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.
