Abstract
Understanding the impact distribution of particles entering the human
respiratory system is of primary importance as it concerns not only
atmospheric pollutants or dusts of various kinds but also the efficiency
of aerosol therapy and drug delivery. To model this process, current
approaches consist of increasingly complex computations of the
aerodynamics and particle capture phenomena, performed in geometries
trying to mimic lungs in a more and more realistic manner for as many
airway generations as possible. Their capture results from the complex
interplay between the details of the aerodynamic streamlines and the
particle drag mechanics in the resulting flow. In contrast, the present
work proposes a major simplification valid for most airway generations
at quiet breathing. Within this context, focusing on particle escape
rather than capture reveals a simpler structure in the entire process.
When gravity can be neglected, we show by computing the escape rates in
various model geometries that, although still complicated, the escape
process can be depicted as a multiplicative escape cascade in which each
elementary step is associated with a single bifurcation. As a net
result, understanding of the particle capture may not require computing
particle deposition in the entire lung structure but can be abbreviated
in some regions using our simpler approach of successive computations in
single realistic bifurcations. Introducing gravity back into our model,
we show that this multiplicative model can still be successfully applied
on up to nine generations, depending on particle type and breathing
conditions.
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