Table 3.
Characteristics of subjects who had follow-up spirometry
| Characteristics | All patients with follow-up spirometry | Patients with normal RV:TLC | Patients with abnormal RV:TLC | Difference (95% CI) | P values |
|---|---|---|---|---|---|
| Demographics | |||||
| n (% of the study cohort) | 1706 (22.8) | 1124 (21.7) | 582 (25.3) | −3.6% (−5.7 to 1.5) | <0.001 |
| Age (years) | 61.3±10.4 | 60.9±10.3 | 62.1±10.6 | −1.2 (−2.2 to 0.2) | 0.023 |
| Sex (female), n (%) | 123 (7.2) | 109 (9.7) | 14 (2.4) | 7.3% (5.2 to 9.4) | <0.001 |
| Height (cm) | 174.7±7.8 | 175.0±7.9 | 173.9±7.7 | 1.1 (0.3 to 1.9) | 0.006 |
| BMI (kg/m2) | 29.7±5.6 | 29.7±5.6 | 29.6±5.7 | 0.004 (−0.6 to 0.6) | 0.989 |
| Years of follow-up | 10.3±4.6 | 10.0±4.6 | 10.8±4.6 | −0.8 (−1.3 to 0.3) | <0.001 |
| Baseline airflow indices | |||||
| FEV1 (L) | 3.07±0.58 | 3.15±0.60 | 2.93±0.52 | 0.22 (0.16 to 0.28) | <0.001 |
| FEV1 (% predicted) | 88±9 | 90±10 | 84±8 | 5.7 (4.8 to 6.6) | <0.001 |
| FVC (L) | 4.00±0.76 | 4.09±0.78 | 3.82±0.68 | 0.27 (0.20 to 0.34) | <0.001 |
| FVC (% predicted) | 89±10 | 91±11 | 86±9 | 5.4 (4.4 to 6.4) | <0.001 |
| FEV1:FVC (%) | 77.0±4.8 | 77.1±4.9 | 76.7±4.6 | 0.4 (−0.1 to 0.9) | 0.093 |
| FEV1:FVC (% predicted) | 98.3±5.8 | 98.5±5.8 | 97.9±5.7 | 0.58 (0.004 to 1.16) | 0.048 |
| FEF25–75 (L) | 2.85±0.94 | 2.92±0.97 | 2.73±0.85 | 0.19 (0.10 to 0.28) | <0.001 |
| FEF25–75 (% predicted) | 86±24 | 87±25 | 82±21 | 5.4 (3.1 to 7.8) | <0.001 |
| Reversibility in FEV1 (mL) | 187±207 | 173±198 | 216±220 | −43 (−64 to 22) | <0.001 |
| Reversibility in FEV1 (%) | 7±9 | 6±8 | 9±11 | −2.5 (−3.5 to 1.6) | <0.001 |
| Reversibility in FEV1, n (%) | 709 (41.6) | 435 (38.7) | 274 (47.1) | −8.4% (−13.3 to 3.4) | <0.001 |
| Lung volume indices | |||||
| TLC (L) | 6.67±1.09 | 6.44±1.01 | 7.12±1.10 | −0.68 (−0.78 to 0.57) | <0.001 |
| TLC (% predicted) | 100±12 | 96±10 | 107±13 | −10.5 (−11.7 to 9.4) | <0.001 |
| RV (L) | 2.67±0.77 | 2.30±0.50 | 3.39±0.69 | −1.09 (−1.14 to 1.03) | <0.001 |
| RV (% predicted) | 121±33 | 104±20 | 154±29 | −50 (−52 to 48) | <0.001 |
| FRC (L) | 3.57±0.86 | 3.33±0.74 | 4.07±0.86 | −0.74 (−0.83 to 0.66) | <0.001 |
| FRC (% predicted) | 103±23 | 95±19 | 118±23 | −22 (−24 to 20) | <0.001 |
| IC (L) | 3.10±0.71 | 3.12±0.71 | 3.06±0.69 | 0.06 (−0.02 to 0.14) | 0.121 |
| IC (% predicted) | 74±14 | 94±14 | 73±14 | 1.3 (−0.2 to 2.8) | 0.089 |
| RV:TLC (%) | 40±8 | 36±6 | 48±5 | −11.7 (−12.3 to 11.2) | <0.001 |
| RV:TLC (% predicted) | 119±22 | 107±14 | 143±14 | −36 (−37 to 34) | <0.001 |
| FRC:TLC (%) | 53±9 | 52±8 | 57±8 | −5 (−6 to 4) | <0.001 |
| FRC:TLC (% predicted) | 95±15 | 92±14 | 101±13 | −9 (−10 to 7) | <0.001 |
| IC:TLC (%) | 47±8 | 48±8 | 43±7 | 5.4 (4.5 to 6.2) | <0.001 |
| IC:TLC (% predicted) | 93±20 | 96±19 | 86±19 | 10 (8 to 12) | <0.001 |
| Follow-up spirometry* | |||||
| Age at follow-up spirometry (years) | 65.4±10.4 | 64.7±10.3 | 66.7±10.4 | −2.0 (−3.0 to 1.0) | <0.001 |
| Height at follow-up spirometry (cm) | 174.5±8.0 | 174.9±8.1 | 173.8±7.8 | 1.1 (0.3 to 1.9) | 0.007 |
| Time from index PFT to follow-up spirometry (years) | 4.1±3.1 | 3.8±2.9 | 4.6±3.3 | −0.8 (−1.1 to 0.5) | <0.001 |
| FEV1 (L) | 2.69±0.65 | 2.77±0.65 | 2.53±0.62 | 0.25 (0.18 to 0.31) | <0.001 |
| FEV1 (% predicted) | 79±15 | 81±15 | 75±14 | 6.5 (5.0 to 7.9) | <0.001 |
| FVC (L) | 3.67±0.84 | 3.75±0.86 | 3.51±0.80 | 0.25 (0.16 to 0.33) | <0.001 |
| FVC (% predicted) | 84±15 | 86±15 | 81±14 | 4.8 (3.3 to 6.3) | <0.001 |
| FEV1:FVC (%) | 74±8 | 74±8 | 72±8 | 2.0 (1.2 to 2.8) | <0.001 |
| FEV1:FVC (% predicted) | 95±10 | 95±10 | 93±10 | 2.5 (1.5 to 3.5) | <0.001 |
| FEF25–75 (L) | 2.26±0.98 | 2.38±1.00 | 2.04±0.88 | 0.34 (0.24 to 0.43) | <0.001 |
| FEF25–75 (% predicted) | 72±29 | 75±29 | 65±25 | 10.0 (7.2 to 12.8) | <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.
Follow-up spirometry (last available postbronchodilator spirometry) was available for a subgroup of patients. Reference equations: Measures of pulmonary function and % predicted of normal values were calculated using Crapo predicted formulas (Crapo et al, 1981 and 1982), except for FRC:TLC, IC and IC:TLC. Quanjer predicted formulas were used for FRC:TLC and IC (Quanjer et al, 1993), and Francisco predicted formulas were used for IC:TLC (Francisco et al, 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; PFT, pulmonary function test; RV, residual volume; TLC, total lung capacity.