Introduction Preschool wheezing affects over 1/3 of children, and is associated with lung function deficits. There is a need for a clinical tool to evaluate lung function in preschool children, which is able to detect pathology associated with wheezing. Spirometry is the most common measurement of lung function in school aged children and adults, however spirometry measurements are a challenge in preschool children when conducted outside of specialised labs due to the complexity of the manoeuvres needed. Impulse oscillometry (IOS) is able to measure the resistance and resonant frequency of the lungs from normal breathing, and may be a suitable tool for assessing lung function in preschool children. This study aimed to measure the success rate of IOS for acquiring high quality lung function data in preschool children, and to evaluate the ability of the technique to detect differences between children with and without a history of wheezing.

Methods We recruited 66 children aged 3–4 years from a hospital paediatric outpatients department. Parents were interviewed about their child's health using a structured questionnaire. Children underwent allergy skin prick testing and lung function assessment using IOS pre- and post-bronchodilator. Variables recorded were resistance across 5–25 Hz, resonant frequency (Fres), reactance at 5 Hz and the percentage change in resistances across all frequencies post-bronchodilator.

Results 42 (64%) of 66 children successfully completed lung function assessment using IOS. Younger children were less likely to successfully complete IOS readings (3–3.5 years children 41% success; 3.5–4 years children 71% success; p=0.03). We found a significant increase in Fres in children with a history of wheezing (mean 23.4 Hz wheeze, 19.4 Hz no wheeze; p=0.01). Furthermore, significant differences were found in the Fres of children who had previously been diagnosed with asthma by a doctor compared to non asthmatics (p=0.015); and those with atopy and wheeze compared to those with no atopic wheeze (p=0.015) (Abstract P79 Figure 1).

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Abstract P79 Figure 1

The differences in resonant frequency between preschool children with a history of wheeze and those without a history of wheeze.

Discussion IOS yields high quality lung function data in most children over 3.5 years age. The technique is able to detect group differences related to wheezing tendency in this age group, and may be a useful clinical tool for use in young children over 3.5 years.