 Introduction Pressure Support Ventilation is widely used in patients in the ICU. Matching the patients respiratory needs with adequate ventilator settings is necessary to ensure a low work of breathing WOB and maximal patient comfort. The inspiratory rise time IRT determines the time to reach the selected airway pressure. A short IRT results in a high peak inspiratory flow and a short time to reach that peak, but is also associated with the development of turbulent flow, resulting in increased WOB. Aim of this study is to investigate the effects of different IRT settings on WOB and patient comfort during pressure support ventilation. 