Figure 2.

Comparison of a prototypical acute lung disorder, acute respiratory distress syndrome (ARDS), with a chronic disorder, idiopathic pulmonary fibrosis (IPF). These conditions highlight two major unresolved questions in the field of lung injury. (1) Are acute and chronic injury qualitatively different or do they just differ in degree and kinetics? (2) Because even catastrophic insults such as ARDS can heal, whereas IPF apparently never does (at least not once it is diagnosed as such), it remains to be determined which injury-induced anatomic derangements are reversible and which are not.