Role of nasal vestibule morphological variations on olfactory airflow dynamics

Abstract

Background: The conductive mechanisms of olfaction are typically given little priority in the evaluation of olfactory function. The objective of this study is to investigate the role of nasal vestibule morphological variations on airflow volume at the olfactory recess in healthy subjects.

Methods: Anatomically realistic three-dimensional nasal airway models were constructed from computed tomography scans in five subjects. Each individual's unilateral nasal cavity (10 total) was classified according to the shape of their nasal vestibule: Standard, Notched, or Elongated. Nasal airflow simulations were performed using computational fluid dynamics modeling at two inspiratory flow rates (15 L/min and 30 L/min) to reflect resting and moderate breathing rates. Olfactory airflow volume and cross-sectional flow resistance were computed.

Findings: Average olfactory airflow volumes (and percent airflow in olfactory) were: 0.25 L/min to 0.64 L/min (3.0%-7.7%; 15 L/min simulations) and 0.53 L/min to 1.30 L/min (3.2%-7.8%; 30 L/min simulations) for Standard; 0.13 L/min - 0.47 L/min (2.0%-6.8%; 15 L/min simulations) and 0.06 L/min - 0.82 L/min (1.7%-6.1%; 30 L/min simulations) for Notched; and 0.07 L/min - 0.39 L/min (1.2%-5.4%; 15 L/min simulations) and 0.30 L/min - 0.99 L/min (2.1%-6.7%; 30 L/min simulations) for Elongated. On average, relative difference in olfactory resistance between left and right sides was 141.5% for patients with different unilateral phenotypes and 82.2% for patients with identical unilateral phenotype.

Interpretation: Olfactory cleft airflow volume was highest in the Standard nasal vestibule phenotype, followed by Notched phenotype for 15 L/min simulations and Elongated phenotype for 30 L/min simulations. Further, intra-patient variation in olfactory cleft airflow resistance differs greatly for patients with different unilateral phenotypes compared to patients with identical unilateral phenotype.

Keywords: Airflow; Computational fluid dynamics; Nasal vestibule morphology; Olfactory airflow transport; Particle transport.

Figure 1.

(A) 3D model illustrating the three nasal phenotypes. This figure is reproduced with permission from Ramprasad and Frank-Ito ; (B) Olfactory Z-axis cross sections with front facing image of the cross section above; (C) Hybrid tetrahedral-prismatic mesh elements; and (D) Olfactory airspace contour plot colored by velocity magnitude for 15 L/min simulation.

Figure 2.

Average olfactory cleft resistance for each patient at (A) 15L/min and (B) 30 L/min. Average flow rate for each phenotype at (C) 15 L/min and (D) 30 L/min. Average flow partition for each phenotype at (E) 15 L/min and (F) 30 L/min.

Figure 3.

Average flow rate for each phenotype at (A) 15 L/min and (B) 30 L/min. Average flow partition for each phenotype at (C) 15 L/min and (D) 30 L/min.

Figure 4.

Nasal and olfactory airflow streamlines colored by velocity magnitude for each patient 15 L/min simulation.

Figure 5.

Contour plot of turbulent kinetic energy at the nasal cavity for 30L/min simulation.