Small airway dysfunction and associated clinical characteristics in severe asthma under omalizumab and mepolizumab...

Small airway dysfunction (SAD) plays a critical role in the pathophysiology of asthma.

This study aimed to evaluate the frequency of SAD in patients with severe asthma, and to assess its association with asthma control.

A total of 84 severe asthma patients were included in the study. Patients were classified into phenotypes according to the presence of allergy, fungal sensitization, obesity, blood eosinophil counts and frequency of asthma exacerbations. Impulse oscillometry (IOS) and spirometry were performed for all patients.

Sixty-nine patients (83.1%) had allergic, 75 (91.5%) eosinophilic, 43 (51.2%) obese asthma, 25 (31.6%) asthma with fungal sensitization, and 24 (28.6%) were frequent-exacerbators. The detection rates of SAD by IOS and spirometry in the overall group, allergic asthma, eosinophilic asthma, obese asthma, asthma with frequent-exacerbations and asthma with fungal sensitization groups were as follows, respectively: 85.7% and 84.0%; 87.0% and 86.4%; 89.3% and 86.1%; 86.0% and 82.5%; 87.5% and 85.7%; 92.0% and 87.0%. The rate of SAD detected by IOS was significantly higher in the eosinophilic group compared with the non-eosinophilic group (89.3% vs. 57.1%, p = 0.047). SAD was detected in 92.5% of patients with controlled and 100% of those with uncontrolled asthma (p = 0.292). Area of reactance (AX) and resonant frequency (Fres ) were lower in the controlled group (p = 0.044, 0.005, respectively).

The frequency of SAD is significantly higher in eosinophilic asthma compared with non-eosinophilic asthma, while similar across allergic, obese, fungal sensitization and frequent-exacerbator phenotypes. Higher AX and Fres values may be potentially indicative of uncontrolled asthma.