EFFECT OF PARTICLE SIZE ON SLOW PARTICLE CLEARANCE FROM THE BRONCHIAL TREE

Abstract

The Human Respiratory Tract Model of the International Commission on Radiological Protection assumes that a fraction of particles deposited in the bronchial tree clears slowly, this fraction decreasing with increasing particle geometric diameter. To test this assumption, volunteers inhaled 5-μ m aerodynamic diameter 111In-polystyrene and 198Au-gold particles simultaneously, as a ‘bolus’ at the end of each breath to minimize alveolar deposition. Because of the different densities (1.05 versus 19.3 g cm3), geometric diameters were about 5 and 1.2 μ m, respectively, and corresponding predicted slowly cleared fractions were about 10% and 50%. However, lung retention of the 2 particles was similar in each subject. Retention at 24 hours, as a percentage of initial lung deposit (mean ± SD) was 34 ± 12 for polystyrene and 31 ± 11 for the gold particles.