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MODELING THE UPTAKE OF GASES BY THE DOG NASAL-PHARYNGEAL REGION: EFFECTS OF MORPHOMETRIC AND PHYSICOCHEMICAL FACTORS
Citation:
Overton, J. AND R. Graham. MODELING THE UPTAKE OF GASES BY THE DOG NASAL-PHARYNGEAL REGION: EFFECTS OF MORPHOMETRIC AND PHYSICOCHEMICAL FACTORS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-95/210, 1995.
Description:
Generally, the uptake of reactive gases by the respiratory tract is simulated assuming that all path from the trachea to the most distal airspaces ore equivalent. s this is not the case, especially for non-humans, the adequacy of this approach to predict doses that con be useful in the fields of toxicology and risk assessment is subject to question. o explore this issue, a dosimetry model is developed which combines the use of one dimensional convection-dispersion equations in conjunction with multiple paths anatomic models so that the dosimetry model simultaneously simulates transport and uptake in all the airways and airspaces of the anatomic model. or this work, the anatomic model of the tracheobronchial (TB) region is patterned on cost data which describes the dimensions and branching network of the 4807 airways of the TB region of a rat. istal to each of the 2404 terminal bronchioles of the anatomical model, the air space is modeled as a single path. he results presented are preliminary; they focus on the predictions themselves to obtain on understanding of what the model has to say about uptake in a complex set of branching airways. esults include the following predictions: (1) -Regardless of path there is a similarity along different paths in the shope of concentration profiles as well as a similarity in the shope of dose profiles. (2) Along a path in the TB or pulmonary region, dose decreases distally. (3) Generally, proximal alveolar region (PAR, a region of major morphological damage due to O3 and NO2) dose decreases the more distal the PAR. (4) There is considerable variation in the doses of the different airway or alveolar surfaces in the same generation. (5) The maximum and minimum PAR doses do not correspond to paths with, respectively, the smallest and largest number of generations from the trachea to the PAR. (6) The ratio of the maximum to minimum PAR dose is very sensitive to tidal volume. hese results give a more realistic understanding of respiratory tract gas transport and uptake. he model also predicts aspects that equivalent path models con not, such as the dose distribution of different but morphologically equivalent sites.