Small Airway Dysfunction and Ventilation Inhomogeneity in Pediatric Bronchiectasis: Toward Earlier Physiological Detection

Abstract

Pediatric bronchiectasis unrelated to cystic fibrosis is increasingly being recognized as a potentially preventable and, in some children, radiographically reversible chronic airway disease, particularly when identified and treated early in its course. Traditionally, the diagnosis has been made using high-resolution computed tomography (HRCT) to demonstrate bronchial dilatation. Nonetheless, emerging evidence suggests that mucus hyperconcentration, neutrophilic inflammation, ventilation inhomogeneity, and small airway dysfunction may occur prior to established structural damage. These observations support the potential value of combining anatomical assessment with physiological evaluation of small airway dysfunction. Emerging evidence suggests that impaired mucociliary clearance, airway surface dehydration, mucus retention, and muco-inflammatory injury may contribute to the pathogenesis and progression of pediatric bronchiectasis. In this context, oscillometry and the Lung Clearance Index (LCI) may provide sensitive evaluations of small airway dysfunction, often undetected by classical spirometry. LCI evaluates the ventilation inhomogeneity due to airway obstruction and mucus plugging, while oscillometry evaluates the respiratory impedance and small airway mechanics during tidal breathing. It is important to note that changes in these physiological indices may be detectable even in children with normal spirometric parameters and relatively mild HRCT abnormalities, suggesting that functional impairment may precede or occur in the absence of established irreversible structural remodeling, though this temporal relationship has not yet been confirmed through large prospective longitudinal studies. This narrative review examines the evolving role of small airway physiology, ventilation inhomogeneity, and oscillometry in the early identification and ongoing assessment of pediatric bronchiectasis.