The aim of the current study was to evaluate a new system (FreeO2) that automatically titrates oxygen flow to maintain stable SpO2, in patients with moderate or severe chronic obstructive pulmonary disease during exercise. The investigators hypothesized that continuous automatic adjustment of the oxygen flows during exercise would better maintain patients within the oxygenation target, reduce episodes of desaturation and hyperoxia and would improve walking exercise tolerance in comparison with fixed levels of low-flow oxygen and with compressed air breathing.

Inclusion Criteria:

• Patients older than 40 years
• Moderate to severe COPD according to the Global Initiative for Chronic Obstructive Lung Disease guidelines
• Who did not require long-term oxygen therapy were included in the study.
• Patients were also selected on the basis of known (end-exercise SpO2 < 90% on a previous exercise test) or suspected (SpO2 < 95% at rest) desaturation during exercise

Exclusion Criteria:

• Episode of exacerbation or hospitalisation within last four weeks
• Current medical condition that could influence exercise tolerance