Background: The target of anti-inflammatory therapy in asthma is thought to be situated, at least partly, in the lung periphery, and inhaled steroid aerosols are being engineered to reach it. However, the potential effect of such aerosols cannot be fully evaluated by conventional lung function tests because these are insensitive to peripheral lung structure.
Objective: A prospective cohort study was conducted to investigate whether ultrafine steroid aerosols can elicit a response in the lung periphery, using a validated multibreath washout technique that can distinguish acinar from conductive lung zone function.
Methods: In 30 stable patients with asthma with a wide range of disease severity (FEV(1) 27% to 108% predicted), we assessed conductive and acinar airway function abnormality at baseline, with patients on a standard dry powder steroid aerosol and after switching them to an ultrafine steroid aerosol.
Results: Only in those patients with abnormal acinar airway function at baseline (n = 16) did acinar heterogeneity show a consistent improvement after switching to an ultrafine steroid aerosol; the improvement was also correlated with baseline acinar heterogeneity (r = -0.67; P = .007). Although all patients with asthma also presented conductive airway abnormality at baseline, no changes were observed in this lung zone with the switch to the ultrafine aerosol (P > .1).
Conclusion: Among stable patients with asthma, those with acinar lung zone abnormality at baseline have the potential to receive functional benefit from an ultrafine steroid aerosol. Clinical studies comparing the efficacy of steroid aerosols targeted to the deep lung should at least include a measurement of peripheral lung zone function.
Clinical implications: A new noninvasive measure of small airways function reveals why, and for which particular patients with asthma, small steroid aerosol particles can be of therapeutic use.