Study objective: To determine whether tidal expiratory airflow patterns cha
nge with increasing airways obstruction in patients with cystic fibrosis,
Design: An observational study,
Setting: Lung function laboratory.
Patients: Sixty-four children and young adults with cystic fibrosis,
Measurements: After measuring FEV1 and airways resistance using body plethy
smography, each subject was seated and asked to mouth breathe through a pne
umotachograph for 2 min. The collected data were analyzed, and three expira
tory airflow pattern-sensitive indexes were computed. The first index was d
erived from the ratio of the time to reach peak expiratory flow to the tota
l expiratory time (tPTEF/tE). The second index, Trs, was an estimate of the
time constant of the passive portion of expiration. The third index, (S) o
ver bar, describes the slope of the whole post-peak expiratory flow pattern
after scaling.
Results: Compared with FEV1, the index tPTEF/tE was a poor indicator of air
ways obstruction (r(2) = 0.15, p = 0.002), Trs showed a strong relationship
with the severity of airways obstruction (r(2) = 0.46, p < 0.001), Using S
, the postexpiratory profile could be categorized into three shapes, and pr
o tided a good indicator of airways obstruction when linear and concave-sha
ped profiles occurred (r(2) = 0.42, p < 0.001), Convex-shaped flow profiles
had to be treated separately and were indicative of normal lung function,
Conclusions: In a cross-sectional study of patients with cystic fibrosis, i
ncrease in airways resistance above normal is reflected by quantifiable cha
nges in the expiratory airflow pattern.