The ratio FEV(1)/FVC and its association to respiratory symptoms—A Swedish general population study

Chronic airflow limitation (CAL) can be defined as fixed ratio of forced expiratory volume in 1 s (FEV(1))/forced vital capacity (FVC) < 0.70 after bronchodilation. It is unclear which is the most optimal ratio in relation to respiratory morbidity. The aim was to investigate to what extent different ratios of FEV(1)/FVC were associated with any respiratory symptom. In a cross‐sectional general population study, 15,128 adults (50–64 years of age), 7,120 never‐smokers and 8,008 ever‐smokers completed a respiratory questionnaire and performed FEV(1) and FVC after bronchodilation. We calculated different ratios of FEV(1)/FVC from 0.40 to 1.0 using 0.70 as reference category. We analysed odds ratios (OR) between different ratios and any respiratory symptom using adjusted multivariable logistic regression. Among all subjects, regardless of smoking habits, the lowest odds for any respiratory symptom was at FEV(1)/FVC = 0.82, OR 0.48 (95% CI 0.41–0.56). Among never‐smokers, the lowest odds for any respiratory symptom was at FEV(1)/FVC = 0.81, OR 0.53 (95% CI 0.41–0.70). Among ever‐smokers, the odds for any respiratory symptom was lowest at FEV(1)/FVC = 0.81, OR 0.43 (95% CI 0.16–1.19), although the rate of inclining in odds was small in the upper part, that is FEV(1)/FVC = 0.85 showed similar odds, OR 0.45 (95% CI 0.38–0.55). We concluded that the odds for any respiratory symptoms continuously decreased with higher FEV(1)/FVC ratios and reached a minimum around 0.80–0.85, with similar results among never‐smokers. These results indicate that the optimal threshold associated with respiratory symptoms may be higher than 0.70 and this should be further investigated in prospective longitudinal studies.