The goal of this physiological cross-over clinical trial is to evaluate the effect of different clinically used weaning trials on regional mechanical ventilation in a population of patients undergoing weaning from mechanical ventilation for acute respiratory failure.

The main question[s] it aims to answer are:

• to evaluate which weaning trial is associated to a better regional ventilation distribution
• to evaluate which weaning trial can be comparable to ventilation distribution after extubation

Participants will undergo 3 clinically used weaning trials in a random order (cross-over trial). Researchers will compare the different steps to see if regional ventilation distribution is different among the different trial .

Inclusion Criteria:

• Age > 18 and < 70 years
• Ready to be weaned from mechanical ventilation according to clinical criteria

Exclusion Criteria:

• Age < 18 years or > 70 years
• Presence of chest drains
• Presence of pacemaker/impantable cardiac device;
• diagnosis of Pneumothorax, or pneumomediastinum
• Diagnois of neuromuscular diseases
• Use of neuromuscular blockers in the 48 hours before screening;
• Body mass index > 35 kg/m2
• Refusal to participate of the patient/next of kin