Participant characteristics
| Participant characteristics | All (N=245) | Unexposed (N=106) | Exposed (N=139) | P value |
| Demographics and anthropometrics | ||||
| Age (years) | 53.8±11.3 | 47.1±11.8 | 58.9±7.7 | <0.001 |
| Female sex (n (%)) | 213 (86.9) | 25 (23.6) | 7 (5.0) | <0.001 |
| Height (cm) | 166.3±7.1 | 167.6±8.6 | 165.4±5.5 | 0.046 |
| Weight (kg) | 66.3±11.5 | 66.9±12.3 | 65.8±11.0 | 0.754 |
| BMI (kg/m2) | 23.9±3.6 | 23.7±3.3 | 24.1±3.9 | 0.733 |
| Haemoglobin (g/dL) | 14.2±1.3 | 14.3±1.4 | 14.1±1.2 | 0.640 |
| Smoking history (pack-years) (min–max) | 0–3 | 0–3 | 0–1 | 0.811 |
| History of hypertension (n (%)) | 11 (4.5) | 5 (4.7) | 6 (4.3) | 0.989 |
| SHS exposure | ||||
| Ever cabin SHS exposure (n (%)) | 139 (56.7) | 0 (0) | 139 (100) | <0.001 |
| Cabin SHS exposure among exposed (years) | 9.3±10.7 | 0±0 | 16.6±9.1 | <0.001 |
| Time since last cabin SHS exposure (years) | 17.3±6.9 | -- | 17.3±6.9 | NA |
| Any form of non-cabin SHS exposure (n (%)) | 245 (100) | 106 (100) | 139 (100) | <0.001 |
| Childhood home SHS exposure (n (%)) | 116 (47.3) | 41 (38.7) | 75 (54.0) | 0.059 |
| Adult home SHS exposure (n (%)) | 59 (24.1) | 17 (16.0) | 42 (30.2) | 0.036 |
| Non-airline occupational SHS exposure (n (%)) | 72 (29.4) | 23 (21.7) | 49 (35.3) | 0.069 |
| Other SHS exposure (n (%)) | 111 (45.3) | 46 (43.4) | 65 (46.8) | 0.872 |
| Symptoms | ||||
| mMRC Dyspnoea Scale ≥1 (n (%)) | 25 (10.2) | 11 (10.4) | 14 (10.1) | 0.997 |
| Participants with any respiratory symptoms (n (%)) | 112 (45.7) | 47 (44.3) | 65 (46.8) | 0.931 |
| Participants ever experiencing shortness of breath (n (%)) | 29 (11.8) | 6 (5.7) | 23 (16.5) | 0.032 |
| Participants with cough ≥2 episodes/year (n (%)) | 103 (42.0) | 45 (42.5) | 58 (41.7) | 0.994 |
| Participants with less activity than peers (n (%)) | 5 (2.0) | 1 (0.9) | 4 (2.9) | 0.570 |
| Pulmonary function tests | ||||
| FEV1 (% predicted) | 103±12 | 104±12 | 102±13 | 0.194 |
| FVC (% predicted) | 107±13 | 109±14 | 106±13 | 0.300 |
| FEV1/FVC | 77±5 | 78±5 | 76±5 | 0.003 |
| FEV1/FVC (% predicted) | 95±6 | 96±6 | 95±6 | 0.784 |
| FEF25–75 (% predicted) | 94±25 | 95±23 | 94±27 | 0.915 |
| FEF75 (% predicted) | 112±44 | 112±42 | 112±45 | 0.999 |
| DLCO adjusted for Hgb (% predicted) | 81±11 | 82±10 | 79±11 | 0.169 |
| DL/VA adjusted for Hgb (% predicted) | 123±16 | 121±18 | 125±15 | 0.190 |
| Alveolar volume (VA) (L) (% predicted) | 95±12 | 97±13 | 94±11 | 0.133 |
| TLC (% predicted) | 103±11 | 104±11 | 103±11 | 0.888 |
| RV (% predicted) | 96±18 | 94±19 | 97±17 | 0.470 |
| RV/TLC | 33±7 | 30±7 | 36±6 | <0.001 |
| RV/TLC (% predicted) | 90±13 | 88±14 | 91±11 | 0.165 |
| FRC (% predicted) | 103±20 | 103±20 | 103±20 | 0.999 |
| FRC/TLC | 53±7 | 52±7 | 54±8 | 0.341 |
| FRC/TLC (% predicted) | 99±13 | 99±13 | 98±14 | 0.966 |
Demographics, secondhand smoke (SHS) exposure, symptoms and lung function in participants with preserved spirometry that underwent exercise testing. Other SHS exposure was defined as non-aircraft cabin SHS exposure outside the work or home environment such as in recreational public places. Data are presented as mean±SD or number of participants with positive value for the variable (n) out of the total number of participants (N) and percentage of participants (%). Reference equations: per cent predicted of normal values of spirometry, diffusing capacity and lung volumes were calculated using Global Lung Function Initiative, Crapo et al and Quanjer et al predicted formulas, respectively.18–20 45
BMI, body mass index; DcoSB, single-breath diffusing capacity of carbon monoxide; FEF75, maximum airflow at low-lung volume; FEF25–75, maximum airflow at mid-lung volume; FEV1, forced expiratory volume in 1 s; FRC, functional residual capacity; FVC, forced vital capacity; Hgb, haemoglobin; mMRC, modified medical research council; RV, residual volume; TLC, total lung capacity.