Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 231

8.2.1 Inhalation Through the Anatomy and Its Physiology

The anatomy and physiology of the nasal cavity during inhalation have been discussed
in detail in Chap. 2, and only a summary of the important features in relation to the
CFD modelling needs are discussed here. In the succeeding descriptions, the x

coordinate is from the anterior tip of the nostril inlet running posterior to the back
of the nose at the nasopharynx, which is referred to as the axial direction (Fig. 8.1 ).

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Fig. 8.1 Side view of the left nasal cavity which is sectioned into ten regions used for local deposition
analysis

The nose can be divided axially into four regions: the vestibule, the nasal valve, the
turbinate and the nasopharynx regions. The first three-quarters of the nasal cavity are
divided into the left and right cavity separated by the nasal septum wall. Air enters
each cavity through the oval-shaped external nostrils into the vestibule. The flow
changes direction, 90 ◦ towards the horizontal, before entering the nasal valve region.
The flow increases in this region where the cross-sectional area is smallest causing
an acceleration of the air. At the end of the nasal valve region, the cross-sectional
area of the nasal cavity increases suddenly. This expansion is the beginning of the
turbinate region where the profile is complicated and asymmetrical. Finally, at the
nasopharyngeal region, the left and right cavities merge together causing the flow in
this region to mix intensely.
The main factors that contribute to the airflow patterns are the nasal cavity ge-
ometry and the flow rate. For a realistic human nasal cavity, geometric variations
between the left and right-sided nasal cavities exist at any one time as a result of a
combination of its natural geometry, due to the nasal cycle, and any other physio-
logical reactions at the time. Inhalation is caused by the negative pressure induced