2. Have spirometric evidence of COPD with an FEV1 of \< 50% predicted and FEV1/FVC \< 0.70, measured within the last 6 months (GOLD stage III and IV). Stable disease since 4 weeks or more prior to randomisation.
3. PCO2 of 7 kPa, combined with a pH of 7.35 or above. These gases must be measured after 30 minutes breathing room air in sitting position
4. No treatment with NPPV and respiratory muscle training in the last 8 weeks
You may not be if
1. Smokers can be excluded;
2. Diseases of the lung or thorax besides COPD: OSA Advanced pulmonary fibrosis, advanced bronchiectases, active tuberculosis, post tuberculosis syndrome, pneumonia, severe kyphoscoliosis, tracheostoma, neuromuscular diseases, or any other disorder, which might result in elevated PCO2
3. Body mass index of 35 kg/m² or above. Severe cardiac disease, NYHA IV, instable angina, severe cardiac arrhythmia, especially of ventricular origin (atrial fibrillation is not an exclusion criterion).
4. Local derangement of the face, skin, tongue, upper airways, larynx and upper oesophagus.
5. Severe chronic diseases except COPD, hindering the patient to follow the schedule of this study
