title: Sample size estimation in studies monitoring exercise-induced bronchoconstriction in asthmatic children.
abstract: BACKGROUND
  The repeatability of the response to standardised treadmill exercise testing using dry air and monitoring of heart rate in asthmatic children suffering from exercise-induced bronchoconstriction (EIB) has not been well established.
  
  
  METHODS
  Twenty seven asthmatic children with known EIB performed standardised exercise testing twice within a period of three weeks. The tests were performed on a treadmill while breathing dry air. During both tests heart rate had to reach 90% of the predicted maximum. Response to exercise was expressed as % fall in forced expiratory volume in one second (FEV1) from baseline and as area under the curve (AUC) of the time-response curve.
  
  
  RESULTS
  The intra-class correlation coefficients for % fall and AUC (log-transformed) were 0.57 and 0.67, respectively. From these data, power curves were constructed that allowed estimations to be made of sample sizes required for studies of EIB in children. These indicated that, if a drug is expected to reduce EIB by 50%, as few as 12 patients would be sufficient to demonstrate this effect (90% power) using a parallel design study.
  
  
  CONCLUSIONS
  Standardised exercise testing for EIB using dry air and monitoring of heart rate is adequately repeatable for use in research and clinical practice in children with asthma.
authors.affiliation: Department of Pulmonary Pediatrics, Juliana Children's Hospital, The Hague, The Netherlands.
authors.forename: W B
authors.initials: WB
authors.lastname: Hofstra
authors.forename: J K
authors.initials: JK
authors.lastname: Sont
authors.forename: P J
authors.initials: PJ
authors.lastname: Sterk
authors.forename: H J
authors.initials: HJ
authors.lastname: Neijens
authors.forename: M C
authors.initials: MC
authors.lastname: Kuethe
authors.forename: E J
authors.initials: EJ
authors.lastname: Duiverman
mesh_terms: D000293:Adolescent; D001250:Asthma, Exercise-Induced / Q000503:physiopathology*; D016084:Bronchoconstriction; D002648:Child; D005080:Exercise Test; D005260:Female; D005541:Forced Expiratory Volume; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D015203:Reproducibility of Results; D018401:Sample Size