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Lung mechanical and vascular changes during positive- and negative-pressure lung inflations: importance of reference pressures in the pulmonary vasculature

¹Department of Medical Informatics and Engineering, University of Szeged, Szeged, Hungary; ²Anesthesiological Investigations Unit, University of Geneva, Geneva, Switzerland; and ³Pediatric Anesthesia Unit, Geneva Children's Hospital, Geneva, Switzerland

Submitted 3 August 2007 ; accepted in final form 12 December 2008

The continuous changes in lung mechanics were related to those in pulmonary vascular resistance (Rv) during lung inflations to clarify the mechanical changes in the bronchoalveolar system and the pulmonary vasculature. Rv and low-frequency lung impedance data (ZL) were measured continuously in isolated, perfused rat lungs during 2-min inflation-deflation maneuvers between transpulmonary pressures of 2.5 and 22 cmH₂O, both by applying positive pressure at the trachea and by generating negative pressure around the lungs in a closed box. ZL was averaged and evaluated for 2-s time windows; airway resistance (Raw), parenchymal damping and elastance (H) were determined in each window. Lung inflation with positive and negative pressures led to very similar changes in lung mechanics, with maximum decreases in Raw [–68 ± 4 (SE) vs. –64 ± 18%] and maximum increases in H (379 ± 36 vs. 348 ± 37%). Rv, however, increased with positive inflation pressure (15 ± 1%), whereas it exhibited mild decreases during negative-pressure expansions (–3 ± 0.3%). These results demonstrate that pulmonary mechanical changes are not affected by the opposing modes of lung inflations and confirm the importance of relating the pulmonary vascular pressures in interpreting changes in Rv.

pulmonary hemodynamics; airway resistance; lung elastance; forced oscillations; lung perfusion; recruitment maneuver