Physiological Small Airways Dysfunction and the Bronchodilator Response in Adults With Asthma and Its Risk Factors: A Retrospective Analysis

Background: Physiological evidence of small airways dysfunction (SAD) is present in some patients with asthma and is associated with poor disease control. It is unclear if this represents a distinct phenotype of asthma or if it is an early manifestation of the disease. The study aimed to evaluate SAD in asthma and its clinical associations.

Methods: A retrospective analysis of routinely collected health data obtained from adults referred for routine spirometric assessment as part of their clinical management. The Maximal Mid-Expiratory Flow (MMEF) z-scores were used to assess the prevalence and association factors for SAD. Pre- and post-bronchodilator data of MMEF and FEV₁ in patients with and without SAD or airflow obstruction (AO) were analysed.

Results: A total of 1094 patients were included. 366 (33.5%) had evidence of SAD of whom 261 (71.3%) also had AO. Current smokers were at an increased risk of having SAD (OR: 2.05; 95% CI: 1.43– 2.93). 214 patients had Bronchodilator response (BDR) data with 157 (73.4%) demonstrating BDR for MMEF and 121 (56.5%) for FEV₁. SAD at baseline was associated with a significant BDR for FEV₁ (OR of 3.59 (95% CI: 1.77– 7.57)) and MMEF (OR of 2.89 (95% CI: 1.41– 5.95)). Males were less likely to have a positive BDR for MMEF than females (OR of 0.46; 95% CI: 0.24– 0.89).

Conclusion: SAD is common in asthma and is related to the presence of AO, cigarette smoking and is associated with increased BDR for both FEV₁ and MMEF. The assessment of SAD in routine clinical practice may help identify airway impairment early for the initiation of targeted therapies.