Expiratory Airflow Patterns in Children and Adults With Cystic Fibrosis

To determine whether tidal expiratory airflow patterns change with increasing airways obstruction in patients with cystic fibrosis. An observational study. Lung function laboratory. Sixty-four children and young adults with cystic fibrosis. After measuring FEV1 and airways resistance using body plethysmography, each subject was seated and asked to mouth breathe through a pneumotachograph for 2 min. The collected data were analyzed, and three expiratory airflow pattern-sensitive indexes were computed. The first index was derived from the ratio of the time to reach peak expiratory flow to the total expiratory time (tptef/te). The second index, Trs, was an estimate of the time constant of the passive portion of expiration. The third index, ▪, describes the slope of the whole post-peak expiratory flow pattern after scaling. Compared with FEV1, the index tptef/te was a poor indicator of airways obstruction (r2 = 0.15, p = 0.002). Trs showed a strong relationship with the severity of airways obstruction (r2 = 0.46, p < 0.001). Using ▪, the postexpiratory profile could be categorized into three shapes, and provided a good indicator of airways obstruction when linear and concave-shaped profiles occurred (r2 = 0.42, p < 0.001). Convex-shaped flow profiles had to be treated separately and were indicative of normal lung function. In a cross-sectional study of patients with cystic fibrosis, increase in airways resistance above normal is reflected by quantifiable changes in the expiratory airflow pattern.