The clinical characteristics of each cluster
| Cluster 1: lower-level cluster I | Cluster 2: lower-level cluster II | Cluster 3: higher-level cluster I | Cluster 4: higher-level cluster II | |
| Female | 34 | 47 | 48 | 33 |
| Age, years | 65±7 | 61±6 | 62±6 | 69±6 |
| Lung function | ||||
| FEV1, L | 1.5±0.5 | 1.4±0.5 | 1.4±0.5 | 1.3±0.6 |
| FEV1, % predicted | 54±16 | 51±19 | 50±15 | 48±16 |
| FEV1/FVC, % | 41±12 | 40±11 | 40±11 | 38±9 |
| DLCO, % predicted | 60±17 | 54±16 | 58±17 | 48±14 |
| ITGV, % predicted | 139±32 | 156±35 | 147±34 | 152±29 |
| RV, % predicted | 153±45 | 175±54 | 162±44 | 165±39 |
| TLC, % predicted | 116±17 | 123±16 | 119±17 | 116±16 |
| PaCO2, kPa | 5.3±0.6 | 5.2±0.5 | 5.5±0.7 | 5.4±0.6 |
| PaO2, kPa | 9.6±1.1 | 9.6±1.2 | 9.3±0.9 | 9.2±0.9 |
| SaO2, % | 95.1±1.9 | 95.2±1.7 | 94.7±2.0 | 94.4±1.8 |
| PImax, % predicted | 85±24 | 77±25 | 78±22 | 75±18 |
| PEmax, % predicted | 64±20 | 62±22 | 60±17 | 56±17 |
| COPD-specific characteristics | ||||
| mMRC dyspnoea grade | 2.0±1.1 | 2.0±1.1 | 2.1±0.9 | 2.4±1.3 |
| Long-term oxygen therapy | 11 | 14 | 17 | 31 |
| Smoking pack-years | 44±21 | 47±28 | 48±30 | 47±23 |
| Current smoker | 14 | 31 | 37 | 36 |
| Hospital admissions for COPD in past 12 months, n | 0.51±1.17 | 0.42±1.17 | 0.49±0.84 | 0.69±1.28 |
| Steroid/antibiotic courses for COPD in past 12 months, n | 1.53±1.95 | 1.42±1.61 | 1.01±1.32 | 1.92±1.92 |
| Exacerbations in past 12 months, n | 2.05±2.60 | 1.85±2.41 | 1.54±1.81 | 2.55±2.18 |
| GOLD group A/B/C/D | 19/30/20/30 | 18/26/15/40 | 11/40/7/40 | 15/18/15/51 |
| Physical fitness | ||||
| 6MWD, m | 493±91 | 497±101 | 461±91 | 402±126 |
| Peak work rate, W | 86±30 | 76±23 | 75±27 | 58±26 |
| Peak work rate, % predicted | 63±25 | 62±25 | 61±29 | 47±22 |
| Constant work-rate test, s | 409±264 | 408±329 | 296±191 | 234±187 |
| Health status | ||||
| SGRQ symptoms domain | 54±19 | 53±21 | 57±18 | 57±25 |
| SGRQ activity domain | 65±22 | 68±22 | 73±17 | 69±27 |
| SGRQ impact domain | 35±19 | 38±18 | 47±16 | 43±26 |
| SGRQ total score | 48±19 | 50±17 | 57±12 | 53±23 |
| Prognostic indices | ||||
| Updated BODE index | 2.2±1.8 | 2.7±2.3 | 2.6±2.0 | 4.6±3.7 |
| Framingham risk score | 9.7±6.1 | 7.5±5.9 | 9.3±7.2 | 12.3±7.2 |
Data are presented as mean±sd or %, unless otherwise stated. ▪ A significantly higher level compared to the remaining three clusters (p<0.01); ▪ a tendency for a significantly higher level compared to the remaining three clusters (p-value between 0.05 and 0.01); ▪ a significantly lower level compared to the remaining three clusters (p<0.01); ▪ a tendency for a significantly lower level compared to the remaining three clusters (p-value between 0.05 and 0.01). FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; DLCO: diffusion capacity of the lung for carbon monoxide; ITGV: intrathoracic gas volume; RV: residual volume; TLC: total lung capacity; PaCO2: arterial carbon dioxide partial pressure; PaO2: arterial oxygen partial pressure; SaO2: arterial haemoglobin oxygen saturation; PImax: maximal inspiratory mouth pressure; PEmax: maximal expiratory mouth pressure; mMRC: modified Medical Research Council; GOLD: Global Initiative for Chronic Obstructive Lung Disease; 6MWD: 6-min walk distance; SGRQ: St George's Respiratory Questionnaire; BODE: body mass index, obstruction, dyspnoea, exercise capacity index.