Inclusion Criteria:  Critically ill patients intubated for more than 48 hours who are ready for weaning with the following criteria.  positive end-expiratory pressure (PEEP) ≤ 5 cm H2O. Fraction of inspired oxygen (FiO2) < 0.5. respiratory rate (RR) < 30 breaths/min. rapid shallow breathing index < 105, PaO2/FiO2 > 200. Age< 65 years.  Exclusion Criteria:  Age<18 years. Patient with history of plural effusion, trauma to chest and history of mechanical ventilation for < 6 months. patient with neuromuscular diseases affect diaphragm .