Anatomical Details of the Rabbit Nasal Passages and Their Implications in Breathing, Air Conditioning, and Olfaction

Abstract

The rabbit is commonly used as a laboratory animal for inhalation toxicology tests and detail knowledge of the rabbit airway morphometry is needed for outcome analysis or theoretical modeling. The objective of this study is to quantify the morphometric dimension of the nasal airway of a New Zealand white rabbit and to relate the morphology and functions through analytical and computational methods. Images of high-resolution MRI scans of the rabbit were processed to measure the axial distribution of the cross-sectional areas, perimeter, and complexity level. The lateral recess, which has functions other than respiration or olfaction, was isolated from the nasal airway and its dimension was quantified separately. A low Reynolds number turbulence model was implemented to simulate the airflow, heat transfer, vapor transport, and wall shear stress. Results of this study provide detailed morphological information of the rabbit that can be used in the studies of olfaction, inhalation toxicology, drug delivery, and physiology-based pharmacokinetics modeling. For the first time, we reported a spiral nasal vestibule that splits into three paths leading to the dorsal meatus, maxilloturbinate, and ventral meatus, respectively. Both non-dimensional functional analysis and CFD simulations suggested that the airflow in the rabbit nose is laminar and the unsteady effect is only significantly during sniffing. Due to the large surface-to-volume ratio, the maxilloturbinate is highly effective in warming and moistening the inhaled air to body conditions. The unique anatomical structure and respiratory airflow pattern may have important implications for designing new odorant detectors or electronic noses. Anat Rec, 299:853-868, 2016. © 2016 Wiley Periodicals, Inc.

Keywords: New Zealand white rabbit; lateral recess; nasal morphology; olfaction; respiration.

Fig. 1

Nose of a New Zealand white (NZW) rabbit: (a) lateral and cross-sectional views of the rabbit nose, (b) MRI scans of the maxilloturbinate region and ethmoidal region, and (c) solid airway model printed with 3D prototyping technique.

Fig. 2

Representation of the NZW rabbit nasal airway: (a) images of sagittal airway as a function of distance from the naris, (b) 3D surface model of the rabbit nasal airway. NV: nasal vestibule, MT: maxilloturbinate region, NM: nasomaxiilary region, ET: ethmoturbinate region, NP: nasopharynx. The pink color denotes the lateral recess.

Fig. 3

Assembly diagram of the NZW rabbit nasal airway: (a) the whole nasal airway with the lateral recess, (b) nasal airway surface after removing the cover of the VR I (MT Cover) and the lateral recess, and (c) nasal airway surface after removing the ventral concha (VR I and II) and the ET. Anatomical details of the nasal vestibule, vemeronasal organ, ethmoidal concha, and ventral conchae are also shown.

Fig. 4

Airway morphometric parameters of the NZW rabbit. (a) The distribution of the cross-sectional area (A_c), perimeter (P), and its hydraulic diameter (d_h) versus the axial distance from the naris. (b) The distribution of the airway surface area and airway volume versus the axial location.

Fig. 5

Complexity of the NZW rabbit nasal airway: (a) log(A_c)–log(P) relation of the maxilloturbinate and ethmoidal regions, and (b) the distribution of the geometrical complexity versus the axial distance from the naris. For comparison, the complexity of a circle is one.

Fig. 6

Morphometric parameters of the left lateral recess of the NZW rabbit. (a) The distribution of the cross-sectional area (A_c) and perimeter (P) versus the axial distance from the naris. (b) The surface area and volume versus the normalized axial location relative to the length of the left lateral recess. The area that connects the main airway and the left lateral recess is 5.79 mm².

Fig. 7

Distribution of airway function parameters versus the axial distance from the naris of the NZW rabbit under quiet and sniffing breathing conditions. (a) Reynolds number, Re is less than 2,000 in all regions of the airway, indicating a dominant laminar flow. (b) Womersley number, Wo is less than one under quiet breathing condition and is around one for sniffing, indicating a quasi-steady flow for quiet breathing and a transient flow for sniffing.

Fig. 8

Inhalation airflow inside the nasal airway under different respiration rates, (a) Q = 0.34 L/min, (b) Q = 0.68 L/min, (b) Q = 1.36 L/min, and (b) Q = 2.04 L/min, using streamlines, cross-sectional view, sagittal view, and selected slices.

Fig. 9

Snapshots of particle locations at different instants after being released into the nostrils. (a) Q = 0.68 L/min, (b) Q = 2.72 L/min. The particle size is 1 μm.

Fig. 10

Numerically predicted pressure variation along the distance in nasal airway. (a) The pressure-drop across the nasal airway under different breathing condition, and (b) the relationship of pressure drop between selected distances with flow rate.

Fig. 11

Thermohumidity distributions inside the rabbit nasal airway by inhaling ambient air at 23°C and RH = 30%. (a) Temperature and (b) relative humidity (RH).

Fig. 12

Wall shear stress in nasal airway under varying breathing conditions. (a) Q = 0.34 L/min, (b) Q = 0.68 L/min, (c) Q = 1.36 L/min, (d) Q = 2.04 L/min, (e) Q = 2.72 L/min.

Fig. 13

Inlet effects on flow distribution and vortices. (a) Inlet flow distribution, and (b) Instantaneous coherent structures (vortices) identified by the iso-surface of the λ2-criterion at 0.03.