Analysis of the roles of air trapping and diffusion in the prognosis of COPD from the prospective KOCOSS Cohort

<bold>Background:</bold> In patients with chronic obstructive pulmonary disease (COPD), the predictive role of air trapping and diffusion capacity may be different and heterogeneous. Therefore, we aimed to investigate the predictive role of air trapping and diffusion capacity on the outcomes of COPD. <bold>Methods:</bold> From the Korean COPD Subgroup Study (KOCOSS) cohort, we identified the ratio of residual volume (RV) to total lung capacity (TLC) and Diffusing Capacity Of The Lungs For Carbon Monoxide (DLCO) in patients with COPD and divided with four groups according to RV/TLC ratio and DLco: group 1 was RV/TLC of less than 40% and DLCO of more than 60%(n=604), group 2 was RV/TLC of less than 40% and a DLCO of less than 60%(n=279), group 3was RV/TLC of 40% or more and DLCO of 60% or more(n=627), and group 4 was RV/TLC of 40% or more and DLCO of less than 60%(n=530). The primary outcome was moderate to severe exacerbation for 3 years. <bold>Results:</bold> Of 2040 patients, patients in group 4 were the oldest and showed the lowest in body mass index (BMI). Additionally, those in group 4 showed most severe in symptom burden and decreased quality of life. When comparing the risk of moderate to severe exacerbation, group 4 patients had the highest risk (OR, [95% CI]) 4.163 [2.232, 7.764]), followed by group 3 (OR 3.305 [1.833, 5.96]), group 2 (OR 2.022 [0.888, 4.603]), and group 1 (Ref.), and group 3, which had higher air trapping, found more frequent in exacerbation, compared to group 2, which showed abnormal diffusion capacity. <bold>Conclusions:</bold> In this prospective cohort study, we found the prognostic role of air trapping and diffusion in COPD patients and air trapping has a greater influence on the exacerbation.