title: The repeatability of forced expiratory volume measurements in adults with cystic fibrosis.
abstract: OBJECTIVE
  To determine the repeatability of measurements of FEV(1) in adults with lung disease due to cystic fibrosis (CF).
  
  
  METHODS
  Single cohort study nested within a randomized controlled trial.
  
  
  METHODS
  Adult CF of a university teaching hospital. Subjects were participants in a randomized trial of an experimental mucolytic drug.
  
  
  METHODS
  Twenty-one adults (mean age, 27.5 +/- 9.2 years [+/- SD]) with CF and mild-to-moderate airflow obstruction (FEV(1) 70 +/- 15% predicted). Patients were in clinically stable condition prior to and during the study.
  
  
  METHODS
  Repeated FEV(1) measurements were obtained at specific times of the day for 9 consecutive days, for a total of 31 measurements from each subject. Statistical measures of repeatability were calculated. Variation over the course of 1 day and variation from 1 day to the next were examined separately.
  
  
  RESULTS
  For day-to-day FEV(1) measurements, the within-subject SD was 0.145 L (4.5% of predicted), indicating greater variation compared to values previously established in normal subjects. The coefficient of repeatability indicated that day-to-day measurements could differ by as much as 13% of predicted in the absence of clinical change. For measurements within a single day, variation was not observed to be greater than normal.
  
  
  CONCLUSIONS
  In adults with CF, day-to-day variation in FEV(1) measurements is greater than normal and similar to that seen in other obstructive lung diseases. Changes in FEV(1) over time in adults with CF can likely be interpreted using the same criteria that apply to asthma or COPD.
authors.affiliation: Adult Cystic Fibrosis Program, St. Michael's Hospital, Toronto, ON, Canada.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Stanbrook
authors.forename: Mary
authors.initials: M
authors.lastname: Corey
authors.forename: D Elizabeth
authors.initials: DE
authors.lastname: Tullis
mesh_terms: D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm; D015331:Cohort Studies; D003550:Cystic Fibrosis / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results