Small airway dysfunction may mediate the association between body mass index and severe asthma exacerbations

TY - JOUR

T1 - Small airway dysfunction may mediate the association between body mass index and severe asthma exacerbations

AU - Portacci, Andrea

AU - Ventura, Laura

AU - Menzella, Francesco

AU - Poto, Remo

AU - Berti, Alvise

AU - Lombardi, Carlo

AU - Comberiati, Pasquale

AU - Carpagnano, Giovanna Elisiana

AU - Diamant, Zuzana

AU - Adcock, Ian M.

AU - Lipworth, Brian

AU - Usmani, Omar

AU - Cottini, Marcello

AU - Chan, Rory

N1 - Copyright: ©The authors 2026. For reproduction rights and permissions contact [email protected].

PY - 2026/9/25

Y1 - 2026/9/25

N2 - Background: Obesity is associated with poorer asthma outcomes and an increased risk of exacerbations, but the underlying mechanisms remain incompletely understood. Small airway dysfunction (SAD) may represent a key mechanistic link between excess body weight and adverse asthma outcomes.Methods: In this multicenter observational study, adult patients with asthma underwent clinical characterization, spirometry and impulse oscillometry (IOS). SAD was defined using a composite criterion based on peripheral airway resistance (R5-20), reactance area (AX) and the ratio of peripheral to total airway resistance (R5-20)/R5. Associations between body mass index (BMI), SAD and severe asthma exacerbations were assessed using multivariable regression models. Non-linear relationships were explored using generalized additive models and mediation analyses quantified the contribution of SAD to the obesity-exacerbation association.Findings: Among 1169 patients, IOS-defined SAD was significantly more prevalent in individuals with BMI≥30 kg·m-2. Increasing BMI was associated with worse oscillometric parameters (p<0.0001), following a non-linear pattern with steeper deterioration beyond BMI values of approximately 28-30 kg·m-2. SAD was independently associated with obesity (adjusted OR 2.11, 95% CI 1.56-2.86) and with severe asthma exacerbations in the previous year (adjusted OR 2.01, 95% CI 1.53-2.65, both p<0.0001). Mediation analyses showed that SAD accounted for 26%-41% of the association between obesity and exacerbation risk (p=0.004 and 0.03). Spirometric indices provided limited additional information.Interpretation: Oscillometry-defined small airways dysfunction (SAD) represents a non-linear functional trait underlying the association between obesity and severe asthma exacerbations, supporting its clinical relevance in obese patients with asthma and identifying SAD as a potential treatable trait.

AB - Background: Obesity is associated with poorer asthma outcomes and an increased risk of exacerbations, but the underlying mechanisms remain incompletely understood. Small airway dysfunction (SAD) may represent a key mechanistic link between excess body weight and adverse asthma outcomes.Methods: In this multicenter observational study, adult patients with asthma underwent clinical characterization, spirometry and impulse oscillometry (IOS). SAD was defined using a composite criterion based on peripheral airway resistance (R5-20), reactance area (AX) and the ratio of peripheral to total airway resistance (R5-20)/R5. Associations between body mass index (BMI), SAD and severe asthma exacerbations were assessed using multivariable regression models. Non-linear relationships were explored using generalized additive models and mediation analyses quantified the contribution of SAD to the obesity-exacerbation association.Findings: Among 1169 patients, IOS-defined SAD was significantly more prevalent in individuals with BMI≥30 kg·m-2. Increasing BMI was associated with worse oscillometric parameters (p<0.0001), following a non-linear pattern with steeper deterioration beyond BMI values of approximately 28-30 kg·m-2. SAD was independently associated with obesity (adjusted OR 2.11, 95% CI 1.56-2.86) and with severe asthma exacerbations in the previous year (adjusted OR 2.01, 95% CI 1.53-2.65, both p<0.0001). Mediation analyses showed that SAD accounted for 26%-41% of the association between obesity and exacerbation risk (p=0.004 and 0.03). Spirometric indices provided limited additional information.Interpretation: Oscillometry-defined small airways dysfunction (SAD) represents a non-linear functional trait underlying the association between obesity and severe asthma exacerbations, supporting its clinical relevance in obese patients with asthma and identifying SAD as a potential treatable trait.

U2 - 10.1183/13993003.00150-2026

DO - 10.1183/13993003.00150-2026

M3 - Article

C2 - 42167779

SN - 0903-1936

VL - 68

JO - European Respiratory Journal

JF - European Respiratory Journal

IS - 3

M1 - 2600150

ER -