Six-Minute Walk Test Comparing Helium/Oxygen to Nitrogen/Oxygen for COPD Rehabilitation

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