Tidal-Breathing Analysis: A Potential Non-Invasive, Bedside Method for Objective Assessment of Respiratory Mechanics and Bronchodilator Responsiveness in Acute Bronchiolitis—Case Report and Review of the Literature

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, a subset of patients may be physiologically responsive. Tidal-breathing analysis (TBA) is a non-invasive, bedside method for objectively assessing respiratory mechanics and may objectively quantify physiological changes following bronchodilator administration in older children. Case Presentation: We report the case of a 23-month-old boy presenting with a severe RSV bronchiolitis-like wheezing illness complicated by acute respiratory failure. Bronchodilator responsiveness was evaluated using predefined TBA parameters before and after administration of an inhaled bronchodilator. Following treatment, the patient’s time to peak tidal expiratory flow (tPTEF) increased from 0.17 to 0.33 s (+94%), while his 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 the best of our knowledge, this is among the first reports of using bedside TBA to characterize acute bronchodilator responsiveness in a severe bronchiolitis-like illness. The improvement in expiratory timing indices, along with the shorter expiratory time without changes in peak expiratory flow, is consistent with improved expiratory flow dynamics following bronchodilator administration. These findings could 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 via TBA, is an indication of this phenotype 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 should be conducted 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.