The purpose of this trial is to study the effects on exercise capacity, physical activity, inflammatory markers and quality of life of supplemental ambulatory oxygen, to be used during physical activity, in patients with COPD who are normoxic at rest but hypoxemic during a six-min walk test.

Our hypothesis is that if patients are able to use supplemental oxygen they will be more physically active and thereby improve health related quality of life.

Study design The study will employ a parallel design for 6 months including 144 patients (72 patients/group). Patients will be randomized to intervention or control group. The intervention comprises supplemental oxygen to be used during physical activity for 6 months. The control group will receive the same physical activity instructions as the intervention group during the 6 months, but they will not be able to use supplemental oxygen during physical activity.

The study will be a prospective, randomized, single-blind multi-centre intervention study with an intention to treat design (last value carry over). Inclusion will continue until 144 patients have fulfilled the 6 months. Patients will be tested at baseline and after 6 months. There will also be a follow-up after 12 months comprising questionnaires. The study will include centers in Sweden Norway, Finland, and Estonia.

Inclusion Criteria:

• COPD, Arterial Oxygen Saturation > 8 kilopascal at rest
• Oxygen Saturation ≤ 88% and a fall in Oxygen Saturation ≥ 4% during a six-minute walk test in ambient air
• No exacerbation within 4 weeks prior to the study
• Post-bronchodilator forced expiratory volume at one second < 80% predicted and forced expiratory volume at one second /Vital capacity < 0.7
• Oxygen Saturation ≥ 92 % during a walk test in self-selected pace with supplemental oxygen. Patients should use supplemental oxygen 10 minutes before the test starts.
• Non-smoker (smoke free for ≥ 6 months)
• Interest in being physically active

Exclusion Criteria:

• Arterial carbon dioxide > 6.5 kilopascal at rest
• Orthopedic, neurologic or mental impairments that would limit physical activity
• Neoplastic disease that is anticipated to influence survival
• Patients exercising with supplemental oxygen
• Long-term oxygen therapy
• Patients with arterial auricular fibrillation and/or heart disease that might hinder physical activity as judged by the physician