RESEARCH AIM & HYPOTHESIS The aim is to investigate the effect of tiotropium from different devices on a panel of small (IOS, MBNW, DLCO, FVC) and large airway (FEV1, PEF) responses in patients with mild-moderate COPD. The investigators will compare Tiotropium Handihaler 18 micrograms once daily with Tiotropium Respimat 5 micrograms once daily.