Detailed characterization and impact of small airway dysfunction in school-age asthma.

Background: Small airway dysfunction (SAD) is increasingly recognized as an important feature of pediatric asthma yet typically relies on spirometry-derived FEF to detect its presence. Multiple breath washout (MBW) and oscillometry potentially offer improved sensitivity for SAD detection, but their utility in comparison to FEF, and correlations with clinical outcomes remains unclear for school-age asthma. We investigated SAD occurrence using these techniques, between-test correlation and links to clinical outcomes in 57 asthmatic children aged 8-18 years.

Methods: MBW and spirometry abnormality were defined as -scores above/below ± 1.96, generating MBW reference equations from contemporaneous controls ( = 69). Abnormal oscillometry was defined as > 97.5 percentile, also from contemporaneous controls ( = 146). Individuals with abnormal FEF, MBW, or oscillometry were considered to have SAD.

Results: Using these limits of normal, SAD was present on oscillometry in 63% (resistance at 5-20 Hz; R5-R20; >97.5 percentile), on MBW in 54% (S; -scores> +1.96) and in spirometry FEF in 44% of participants (-scores< -1.96). SAD, defined by oscillometry and/or MBW abnormality, occurred in 77%. Among those with abnormal R5-R20, S was abnormal in 71%. Correlations indicated both R5-R20 and S were linked to asthma medication burden, baseline FEV and reversibility. Additionally, S correlated with FNO and magnitude of bronchial hyper-responsiveness. SAD, detected by oscillometry and/or MBW, occurred in almost 80% of school-aged asthmatic children, surpassing FEF detection rates.

Conclusions: Discordant oscillometry and MBW abnormality suggests they reflect different aspects of SAD, serving as complementary tools. Key asthma clinical features, like reversibility, had stronger correlation with MBW-derived S than oscillometry-derived R5-R20.