Prolong mechanical ventilation cause to respiratory muscle weakness and high risk to weaning failure,the investigators hypothesize that

1. Specific inspiratory muscle training (SIMT) using threshold loaded breathing device (BreatheMAX V.1)in patients with ventilator dependence will improve inspiratory muscle strength
2. SIMT will improve lung function in patients with ventilatory dependence.
3. SIMT will improve weaning success in patients with ventilatory dependence.

Prolonged mechanical ventilation cause detrimental effects on lung function and high risk of lung complications and standard weaning protocols are not successful in a number of patients. The strength of the inspiratory muscles is important factors in the success of weaning. Although, the inspiratory muscles are trained by manipulating the ventilator sensitivity and made of ventilation in the traditional protocol, the muscle function might not improved sufficiently to sustain independent and spontaneous breathing. Consequently, specific inspiratory muscle training is indicated and has been studied in patient with weaning failure. However, there is little evidence available and no firm conclusion can be drown. Therefore, the purpose of this study is to determine whether specific IMT training using the local made loaded threshold IMT device can improve lung function and accelerate the weaning process.

Inclusion Criteria:

• Patient who have been mechanically ventilated > 72 hours and start to weaning from medical order or ventilator dependent patients who have failed to wean prior to study.
• Normal arterial blood gas (PaCO2 < 50mmHg, PaO2 > 60 mmHg on FiO2 <0.5 or SaO2 > 90%, PH 7.35-7.45).
• Cardiovascular stability (HR ≤ 140 beats/min, systolic BP 90-140 mmHg and diastolic BP 60-90 mmHg, with no or minimal vasopressors)
• Good consciousness, cooperation and can sit in an upright position > 30 minutes

Exclusion Criteria:

• Persistent homodynamic instability.
• Severe breathlessness at rest when spontaneous breathing.
• Coronary heart disease with angina.
• Life threatening arrhythmia (VF, VT).
• Sedation Ramsay scale > 2
• Severity of disease APACHE II score > 29