SLOW CLEARANCE OF DIFFERENT-SIZED PARTICLES FROM RAT TRACHEA

Previous studies have shown that particle clearance from the conductin g airways includes a slow component. In humans, there is evidence that the proportion subject to slow clearance depends on particle size. Th e effect of particle diameter on slow clearance was determined in the trachea of the F-344 rat by comparing 1.4-mu m (BaSO4)-Ba-133 particle s and 22- to 30-nm Au-195-labeled gold colloid particles. In both case s, clearance over 2 days could be described by the sum of two exponent ial terms: fast mucociliary clearance and slow clearance. The fraction of particles subject to slow clearance was not significantly differen t: 29% for (BaSO4)-Ba-133 and 32% for colloidal gold. The half-time fo r the fast component was also similar in the two cases, but for the sl ow 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 significant difference be tween the two particle sizes regarding either the amount washed from t he lumen of the trachea or the amount retained in the tracheal wall.