Figure 1a:

Three-dimensional surface plots demonstrate relationships between emphysema percentage, wall thickness, and COPD exacerbation frequency (vertical axis). Different panels show the plot rotated to allow appreciation of different aspects. (a) Surface view of entire relationship 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. Also note the very strong effect of bronchial wall thickness at low levels of emphysema. (c) Depth view emphasizes relationship between increasing wall thickness and exacerbation frequency at low levels of emphysema.