The study aims to assess the agreement between respiratory mechanics parameters measured noninvasively by means of brief airways occlusions at the beginning of inspiration and the reference parameters obtained with standard techniques of esophageal and gastric pressure under static and dynamic conditions in a mixed population of ICU patients mechanically ventilated in pressure support ventilation mode.

Inclusion Criteria:

• intact respiratory drive;
• PaO2/FiO2 ratio > 150 with a positive end-expiratory pressure (PEEP) ≤ 8 cmH2O;
• pH between 7.35 and 7.45;
• patient alert, conscious, and cooperative with a Glasgow Coma Scale ≥ 10.

Exclusion Criteria:

• infection, sepsis or septic shock; (with fever no)
• hemodynamic instability;
• respiratory centres depression;
• esophageal deformity, or gastric/esophageal illnesses;
• previous recent gastric/esophageal surgery.