Characteristics of the patient groups
| Control | Stage II | Stage IV | |
| Subjects n | 8 | 11 | 8 |
| Age yrs | 63 (36–78) | 68 (44–81) | 54 (44–61) |
| Male/female | 4/4 | 10/1 | 1/7 |
| Smoking (C/Ex/N) | 3/3/2 | 6/5/0 | 0/8/0 |
| Pack-yrs smoking | 27 (0–75) | 40 (14–58) | 31 (12–54) |
| FEV1 % pred | 104 (83–134) | 68 (50–76)# | 21 (13–29)# |
| FEV1/FVC % | 74 (70–81) | 53 (37–68)# | 35 (24–66)# |
| Chronic bronchitis | No | No | No |
Data are presented as mean (range), unless otherwise stated. Stage II: Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage II chronic obstructive pulmonary disease (COPD); Stage IV: GOLD stage IV COPD; C: current smoker; Ex: ex-smoker, not smoking for ≥1 yr; N: never-smoker; FEV1: forced expiratory volume in one second; % pred: percentage of predicted value; FVC: forced vital capacity. #: indicates a significant difference compared with the control group.