 Methods enrolled patients are connected to a S5 ICU monitor GE, Helsinki, Finland and are mechanically ventilated with a Servo-I ventilator Maquet, Germany provided with diaphragmatic electrical activity module EAdi, Maquet, Germany. A nasogastric 16-Fr EAdi catheter is positioned in all patients. A sequence of three consecutive study phases of different mechanical ventilation modes PCV, PSV, and NAVA is started. The sequence of ventilatory modes is randomized for every patient. After a 10 min acclimation period for each study phase, electrocardiographic, arterial pressure and ventilatory waves are collected for consecutive 30 min to a laptop pc via S5 Collect GE, Helsinki, Finland and NAVA Tracker Maquet, Germany software for Windows. 