title: The relation between age and time to maximal bronchoconstriction following exercise in children.
abstract: BACKGROUND
  The exercise challenge test (ECT) is a common tool for assessment of asthma in children. Many studies suggest that the "time to maximal bronchoconstriction" (Nadir-t) after exercise challenge in asthmatic children may be age-dependent, although this has never been systematically studied. Such findings may influence epidemiological surveys where the schedule of post-exercise measurements is trimmed. This study systematically assesses the relation between age and time to maximal bronchoconstriction post-ECT.
  
  
  METHODS
  Data were collected retrospectively from 131 subjects (87 male; 3-18 years) who were referred for ECT. The routine ECT was performed according to ATS recommendation of a 6-min run. Spirometry was measured at 1, 3, 5, 10, 15, and 20 min post-exercise. The post-exercise nadir of FEV1 (%baseline) (FEV1-nadir) and the time to maximal fall in Nadir-t (minutes) were sought and values were related to age.
  
  
  RESULTS
  Baseline FEV1 values (mean+/-SD) were 90.5+/-13.8% predicted. FEV1-nadir was -23.6+/-11.7% from baseline values. The Nadir-t was reached at 5.1+/-2.6 min (range 2-12 min). A positive correlation between children's age and Nadir-t was observed (r2=0.542; SD of residuals=1.79; p<0.001), regardless of FEV1-nadir, whether the cutoff of point was -10% or -15% of baseline FEV1. Children <10 years of age showed Nadir-t at 3.4+/-1.7 min post-exercise and older children at 6.6+/-2.5 min post-exercise (p<0.0001).
  
  
  CONCLUSIONS
  Our results indicate that the time to maximal bronchoconstriction is age-dependent in children and adolescents, and imply that the schedule of post-exercise FEV(1) measurements should be cautiously trimmed.
authors.affiliation: Pediatric Pulmonary Unit, The Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel-HaShomer, Ramat Gan 52625, Affiliated to the Sackler Medical School, Tel-Aviv University, Israel. avi_vil@bezeqint.net
authors.forename: Daphna
authors.initials: D
authors.lastname: Vilozni
authors.forename: Amir
authors.initials: A
authors.lastname: Szeinberg
authors.forename: Asher
authors.initials: A
authors.lastname: Barak
authors.forename: Yaacov
authors.initials: Y
authors.lastname: Yahav
authors.forename: Arie
authors.initials: A
authors.lastname: Augarten
authors.forename: Ori
authors.initials: O
authors.lastname: Efrati
mesh_terms: D000293:Adolescent; D000367:Age Factors; D001250:Asthma, Exercise-Induced / Q000175:diagnosis / Q000503:physiopathology*; D016084:Bronchoconstriction / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D017410:Practice Guidelines as Topic; D012189:Retrospective Studies; D013147:Spirometry / Q000379:methods; D013997:Time Factors