title: Expiratory airflow patterns in children and adults with cystic fibrosis.
abstract: 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.
authors.affiliation: Osler Chest Unit, Churchill Hospital, Oxford, United Kingdom. Jmorris@radius.jr2.ox.ac.uk
authors.forename: E M
authors.initials: EM
authors.lastname: Williams
authors.forename: R G
authors.initials: RG
authors.lastname: Madgwick
authors.forename: A H
authors.initials: AH
authors.lastname: Thomson
authors.forename: M J
authors.initials: MJ
authors.lastname: Morris
mesh_terms: 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