Anatomic localization of 24-and 96-h particle retention in canine airways

Anatomic localization of 24- and 96-h particle retention in canine airways. J. Appl. Physiol. 87(1): 269-284, 1999.-Long-term retention of particles i n airways is controversial. However, precise anatomic localization of the p articles is not possible in people. In this study the anatomic location of retained particles after shallow bolus inhalation was determined in anesthe tized, ventilated beagle dogs. Fifty 30-cm(3) boluses containing monodisper se 2.5-mu m polystyrene particles (PSL) were delivered to a shallow lung de pth of 81-129 cm(3). At 96 h before euthanasia, red fluorescent PSL were us ed; at 24 h, green fluorescent PSL and Tc-99m-labeled PSL were used. Cleara nce of Tc-99m-PSL was measured during the next 24 h. Sites of particle rete ntion were determined in systematic, volume-weighted random samples of micr owave-fixed lung tissue. Precise particle localization and distribution was analyzed by using gamma counting, conventional fluorescence microscopy, an d confocal microscopy. Within 24 h after shallow bolus inhalation, 50-95% o f the deposited Tc-99m-PSL were cleared, but the remaining fraction was cle ared slowly in all dogs, similar to previous human results. The three-dimen sional deposition patterns showed particles across the entire cross-section al plane of the lungs at the level of the carina. In these locations, 33+/- 9.9%; of the retained particles were found in small, nonrespiratory airways (0.3- to 1-mm diameter) and 49 +/- 10% of the particles in alveoli; the re maining fraction was found in larger airways. After 96 h, a similar pattern was found. These findings suggest that long-term retention in airways is a t the bronchiolar level.