Chronic Obstructive Pulmonary Disease (COPD) is a major cause of chronic morbidity, mortality and disability throughout the world, leading to a heavy social and economic burden.Bronchodilators, the most commonly used drugs in COPD patients, have been shown to reduce dyspnea, improve exercise tolerance and improve health status. However,conventional lung function parameters such as forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) frequently fail to detect significant functional responses to bronchodilators in patients with chronic airflow obstruction. It is necessary for clinical and scientific reasons to develop a new tool to objectively assess the effect of different treatments including bronchodilator on COPD. Our previous study showed that Ventilation-drive coupling may be more sensitive and accurate to evaluate the efficacy of inhaled bronchodilators in patients with COPD because it could better reflect the pathological and physiological characteristics of COPD.

Based on the above conclusion, the present study were performed using the experimental methods of placebo and self-controlled. We aimd to explore the value of ventilation-drive coupling in evaluating the efficacy of bronchodilators on COPD and provide a reasonable basis for the clinical application of this index.

Patients were randomly assigned to one of two intervention groups:

1. Group A: Patients inhaled placebo, ipratropium 80μg, salbutamol 400 μg in sequence;
2. Group B: Patients inhaled placebo, salbutamol 400μg, ipratropium 80 μg in sequence.

The data were collected in 30 minutes after patients inhaled placebo,in 30 minutes after ipratropium and in 15 minutes after salbutamol.

Inclusion Criteria:

Patients aged 40-70 years old; Patients with pulmonary function test of FEV1/FVC < 70% and FEV1%pred < 50%; Patients in a clinically stable state; Patients who signed informed consent.

Exclusion Criteria:

Patients with signs of an airway infection; Patients with an acute exacerbation during the previous 4 weeks; Patients with giant bulla(≥3cm in diameter); Patients with recent upper abdominal surgery; Patients with one or more of the following diseases: esophageal cancer, reflux esophagitis, severe obstructive sleep apnea (apnea hypopnea index>15/hr), neuromuscular disease, or significant heart failure; Patients with poor compliance.