Impact of Small Airway Dysfunction on Asthma Presentation and Future Exacerbation Risk: A Cohort Study.

BACKGROUND: Small airway dysfunction is increasingly recognized in asthma, but its associations with future exacerbation risk and follow-up physiologic changes remain incompletely defined. This study aimed to examine the association of small airway dysfunction with future exacerbation risk in an asthma care cohort and to characterize physiologic changes during follow-up. MATERIALS AND METHODS: We enrolled 167 adults with stable asthma who had paired baseline and follow-up spirometry and oscillometry assessments, with a median interval of 12 months between assessments. Small airway dysfunction was defined as R5-R20 >0.07 kPa/(L/s) by impulse oscillometry. Baseline characteristics were compared by small airway dysfunction status. Time to future acute exacerbation was analyzed using multivariable Cox proportional hazards regression. Longitudinal changes in clinical and physiologic measures among participants with small airway dysfunction were also assessed. RESULTS: Small airway dysfunction was present in 134 of 167 participants (80.2%). Participants with small airway dysfunction had a higher rate of future acute exacerbations than those without (43.3% vs 21.2%, p=0.020). After multivariable adjustment, prior acute exacerbation history (aHR:2.61, 95% CI:1.40-4.85) and small airway dysfunction (aHR:3.26, 95% CI:1.47-7.23) were independently associated with future acute exacerbation risk. Among participants with small airway dysfunction, asthma symptom control and selected spirometric measures improved from baseline to follow-up. CONCLUSIONS: In adults with asthma, small airway dysfunction defined by impulse oscillometry was independently associated with an increased risk of future acute exacerbations. Among those with small airway dysfunction, asthma symptom control and selected spirometric measures improved from baseline to follow-up.