Baseline characteristics
| Cohort 1: patients with COPD and isolated nocturnal desaturation | Cohort 2: patients with COPD and severe hypoxaemia | Cohort 3: unselected patients | |
| Subjects n | 240 | 212 | 848 |
| Age years | 69±8 | 72±10 | 72±12 |
| Sex, male n (%) | 157 (65%) | 97 (46%) | 460 (54%) |
| PaO2 mmHg | 67±7 | 52±5 | 57±10 |
| SaO2 % | 93±2 | 87±4 | 89±5 |
| SpO2 % | 93±2 | N/A | N/A |
| PaCO2 mmHg | 42±6 | 47±8 | 44±8 |
| pH | 7.42±0.03 | 7.41±0.04 | 7.43±0.04 |
Data expressed as mean±sd unless otherwise stated. 1 mmHg=0.133 kPa; 1 kPa=7.50 mmHg. N/A: not available. PaO2: arterial oxygen tension; SaO2: arterial oxygen saturation; SpO2: pulse oximetry saturation; PaCO2: arterial carbon dioxide tension.