Complementing longitudinal spirometry with electrical impedance tomography: a novel strategy to evaluate biological efficacy in severe asthma

Objective Standard spirometry often fails to capture regional functional heterogeneity in severe asthma. This study aimed to evaluate the differential effects of biological versus conventional therapy on small airway function and ventilation homogeneity, utilizing a combined strategy of longitudinal spirometry and cross-sectional electrical impedance tomography (EIT) assessment at the 6-month endpoint. Methods In this observational study, 111 patients with severe asthma were stratified into two groups based on their clinical treatment regimen: a conventional group (high-dose ICS/LABA, n = 79) and a biological group (add-on biologic therapy, n = 32). Spirometry was performed at baseline and after 6 months. Electrical impedance tomography (EIT) measurements were only conducted at the 6-month follow-up to quantify regional ventilation dynamics, utilizing parameters such as the regional expiratory time constant (τ), global inhomogeneity (GI) index, and regional obstruction ratio (rOR). Results Over the 6-month period, the biological group demonstrated superior improvements compared to the conventional group. Significant Time×Group interactions were observed for all large airway parameters, including FEV1( P _Interaction =0.01), FVC( P _Interaction =0.047) and the FEV1/FVC ratio ( P _Interaction =0.02) and FEV1% pred ( P _Interaction =0.01). Small airway function also improved significantly more in the Biological group (MEF50, P _Interaction =0.02; MEF25, P _Interaction =0.04). EIT assessment at the endpoint confirmed these physiological benefits, showing significantly greater ventilation homogeneity (lower GI _T75 , P  = 0.01), faster lung emptying (shorter τ, P < 0.01), and reduced regional obstruction (lower rOR, P  = 0.01) in the biological group. Conclusion Biological treatments demonstrated superior efficacy in restoring large and small airway function and improving ventilation homogeneity, compared to conventional therapy. While global spirometry tracks overall airflow trends, EIT provides critical insights into regional lung mechanics. Integrating both modalities offers a more comprehensive approach to uncovering the potential physiological improvements in severe asthma management.