Subclinical small airway dysfunction in well‐controlled asthmatic children with normal FEV1z‐score

Abstract Background This study aimed to evaluate the presence of subclinical small airway dysfunction (SAD), which is associated with risk for persistence, loss of control, and exacerbations, using the impulse oscillometry system (IOS) in children with well‐controlled asthma and normal forced expiratory volume in one second (FEV 1 ) z ‐scores and to identify predictive pulmonary function test (PFT) parameters and associated risk factors for SAD. Methods A retrospective cohort study was conducted in children aged 6–18 years with well‐controlled asthma and normal FEV 1 , compared to healthy controls matched for age and sex. Spirometry and IOS parameters were assessed. Logistic regression and receiver operating characteristic (ROC) curve analyses were used to determine predictive PFT parameters. Results A total of 194 asthmatic children and 151 healthy controls were included. Although spirometry parameters were within normal limits, FEV 1 /FVC and FEF 25–75 (% predicted and z‐scores) were significantly lower in the asthma group ( p < .01). IOS parameters, including R5, R10, Fres, Ax, and ΔR5–20, were significantly higher in asthmatic children ( p < .05), and reactance values (X5–X20) were more negative. ΔR5–20 was the moderately predictive parameter for SAD OR (95% CI): 1.086 (1.017–1.159), p < .01 with a cutoff value of ≥22.15% (AUC 0.660, sensitivity 60%, specificity 68%). Younger age and atopy were independent risk factors for higher ΔR5–20. Conclusion Subclinical SAD may be present in children with well‐controlled asthma and normal FEV 1 . IOS, particularly ΔR5–20, provides a sensitive, effort‐independent tool for detecting SAD and should be considered for routine evaluation, especially in younger and atopic children.