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Analysis of Exposure-Dose Variation of Inhaled Particles in Adult Subjects.
Citation:
KIM, C. S., S. Hu, AND J. Choi. Analysis of Exposure-Dose Variation of Inhaled Particles in Adult Subjects. Presented at American Association of Aerosol Research (AAAR), San Diego, CA, March 22 - 26, 2010.
Impact/Purpose:
an abstract of a proposed presentation- was originally submitted in March
Description:
Although internal dose is a key factor for determining the health risk of inhaled pollutant particles, available dose information is largely limited to young healthy adults under a few typical exposure conditions. Extrapolation of the limited dose information to different population groups (age, gender and disease) and to widely varying real life exposure conditions is not warranted. Accurate and expanded dose information is needed to help improve our understanding of causal relationship of particulate matter with host responses and potential health effects, particularly in susceptible populations. We measured total and regional lung deposition in a large number of healthy adult subjects: 62 young adults (age = 24-39 years), 24 old adults (age = 61-78 years) in both males (N=48) and females (N=38). Subjects sitting upright on a chair inhaled monodispersed test aerosols in the size range of 0.04 -5 micron in diameter with prescribed breathing patterns. Both tidal volume and breathing frequency were varied to cover a wide range of breathing patterns expected from individual variability and activity pattern. The deposition data were analyzed for effects of age, sex and breathing pattern. Parametric analyses were performed to identify dominant factors affecting lung deposition and to find a unifying composite parameter consolidating all deposition data. A comprehensive mathematical model was then developed and validated with the broad range of experimental data. Using the model, variability of lung deposition was further analyzed for effects of particle size distribution (i.e., polydispersity) and exercise breathing (minute ventilation 7.5 -50 lpm and oro-nasal breathing). Results showed that deposition values vary 2-3 times depending on breathing pattern and that the variability is closely related with a composite parameter consisted of particle size, tidal volume and respiratory flow rate (or breathing frequency). The variability was similar among different subject groups studied. For a given breathing pattern there was no significant difference between young and old adults in both total and regional deposition for all particle sizes tested. Compared to male subjects, female subjects showed a slight increase in deposition in the ultrafine (<0.06 um) and coarse (>3 um) size ranges, particularly in the tracheobronchial airway regions. Polydispersity of size distribution affected lung deposition variably in the different size ranges. With exercise, overall lung deposition increased nearly linearly with increasing minute ventilation. However, in the tracheobronchial airways deposition was much greater with coarse particles and smaller with ultrafine particles than expected from ventilation ratios. The trend was opposite for alveolar deposition. In conclusion, combination of parametric analysis of systematic experimental data and mathematical model analysis would provide a means ofexpanding and improving exposure-dose information that may help us to interpret and understand PM induced response measures. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.