Figure 2.

Three-dimensional surface plots showing the relations between emphysema percentage, wall thickness, and COPD exacerbation frequency (vertical axis). A, Surface view of entire relation shows the largely independent effects of emphysema percentage and segmental wall thickness. B, Horizontal view emphasizes the increased exacerbation frequency at greater levels of emphysema. The very strong effect of the bronchial wall thickness at low levels of emphysema is also noted. (Adapted with permission from Han et al.²⁹)