Computational Fluid and Particle Dynamics (CFPD): An Introduction - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 14

and it can be deduced that the most collapsible area in the pharyngeal airway of OSA
patients is the velopharynx where minimum intraluminal pressure and maximum
aerodynamic force lie.

1.3.7 Studies in the Acinus and Olfactory Regions

Gas exchange during respiration and the process of olfaction, the primary functions
of the nose, are often difficult to assess experimentally. Respiration occurs in the
distal regions of the lung called the acinar airways where the gas exchange takes
place within the alveoli (Fig. 1.11 ). However, inhaled particles transported in the
alveolar region of the lung are important for possible health risks or as a therapeutic
inhaled drug therapy. Olfaction takes place in the upper regions of the main nasal
passage within the nasal cavity, and this can lead to translocation of inhaled ultrafine
particles to the brain. In this section we present some CFPD results in the literature
firstly for the acinar airway, then for olfactory uptake.

Fig. 1.11 a 3D flow structure inside a geometry of a honeycomb-like alveolar duct (Re = 1.0).
Image taken from Kumar et al. (2009). b Velocity field in the symmetry plane of an alveolar duct
bend from the work of van Ertbruggen et al. (2008) for Re = 0.07

While the alveoli are normally depicted as little spheres or hemispheres attached
to terminal ends of the lung airways, they have actually been modeled as densely-
packed hollow polyhedron (Fung 1988; Mead et al. 1970). Some CFPD results
are given in (Fig. 1.12 ) which include that of Kumar et al. (2009) which used a
flexible-walled honeycomb-like polygonal geometry to examine the fluid flow under
rhythmic breathing. The results show the flow structure dominated by the presence