Impulse oscillometry compared with spirometry in detecting small airway dysfunction in children with uncontrolled asthma

Small airway dysfunction is closely related to asthma control and may not always be adequately detected by spirometry. This study aimed to compare spirometry and impulse oscillometry (IOS) parameters between well-controlled and uncontrolled asthma groups in children with moderate-to-severe persistent asthma and to evaluate small airway involvement. Sixty-one pediatric patients aged 6–17 years who had been diagnosed with asthma according to GINA criteria were included in the study. Asthma control was assessed using the Childhood Asthma Control Test (cACT), and patients were divided into two groups: well-controlled (n = 27) and uncontrolled (n = 34). Spirometry and IOS measurements were performed on all patients according to ATS/ERS standards. Demographic, clinical, and laboratory data were recorded. No significant differences were found between the groups in terms of age, gender, smoking exposure, and atopic sensitization (p > 0.05). The cACT score was lower (p = 0.001) and total IgE level was higher (p = 0.016) in the uncontrolled group. In spirometric evaluation, FEV1, FEV1/FVC, and MEF25–75 values were significantly lower in the uncontrolled group (p = 0.005, p = 0.01, p = 0.028, respectively); however, most values were not below pathological thresholds. Among the IOS parameters, R5–R20 (kPa·s/L), R5–R20 (%), and AX values were significantly higher in the uncontrolled group (p < 0.05). Although spirometry can demonstrate differences between groups in children with moderate-to-severe persistent asthma, it may be limited in identifying small airway dysfunction. IOS, particularly with the R5–R20 parameter, reveals small airway involvement more sensitively. The use of IOS as a complementary method in the evaluation of small airways in uncontrolled asthma may be clinically beneficial.