Inclusion Criteria:  more than 48 hours of invasive mechanical ventilation presence of tracheostomy need for two or more broncoaspirations per hour in the previous 8 hours  Exclusion Criteria:  life threatening cardiac arrythmia pneumothorax acute spinal injury chest trauma brain injury in the previous 15 days hemodynamic instability chest or abdominal surgery in the previous 7 days pregnancy enrollment in other study protocols