SEVERE asthma (SA) is a heterogeneous condition, and a key factor influencing patient outcomes is whether airway obstruction is fixed or reversible. Recent analysis from the Severe Asthma Network in Italy (SANI) registry has provided new insights into the prevalence and characteristics of fixed airway obstruction (FAO) among severe asthma patients.
Fixed Airway Obstruction Versus Bronchodilator Responsiveness
Among 354 patients enrolled in the registry, 190 (53.7%) had airway obstruction, of whom 116 (60.1%) were classified as having FAO. This represents an overall FAO rate of 32.8%. Patients with FAO displayed significantly better asthma control than those with bronchodilator responsiveness (BDR), with 34.5% achieving well-controlled asthma compared with 20.3% in the BDR group. FAO patients also had higher asthma control test (ACT) scores (17.4 vs 15.2) and asthma quality of life questionnaire (AQLQ) scores (4.6 vs 3.8).
Hospitalisations and emergency visits were less frequent in FAO patients than in BDR patients, although overall exacerbation rates were similar. Interestingly, fractional exhaled nitric oxide (FeNO) levels were lower in FAO patients (29.5 ppb) than BDR patients (46.0 ppb), suggesting airway calibre rather than type 2 inflammation contributed to differences in biomarker expression.
Potential Reversibility of FAO
The study also highlighted that FAO is not necessarily permanent. Transition from FAO to BDR or normal lung function was observed, particularly in patients with late-onset severe asthma (ages 30–39) and lower inhaled corticosteroid use. The Global Initiative for Asthma classification influenced this shift, with step 4 versus step 5 patients showing higher rates of improvement.
Implications for Clinical Practice
These findings emphasise the importance of phenotyping severe asthma patients. Identifying FAO can guide personalised management strategies, including monitoring for potential reversibility and optimising therapy based on airway obstruction type. This approach may improve patient outcomes and reduce unnecessary hospitalisations.
Reference
Guida G et al. Fixed airway obstruction and bronchodilator responsiveness phenotypes in severe asthma population from SANI registry. BMJ Open Respir Res. 2025;12:e002992.
