Does a solitary lobar collapse give pressure-lung volume relationship similar to that found in acute respiratory distress syndrome? A porcine experimental study.

Background: The underlying pathophysiology causing different shapes of static pressure-lung volume (PV) curves is not fully elucidated. In this study the aim was to examine the influence of a solitary lobar collapse on inflation-deflation PV curves. The hypothesis was that a lobar collapse would induce the same changes in the PV-curve as those found in experimental acute lung injury (ALI) and in acute respiratory distress syndrome (ARDS).

Methods: In four mechanically ventilated, anaesthetized pigs, the right lower lobe was collapsed by selective lavage and exsufflation. End-expiratory lung volume and static inflation-deflation PV curves of the respiratory system, the chest wall and the lung were obtained before formation of the collapse. After creation of the collapse, the same measurements were performed in the non-collapsed lung and in the whole lung including the lobar collapse. In two animals computed tomography was performed to verify the lobar collapse.

Results: The solitary lobar collapse changed the PV curve by inducing a significant hysteresis and a right shift of lower inflexion point (LIP) on the inflation limb, but had minimal influence on the deflation limb. After creation of the lobar collapse, LIP was found at the pressure at which the collapse started to expand.

Conclusions: PV curves of lungs with solitary lobar collapse are similar to those found in ALI/ARDS. Inspiratory LIP indicated start of recruitment, and expiratory curves did not indicate the pressure at which collapse occurred.