Fig 1.
CT scans showing nasal cavity cross sections of a) human, b) rat, and c) domestic cat. The dark spaces on the scans are the nasal airways. As odorous air is drawn into the nose, it flows through these labyrinthine structures. The full set of CT scans for domestic cat can be found in [26].
Fig 2.
a) The distributions of various types of epithelia were determined through sequential histological sections: respiratory epithelium is thin and contains goblet cells, whereas olfactory epithelium is thicker and contains Bowman’s glands. Skin-like squamous epithelium is located in the anterior tip of the nose. Each histological section is then aligned with micro-CT images, on which locations of epithelium types are labeled based on histology features. b) The final computational model with different types of epithelia, inlet (naris box), and outlet (nasopharynx). c) The nasal surface area and percentages of various types of epithelia plotted as a function of distance to the nostril.
Fig 3.
(a-c) In the cat, during inspiration, the bulk of inspired air passes through the respiratory (maxillary) turbinates (a), whereas a portion (~15–20%) enters the olfactory region (b), conveyed by the high-speed dorsal medial (DM) stream (c). Snapshot at 0.1s after inhalation showed that streamlines in the DM stream reaches deep into the olfactory region (see blue lines), faster than those spread across the respiratory turbinate region (see green lines). The axial flow component (flow in the direction from nostrils to pharynx) is positive in most of maxillary turbinate regions (a) but is positive only in the central DM region of the ethmoid turbinates. The axial flow component in the lateral ethmoid turbinate is mostly negative (no color), which indicates reversing or lateral flow. These different flow patterns suggest that respiratory turbinates branch in directions that do not block or redirect the airflow, spreading incoming airflow into parallel channels to increase heat and water exchange efficiency, whereas the olfactory turbinates are scroll-shaped, extending centrally to laterally and redirecting flow from the DM stream into lateral channels. d) Based on these observations, we hypothesize that olfactory turbinates function as a coiled parallel gas chromatograph, with the high-speed DM stream feeding airflow into parallel lateral ethmoid coils, each serving as a CG column.
Fig 4.
The dorsal medial (DM) air stream in cross sections of the cat nasal model (a) as the percentage of total flow rate (b), which decreases as it enters the olfactory region, where flow is diverted to the lateral regions. Airflow remains similar between restful breathing (22 ml/s) and sniffing (140 ml/s) but is slightly smaller during expiration than during inhalation.
Fig 5.
Odor absorption map of two odorants with different solubilities, 2-acetylthiazole (2AE, high) and 2-(1-mercaptoethyl) furan (FN, intermediate), at all nasal mucosal surfaces (left) and at the olfactory region only (right). The highly soluble odorant 2AE is more strongly absorbed anteriorly, depleting available molecules in air stream when reaching the posterior ethmoid region, whereas the intermediate-soluble odorant FN has optimal sorption in the olfactory region.
Fig 6.
(a, b) Total nasal odor absorption (a) and absorption in the olfactory region (b) in human [[30,33]] and cat [present study]. (c) The nasal cavity is divided into three parts, anterior respiratory region, olfactory region, and posterior respiratory region. (d) Quantitative testing of the hypothesis that the dorsal medial stream allows odorous air to reach the olfactory region more efficiently by computing absorption in two scenarios: with and without absorption in the anterior respiratory region.
Fig 7.
(a) A snapshot of parallel trajectories of odor particles in the cat olfactory region (colored dots). (b) Comparison of GC efficiency between cat coiled (left) and amphibian-like “straight tube” (right) olfactory regions of the same length based on plate number theory (c) The calculated plate number for olfactory regions of cat (blue curve), rat (red curve), human (green curve), and the straight “tube” (black curve). The thickened lines represent the actual airflow velocity range in the olfactory regions of the different species.