Increased interrupter resistance (Rint) in preschool-aged children with asthma may be described by 2 mechanistic respiratory system models, both of which include factors characterizing asthma-related small-airways dysfunction (SAD), according to study results published in the Journal of Asthma.

Researchers used 6 respiratory system models to examine the location of abnormalities in the respiratory system and their bronchodilator response in children (median age, 5.5 years; n=102) with asthma. In lung function tests, Rint was measured first, followed by the use of an impulse oscillometry system (IOS) to measure impedance of the respiratory system.

Data for 90% of the children with asthma were described by the extended RIC (central and peripheral resistance, inertance, and peripheral airway compliance; eRIC) model (95% CI, 64%-81%) and the Mead1969 model (95% CI, 10%-25%). Based on these findings, the researchers suggested that both peripheral airway compliance and resistance were necessary to describe abnormalities in lung function of these children. Approximately 78% (95% CI, 70%-86%) of children had a significant bronchodilator response.

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The response to salbutamol mainly involved a peripheral compartment. Following salbutamol, there was a reduction in peripheral airway resistance and an increase in peripheral airway compliance. An increase in any of the IOS parameters, including R5Hz, R20Hz, R5-20Hz, X5Hz >150% predicted, was noted in 74% (95% CI, 65%-83%) of patients.

A limitation of the study was the inclusion of children with increased Rint, which may have precluded the researchers’ ability to evaluate SAD prevalence in childhood asthma.

The investigators concluded that “…additional modeling of IOS results can be a reliable tool to assess the presence and extent of SAD” in young children with asthma.


Bokov P, Bafunyembaka G, Medjahdi N, et al. Cross-sectional phenotyping of small airway dysfunction in preschool asthma using the impulse oscillometry system [published online January 26, 2020]. J Asthma. doi: 10.1080/02770903.2020.1719133