Small Airway Dysfunction in Asthma: Associations with Control and Quality of Life

Small airway dysfunction (SAD) is an important but frequently underrecognized component of asthma. This study aimed to determine the prevalence of SAD in asthma, as assessed by impulse oscillometry (IOS), and to evaluate its association with clinical outcomes.

This cross-sectional study, with a 12-month prospective follow-up, included adult patients with asthma. SAD was defined by IOS as R5-R20 ≥0.07 kPa·s·L-¹. The asthma control test (ACT) and the asthma quality of life questionnaire (AQLQ) were administered. Exacerbations were prospectively recorded during the 12 months after enrollment. Patients were stratified according to the presence of SAD. Clinical and functional parameters were compared between groups.

SAD was identified in 63 of 98 participants (64.3%). SAD prevalence differed significantly across the five Global Initiative for Asthma treatment steps (P < 0.001). Patients with SAD had significantly lower ACT scores (P = 0.021), poorer quality of life (AQLQ, P = 0.002), and more frequent exacerbations (P < 0.001) than those without SAD. In multivariable regression analyses, higher R5-R20 was independently associated with a lower AQLQ score (β = -0.18, 95% confidence interval -0.30 to -0.07; P = 0.002) and higher odds of being in a worse asthma control category (odds ratio 1.33, P = 0.010).

SAD is common among patients with asthma and is associated with poorer asthma control, lower quality of life, and an increased exacerbation burden. Higher R5-R20 remained associated with poorer quality of life after adjustment for spirometry, whereas its association with asthma control was attenuated and became non-significant after adjustment for forced expiratory volume in the first second. These findings support further evaluation of IOS-defined SAD as a potentially clinically relevant trait in asthma.