So far, there is no large-scale clinical trial on long-term intervention with tiotropium bromide (Spiriva) in patients with early stages of COPD (i.e. GOLD Stage I-II COPD or asymptomatic COPD). It would be of great significance for COPD prevention and treatment if the investigators could prove that tiotropium decreases the lung function decline and reverses disease progression in patients with early-stage COPD.