Table 2.
Results of Lung Function Test According to the FEF25-75% z-Score
| Variables | Total | Normal FEF25-75% | Low FEF25-75%* | P-value |
|---|---|---|---|---|
| (n=307) | (n=216) | (n=91) | ||
| FEV1 (L) | 2.5±0.6 | 2.6±0.6 | 2.2±0.6 | <0.001 |
| FEV1 (% predicted) | 105.0±16.6 | 109.8±16.2 | 93.5±11.2 | <0.001 |
| FVC (L) | 3.2±0.8 | 3.3±0.8 | 3.0±0.8 | 0.007 |
| FVC (% predicted) | 97.6±13.5 | 99.7±14.3 | 92.7±10.0 | <0.001 |
| FEF25-75% (L/sec) | 2.2±0.8 | 2.4±0.8 | 1.6±0.5 | <0.001 |
| FEF25-75% (% predicted) | 82.9±25.7 | 93.0±23.4 | 58.7±10.0 | <0.001 |
| FEV1/FVC | 77.1±4.8 | 78.6±4.7 | 73.6±2.9 | <0.001 |
Notes: *Low FEF25-75%: FEF25-75% z-score below −0.8435 (the optimal cut-off value for predicting COPD development)
Abbreviations: FEF, forced mid-expiratory flow; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity.