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Effect of positive end-expiratory pressure on regional ventilation distribution during bronchoconstriction in rabbit studied by synchrotron radiation imaging*

Porra, Liisa PhD; Suhonen, Heikki PhD; Suortti, Pekka PhD; Sovijärvi, Anssi R. A. MD, PhD; Bayat, Sam MD, PhD

doi: 10.1097/CCM.0b013e318218a375
Laboratory Investigations

Objective: To assess the effects of positive end-expiratory pressure on regional ventilation distribution in normal lung and after histamine-induced bronchoconstriction.

Design: Experimental study.

Setting: International research laboratory.

Subjects: Six healthy New Zealand rabbits weighing 2.5 ± 0.1 kg.

Interventions: Rabbits were anesthetized, tracheostomized, paralyzed, and mechanically ventilated. Synchrotron radiation computed tomography images of tissue density and specific ventilation were acquired using K-edge subtraction imaging with inhaled stable xenon gas in middle and caudal thoracic levels on 0 and 5 cm H2O positive end-expiratory pressure at baseline and twice after histamine inhalation.

Measurements and Main Results: At baseline, a positive end-expiratory pressure of 5 cm H2O significantly increased lung volume. Histamine inhalation caused patchy areas of decreased specific ventilation, including some areas with no ventilation. After histamine, positive end-expiratory pressure significantly increased the area of well-ventilated lung regions and decreased the heterogeneity of specific ventilation. This improvement went together with a significant but limited increase in the area of hyperinflated lung zones.

Conclusions: The findings of this study suggest that in mechanically ventilated rabbit with severely heterogeneous bronchoconstriction, a positive end-expiratory pressure of 5 cm H2O significantly improves regional ventilation homogeneity through dilation of flow-limited airways and recruitment of closed airways.

From the European Synchrotron Radiation Facility (LP, HS), Grenoble, France; the Department of Physics (LP, PS), University of Helsinki, Helsinki, Finland; the Department of Clinical Physiology and Nuclear Medicine (ARAS), Helsinki University Central Hospital, Helsinki, Finland; and Université de Picardie Jules Verne (SB), EA4285 Péritox UMI01 INERIS and CHU Amiens, Amiens, France.

This work was supported by the Academy of Finland, by the Tampere Tuberculosis Foundation, and by the European Synchrotron Radiation Facility. S.B. is supported by the Conseil Régional de Picardie grant REG08009.

The authors have not disclosed any potential conflicts of interest.

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© 2011 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins