Evaluation of the Reversibility of the Bronchial Obstruction by Impulse Oscillometry Technique in Chronic Obstructive Pulmonary Disease (COPD): Correlation With Functional Features Measured by Plethysmography and Dyspnoea

Inclusion Criteria: * COPD with dyspnoea with Medical Research Council scale (MRC) \>1, * No exacerbation for 6 weeks * No bronchodilatator short action(share) (ß 2 agonist or ipratropium) within 6 hours before the respiratory evaluation and the test of reversibility. * Patient under current treatment (ß2 long-acting agonist (LABA) or anticholinergic long-acting (LLAMA(LAMA)) or LABA-corticoid association inhaled (CSI), or triples LABA-CSI-LAMA association) stable for at least 4 weeks, and taken for at least the 1 hour the day of the visit * Having given a written consent Exclusion Criteria: * Patient Under 18 * Other respiratory illness * Clinically significant left cardiac failure * Obesity with BMI \> 35 kg / m2) * Unable to perform respiratory evaluations * Contraindication to the salbutamol or to the ipratropium bromide or to one of its components * Pregnant or breast-feeding woman * Unable to agree * No social security scheme