Protocol: Once enrolled, the patients are ventilated in PS (PScli1) as set by the clinician. They are then ventilated in NAVA at 3 different levels of muscle unloading in randomized order. At NAVAcli, the assist level matches to PScli1 in terms of muscle unloading. With NAVA40% and NAVA60%, the patients have 40% and 60% unloading, respectively. In the last study step the patients are back to PS (PScli2). Each patient is his/her own control and goes through the 5 ventilation periods, of 30min each. In the last 5 min of each study step, the CoV (obtained through the EIT data), blood gas samples (for oxygenation and ventilation) and ventilatory parameters are obtained and analyzed.