Participant demographics
| NC | NLFS | SAD | COPD-CS | COPD-ES | |
| Subjects, n | 12 | 5+1# | 8+1# | 9 | 10 |
| Sex, n | |||||
| Female | 6 | 4 | 7 | 5 | 3 |
| Male | 6 | 2 | 2 | 4 | 7 |
| Age (years) | 42 (19–63) | 68.5 (52–79) | 59 (42–84) | 63 (59–78) | 68 (56–85) |
| Smoking (pack-years) | 0 | 27 (1–60) | 40 (20–72) | 30 (2–50) | 30 (18–60) |
| Passive smoking, n=1 | 10 | 20 | |||
| FEV1 (% predicted) | 100 (87–143) | 83 (60–109) | 77 (57–109) | 81.5 (63–98) | |
| FEV1/FVC (%) | 81.5 (70–90) | 73.4 (69–78) | 66 (60–70) | 63.9 (55–69) | |
| FEF25–75% (% predicted) | 81.5 (71–116) | 46.5 (31–69) | 37 (28–47) | 38 (20–55) | |
| DLCO (% predicted) | 84.4 (50–95) | 78.1 (54–91) | 71 (34–84) | 78 (51–105) |
Data expressed as median (range), unless otherwise indicated. NC: never-smoker normal controls; NLFS: normal lung function smokers; SAD: patients with small airway disease; COPD-CS: current smokers with chronic obstructive pulmonary disease; COPD-ES: ex-smokers with chronic obstructive pulmonary disease; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; FEF25–75%: forced expiratory flow at 25–75% of FVC (L·s−1); DLCO: diffusing capacity of the lungs for carbon monoxide. #: number of subjects with passive smoking history.