1 year RV/TLC change as a predictor of long term decline of FEV1

Backgrounds: The impact of the 1 year-change of Residual volume/Total Lung Capacity (RV/TLC) in patients with COPD has not been studied in a long term prospective cohort. We explored the effect of 1 year-change of RV/TLC to identify predictors in FEV1 decline for 3 years in COPD patients treated by respiratory physicians. Methods: The study population included 240 patients from a multi-center observational COPD, who followed up for more than 3 years in KOCOSS cohort. With the 1 years change of RV/TLC, patients were classified into the aggravation group (△3% increased), the stable group (-3% ≤△RV/TLC≤3% ), and the improved group (△RV/TLC＜-3%). We compared the FEV1 decline in each group to identify correlation between RV/TLC with FEV1 decline by mixed regression model. Results: The patients of the aggravation group were older, had lower lung function and showed significantly less bronchodilator response. The amount of three year FEV1 decline was -130 ml in the aggravation group (n=64) and it was -20 ml in the stable group (n=89), while it increased by 123 ml in the improved group (n=87)(p＜0.001). The annual change in FEV1 was 67.8ml/year in the improving group, 30.4ml/year in the stable group and -36ml/year in the aggravation group. The multivariate logistic regression analysis showed that lower FEV1 and less positive bronchodilator response were significantly associated with RV/TLC aggravation. Conclusion: 1 year change in RV/TLC is a predictor of long term FEV1 decline in the COPD patients treated by bronchodilator inhaler therapy.