 Methods We will performed a prospective, single blind cohort study in patients on Pressure Support Ventilation. 10 healthy adult patients admitted to the ICU after elective facial or neck surgery will be included. All patients will be ventilated in pressure support mode using a Servo 300 ventilator Siemens. Elema, Solna, Sweden, with a positive end expiratory pressure of 5 cm H2O, pressure support level of 12 cm H2O above PEEP and an inspiratory oxygen fraction of 0.40. Patients have to be awake and cooperative Ramsay 2. WOB will be measured with an esophageal balloon, and miniature flowmeter Bicore system. Breathing comfort will be evaluated using a visual analogue scale VAS ranging from 1 to 10. WOB and patient comfort will be measured in random order at 0, 5, and 10 IRT. For statistical analysis the two-way analysis of variance will used. A p value of 0.05 will be considered statistically significant. 