Clin Physiol Funct Imaging. 2020 Dec 7. doi: 10.1111/cpf.12684. Online ahead of print.
Chronic airflow limitation (CAL) can be defined as fixed ratio of forced expiratory volume in 1 second (FEV1 )/forced vital capacity (FVC)<0.70 after bronchodilation. It is still unclear which is the most optimal ratio in relation to respiratory morbidity. We investigated to what extent different ratios of FEV1 /FVC were associated with key respiratory symptoms, i.e. cough with phlegm, dyspnea, or wheeze. We utilized a cross-sectional general-population study consisting of 15 128 adults (50 to 64 years of age), 7 120 never-smokers and 8 008 ever-smokers (current and former), with a completed respiratory questionnaire and examined with dynamic spirometry after bronchodilation. We calculated FEV1 /FVC from 0.40 to 1.0, using 0.70 as reference category. We analyzed odds ratios (OR) between different ratios and respiratory symptoms using adjusted multivariable logistic regression. Among all subjects, regardless of smoking habits, the lowest odds for respiratory symptoms was at FEV1 /FVC=0.82, OR 0.48 (95% CI 0.41-0.56). Among never-smokers the lowest odds for respiratory symptoms was at FEV1 /FVC=0.81, OR 0.53 (95% CI 0.41-0.70). Among ever-smokers, the odds for respiratory symptoms was lowest at FEV1 /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, i.e. FEV1 /FVC=0.85 showing similar odds, OR 0.45 (95% CI 0.38-0.55). We conclude that the odds for respiratory symptoms continuously decrease with higher FEV1 /FVC ratios and reaches 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.