Baseline characteristics of chronic obstructive pulmonary disease subjects without chronic bronchitis (CB−) and with chronic bronchitis (CB+)
| CB− | CB+ | p-value | |
| Subjects n | 752 | 172 | |
| Age years | 70.5 (15.2) | 74.1 (13.6) | 0.004 |
| Male | 380 (50.5%) | 96 (55.8%) | 0.211 |
| Smoking status | 0.005 | ||
| Never-smoker | 134 (17.8%) | 17 (9.9%) | |
| Former smoker | 407 (54.1%) | 89 (51.7%) | |
| Current smoker | 211 (28.1%) | 66 (38.4%) | |
| Cigarette smoking pack-years | 23.0 (41.2) | 30.6 (35.1) | <0.001 |
| Height m | 1.69 (0.14) | 1.68 (0.12) | 0.529 |
| Weight kg | 76.7 (18.8) | 74.8 (17.3) | 0.082 |
| BMI kg·m−2 | 26.6 (5.3) | 26.0 (5.5) | 0.093 |
| FEV1 L | 2.0 (1.1) | 1.8 (0.9) | <0.001 |
| FEV1 % pred | 82.0 (26.7) | 70.5 (27.8) | <0.001 |
| FVC L | 3.1 (1.6) | 2.9 (1.4) | 0.034 |
| FVC % pred | 101.0 (29.5) | 91.9 (33.0) | 0.008 |
| FEV1/FVC % | 65.4 (7.0) | 61.0 (10.0) | <0.001 |
| Quality of life % | 80.0 (21.9) | 71.9 (31.3) | <0.001 |
Data are presented as median (interquartile range) unless otherwise stated. Quality of life was based on the EuroQol five-dimensions questionnaire (EQ-5D; www.euroqol.org) measuring how satisfied/troubled participants are in terms of mobility, ability and activity, self-care, pain and anxiety. A score out of 100 was calculated as the weighted average of scores (minimum=unsatisfied/seriously troubled; maximum=very satisfied/not troubled at all) given to the individual questions. Data were missing on pack-years in 46 subjects, height/weight/BMI in 43 subjects, interpretable baseline lung function measurement in 330 subjects and quality of life in 12 subjects. BMI: body mass index; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity.