Assessment of the effect and safety of noninvasive positive pressure ventilation for severe stable chronic obstructive pulmonary disease

Inclusion Criteria:

• clinically stable, hypercapnic GOLD stage IV COPD, aged 18 years or older, baseline arterial carbon dioxide pressure (PaCO2) of 6.7 kPa (50 mmHg) or higher and a pH higher than 7·35, measured after at least 1 h rest in a sitting position.

Exclusion Criteria:

• thorax or the lung other than COPD
• No smoking or Cigarette≤10/day
• obesity with a bodymass index (BMI) ≥40 kg/m²
• malignant co-morbidities,severe heart failure (New York Heart Association stage IV),unstable angina, and severe arrhythmias.