Figure 2.

Airway wall thickening (left) and emphysema (right) trends in COPDGene (Genetic Epidemiology of COPD Study) by trajectory assignment, stratified by age. Airway wall thickening is assessed as the square root of the wall area ($\sqrt{\text{WA}}$) of a theoretical airway with an internal lumen perimeter of 10 mm (14). Emphysema is assessed as the Hounsfield unit (HU) value representing the 15th percentile of the lung region HU histogram (Perc15) (13). Greater amounts of emphysema are seen in the trajectory 2 subgroup relative to trajectories 3 and 4 only within older age strata, and thicker airway walls are observed in trajectory 2 individuals throughout (P < 0.001 for all airway thickness comparisons).