Total Respiratory Tract Deposition of Fine Micrometer-sized Particles in Healthy Adults: Empirical Equations for Sex and Breathing Pattern

Accurate dose estimation under various inhalation conditions is important for assessing both the potential health effects of pollutant particles and the therapeutic efficacy of medicinal aerosols. We measured total deposition fraction (TDF) of monodisperse micrometer-sized particles [particle diameter (Dp) = 1, 3, and 5 microm in diameter] in healthy adults (8 men and 7 women) in a wide range of breathing patterns; tidal volumes (Vt) of 350-1500 ml and respiratory flow rates (Q) of 175-1,000 ml/s. The subject inhaled test aerosols for 10-20 breaths with each of the prescribed breathing patterns, and TDF was obtained by monitoring inhaled and exhaled aerosols breath by breath by a laser aerosol photometer. Results show that TDF varied from 0.12-0.25, 0.26-0.68, and 0.45-0.83 for Dp = 1, 3, and 5 microm, respectively, depending on the breathing pattern used. TDF was comparable between men and women for Dp = 1 microm but was greater in women than men for Dp = 3 and 5 microm for all breathing patterns used (P < 0.05). TDF increased with an increase in Vt regardless of Dp and Q used. At a fixed Vt TDF decreased with an increase in Q for Dp = 1 and 3 microm but did not show any significant changes for Dp = 5 microm. The varying TDF values, however, could be consolidated by a single composite parameter (omega) consisting of Dp, Vt, and Q. The results indicate that unifying empirical formulas provide a convenient means of assessing deposition dose of particles under varying inhalation conditions.