Within- and between-visit repeatability of impulse oscillometry in healthy and symptomatic young children

Background: Impulse oscillometry (IOS) is feasible for preschool children and postulated to enable assessment of small airways function. Yet, limited data on the repeatability of IOS in young children exist. Aims: To clarify the within- and between-visit repeatability of IOS in healthy and symptomatic children, with special regard to the putative indices of small airways function: the difference between respiratory resistance at 5 and 20 Hz (R5-20) and area under the reactance curve (AX). Methods: We retrospectively analysed the within-measurement repeatability of triplicate IOS measurements in 103 healthy children (aged 2.1-7.0 years) at baseline condition, and the between-measurement repeatability before and after placebo inhalation (n=19). In 45 children (aged 3.7-7.9 years) with a history of respiratory symptoms, we analysed the within- and between-visit IOS repeatability of two visits 7-14 days apart. Results: In healthy children, the repeatability of R5-20 and AX was high: within-measurement intraclass correlation coefficient (ICC) 0.89-0.94, 95% confidence interval (CI) 0.85-0.96, and between-measurement ICC 0.95-0.97, 95% CI 0.87-0.99. Similar results were observed among symptomatic children: within-visit ICC 0.96-0.98, 95% CI 0.94-0.99, and between-visit ICC 0.72-0.83, 95% CI 0.49-0.90. Discussion: R5-20 and AX measured with IOS have high repeatability also in young children and remain relatively stable in a one- to two-week period in symptomatic children. IOS may therefore be useful as an outcome measure for treatment interventions.