Due to low recruitment rate the sponsor decided to discontinue the study.

The purpose of this study is to evaluate effects of inspired gas mixtures on the distance walked by patients with severe Chronic Obstructive Pulmonary Disease (COPD) during a Six-Minute Walk test.

the purpose of this study is to evaluate the distance walked by patients with severe Chronic Obstructive Pulmonary Disease (COPD) during a Six-Minute Walk test (6MWT) while breathing Helium/Oxygen 65%/35% compared to either breathing Nitrogen/Oxygen 65%/35% or receiving Non-Invasive Ventilation (NIV) with a FiO2 of 0.35 and to evaluate exercise related symptoms

Inclusion Criteria:

• Male or female aged >= 45 and <= 75 years old
• Patient with documented clinical diagnosis of stage III/IV COPD
• Patient with stable COPD defined by no significant increase in COPD medication, no treatment for COPD in an emergency, no acute intensive care setting and no intake of antibiotics in the four weeks prior to selection

Exclusion Criteria:

• Inability or contra-indication to perform pulmonary function tests
• Inability or contra-indication to perform the 6MWT with a trolley
• Any contra-indication to receive NIV
• Obese patient having a Body Mass Index (BMI) > 35
• Pregnant or lactating woman
• Female or chil-bearing potential with lack of efficient contraception