The purpose of the study is to determine the efficacy and safety of the combination of ADVAIR DISKUS® 250/50mcg (FLUTICASONE PROPIONATE/SALMETEROL COMBINATION PRODUCT) plus SPIRIVA® HANDIHALER® inhaler 18mcg (TIOTROPIUM) compared to SPIRIVA® HANDIHALER® inhaler 18mcg (TIOTROPIUM) in patients with COPD.