Slow Clearance of Different-Sized Particles from Rat Trachea

ABSTRACT Previous studies have shown that particle clearance from the conducting airways includes a slow component. In humans, there is evidence that the proportion subject to slow clearance depends on particle size. The effect of particle diameter on slow clearance was determined in the trachea of the F-344 rat by comparing 1.4-μm 133BaSO4 particles and 22- to 30-nm 195Au-labeled gold colloid particles. In both cases, clearance over 2 days could be described by the sum of two exponential terms: fast mucociliary clearance and slow clearance. The fraction of particles subject to slow clearance was not significantly different: 29% for 133BaSO4 and 32% for colloidal gold. The half-time for the fast component was also similar in the two cases, but for the slow phase, the half-time was 31 hours for BaSO4 particles and 177 hours for colloidal gold particles. These results differ somewhat from the kinetics of slow clearance in humans for particles of different sizes. Seven days after instillation, there was no s...