Aberrant small airways function relates to asthma severity in young children

- Frequency dependence of resistance (R5-20) indicates small airway obstruction.
- Small airway dysfunction during methacholine induced bronchoconstriction varies.
- Higher increase in R5-20 associates with severe exercise induced bronchoconstriction.
- Severe EIB and more frequent use of short-acting beta-agonist was connected.
- Small airways may be determinants of asthma severity in young children.

BackgroundFrequency dependence of resistance (R5-20) assessed by impulse oscillometry (IOS) is suggested to be a measure of small airways. Small airways involvement during induced bronchoconstriction has been shown to reflect severity of asthma in adults.ObjectiveOur aim was to evaluate if methacholine (Mch) induced changes in R5-20 are associated with the severity of exercise induced bronchoconstriction (EIB) in young children.MethodsA total of 109 children aged 3-8 years were studied, 95 with obstructive symptoms and 14 in good health, to assess small airways function during a Mch challenge. R5-20 and other IOS resistance and reactance parameters were measured at baseline and after the Mch challenge. In a standardized exercise test, the children were grouped according to the severity of EIB expressed as the percentage increase in resistance at 5 Hz (ΔR5) after exercise, indicating either no EIB (ΔR5 < 40%, n = 84), moderate EIB (ΔR5 40-80%, n = 13) and severe EIB (ΔR5 > 80%, n = 12).ResultsThe baseline R5-20 was not associated with the severity of EIB, but during Mch induced bronchoconstriction the change in R5-20 was significantly higher in children with severe EIB (2.61 fold increase) than in children with moderate EIB (1.48) or no EIB (1.74, p = 0.036). No significant associations were found in changes of other IOS parameters. The children with severe EIB also used more short-acting beta-agonists during the past two months than the other two groups (p < 0.001).ConclusionFrequency dependence of resistance (R5-20) measured by IOS during the Mch induced bronchoconstriction and more frequent use of beta-agonists are associated with severe EIB in young children.