1. The first objective of this study is to determine the differences between, while the airway obstruction severity is the same, and the acute continuous positive airway pressure (CPAP) effect on chronic obstructive pulmonary disease (COPD) patients with overlap syndrome compared with COPD patients without in terms of sleep quality, autonomic nerve activity, biologic markers of systemic inflammatory, and exercise performance.
2. The second objective of this study is to evaluate the subacute (3 months treatment) CPAP effect on COPD patients with overlap syndrome in terms of pulmonary hemodynamic and right heart function, We will also determine the subacute effect of CPAP on sleep and life quality, autonomic nerve activity, biologic markers of systemic inflammatory, as well as exercise performance.
3. The last objective of this study is to evaluate the long term (12 months treatment) CPAP effect on COPD patients with overlap syndrome. The un-scheduled clinic or emergency department visiting, hospitalization, or mortality will be recorded to see if there is significant treatment effect in terms of reducing morbidity and mortality. The long term CPAP effect on sleep and life quality, autonomic nerve activity, biologic markers of systemic inflammatory, exercise performance, as well as pulmonary hemodynamic and right heart function will be re-evaluation.

COPD patients will be disturbed by season 12 months follow up is better than 18 months

Inclusion Criteria:

• chronic stable COPD
• FEV1/FVC < 70%
• No response to beta-agonist
• without acute exacerbation within2 months

Exclusion Criteria:

• Chronic respiratory failure (PaO2<60 mmHg, PaCO2>50 mmHg)
• Clinical evidence of congestive heart failure
• Facial defect and all the other condition that can't tolerate nasal mask
• Malignancy

from outpatient clinic of CGMH and those in COPD cohort