title: Relationships between specific airway resistance and forced expiratory flows in asthmatic children.
abstract: BACKGROUND
  The earliest changes associated with airflow obstruction in asthmatic children are a proportionally greater reduction in FEF(50%) than in FEV(1) using spirometry, and an increase in specific airway resistance (sRaw) using body plethysmography. Consequently, we hypothesized that sRaw could be better linked to FEF(50%) than to FEV(1). The first aim was to assess the relationships between forced expiratory flows and sRaw in a large group of asthmatic children in a transversal study. We then performed a longitudinal study in order to determine whether sRaw of preschool children could predict subsequent impairment of forced expiratory flows at school age.
  
  
  METHODS
  Pulmonary function tests (sRaw and forced expiratory flows) of 2193 asthmatic children were selected for a transversal analysis, while 365 children were retrospectively selected for longitudinal assessment from preschool to school age.
  
  
  RESULTS
  The transversal data showed that sRaw is differently related to FEF(50%) (-1/sRaw) and to FEV(1) (near linearly). These results were further explained by a simple one-compartment lung model, which justified the shape of the observed relationships. As hypothesized, sRaw correlated more strongly to FEF(50%) than to FEV(1) (r = -0.64 versus -0.39, respectively; p<0.001). In the longitudinal part of the study, sRaw at preschool age correlated with subsequent FEF(50%) (% predicted) (-0.31, 95% CI, -0.40 to -0.22), but weakly with subsequent FEV(1) (% predicted) (-0.09, 95% CI, -0.20 to 0).
  
  
  CONCLUSIONS
  Specific Raw is more strongly related to FEF(50%) than to FEV(1) and could be used in preschool children to predict subsequent mild airflow limitation.
authors.affiliation: Cabinet La Berma, Antony, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Mahut
authors.forename: Ludovic
authors.initials: L
authors.lastname: Trinquart
authors.forename: Plamen
authors.initials: P
authors.lastname: Bokov
authors.forename: Muriel
authors.initials: M
authors.lastname: Le Bourgeois
authors.forename: Serge
authors.initials: S
authors.lastname: Waernessyckle
authors.forename: Claudine
authors.initials: C
authors.lastname: Peiffer
authors.forename: Christophe
authors.initials: C
authors.lastname: Delclaux
mesh_terms: D000403:Airway Resistance; D001249:Asthma / Q000503:physiopathology*; D002648:Child; D005540:Forced Expiratory Flow Rates; D006801:Humans