Fluid-like behavior presented in normal lung vs. solid-like behavior presented in injured lung. (A) The normal lung is traditionally considered to be a continuous elastic system—exhibiting fluid-like behavior—such that distending pressure applied to a local region of the pleura (the negative swing in pleural pressure generated by diaphragmatic contraction is −10 cm H2O) becomes generalized over the whole lung (pleural) surface (the negative swings in pleural pressure at any regions are the same −10 cm H2O). (B) In injured lung, the negative swing in pleural pressure generated by diaphragmatic contraction is not uniformly transmitted, but rather concentrated in the dependent lung regions, thus a huge difference in negative pleural pressure between nondependent and dependent lung regions was generated at the early phase of inspiration, causing Pendelluft. Adapted with permission of the Wolters Kluwer Health (Ref. ).