Gastroesophageal Reflux Burden Before and After Exercise Challenge in Children with Poorly Controlled Asthma: A 48-Hour MII-pH Study

Background: Gastroesophageal reflux and exercise-induced bronchoconstriction (EIB) commonly coexist with asthma, but the effect of exercise on reflux remains unclear. We aimed to assess the prevalence of abnormal impedance-detected acid exposure in children with partially controlled or uncontrolled asthma, its association with EIB, and changes in reflux parameters after an exercise challenge test (ECT). Methods: Thirty patients aged 7–18 years underwent spirometry, treadmill ECT, and 48 h multichannel intraluminal impedance-pH monitoring. EIB was defined as a ≥10% fall in FEV1, and abnormal acid exposure as impedance-detected acid reflux lasting ≥1.2% of recording time. Results: Abnormal acid exposure was identified in 14/30 patients (46.7%), whereas EIB occurred in 6/30 (20.0%), with no significant association between them. The absolute number of reflux episodes was higher after ECT in the count-based analysis (43.0 [35.2–69.8] vs. 33.5 [21.2–54.5], p = 0.006); however, this finding was not confirmed after normalization to analyzable recording time in a sensitivity analysis. Overweight or obesity was present in 9 patients (30.0%) and correlated positively with acid exposure. BMI-for-age z-score correlated positively with acid exposure (ρ = 0.41, p = 0.025), but these findings did not remain significant after correction for multiple testing. Conclusions: Using the prespecified acid-exposure criterion, abnormal acid exposure was frequently identified in this cohort. No statistically significant association with EIB was demonstrated; however, the small number of EIB events limits definitive conclusions. The higher absolute post-ECT reflux episode count was not confirmed in a rate-based sensitivity analysis, and a causal effect of exercise on reflux cannot be established.