Associations between life-course FEV1/FVC trajectories and respiratory symptoms up to middle age: analysis of data from two prospective cohort studies

Life-course lung function trajectories leading to airflow obstruction, as measured by impaired FEV1/FVC (forced vital capacity), precede the onset of chronic obstructive pulmonary disease (COPD). We aimed to investigate whether individuals on impaired FEV1/FVC trajectories have an increased burden of respiratory symptoms, including those who do not meet the spirometric criteria for COPD. We analysed serial life-course data from two population-based cohort studies separately, which included respiratory symptoms and spirometry: the Tasmanian Longitudinal Health Study (TAHS, Australia) cohort was recruited at age 6–7 years and followed up until middle age (mean age 53 years; range 51–55); and the Coronary Artery Risk Development in Young Adults (CARDIA, USA) cohort was recruited at a mean age of 25 years (range 18–30) and followed up to a mean age of 55 years (range 47–64). Participants' symptom profiles at ages 53 and 55 years were derived by latent class analysis. Symptom profiles were compared across pre-bronchodilator FEV1/FVC trajectories derived by group-based modelling, then restricted to those without COPD defined by post-bronchodilator airflow obstruction (FEV1/FVC