Regional aerosol deposition and flow measurements in an idealized mouth and throat

Extrathoracic deposition was studied using an idealized average human mouth and throat replica. Effects of particle size, flow rate and flow Reynolds number were examined using gamma scintigraphy and gravimetry. Radiolabeled monodisperse sebacate (DEHS) oil particles of mass median diameter dp=3, 5 and 6.5 μm and two constant flow rates Q=30 and 90 l/min were used. Total and regional depositions were measured using costumized image analysis software that allowed extraction of position and intensity of radioactive sites. Aerosol deposition is mostly in the larynx and trachea, and is dictated by pharyngeal and glottal morphological constrictions and consequent flow jets. It was found that deposition efficiency is correlated with the inertial parameter (ρdp2Q) indicating that inertial impaction is the dominant deposition mechanism. Regional deposition results are correlated with fluid flow measurements obtained using particle image velocimetry. Deposition efficiency is enhanced with increasing flow Reynolds number, even if the Stokes number is held constant, due to changes in the cross-sectional velocity profile. An empirical correction is derived that takes into account this effect.