The following is a summary of “Impulse oscillometry defined small airway dysfunction in asthmatic patients with normal spirometry: Prevalence, clinical associations, and impact on asthma control,” published in the NOVEMBER 2023 issue of Pulmonology by Cottini, et al.
Small-airway dysfunction (SAD), identified through impulse oscillometry (IOS), has recently gained recognition in asthma patients. However, there’s limited knowledge about SAD in asthma patients with normal spirometry (NS). For a study, researchers sought to investigate the prevalence, clinical characterization, and impact on asthma control of IOS-defined SAD in 321 patients with physician-diagnosed asthma and NS. Additionally, they compared differences between IOS- and spirometry-defined SAD.
Patients with asthma and NS were categorized by the presence of IOS-defined SAD (determined by a difference in resistance at 5 Hz and at 20 Hz [R5-R20] greater than 0.07 kPa x s x L-1). Spirometry-defined SAD was assessed using FEF 25–75 < 65% of predicted. Clinical and laboratory data were collected, and statistical analyses explored associations between clinical variables and SAD.
IOS-defined SAD was present in 54.1% of the cohort, while spirometry-defined SAD was found in only 10% of patients. Subjects with IOS-defined SAD had poorer asthma control and higher mean inhaled corticosteroid usage compared to those without SAD (both P < .001). Overweight (odds ratio [OR], 1.14; 95% CI, 1.05–1.23), exacerbation history (OR, 3.06; 95% CI, 1.34–6.97), nocturnal asthma awakenings (OR, 6.88; 95% CI, 2.13–22.23), exercise-induced asthma symptoms (OR, 33.5; 95% CI, 9.51–117.8), and uncontrolled asthma (OR, 0.22; 95% CI, 0.06–0.84) were independently associated with SAD.
Asthma patients with IOS-defined SAD exhibited poorer asthma control, more severe exacerbations, and higher corticosteroid usage. Exercise-induced asthma, nocturnal awakenings, exacerbation history, and being overweight were independently associated with SAD, while well-controlled asthma was inversely associated. SAD may be underdiagnosed via standard spirometry.