FIGURE 3.

Kaplan–Meier survival plot of 101 cases of severe (Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 3) and very severe (GOLD stage 4) chronic obstructive pulmonary disease following lung volume reduction surgery. The median survival was shortened in the quartile with the most severe occlusion by mucous exudate on the fully expanded lumen (HR 3.28, 95% CI 1.55–6.92; p = 0.002) after adjustment for several factors. ––––: quartile 1 (smallest); ········: quartile 2; ·-·-·-: quartile 3; - - - -: quartile 4 (largest). Reproduced from [25] with permission from the publisher.