Baseline characteristics of the study participants.

Data are presented as mean±Std (range), COPD: chronic obstructive pulmonary disease, M: male, F: female, BMI: body mass index, pack years: the number of cigarettes smoked per day x number of years smoked)/20 (1 pack has 20 cigarettes), 6MWD: 6-minutes walking distance, FEV1: forced expiratory volume in one second, VC: vital capacity, BODE score: index, which incorporate body mass index, airflow obstruction, dyspnoea and exercise capacity 18, % of predicted value, † not determined. Stages 1 through 4 denote severity of disease according to the Deutsche Atemwegsliga and the Deutsche Gesellschaft für Pneumologie und Beatmungsmedizin 27, with higher number indicating greater severity. (Additional characteristics of all study participants are summarized in Table S1 in the supporting information).