Deposition of particles in human nasal replicate casts

Abstract

Studies of aerosol deposition in the nasal airways play a significant role in developing our understanding of deposition and retention in the respiratory tract.  The nose not only determines the amount of particles reaching the lungs, but also contributes to systemic uptake.  Artificial nasal replicate casts were used for quite some time to determine the influence of particle size and flow rate on deposition, without validating the results by comparing them to the data gained with a human volunteer.  To be able to make this comparison realistic human breathing patterns need to be simulated, the case needs to be anatomically accurate and nasal deposition needs to be measured on a human volunteer.

To simulate human breathing patterns, a breathing simulator has been designed and constructed.  It allows artificial breathing patterns as well as recorded human breathing patterns to be implemented.  Additionally, two artificial nasal cavities were built utilising magnetic resonance imaging (MRI) of different human volunteers.  One of the casts was made from a human volunteer taking part in nasal deposition and clearance experiments.  In this study the ability to use both the cast of a human volunteer and his exact breathing pattern provided the ground for comparisons between in-vivo and in-vitro experiments.  Furthermore the influence of different breathing patterns, flow rates and particle sizes has been studied.  Thirdly, the exact location of particles deposited in the cast was obtained under the same experimental conditions as in-vivo.  Also the cast was dismantled and deposition on each plate was measured independently to determine regional deposition.

The results show that constant flow (as used in most previous studies) causes significantly more deposition than realistic human breathing patterns.  The comparison of the nasal cast and the human volunteer showed significant higher deposition in the cast for light exercise, which is apparently caused by the change of cross-sectional area of the volunteers airways with exercise.

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