Microscopic distribution patterns of microspheres deposited by inhalation in lungs of rats, guinea pigs, and dogs

Acute inhalation exposures of mammalian species to small amounts of poorly soluble particles result in deposition of the particles in the head airways, tracheobronchial region, and pulmonary region of the respiratory tract. Most of the particles that deposit in the head airways and tracheobronchial region are believed to clear rapidly, but some as yet undefined fraction of the particles is retained in the airway epithelium or subepithelial interstitium for extended times. This long-term retention has important implications for the new respiratory tract dosimetry model of the International Commission on Radiological Protection because particles retained within the region can result in long-term exposure of airway epithelial cells. Preliminary results from this study demonstrate that a substantial fraction of the PSL microspheres inhaled by these rats, guinea pigs, and dogs was incorporated into the epithelium and interstitium of the tracheobronchial region