• Edgardo D'Angelo, Matteo Pecchiari, Paolo Baraggia, Marina Saetta, Elisabetta Balestro, and Joseph Milic-Emili.
• Istituto di Fisiologia Umana I, Università di Milano, 20133 Milan, Italy. edgardo.dangelo@unimi.it
• J. Appl. Physiol. 2002 Mar 1;92(3):949-56.

AbstractLung mechanics and morphometry of 10 normal open-chest rabbits (group A), mechanically ventilated (MV) with physiological tidal volumes (8-12 ml/kg), at zero end-expiratory pressure (ZEEP), for 3-4 h, were compared with those of five rabbits (group B) after 3-4 h of MV with a positive end-expiratory pressure (PEEP) of 2.3 cmH(2)O. Relative to initial MV on PEEP, MV on ZEEP caused a progressive increase in quasi-static elastance (+36%) and airway (Rint; +71%) and viscoelastic resistance (+29%), with no change in the viscoelastic time constant. After restoration of PEEP, quasi-static elastance and viscoelastic resistance returned to control levels, whereas Rint remained elevated (+22%). On PEEP, MV had no effect on lung mechanics. Gas exchange on PEEP was equally preserved in groups A and B, and the lung wet-to-dry ratios were normal. Both groups had normal alveolar morphology, whereas only group A had injured respiratory and membranous bronchioles. In conclusion, prolonged MV on ZEEP induces histological evidence of peripheral airway injury with a concurrent increase in Rint, which persists after restoration of normal end-expiratory volumes. This is probably due to cyclic opening and closing of peripheral airways on ZEEP.

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