The characteristics of the 116 patients with COPD are shown in Table 1. All patients, except one, had a smoking history, with a median of 51 pack-years, and 34 (29%) patients were currently smoking. All of the patients had FEV1/FVC ratios of < 70%, and the median predicted FEV1 was 62.4%. The patients were well distributed into the four GOLD stages (stage I, 32 [28%]; stage II, 40 [34%]; stage III, 24 [21%]; stage IV, 20 [17%]). With regard to the treatments for COPD, 42 (35%) patients were treated with single-agent therapy, and 24 were treated with combinations of two or three drugs. Although anticholinergic therapy was widely used for all stages, the use of a long-acting β2-agonist and inhaled corticosteroids increased with advancing disease severity. Ninety-six percent of the patients with COPD showed low attenuation areas on high-resolution CT scan, and most had moderate to severe emphysematous changes. In the reference population, 75 subjects had never smoked (non-COPD never smokers), and 82 had smoking statuses and pack-year histories similar to those of the patients with COPD but who had normal spirometry (non-COPD smokers). As shown in Table 1, the reference population had similar clinical features of being elderly, a predominance of men, and a lower BMI. The patients with COPD had a significantly more-frequent smoking status (P < .001) and a larger number of pack-years (P < .001) than the reference population. As expected, the patients with COPD showed a significantly lower FEV1 (P < .001), percent-predicted FEV1 (P < .001), and FEV1/FVC ratio (P < .001) than the reference population. Even when compared with the non-COPD smokers, the patients with COPD showed a significantly lower FEV1 (P < .001), percent-predicted FEV1 (P < .001), and FEV1/FVC ratio (P < .001).