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

Mohammed A Almeshari,1,2 Nowaf Y Alobaidi,3 James A Stockley,4 Robert A Stockley,4 Prasad Nagakumar,5 Benjamin Paul Sutton,2 Elizabeth Sapey2,6 1Rehabilitation Health Sciences Department, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia; 2Institute of Inflammation and Ageing, University of Birmingham, Birmingham, UK; 3Respiratory Therapy Department, College of Applied Medical Sciences, King Saud Bin Abdulaziz University for Health Sciences, Alahsa, Saudi Arabia; 4Lung Function & Sleep Department, Respiratory Medicine, University Hospitals Birmingham NHS Foundation Trust, Queen Elizabeth Hospital Birmingham, Birmingham, UK; 5Department of Paediatric Respiratory Medicine, Birmingham Women’s and Children’s Hospital NHS Trust, Birmingham, UK; 6Acute Medicine, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UKCorrespondence: Mohammed A Almeshari, Rehabilitation Health Sciences Department, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia, Email malmeshari@ksu.edu.saBackground: 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.Keywords: asthma, small airways dysfunction, bronchodilator response