Evaluation of respiratory mechanics and lung histology in a model of atelectasis.

To develop a reproducible model of atelectasis, 15 mechanically ventilated Wistar rats were wrapped around the thorax/abdomen with a sphygmomanometer. The cuff was inflated to transpulmonary pressures (PL) of -4 cmH2O (group A) and -8 cmH2O (group B) for 5 sec. Group C was not compressed. Airflow, volume, tracheal and oesophageal pressures were registered. Respiratory system (rs), lung (L), and chest wall resistive (DeltaP1), viscoelastic/inhomogeneous pressures (DeltaP2), DeltaPtot (=DeltaP1 + DeltaP2), static (Est) and dynamic (Edyn) elastances, and DeltaE (=Edyn - Est) were determined before and after compression. In A, respiratory mechanics remained unaltered. In B, Est,rs (+99%), Est,L (+111%), DeltaE,rs (+41%), DeltaE,L (+73%), DeltaP1,rs (+45%), DeltaP1,L (+44%), DeltaP2,rs (+41%), DeltaP2,L (+69%), DeltaPtot,rs (+40%), and DeltaPtot,L (+58%) increased after compression. Mean alveolar diameter and bronchiolar lumen decreased in A, and were even smaller in B. In conclusion, chest wall compression with PL of -8 cmH2O yielded a reproducible alveolar collapse, which resulted in increased elastic, resistive and viscoelastic/inhomogeneous pressures.