The objective of this study is to evaluate the effect of the combination of formoterol and beclometasone dipropionate on central and peripheral airway dimensions in COPD patients using Computational Fluid Dynamics (CFD). Further more, the effect of this combination therapy on lung function (spirometry, body plethysmography), the BODE index, COPD assessment test (CAT) and Borg CR10 scale will be assessed and the safety will be evaluated.