Charting the human respiratory tract with airborne nanoparticles: evaluation of the Airspace Dimension Assessment technique

Airspace Dimension Assessment (AiDA) is a technique to assess lung morphology by measuring lung deposition of inhaled nanoparticles. Nanoparticles deposit in the lungs predominately by diffusion, and average diffusion distances, corresponding to effective airspace radii ( r AiDA ), can be inferred from measurements of particle recovery after varied breath holds. Also, particle recovery after a 0-s breath hold ( R 0 ) may hold information about the small conducting airways. This study investigates r AiDA at different volumetric sample depths in the lungs of healthy subjects. Measurements were performed with 50-nm polystyrene nanospheres on 19 healthy subjects aged 17-67 yr. Volumetric sample depths ranged from 200 to 5,000 ml and breath-hold times from 5 to 20 s. At the examined volumetric sample depths, r AiDA values ranged from ~200-600 μm, which correspond to dimensions of the bronchiolar and the gas-exchanging regions of the lungs. R 0 decreased with volumetric sample depth and showed more intersubject variation than r AiDA . Correlations were found between the AiDA parameters, anthropometry, and lung function tests, but not between r AiDA and R 0 . For repeated measurements on 3 subjects over an 18-mo period, r AiDA varied on average within ± 7 μm (± 2.4%). The results indicate that AiDA has potential as an efficient new in vivo technique to assess individual lung properties. The information obtained by such measurements may be of value for lung diagnostics, especially for the distal lungs, which are challenging to examine directly by other means. NEW & NOTEWORTHY This is the first study to measure effective airspace radii ( r AiDA ) at volumetric sample depths 200-5,000 ml in healthy subjects by Airspace Dimension Assessment (AiDA). Observed r AiDA were 200-600 μm, which corresponds to airspaces for the bronchiolar and the gas-exchanging regions around airway generation 14-17. r AiDA correlated with lung function tests and anthropometry. Measurements of r AiDA on 3 subjects over 11-18 mo were within ± 7 μm.