Fig. 1. Ensemble average of records of flow (V̇) and changes in transpulmonary pressure (PL) and esophageal (Pes) pressure from 25 consecutive breaths in a representative subject during hypo- (Paco2= 21 mmHg;left ), normo- (Paco2= 39 mmHg;middle ) and hypercapnic conditions (Paco2= 66 mmHg; right ).