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.
Bibliographical noteFunding Information:
The authors wish to express their appreciation to the volunteers for their invaluable cooperation, to Dr. J. Scott and Mrs. S. Hodgson for assistance with measurements, and Dr. M. Puncher for deriving the statistical test used. This study was partly funded by the European Commission under Contract Number FIGD-CT2000-00053 (BIODOS: Biokinetics and dosimetry of internal contamination). The authors are grateful to their colleagues in the BIODOS project for useful discussions, in particular Dr. W. G. Kreyling (GSF), who suggested the use of metal particles to provide a high density, and Prof .W. Hofmann and Dr. R. Winkler-Heil (University of Salzburg), for calculations of deposition used in the experimental design.
- Bolus inhalation
- Lung retention
- Mucociliary clearance
- Particle deposition