title: Forced expiratory decay in asthmatic preschool children--is it adult type?
abstract: BACKGROUND
  The forced expiratory decay in healthy preschool children portrays a convex shape that differs from the linear decay in the older healthy population. The "adult-type" expiratory decay during airway obstruction is concave. The study objective was to determine if the expiratory decay in young asthmatic children is "adult-type".
  
  
  METHODS
  Among 245 children (age 3-7 yrs), 178 had asthma (asthmatics) and 67 were non-asthmatic (controls). The expiratory flow decay was inspected by FEF25-75/FVC ratio (=1.0 when linear). Values were compared to those of our formerly studied (n = 108) healthy children. A meaningful obstruction in FEF25-75/FVC ratio was defined as 2-zScores from healthy. A meaningful response to bronchodilators was related to non-asthmatics.
  
  
  RESULTS
  In healthy subjects FEF25-75/FVC ratio declined with age from 1.73 ± 0.17 to 1.28 ± 0.11. Non-asthmatics portrayed ratio values similar to those of healthy subjects. In asthmatics, 118/178 displayed a convex to linear expiratory decay (FEF25-75/FVC = 1.33 ± 0.22). Sixty/178 asthmatics portrayed concavity (FEF25-75/FVC-0.79 ± 0.16) that appeared when FEF50 was 43.4 ± 12%healthy. Concavity appearance was also age-dependent (30.4% of 3-4 y old and 59.1% of 6-7 y). Vital-Capacity decreased in either decays, forming a visually petit curve. Most asthmatic children respond to bronchodilators by a meaningful elevation in FEF25-75/FVC values and by a visual change in the shape of the curve. Other common spirometry indices also increased meaningfully.
  
  
  CONCLUSIONS
  Most asthmatic preschool children portray convex to linear expiratory decay with diminished vital-capacity, resulting in a visually smaller than healthy curve, with seemingly normal expiratory decay. These curves may be misinterpreted as "normal" or as "no-cooperation" and may lead to misinterpretation. In response to bronchodilators, FEF25-75/FVC value increases in asthmatics and the curve changes from concave to linear or from linear to convex contour.
authors.affiliation: The Edmond and Lili Safra Children's Hospital, Sheba Medical Center, Ramat-Gan, Affiliated with Sackler Medical School, Tel-Aviv, Israel. avi_vil@bezeqint.net
authors.forename: Daphna
authors.initials: D
authors.lastname: Vilozni
authors.forename: Fahed
authors.initials: F
authors.lastname: Hakim
authors.forename: Galit
authors.initials: G
authors.lastname: Livnat
authors.forename: Lea
authors.initials: L
authors.lastname: Bentur
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology*; D001993:Bronchodilator Agents / Q000494:pharmacology / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D008450:Maximal Midexpiratory Flow Rate / Q000187:drug effects / Q000502:physiology*; D012189:Retrospective Studies; D013147:Spirometry / Q000379:methods; D014797:Vital Capacity / Q000187:drug effects / Q000502:physiology
chemical_list: D001993:Bronchodilator Agents