The aim of this study is to investigate the effects of supplemental oxygen on blood oxygenation at rest in Patients with severe to very severe COPD comparing the portable oxygen concentrator (Activox™ 4L) to a liquid continuous oxygen device (Companion®).

It has been proven that supplemental oxygen increases oxygen saturation and reduces dyspnea in hypoxemic COPD Patients. There are different oxygen delivery systems available, some of them operating with liquid oxygen and others by concentrating the ambient air (concentrators). An advantage of the concentrator system is, that there is no refill required, but only a power plug and plug socket, enabling the patient for higher mobility and to be more autonomous. There are only few publications about whether portable oxygen concentrators have a comparable efficiency on oxygen saturation to liquid oxygen devices with continuous flow (LOD) or not. Until now there are no official recommendations about how to convert the oxygen flow rate for LOD (liter per minute) into the corresponding level of the POC.

Therefore, we investigate the comparability of the portable oxygen concentrator Activox™ 4L (POC) to a liquid oxygen device (Companion®) in 30 hypoxemic COPD patients at rest.

As a baseline assessment, the patients will receive a bodyplethysmography, blood gas analysis without using supplemental oxygen and an evaluation of the diffusion capacity of the lung for CO.

The study will be conducted on 2 consecutive days. 15 patients will be randomized into two different groups: First group will start with POC and will continue the following day with LOD; The second group will start with LOD and continue with POC (cross-over design). All patients will use the same oxygen devices during the study assessments (LOD: Companion 1000 (CE 0050), Chart Industries Inc., Garfiel Heights, OH, USA; POC: Activox™ 4L, Inovalabs Inc., Texas, USA). On both days of the study, patients will be connected to one of the two systems via nasal cannula for a total time period of 40 minutes, while the patient remains in a sitting position without talking. The oxygen flow rate starts at 1liter/min (LOD) or Level 1 (POC) and will be increased every 10 minutes to the next higher level until the maximum of 4l/min (LOD) or level 4 (POC) is reached. Blood gases were taken and breathing frequency will be recorded at the end of each Oxygen Level.

Inclusion Criteria:

• COPD patients with hypoxemia at rest (paO2 < 55 or 60 mmHg, according to the recent supplemental oxygen guidelines [Hadringe, M., et al., British Thoracic Society guidelines for home oxygen use in adults. Thorax, 2015. 70 Suppl 1: p. i1-43.]
• Participation in an inpatient pulmonary rehabilitation program (Schön Klinik BGL)
• Written informed consent

Exclusion Criteria:

• The Need of more than 4 Liter/min Oxygen at rest to achieve PaO2 > 55 or 60mmHg
• Signs of acute exacerbation
• General exclusion criteria for exercise tests, e.g. acute coronary syndrome, acute myo- or pericarditis, acute lung embolism, pulmonary infarction, acute uncontrolled heart insufficiency