Domiciliary application of non-invasive positive pressure ventilation with average volume assured pressure support to subjects with chronic obstructive pulmonary disease (COPD) who remain hypercapnic following the application of non-invasive positive pressure ventilation (NPPV) for an acute exacerbation

1. Daytime PCO2, measured by arterial blood gases at baseline, 1, 3, 6 months and 1 year
2. Endothelial dysfunction, measured by peripheral arterial tone (PAT) at baseline, 1, 3, 6 months and 1 year

1. Lung function, measured by spirometry, according to the joint recommendations of the ERS/ATS. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year
2. Dyspnoea, measured at rest by the Borg scale. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
3. Fatigue, measured by Fatigue Severity Scale (FSS). The FSS questionnaires contains nine statements that rate the severity of the subject's fatigue symptoms an a scale from 1 to 7. A total score of less than 36 suggests that the subject may not be suffering from fatigue, while a score of greater than or equal to 36 indicates excessive fatigue. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
4. Sleep quality, measured by polysomnography (PSG), including transcutaneous PCO2. At baseline, PSG will be performed in spontaneous breathing in order to characterise the abnormal respiratory events associated with COPD and identify obstructive sleep apnoea (OSA). Sleep and respiratory events will be recorded and scored manually according to standard criteria. REM hypoventilation will be scored when a progressive oxygen desaturation is associated with a sustained reduction in both flow and thoracic components of ventilation. During the same period, a constant or reduced respiratory drive (assessed by a reduction in respiratory effort as demonstrated by pulse transit time) should be observed without characteristic apnoeic or hypopnoeic episodes. At 3 months and 1 year, polysomnography will be done in spontaneous breathing or using non-invasive ventilation depending the arm of the study. Timepoints of assessment: baseline, 3 months and 1 year.
5. Objective sleepiness as measured by the Osler Test. This test consists of a 40 minutes sleep-resistance challenge conducted in a dark and quiet room. The subject will be asked to remain awake while reacting to a visual stimulus, which appears for 1 second every 3 seconds, by hitting a button. Sleep latency will be defined as the delay between the onset of the test and the moment corresponding to seven consecutive flashes (i.e. 21 seconds) without response. Fluctuations in vigilance and micro-sleep episodes will be quantified as the number of occasions that 3 to 6 consecutive flashes occur without response (i.e. 9 to 18 seconds without response of the patient). Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
6. Exercise capacity. At baseline a practice test will be performed at least one hour before the actual test. The highest 6-minute walk distance will be reported as the patient's 6-minute walk distance at baseline. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
7. Physical activity. This will be objectively measured using the Actiwatch®. The Actiwatch® measures activity with a piezo-electric accelerometer that records intensity, amount and duration of movement in all directions. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
8. Quality of life, measured using the validated French version of the St Georges Respiratory Questionnaire. Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
9. Arterial stiffness, determined by pulse wave velocity (PWV). Timepoints of assessment: baseline, 1, 3, 6 months and 1 year.
10. Time in hospital over course of follow up period