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LOWER RESPIRATORY TRACT STRUCTURE OF LABORATORY ANIMALS AND HUMANS: DOSIMETRY IMPLICATIONS
Citation:
Miller, F., R. Mercer, AND J. Crapo. LOWER RESPIRATORY TRACT STRUCTURE OF LABORATORY ANIMALS AND HUMANS: DOSIMETRY IMPLICATIONS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-94/051.
Description:
Significant differences in lower respiratory tract structure exist both within an animal and between species at each level of anatomy. rregular bipodial and tripodial branching patterns of airways are present in human an nonhuman primate lungs. n contrast, the dog and common laboratory rodents exhibit a predominantly monopodial branching system. he effects of these various branching patterns on airflow distribution, gas uptake, and the deposition of particles have not been sufficiently studies to determine the extent to which branching patterns impart regional inhomogeneities or hot spots in the deposition of inhaled material. hree-dimensional reconstruction techniques were used to examine various aspects of lung structure. tudies vary from the reconstruction of individual cells to reconstructing conducting airway and alveolar duct branching systems. hen using physical models for dosimetric calculations, realistic geometry is critical to be certain the model appropriately captures the complexity of the branching system being studied. nalyses in mouse, rat, and baboon lungs demonstrate that the greater lung size in larger species is the result of both an increase in the number and size of ventilatory units with the major contribution being associated with the change in number of ventilatory units. he ratio of ventilatory unit diameter is constant over a range of lung sized from those of mice to men. entilatory unit is typically about 17.5 alveolar diameters in size. his new knowledge about lung structure and geometry offers great promise in a number of areas. mong these are: ) examining lobar and path-specific deposition patterns for pharmaceutical aerosol distributions, 2) selecting critical sites for potential lung injury, and 3) establishing respiratory tract structure based criteria for the optimum design of pharmaceutical aerosols.