Analyses on the influence of normal nasal morphological variations on odorant transport to the olfactory cleft

Abstract

Objective: Olfaction requires a combination of sensorineural components and conductive components, but conductive mechanisms have not typically received much attention. This study investigates the role of normal nasal vestibule morphological variations in ten healthy subjects on odorant flux in the olfactory cleft.

Materials and methods: Computed tomography images were used to create subject-specific nasal models. Each subject's unilateral nasal cavity was classified according to its nasal vestibule shape as Standard or Notched. Inspiratory airflow simulations were performed at 15 L/min, simulating resting inspiration using computational fluid dynamics modeling. Odorant transport simulations for three odorants (limonene, 2,4-dinitrotoluene, and acetaldehyde) were then performed at concentrations of 200 ppm for limonene and acetaldehyde, and 0.2 ppm for dinitrotoluene. Olfactory cleft odorant flux was computed for each simulation.

Results and discussion and conclusion: Simulated results showed airflow in the olfactory cleft was greater in the Standard phenotype compared to the Notched phenotype. For Standard, median airflow was greatest in the anterior region (0.5006 L/min) and lowest in the posterior region (0.1009 L/min). Median airflow in Notched was greatest in the medial region (0.3267 L/min) and lowest in the posterior region (0.0756 L/min). Median olfactory odorant flux for acetaldehyde and limonene was greater in Standard (Acetaldehyde: Standard = 140.45 pg/cm²-s; Notched = 122.20 pg/cm²-s. Limonene: Standard = 0.67 pg/cm²-s; Notched = 0.65 pg/cm²-s). Median dinitrotoluene flux was greater in Notched (Standard = 2.86 × 10^-4pg/cm²-s; Notched = 4.29 × 10^-4 pg/cm²-s). The impact of nasal vestibule morphological variations on odorant flux at the olfactory cleft may have implications on individual differences in olfaction, which should be investigated further.

Keywords: Acetaldehyde; computational fluid dynamics; dinitrotoluene; limonene; olfaction.

Figure 1.

Sagittal view of the nasal vestibule airspace showing the soft tissue (transparent) and morphology of each phenotype. Reproduced with permission from Ramprasad and Frank-Ito.(11)

Figure 2.

Box plot comparing anatomical size of Standard and Notched airspace and nasal vestibules. (A) Nasal Surface Area; (B) Nasal Volume; and (C) Nasal Surface Area to Volume ratio (SA:V)

Figure 3.

Streamlines of airflow through the nasal airspace of five representative subjects (MIDDLE PANEL) with arrow points at Standard (S) and Notched (N) nasal vestibule morphologies. Velocity contour plots (LEFT PANEL) and pressure contour plots (RIGHT PANEL) from four cross-sections (X1 – X4) across the left (L) and right (R) nasal airspace.

Figure 4.

(A) Air flow rate at five slices anteriorly (OZ1) to posteriorly (OZ4) across the olfactory cleft; and (B) air flow partition at five slices across the olfactory cleft.

Figure 5.

Odorant flux at the olfactory cleft for (A) acetaldehyde; (B) dinitrotoluene; and (C) limonene.

Figure 6.

Contour plot of odorant flux at the olfactory cleft of a representative subject for acetaldehyde (TOP), dinitrotolune (MIDDLE), and limonene (BOTTOM).