D2.112 - The Impact of Obesity in Asthma and Small Airway Dysfunction: Prevalence, Clinical characteristics, and Predictors

Obesity is a growing global health threat and a well-recognized comorbidity that worsens asthma outcomes. Small Airway Dysfunction (SAD) is another significant, but often overlooked, contributor to asthma pathophysiology and poor control. Recent findings showed that SAD is common in obese asthmatic patients, but its relationship with BMI and its role as a clinical predictor remain poorly understood.

We performed a 3-year observational study collecting clinical, demographic, and functional data from 660 asthmatic patients undergoing functional tests (spirometry, impulse oscillometry (IOS) and FeNO). Patients were divided into non-obese (n=556, BMI 20-29.99 kg/m²) and obese (n=102, BMI ≥ 30 kg/m²) groups. A further stratification into mild obesity (n=87, BMI 30-39.99 kg/m²) and morbid obesity (n=15, BMI ≥ 40 kg/m²) was performed to provide more detailed results about the effects of increasing BMI on SAD and clinical symptomatology. Finally, a multivariate analysis was conducted to identify determinants of SAD, defined as R5-R20 > 0.07 kPa/L/s.

Significant differences were found between non-obese and obese groups in atopic phenotype (respectively, 65.3% vs 42.2%, Chi-square <0.005), nocturnal awakenings (38.1% vs 70.6%, Chi-square <0.005), exercise-induced asthma (48.2% vs 78.4%, Chi-square <0.005), exacerbation rates (0.44±0.70 vs 0.64±0.701, p <0.005), and ER accesses (0.08±0.273 vs 0.24±0.470, p <0.005). IOS proved a superior sensitivity in detecting SAD compared to spirometry: SAD prevalence was significantly higher in obese patients (90.2% vs. 57.7%, p <0.05) using IOS, while no correlation was observed between BMI and FEF 25-75%. Multivariate analysis identified BMI, age, asthma duration, smoking, and systemic eosinophils as significant SAD predictors.

This study highlights the multifactorial nature of SAD and the potential use of BMI as a predictor of its prevalence and clinical severity of asthma. Our findings proved a superior sensitivity of IOS over spirometry in detecting SAD, showing the limitations of standard function tests for detecting distal airway impairment. Early identification of SAD and patient-tailored therapies, including use of extra-fine particle formulations, are critical to improve outcomes and quality of life, particularly in in the growing population of obese asthmatics patients.