Pulmonary function was measured by forced expiratory volume in one second (FEV1), defined as the maximal amount of air that can be forcefully exhaled in one second. Trough FEV1 is defined as the mean of the FEV1 values obtained at the last two scheduled time points at the Day 7 clinic visit (i.e., 11 and 12 hours after the morning dose, or 23 and 24 hours after the evening dose). Change from Baseline was calculated as the Day 7 value minus the Baseline value. Analysis was performed using a mixed model analysis of covariance (ANCOVA) with fixed effects of treatment, period, sex, and age. Participants is fitted as a random effect, and the period Baseline measurement is included as part of a bivariate response. The model for the period Baseline value is not affected by treatment group.