Fig. 1. Idealized volume–pressure curve of the respiratory system of a normal subject (  black circles ) and a patient with acute respiratory distress syndrome (ARDS;  white circles ). The volume–pressure curve of the patient with ARDS has a low compliance, an “upper inflection point” at which overdistention of the lung may occur, and a “lower inflection point” above which optimal recruitment may occur. FRC = functional residual capacity.