title: Reference ranges for shape indices of the flow-volume loop of healthy children.
abstract: BACKGROUND
  The concavity of the descending limb of the maximum expiratory flow-volume loop (MEFVL) is the earliest change associated with airflow obstruction in small airways (ATS/ERS Task Force). The shape of the MEFVL changes with age but there are no reference values for shape indices for preschool and school children.
  
  
  OBJECTIVE
  To define pediatric reference values for spirometric data and 3 shape indices of MEFVL: 2 geometric indices: the β angle i.e., the angle between the first ½ part and the 2nd part of the MEFVL and the forced expiratory flow after 50% of the forced vital capacity (FVC) has been exhaled/peak expiratory flow (FEF50 /PEF) ratio; and a ratio that describes relative growth between airway and lung parenchyma, the forced expiratory flow between 25 and 75% of FVC/FVC ratio (FEF25-75 /FVC ratio).
  
  
  METHODS
  Data were obtained from 446 Caucasian children (2.5 to 15-year-old). The lambda, mu, sigma method was applied.
  
  
  RESULTS
  References for spirometric parameters and 3 shape indices. The geometric indices decreased with age from 3 years of age (mean β angle was 215° and FEF50 /PEF ratio was 0.82) until 8 years of age (mean β angle was 191° and FEF50 /PEF ratio was 0.60) and then remained constant. The FEF25-75 /FVC ratio also decreased with age. Sex was a significant determinant for FEF25-75 /FVC ratio predicted values.
  
  
  CONCLUSIONS
  This study provides standard reference equations for indices of mid-expiratory flows in children and we suggest using the FEF50 /PEF index.
authors.affiliation: Pulmonary Function Testing Unit, CHU de Lille, Lille, France.|Univ Lille Nord de France, UDSL, Lille, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Nève
authors.affiliation: Pulmonary Function Testing Unit, CHU de Lille, Lille, France.|Univ Lille Nord de France, UDSL, Lille, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Edmé
authors.affiliation: Univ Lille Nord de France, UDSL, Lille, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Baquet
authors.affiliation: Pulmonary Function Testing Unit, CHU de Lille, Lille, France.|Univ Lille Nord de France, UDSL, Lille, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Matran
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D008297:Male; D008449:Maximal Expiratory Flow-Volume Curves / Q000502:physiology*; D012016:Reference Values; D013147:Spirometry; D014797:Vital Capacity / Q000502:physiology*
keywords: Pediatric lung function testing; Spirometry refference values; preschool and school lung function