Effects of Once Daily Tiotropium in Patients With Chronic Obstructive Pulmonary Disease (COPD) of Different Severity

The primary objective of this study is to investigate the effect of tiotropium vs. placebo on trough FEV1 and FEV1 2 hours post inhalation after 12 weeks of treatment. For both endpoints changes from baseline will be analysed. Three strata of patients will be included (severe COPD, i.e. \<35% of predicted FEV1, moderate COPD, i.e. 35% - \<50% of predicted FEV1, mild COPD, i.e. 50% - 70% of predicted FEV1, according to American Thoracic Society \[ATS\] criteria). The study is conducted in order to find out for which endpoint tiotropium is different from placebo in which stratum.