Abstract
<jats:p>Background Acute bronchiolitis is among the most common causes of lower respiratory tract infection in infancy and remains a clinically heterogeneous syndrome. Current international guidelines recommend supportive management and generally discourage routine bronchodilator administration; however, physiological responsiveness may exist in a subset of patients. Tidal breathing analysis (TBA) provides a non-invasive, bedside method for objectively assessing respiratory mechanics and may objectively quantify physiological changes following bronchodilator administration. Case Presentation We report a 23-month-old boy presenting with severe RSV bronchiolitis-like wheezing illness complicated by acute respiratory failure. Bronchodilator responsiveness was evaluated using predefined TBA parameters before and after inhaled bronchodilator administration. Following treatment, time to peak tidal expiratory flow (tPTEF) increased from 0.17 to 0.33 s (+94%), while the tPTEF/TE ratio increased from 0.12 to 0.27 (+125%). Expiratory time (TE) and total respiratory cycle duration (Ttot) decreased by 12.6% and 5.1%, respectively, whereas tidal volume (VT) and minute ventilation (MV) increased by 12.1% and 18.3%. Peak expiratory flow remained unchanged (0.14 L/s before and after bronchodilator administration). Discussion To our knowledge, this is among the first reports using bedside TBA to characterize acute bronchodilator responsiveness in severe bronchiolitis-like illness. The improvement in expiratory timing indices, accompanied by shorter expiratory time without changes in peak expiratory flow, is consistent with improved expiratory flow dynamics following bronchodilator administration. These findings support the hypothesis that a bronchodilator-responsive physiological phenotype may exist. Previous studies have demonstrated an association between severe bronchiolitis during infancy and subsequent recurrent wheezing or asthma; however, whether acute bronchodilator responsiveness, measured objectively by TBA, represents a testable hypothesis for future longitudinal studies. Conclusions This case illustrates the feasibility of bedside TBA for identifying physiological bronchodilator responsiveness in severe bronchiolitis-like illness. Prospective longitudinal studies are warranted to determine whether TBA-defined responsiveness represents an early physiological marker requiring prospective validation and whether such physiological stratification may support individualized follow-up strategies.</jats:p>