An in vitro study on the deposition of micrometer-sized particles in the extrathoracic airways of adults during tidal oral breathing.

Deposition of particles in the aerodynamic diameter range of 0.5-6.7 μm was measured in nine replicas of the extrathoracic airways of adults with four sinusoidal patterns and oral breathing. The four chosen breathing patterns are typical of those occurring during natural resting breathing and during nebulization therapy. Additionally, deposition of micrometer-sized particles in the "Alberta Idealized Adult Throat," which was previously found useful in simulating the average deposition of particles during inhalation of constant flow rates, was measured during inhalation of the four sinusoidal patterns in this study. To reduce intersubject scatter in developing predictive correlations, the non-dimensional Reynolds (Re) and Stokes (Stk) numbers are used with the square root of the average cross sectional area of the oral airways as the characteristic diameter being found to reduce intersubject variability to the highest extent. Our best fit to the deposition data is given by η = [1 - 1/(1.51 x 10(5)(Stk(3.03)Re(0.25)) + 1)] x 100. Moreover, the "Alberta Idealized Adult Throat" is found to mimic average deposition, given in past in vivo studies, in the upper airways of adults during natural tidal breathing.