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 FEV 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 FEV. SAD at baseline was associated with a significant BDR for FEV (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 FEV and MMEF. The assessment of SAD in routine clinical practice may help identify airway impairment early for the initiation of targeted therapies.