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, rAiDA, can be inferred from measurements of particle recovery, after varied breath-holds. Also, particle recovery after a zero second breath-hold, R0, may hold information about the small conducting airways. This study investigates rAiDA 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 yrs. Volumetric sample depths ranged from 200 to 5000 mL and breath-hold times from 5 to 20 s. At the examined volumetric sample depths, rAiDA values ranged from approximately 200-600 μm, which correspond to dimensions of the bronchiolar and the gas-exchanging regions of the lungs. R0 decreased with volumetric sample depth and showed more inter-subject variation than rAiDA. Correlations were found between the AiDA parameters, anthropometry and lung function tests, but not between rAiDA and R0. For repeated measurements on three subjects over an 18 months period, rAiDA 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.