Non Invasive Evaluation of Muscle Hypoxia in COPD Patient (EVANIMUS)

Investigator will compare mVO2 time constant in 2 groups of COPD (chronic obstrutive pulmonary disease) patients matched for age, sex, physical activity (estimated by GPAQ questionnaire (Global Physical Activity Questionnaire)), one with chronic hypoxemia (LTOT+ group) and one without blood gas abnormalities (LTOT- group).. Inclusion visit It will allow to calculate physical activity in Mets.min/week, from the GPAQ questionnaire. The patient will also be accustomed to the repeated arterial occlusion procedure. A pneumatic cuff will be wrapped around the thigh and will be progressively inflated to a suprasystolic value (rapid air inflation system Hokanson), from 160 mmHg up to tolerated maximal pressure (max 220 mmHg). Experimental visit * Muscle biopsy. A biopsy of the vastus lateralis will be performed while breathing ambient air. After disinfection and anesthesia of skin and subcutaneous tissue, an automatic biopsy gun (Monopty Bard 14G) will be introduced in the muscle and a 20 mg biopsy will be withdrawn. The maximal mitochondrial O2 consumption and mitochondrial affinity for O2 will be immediately measured with high resolution respirometry (Oroboros, 10 mg tissue). A 10 mg fragment will be stored in liquid nitrogen for mRNA analysis of hypoxia driven genes (Hypoxia-inducible Factor 1, Vascular Endothelial Growth Factor, Carbonic Anhydrase 9, Heme Oxygenase 1). * mVO2 time constant measurement (k, min-1) in ambient air. A NIRS probe (Oxymon III) will be placed on the thigh (contralateral to the muscle biopsy) and secured with an elastic wrap. The NIRS signal will be displayed continuously and recorded on a software (Oxysoft) The inflation cuff will be placed upstream the NIRS probe. After 5 to 10 isometric contractions of the quadriceps, the cuff will be rapidly inflated (maximal tolerated pressure determined during the inclusion visit) and deflated according to a predetermined protocol: 5 s /5 s 5 times, followed by 7 s /7 s 5 times and then 10 s/10 s 10 times. The deoxygenation kinetics (% deoxygenation/min) will be calculated for every occlusion and these deoxygenation indices will be expressed over time in order to calculate the time constant of the exponential relationship (k, min-1). This sequence will be repeated twice and the k values will be averaged. * mVO2 time constant measurement with O2. Oxygen therapy will be given to the patient for 1 hour before repeating the k determination as described above. Oxygen flow will be set to the habitual flow rate in the LTOT+ group, and an arbitrary 3 L/min flow rate in the LTOT- group.