A Model of Tracer Transport in Airway Surface Liquid |
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Authors: | D J Smith E A Gaffney J R Blake |
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Institution: | (1) School of Mathematics, University of Birmingham, Birmingham, B15 2TT, UK |
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Abstract: | This study is concerned with reconciling theoretical modelling of the fluid flow in the airway surface liquid with experimental
visualisation of tracer transport in human airway epithelial cultures. The airways are covered by a dense mat of cilia of
length ∼ 6 μm beating in a watery periciliary liquid (PCL). Above this there is a layer of viscoelastic mucus which traps
inhaled pathogens. Cilia propel mucus along the airway towards the trachea and mouth. Theoretical analyses of the beat cycle
smithd, fulb predict small transport of PCL compared with mucus, based on the assumption that the epithelium is impermeable
to fluid. However, an experimental study coord indicates nearly equal transport of PCL and mucus. Building on existing understanding
of steady advection-diffusion in the ASL (Blake and Gaffney, 2001; Mitran,2004) numerical simulation of an advection-diffusion
model of tracer transport is used to test several proposed flow profiles and to test the importance of oscillatory shearing
caused by the beating cilia. A mechanically derived oscillatory flow with very low mean transport of PCL results in relatively
little ‘smearing’ of the tracer pulses. Other effects such as mixing between the PCL and mucus, and significant transport
in the upper part of the PCL above the cilia tips are tested and result in still closer transport, with separation between
the tracer pulses in the two layers being less than 9%. Furthermore, experimental results may be replicated to a very high
degree of accuracy if mean transport of PCL is only 50% of mucus transport, significantly less than the mean PCL transport
first inferred on the basis of experimental results. |
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Keywords: | Mucus Cilia Tonicity Advection Diffusion Dispersion |
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