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 cmH(2)O, 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.
Our results on a denervated isolated perfused lung model demonstrate the potential of Des and Sev to decrease the basal airway tone, whereas Iso and Hal are ineffective in this regard. All of these volatile agents markedly protect against Ach-induced bronchoconstriction.
Our results reveal the lack of potential of the commonly used volatile anesthetics to inhibit the most severe acute phase of the constrictor response to allergen after anaphylaxis in both the central airway and peripheral lung compartments. Inhalation of volatile anesthetics, particularly sevoflurane, promotes an earlier easing of the bronchospasm; this beneficial profile may be advantageous in children with atopic lung diseases.
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