Associations of pre-COPD indicators with lung function decline and their longitudinal transitions.

Background: Pre-chronic obstructive pulmonary disease (COPD) indicators are associated with COPD development, but their associations with lung function decline in persons without COPD and their longitudinal transitions remain uncertain.

Methods: In this prospective cohort study, 3526 subjects without COPD from the 2014-2015 national COPD surveillance in China were investigated for a second time during 2018-2020. Four potential pre-COPD indicators at baseline were chronic bronchitis, preserved ratio impaired spirometry (PRISm), low peak expiratory flow (PEF), and spirometric small airway dysfunction (sSAD). To include the incident COPD subjects in the lung function decline analysis for consistent indicators, forced expiratory volume in 1 s (FEV₁) <80% predicted was used instead of PRISm. Lung function outcomes were the declines in post-bronchodilator FEV₁, forced vital capacity (FVC), and FEV₁/FVC.

Results: Subjects with initial chronic bronchitis had faster declines in FEV₁ and FVC compared with those without initial chronic bronchitis among smokers. Consistent chronic bronchitis was associated with faster declines in FEV₁ and FVC among non-smokers. Consistent sSAD was associated with faster declines in FEV₁/FVC among smokers and non-smokers. Consistent FEV₁ <80% predicted and consistent low PEF were associated with a faster decline in FEV₁/FVC among smokers. Incident COPD developed from sSAD in almost half of the cases.

Conclusions: Initial chronic bronchitis and consistent FEV₁ <80% predicted, sSAD, and low PEF are associated with excessive lung function decline among smokers, while consistent chronic bronchitis and sSAD are associated with excessive lung function decline among non-smokers. Initial sSAD accounts for a larger proportion of incident COPD than initial chronic bronchitis, PRISm, and low PEF.