Assessment of Reactance Parameters Measured by the Forced Oscillation Technique for the Bronchodilator Response in Subjects With Chronic Obstructive Pulmonary Disease (COPD)

Different techniques will be used during this study : First, the FOT. The measurements will be performed using a Tremoflo-type (Thorasys Thoracic Medical System Inc.) device that generates an oscillating pressure waveform and measures impedance of the respiratory system and its components (resistance and reactance) as a function of frequency, as well as the respiratory system resonant frequency. Measurements will be performed during tidal breathing, the subjects breathing through the pneumotachograph of the system, with nose occluded, the cheeks supported by the hands (of the subjects or of an operator) to reduce the influence of the compliant upper airways. Three measurements of minimum 20 seconds duration will be recorded in the sitting position. Second, the spirometry. The measurements will be carried out using a Medisoft Exp'air type of equipment. The parameters will be successively measured in the sitting position : * The inspiratory capacity (IC) will be measured by maximal inspiratory maneuver starting from the functional residual capacity * The thoracic gas volume (TGV), total lung capacity (TLC), as well as the airway resistance will be measured by plethysmography * The diffusion indices (CO transfer factor (DL,CO) and CO transfer coefficient (KCO)) will be measured in apnea * A spirometry will then be carried out. Three maneuvers with acceptability and reproducibility criteria will be performed All these measurements will be carried out before the administration of the bronchodilator and 30 minutes after the administration of the bronchodilator (4 puffs of DUOVENT HFA, using an inhalation chamber).