Characteristics of all subjects
| Characteristics | All patients | Patients with normal RV:TLC | Patients with abnormal RV:TLC | Difference (95% CI) | P values |
| Demographics | |||||
| n | 7479 | 5179 | 2300 | – | – |
| Age (years) | 61.7±10.8 | 60.8±10.7 | 63.6±10.8 | −2.8 (−3.3 to 2.3) | <0.001 |
| Sex (female), n (%) | 560 (7.5) | 477 (9.2) | 83 (3.6) | 5.6% (4.5 to 6.7) | <0.001 |
| Height (cm) | 174.6±7.8 | 174.9±7.8 | 173.7±7.7 | 1.2 (0.8 to 1.6) | <0.001 |
| BMI (kg/m2) | 29.5±5.7 | 29.5±5.7 | 29.5±5.9 | −0.03 (−0.3 to 0.3) | 0.853 |
| Years of follow-up | 8.6±4.8 | 8.5±4.7 | 8.8±5.0 | −0.3 (−0.5 to 0.7) | 0.009 |
| Airflow indices | |||||
| FEV1 (L) | 3.09±0.59 | 3.18±0.59 | 2.90±0.54 | 0.28 (0.25 to 0.30) | <0.001 |
| FEV1 (% predicted) | 89±10 | 90±10 | 84±8 | 6.0 (5.5 to 6.5) | <0.001 |
| FVC (L) | 4.02±0.77 | 4.12±0.77 | 3.80±0.71 | 0.33 (0.29 to 0.36) | <0.001 |
| FVC (% predicted) | 90±11 | 92±11 | 86±9 | 5.7 (5.1 to 6.2) | <0.001 |
| FEV1:FVC (%) | 77.0±4.8 | 77.2±4.9 | 76.5±4.7 | 0.7 (0.5 to 0.9) | <0.001 |
| FEV1:FVC (% predicted) | 98±6 | 99±6 | 98±6 | 0.6 (0.3 to 0.9) | <0.001 |
| FEF25–75 (L) | 2.85±0.95 | 2.93±0.97 | 2.68±0.88 | 0.25 (0.20 to 0.30) | <0.001 |
| FEF25–75 (% predicted) | 86±25 | 88±25 | 82±22 | 5.3 (4.1 to 6.5) | <0.001 |
| Reversibility in FEV1 (mL) | 186±204 | 167±192 | 227±222 | −59 (−69 to 49) | <0.001 |
| Reversibility in FEV1 (%) | 7±9 | 6±7 | 9±10 | −3.3 (−3.7 to 2.8) | <0.001 |
| Reversibility in FEV1, n (%) | 3050 (40.8) | 1929 (37.3) | 1121 (48.7) | −11% (−14 to 9) | <0.001 |
| Lung volume indices | |||||
| TLC (L) | 6.64±1.08 | 6.46±1.01 | 7.05±1.11 | −0.59 (−0.64 to 0.54) | <0.001 |
| TLC (% predicted) | 99±12 | 96±11 | 106±13 | −9.6 (−10.1 to 9.0) | <0.001 |
| RV (L) | 2.62±0.75 | 2.29±0.51 | 3.37±0.68 | −1.08 (−1.11 to 1.06) | <0.001 |
| RV (% predicted) | 118±32 | 104±20 | 151±28 | −48 (−49 to 47) | <0.001 |
| FRC (L) | 3.56±0.87 | 3.34±0.77 | 4.07±0.86 | −0.73 (−0.77 to 0.69) | <0.001 |
| FRC (% predicted) | 102±23 | 96±19 | 118±23 | −22 (−23 to 21) | <0.001 |
| IC (L) | 3.06±0.73 | 3.11±0.73 | 2.96±0.71 | 0.15 (0.11 to 0.19) | <0.001 |
| IC (% predicted) | 73±14 | 74±15 | 72±14 | 2 (1 to 3) | <0.001 |
| RV:TLC (%) | 39±8 | 35±6 | 48±5 | −12.3 (−12.6 to 12.0) | <0.001 |
| RV:TLC (% predicted) | 117±21 | 106±14 | 141±13 | −35 (−36 to 34) | <0.001 |
| FRC:TLC (%) | 54±9 | 52±9 | 58±8 | −6.1 (−6.5 to 5.6) | <0.001 |
| FRC:TLC (% predicted) | 95±15 | 92±15 | 101±13 | −9.6 (−10.4 to 8.8) | <0.001 |
| IC:TLC (%) | 46±9 | 48±9 | 42±8 | 6.1 (5.6 to 6.5) | <0.001 |
| IC:TLC (% predicted) | 93±21 | 96±21 | 87±19 | 9.3 (8.2 to 10.4) | <0.001 |
P-values for significant comparisons are shown in bold.
Demographics and lung function in patients with preserved spirometry. Patients were stratified according to abnormal and normal RV:TLC by the upper limit of normal. Data are presented as mean±SD or number of patients with positive value for the variable (n) out of the total number of patients (N) and percentage of patients (%) and difference (95% CI) with p value for unadjusted comparison between normal and abnormal RV:TLC. Reference equations: Measures of pulmonary function and % predicted of normal values were calculated using Crapo predicted formulas (Crapo et al 11 12 , 1981 and 1982), except for FRC:TLC, IC and IC:TLC. Quanjer predicted formulas were used for FRC:TLC and IC (Quanjer et al,2 1993), and Francisco predicted formulas were used for IC:TLC (Francisco et al 13 2009). Reversibility defined as ≥12% and ≥200 mL increase in FEV1 after bronchodilator administration.
BMI, body mass index; FEF25–75, maximum airflow at mid-lung volume; FRC, functional residual capacity; IC, inspiratory capacity; RV, residual volume; TLC, total lung capacity.