Figure 2.

Plots of 5-year changes in FEV₁ as a function of the 15th percentile of lung density adjusted for total lung capacity (TLC-PD15) changes according to smoking group. The plots were performed by using unadjusted linear regression analysis. The longitudinal association between FEV₁ and within-subject TLC-PD15 remained significant in adjusted mixed models (see text and Table 2) for smokers with PRISm and smokers with GOLD III to IV COPD. GOLD, Global Initiative for Chronic Obstructive Lung Disease; PRISm, smokers with preserved ratio and impaired spirometry.