Aerosol deposition in the lung as a biomarker in asthma and chronic obstruction

The objective of this study was to explore the potential of Airspace Dimension Assessment (AiDA) to rapidly determine the type and severity of airway obstruction, detect emphysema in individuals with chronic airflow limitation (CAL), and distinguish it from non-emphysematous obstruction, asthma, and absence of respiratory disease with normal spirometry.

Among the 744 participants measured with AiDA within the Swedish CArdioPulmonary bioImage Study (SCAPIS) cohort, 40 had asthma, and 34 had a CAL (defined by a post-bronchodilator FEV₁/FVC < 0.7), whereof 12 had CT-detected emphysema. AiDA measurements were compared across these groups and to 111 healthy controls (never-smokers with normal spirometry and no history of respiratory disease).

Subjects with CAL had significantly larger distal airspaces radii (median r_AiDA=298 μm) than controls (r_AiDA=278 μm, p < 0.001), but no significant difference was observed in asthmatics (r_AiDA=273 μm, p = 0.79). Subjects with CT-detected emphysema in the CAL group displayed further differentiation from the control (r_AiDA=349 μm, p < 0.001), while those without emphysema displayed no significant increase. Unlike r_AiDA, neither low attenuation volume nor 15th percentile density could clearly distinguish between obstruction and radiologist-assessed emphysema. In addition, the zero-second particle recovery (R₀), which is theorized to reflect conducting airway dysfunction, was decreased in both asthmatics (R₀ = 0.41, p = 0.011), and in the CAL group (R₀ = 0.45, p = 0.020) when compared to controls (R₀ = 0.56).

These findings display AiDA's potential in identifying emphysema as well as obstructive airway disease. The absence of an increased distal airspace radius in asthmatics confirm that r_AiDA is a measure of the distal airspaces, unaffected by abnormalities in the conducting airways. However, the decreased R₀ in both asthma and CAL suggests that R₀ does reflect conducting airway abnormality.