Distribution of CT-quantified emphysema in heavy smokers participating in a lung cancer screening trial: Association with lung function decline

Purpose: To assess the association between CT-quantified emphysema distribution (upper/lower lobe) and lung function decline in heavy current and former smokers participating in a lung cancer screening trial. Material and Methods: In this medical ethical approved study, 587 participants underwent CT-scanning of the lungs and pulmonary function testing at baseline and after a median (interquartile range) follow-up of 2.9 (2.8-3.0) years. The lungs were automatically segmented based on anatomically defined lung lobes. Severity of emphysema was automatically quantified per anatomical lung lobe and was expressed as the 15th percentile; [HU point below which 15% of the low attenuation voxels are distributed (Perc15)]. The emphysema distribution was based on principal component analysis. Linear mixed models, correcting for age, height, BMI, pack-years and smoking status, were used to assess the association of emphysema distribution and FEV1/FVC-decline. Results: Mean (SD) age was 60.2 (5.4) years, mean baseline FEV1/FVC was 71.6 (9.0) % and overall mean Perc15 was -908.5 (20.9) HU. Participants with upper lobe predominant emphysema had a lower FEV1/FVC after follow-up compared to participants with lower predominant emphysema (p =0.001), independent of the total extent of emphysema. Conclusion: Heavy current and former smokers with upper lobe predominant emphysema have a more rapid decrease in FEV1/FVC than those with lower lobe predominant emphysema, independent of the overall extent of emphysema. These results seem to indicate that upper and lower lobe predominant emphysema may be different phenotypes.