%0 Journal Article %A Ellie Oostveen %A Sandra Dom %A Margo Hagendorens %A Elke Dierckx %A Wilfried De Backer %A Joost Weyler %T Nonuniform growth in pediatric lung function between 4 and 9 years of age %D 2011 %J European Respiratory Journal %P 3220 %V 38 %N Suppl 55 %X Aim: To our knowledge, the longitudinal change in respiratory resistance (R) in children at the preschool age has not been studied before.Methods: Lung function was assessed with the forced oscillation technique at 4 and 9 years of age in 111 children (54 M: 57 F) who participated in a prospective birth-cohort in the region of Antwerp, Belgium. Respiratory impedance (4-32 Hz) was measured with a custom-built device at baseline and 15 min after bronchodilation.Results: The drop in R at 4 Hz (R4) with increasing age was linearly related to the magnitude of R4 at 4 years of age (Pearson's correlation coefficient of 0.87 and 0.88 at baseline and after bronchodilation, respectively). Interestingly, the slope characterizing this relationship was almost similar for the baseline (0.75) and the postbronchodilator values of R4 (0.81). Division of the group of children based on the magnitude of R4 at 4 years revealed that the change in R4 with increasing age was not related to differences in growth rate (see figure). Although the differences in R4 in 4-year-old children disappeared to a large extent with the increase in age, the subgroups of children still had significantly different R4 values by the age of 9 years.Conclusion: Four-year-old children with high airway resistance exhibit the largest drop in resistance with growth to 9 years of age; this drop in resistance is independent of airway muscle tone at young age. %U