Retention of particles on the first bifurcation and the trachea of rabbits.

Retention of 6 micron, intratracheally-administered radioactively-tagged, teflon particles on the lower trachea and the first bifurcation of rabbits was measured externally for 2-3 days. Clearance occurred in a fast and a slow phase. The fast phase was finished after 1-2 h. The slow phase differed markedly between the lower trachea and the first bifurcation. The mean half-times were 19 and 39 h i trachea and first bifurcation, respectively. On average, 39% of the particles on the trachea and 71% on the first bifurcation cleared with the slow phase. Thus the bifurcation is more exposed to pollutants not only from deposition of more particles caused by impaction but also because of less efficient clearance.