Diaphragmatic Tissue Doppler During Weaning From Mechanical Ventilation

"Patients will be subjected to a spontaneous breathing test (Cpap 5), that consists in applying a positive end-expiratory pressure of 5 cm H2O for 20 minutes.~A tissue doppler evaluation will then be performed by analyzing the diaphragmatic displacement velocity during inspiration and expiration and calculating the speed of muscles displacement and other derived index of muscle function in the modality of ventilation which precedes the trial, during the SBT and after extubation."