 Patients with chronic obstructive pulmonary disease COPD have poor sleep quality as a result of various alterations in oxygenation parameters and sleep macro- and micro-architecture. We aimed to compare the tiotropium Respimat Soft Mist Inhaler and the HandiHaler in terms of their effects on sleeping oxygen saturation SaO2 and sleep quality in patients with COPD. In a randomized, parallel-group trial involving 200 patients with mild to moderate COPD resting arterial oxygen tension 60 mmHg while awake, we compared the effects of 6 months treatment with the two devices on sleeping SaO2 and sleep quality. 