Fig. 3.

Representative example of over-assistance during pressure support ventilation (PSV). The patient was ventilated with an inspiratory pressure set at 10 cmH₂O above a positive end-expiratory pressure of 8 cmH₂O. A double-balloon nasogastric catheter was placed for measurements of esophageal pressure (Pes) and gastric pressure. Transdiaphragmatic pressure (Pdi) was calculated as gastric pressure minus Pes. As can be seen in the Pes waveform, the patient only triggers the ventilator (small drop in Pes) and relaxes inspiratory muscles thereafter, as demonstrated by the increase in Pes during the remaining of the inspiratory cycle and the absence of increases in Pdi