Deposition and Clearance of Radiolabeled Particles from Small Ciliated Airways in Beagle Dogs

Abstract

ABSTRACT

Clearance rates of particles from small ciliated airways were measured in five Beagle dogs to determine if clearance was virtually complete in a few days, as predicted by most models. Both 3–μm latex microspheres radiolabeled with ⁸⁵Sr and 9–μm latex microspheres radiolabeled with ^l41Ce were used. A powder aerosol generator was developed to produce a puff of the mixed microspheres for deposition limited to selected airway segments. This aerosol was introduced through a catheter in the biopsy channel of a fiberoptic bronchoscope. The tip of the bronchoscope was located in a 6th–generation airway of the anesthetized dogs. Deposition of fluorescent particles followed by immediate sacrifice, drying of the lung, and sectioning, showed that deposition occurred predominantly in the 6th–10th generation bronchi without significant deposition in the alveolar region. Gamma–camera images of radiolabeled particles were consistent with this finding; deposition was restricted to discrete spots in the five dogs. Eighty–six to 76% of the deposited particles cleared rapidly from the airways with half–times of 0.3 and 0.5 days for the 3– and 9–μm particles, respectively. Fourteen to 24% of the initially deposited particles were retained, with half–times of 27–36 days for the 3– and 9–μm particles, respectively. These data suggest that the majority of particles clear rapidly from small conducting airways as predicted by most models, but a substantial percentage might clear much more slowly. Slow clearance of radioactive or toxic particles might cause damage to ciliated epithelium.