AIRWAY SURFACE IRREGULARITIES PROMOTE PARTICLE DIFFUSION IN THE HUMANLUNG

Current NCRP and ICRP particle deposition models employed in risk asse ssment analyses treat the airways of the human lung as smooth-walled t ubes. However, the upper airways of the tracheobronchial (TB) tree are lined with cartilaginous rings. Recent supercomputer simulations of i n vivo conditions (cited herein), where cartilaginous ring morphologie s were based upon fibre-optic bronchoscope examinations, have clearly demonstrated their profound effects upon fluid dynamics. Since inhaled radionuclides of health effects concern such as radon progeny are ent rained and transported by airstreams, their trajectories and depositio n probabilities will be influenced by the very character (i.e. laminar or turbulent) of air motion and its local velocity profiles. A physio logically based analytical model of fluid dynamics is presented, focus ing upon applications to particle diffusion within the TB tree. The ne w model is the first to describe particle motion while simultaneously simulating effects of wall irregularities, entrance conditions and tub e curvatures. The results show that particle dose to the large bronchi may be underestimated by up to 35% if cartilaginous rings are not con sidered. The work has fundamental implications for modelling concepts and health effects applications. The findings indicate that caution mu st be exercised when extrapolating heat and/or mass transfer correlati ons derived from standard thermodynamic-hydrodynamic engineering probl ems to biological issues, and that human subject activity levels have pronounced effects on particle diffusion in the lung. For instance, th e submicron particle deposition efficiency differences between a seden tary condition (i.e. office worker) and light activity (i.e. manual la bourer) approach 40%. This study may explain the enhanced deposition b y particle diffusion detected in replica case experiments and have sal ient implications for the clinically observed preferential distributio ns of bronchogenic carcinomas associated with inhaled radionuclides.