Non-invasive Positive Pressure (NPPV ) 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.