVA: diva2:765620
Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2014-11-24Bibliographically approved
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.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1425
National Category
Anesthesiology and Intensive Care
Identifiers
urn:nbn:se:liu:diva-112364 (URN)10.3384/diss.diva-112364 (DOI)978-91-7519-219-2 (ISBN)
Public defence
2014-12-12, Berzeliussalen, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
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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