Fig. 2. Pressure–volume relations obtained in each measurement sequence. Each point represents the data obtained in one occlusion where a flat plateau tracing was seen. The volume delivered to the patient is plotted as a function of the difference between the airway pressure during the plateau phase and the positive end-expiratory pressure (Ppl, aw− PEEP), i.e. , the elastic recoil pressure of the respiratory system. In each measurement sequence, a good linear relation could be disclosed, suggesting that effective muscle relaxation had been achieved. PS = pressure support; VDEL= volume effectively delivered to the patient from the beginning of inspiration to the time of occlusion.