Pulmonary rehabilitation programmes including aerobic exercise training have strong evidence of effectiveness in improving exercise capacity, dyspnoea and HRQL in patients with COPD. Therefore, current guidelines recommend pulmonary rehabilitation, including exercise training, in these patients. Non-invasive ventilation(NIV) is increasingly used during exercise training programmes in order to train patients at intensity levels higher than allowed by their clinical and pathophysiological conditions. Patient-ventilator asynchrony (PVA) describes the poor interaction between the patient and the ventilator and is the consequence of the respiratory muscle activity of the patient being opposed to the action of the ventilator.PVA have unfavourable clinical impace on gas exchange, dyspnoea perception, patient comfort and tolerance and reduced adherence to NIV. This study is going to detect whether the PVA will increase when COPD patients exercise with NIV supporingt

Inclusion Criteria:

1. Age 40-80, males and females;
2. Stage III and IV COPD;
3. Similar with non-invasive ventilation;
4. Willing to participate in the study;
5. Able to provide informed consent.

Exclusion Criteria:

1. Presented with an acute exacerbation during previous 3 months;
2. Bronchiectasis; post-tuberculosis sequelae; rib cage deformities; neuromuscular disorders; and bronchial carcinoma.
3. Intolerant with NIV

Patients with COPD, according to the criteria set by the Global Initiative for Obstructive Lung Disease scientific committee, were asked to participate in the present study. Patients had to meet the following inclusion criteria: 1) Age 40-80, males and females; 2) Stage III and IV COPD; 3) Similar with non-invasive ventilation; 4) Willing to participate in the study; 5) Able to provide informed consent.