Introduction. It is unclear whether airway dimension has a role in determining the clinical severity of bronchiolitis and the following developing of pre-school wheezing.

Aims and objectives. To correlate the degree of airway obstruction, through the analysis of tidal breathing flow-volume loop (TBFVL), with the clinical severity of bronchiolitis and the presence of wheezing in a 12-months follow up.

Methods. Infants hospitalized for bronchiolitis were prospectively enrolled from October to December 2021. They were evaluated and underwent a lung function test (TBFVL) at discharge (T0), after 1 (T1), 3 (T3), and 6 months (T6) and at 12 months of age (T12).

Results. 87 infants with a diagnosis of bronchiolitis underwent lung function test at discharge. Patients with respiratory distress had significant lower values of peak expiratory flow (PEF) at T0 (81.6 ± 13.5 ml/s vs 97.8 ± 33 ml/s, p-value 0.05) and patients who needed oxygen supplementation had lower inspiratory volume (IV) (36.6 ± 13.5 ml vs 46.7 ± 29.8 ml, p-value 0.03) and tidal volume/Kg (TV/Kg) (6.13 ± 1.9 ml/Kg vs 7.23 ± 2.1 ml/Kg, p-value 0.03). Infants with values of time to peak tidal expiratory flow/expiratory time (TPTEF/TE) <25% at T0 had more frequently wheezing at chest auscultation (61.5% vs 36.4%, p-value 0.02) and more frequently wheezing at T1 (43.8% vs 0%, p-value 0.04) and at T3 (42.9% vs 0%, p-value 0.05).

Conclusions. Airway obstruction, indirectly evaluated through TBFVL, is associated with a more severe presentation of bronchiolitis and with wheezing in the first months after the acute episode. Later on, other factors (e.g. atopic predisposition, environment, etc) could be predominant.