We investigated the axial dispersive effect of the upper airway structure (comprising
mouth cavity, oropharynx and trachea) on a traversing aerosol bolus. This was done
by means of aerosol bolus experiments on a hollow cast of a realistic upper airway
model (UAM) and 3D computational fluid dynamics (CFD) simulations in the same UAM
geometry. The experiments showed that 50ml boluses injected into the UAM,
dispersed to boluses with a halfwidth ranging 80-90ml at the UAM exit, across both flow
rates (250,500ml/s) and both flow directions (inspiration, expiration). These
experimental results imply that the net halfwidth induced by the UAM typically was
69ml. Comparison of experimental bolus traces with a 1D Gaussian derived analytical
solution resulted in an axial dispersion coefficient of 200-250cm2/s, depending on
whether the bolus peak and its halfwidth, or the bolus tail needed to be fully accounted
for. CFD simulations agreed well with experimental results for inspiratory boluses, and
were compatible with an axial dispersion of 200cm2/s. However, for expiratory boluses,
the CFD simulations showed a very tight bolus peak followed by an elongated tail, in
sharp contrast to the expiratory bolus experiments. This indicates that CFD methods
which are widely used to predict the fate of aerosols in the human upper airway, where
flow is transitional, need to be critically assessed, possibly via aerosol bolus
simulations. We conclude that, with all its geometric complexity, the upper airway
introduces a relatively mild dispersion on a traversing aerosol bolus for normal
breathing flow rates in inspiratory and expiratory flow directions.
Original languageEnglish
Pages (from-to)1733-1740
Number of pages8
JournalJournal of Applied Physiology
Publication statusPublished - 26 Sep 2008

    Research areas

  • mouth cavity, glottis, aerosol deposition

ID: 1689662