[The ultrastructural morphogenetic bases of the adult respiratory distress syndrome].

Sequential study of the submicroscopic pathological events characterising the natural history of the adult respiratory distress syndrome has pinpointed three different development stages related to clinical course and prognosis. In the first stage, the decisive biological element is represented by the increase in capillary permeability, whose morphological substrate consists of the distension of intercellular junctions. The result is the formation of interstitial oedema with the characteristics of the exudate. In the second stage, when reversibility is still possible, fluid and proteins pass into the alveolus. Finally, in the third stage, the persisting stimulus of pulmonary capillaries leads on the one hand to the formation of hyaline membranes and, on the other, to a reactive lung response in the form of interstitial fibrinogenesis and hyperplasia of granular pneumocytes.