Analysis of Total Respiratory Deposition of Inhaled Ultrafine Particles in Adult Subjects at Various Breathing Patterns

Ultrafine particles are ubiquitous in the ambient air, and their unique physicochemical characteristics may pose a potential health hazard. Accurate lung dose information is essential to assess a potential health risk from exposure to these particles. In the present study, we measured total respiratory tract deposition fraction (TDF) of inert ultrafine aerosols (NMD = 0.04, 0.06, 0.08, and 0.10 μm and σg 1.3) in a group of young healthy adults (11 males and 11 females). A fast-response ultrafine condensation particle counter was used for continuous monitoring of inhaling aerosols breath by breath. Six different breathing patterns were used: three different tidal volumes (Vt = 500, 750, and 1000 ml) and two different flow rates for each Vt. The mean respiratory time (Tm) ranged from 2 to 4 s. The measured data showed that TDF increased with a decrease in particle size, thereby an increase in diffusion coefficient (D), and with an increase in Tm and Vt. For a given particle size both Tm and Vt were almost equally influential to TDF. TDF was generally comparable for men and women at the same breathing pattern. A slight increase in TDF was noticed for women only for smaller size particles (e.g., 0.04 μm). From the parametric analysis a composite parameter, (DTm)0.5Vk t, was identified by which all TDF data could be consolidated into a single curve (k = 0.49, (σ2 = 0.97). The results show that TDF of ultrafine particles can be reliably estimated by a unique empirical formula, and this may provide a convenient means of assessing respiratory dose of ultrafine particles.

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