Impact of Surgical Mask, FFP2 Mask and FFP3 Mask (With and Without Exhalation Valve) on Exercise Tolerance and Blood Gas Parameters of Patients With Known Lung Disease and Long-term Oxygen Therapy

The aim of the study is to find out how blood gas parameters change under the use of surgical mask, FFP2 masks and FFP3 masks (with and without exhalation valve) in patients with known lung disease and long-term oxygen therapy. In particular, the question arises whether patients become hypoxemic or hypercapnic by using a mask. Or whether wearing a mask increases oxygen saturation by its reservoir function.