Accuracy and resolution power of aerosol-derived airway morphometry in a simple lung model

Aerosol-derived airway morphometry (ADAM) uses sedimentational deposition of monodisperse aerosol particles during breathhold to estimate intrapulmonary air-space dimensions. To determine the accuracy and resolution power of this technique a simple physical lung model comprised of uniform glass beads was investigated. Using the chordlength model, aerosol recovery from this porous medium was calculated by computer simulation of the geometrical structure of air-spaces between glass beads. The results of this calculation were then compared with experimental data: Calculated and measured air-space dimensions differ less than 2% for particles with diameters above about 1 micron. The measured air-space dimension can be described geometrically by the mean chordlength of the porous medium. To estimate the resolution power of ADAM, a defined change in air-space dimensions represented by a horizontal air slit was introduced into the porous medium. This air slit induces a marked increase of measured air-space dimensions. The volumetric width of this increase is the higher the deeper the slit is situated within the medium. Intercomparison of these data with the results of aerosol bolus dispersion measurements suggests that the resolution power of ADAM is decreased by the same mechanisms that increase dispersion of aerosol boluses, demonstrating the close relationship between both methods.