  Generating anatomically realistic three-dimensional (3D) models of the human
sinonasal cavity for numerical investigations of sprayed drug transport
presents a host of methodological ambiguities. For example, subject-specific
radiographic images used for 3D reconstructions typically exclude spray
bottles. Subtracting a bottle contour from the 3D airspace and dilating the
anterior nasal vestibule for nozzle placement augment the complexity of
model-building. So, we explored the question: how essential are these steps to
adequately simulate nasal airflow and identify the optimal delivery conditions
for intranasal sprays? In particular, we focused on particle deposition
patterns in the maxillary sinus, a critical target site for chronic
rhinosinusitis (CRS). The models were reconstructed from post-surgery computed
tomography scans for a 39-year-old Caucasian male, with CRS history.
Inspiratory airflow patterns during resting breathing are reliably tracked
through CFD-based steady state laminar-viscous modeling and such regimes
portray relative lack of sensitivity to inlet perturbations. Consequently, we
hypothesized that the posterior airflow transport and the particle deposition
trends should not be radically affected by the nozzle subtraction and
vestibular dilation. The study involved 1 base model and 2 derived models; the
latter two with nozzle contours (two different orientations) subtracted from
the dilated anterior segment of the left vestibule. We analyzed spray transport
in the left maxillary sinus for multiple release conditions. Similar release
points, localized on an approximately 2mm-by-4.5mm contour, facilitated
improved maxillary deposition in all three test cases. This suggests functional
redundancy of nozzle insertion in a 3D numerical model for identifying the
optimal spray release locations.
