Different stage COPD subjects were recruited. Administration of bronchodilators was prohibited 24 hours prior to the experiment. After the application of topical anesthesia (10% xylocaine) the subject was asked to swallow the multipair esophageal electrode catheter through the nose into their right position. At the first period, the stable signals of spontaneous breathing (about 10 minutes) were collected as the baseline data. At the second period, each subject inhaled compound ipratropium bromide solution (3mg salbutamol and 500μg ipratropium, Boehringer Ingelheim Limited, Germany). A multi-pair esophageal electrode catheter with 10 coils that provided five pairs of electrodes was used to obtain the NRD signals. All NRD signals the were recorded before and after the compound ipratropium bromide solution was inhaled (about 10 minutes). The subjects scored their comfort sensation with a visual analog scale (VAS) ranging from 0 (best) to 10 (worst) at each period.
