Fig. 1

Physiologic waveforms of airway pressure and esophageal pressure during the end-inspiratory (A) and end-expiratory hold (B). The elements of airway and esophageal pressure used for analysis are as follows. Peak pressure (Ppeak): the highest airway pressure before the start of an end-inspiratory hold. Plateau pressure (Pplat): the airway pressure that reached a plateau during an end-inspiratory hold. Respiratory muscle pressure index (PMI): Pplat minus Ppeak. Airway occlusion pressure (P0.1): the drop in airway pressure during expiratory occlusion from the beginning of the drop to 100 ms after the first drop in airway pressure. Expiratory occlusion pressure (Pocc): the difference from positive end-expiratory pressure (PEEP) to the lowest airway pressure during the first inspiratory cycle during an expiratory hold maneuver. Delta Pes (∆Pes): the difference from end-expiratory Pes to maximum negative Pes during non-occluded (PC or PS) breaths. A In airway occlusion at the end of inspiration, if the patient became relaxed during occlusion, Pplat is achieved. The difference between the plateau pressure and Ppeak is the PMI. B In airway occlusion at the end of expiration, the maximum negative pressure during the next spontaneous breath is Pocc, and the negative pressure 0.1 ms after the start of inspiration is P0.1