Expiratory airflow patterns in children and adults with cystic fibrosis.
OBJECTIVE
To determine whether tidal expiratory airflow patterns change with increasing airways obstruction in patients with cystic fibrosis.


METHODS
An observational study.


METHODS
Lung function laboratory.


METHODS
Sixty-four children and young adults with cystic fibrosis.


METHODS
After measuring FEV(1) 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, f1.gif" BORDER="0">, describes the slope of the whole post-peak expiratory flow pattern after scaling.


RESULTS
Compared with FEV(1), the index tPTEF/tE was a poor indicator of airways 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 f1.gif" BORDER="0">, the postexpiratory profile could be categorized into three shapes, and provided a good indicator of airways obstruction when linear and concave-shaped 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, increase in airways resistance above normal is reflected by quantifiable changes in the expiratory airflow pattern.
Williams
E M
EM
Osler Chest Unit, Churchill Hospital, Oxford, United Kingdom. Jmorris@radius.jr2.ox.ac.uk
Madgwick
R G
RG
Thomson
A H
AH
Morris
M J
MJ
D000293:Adolescent; D000328:Adult; D000402:Airway Obstruction / Q000209:etiology / Q000503:physiopathology*; D000403:Airway Resistance; D002648:Child; D003550:Cystic Fibrosis / Q000150:complications / Q000503:physiopathology*; D005541:Forced Expiratory Volume; D006801:Humans; D010366:Peak Expiratory Flow Rate; D010991:Plethysmography; D011237:Predictive Value of Tests; D012720:Severity of Illness Index