Keyhani K, Scherer P W, Mozell M M
Department of Bioengineering, University of Pennsylvania, Philadelphia 19104-6392, USA.
J Theor Biol. 1997 Jun 7;186(3):279-301. doi: 10.1006/jtbi.1996.0347.
The transport and uptake of inspired odorant molecules in the human nasal cavity were determined using an anatomically correct three-dimensional finite element model. The steady-state equations of motion and continuity were first solved to determine laminar flow patterns of odorous air at quiet breathing flow rates. The air stream entering the ventral tip of the naris traveled to the olfactory slit, and then passed through the slit in nearly a straight path without forming separated recirculating zones. The fraction of volumetric flow passing through the olfactory airway was about 10%, and remained nearly constant with variation in flow rate. The three-dimensional inspiratory velocity field was used in the solution of the uncoupled steady convective-diffusion equation to determine the concentration field in the airways and odorant mass flux at the nasal walls. The mass-transfer boundary condition used at the nasal cavity wall included the effects of solubility and diffusivity of odorants in the mucosal lining, and the thickness of the mucus layer. The total olfactory flux of odorants, that is highly correlated with perceived odor intensity, was determined as a function of all transport parameters in our model. Increase in nasal flow rate at a constant inlet concentration resulted in an increase in total olfactory uptake for all odorants. However, with increase in flow rate, the fractional uptake, i.e., total olfactory flux normalized by convective flux at the inlet, decreased for poorly soluble odorants, while it increased for highly soluble odorants. The pattern of flux (or imposed patterning) across the olfactory mucosa, that carries information concerning odor identity, was also determined as a function of transport parameters. There was an overall decrease in odorant flux as the location on the olfactory surface was varied from the anterior towards the posterior and from the inferior towards the superior ends. The flux pattern became more uniform, i.e., the steepness of the flux gradients across the olfactory surface decreased, as the mucus solubility of the odorants decreased. Different odorants generated discernibly different flux patterns across the olfactory mucosa that may contribute to the encoding of odor quality. Variation of total olfactory flux with time after cessation of airflow was determined by solving the unsteady diffusion equation in the air-phase. The flux decreased approximately exponentially with time. The rate of decay decreased as solubility and diffusivity decreased, but was very rapid over a wide range of the parameters, with time constants of less than 0.5 s for most odorants, implying a rapid decrease in perceived odor intensity with cessation of nasal airflow.
利用一个解剖结构正确的三维有限元模型，确定了人体鼻腔中吸入的气味分子的传输和摄取情况。首先求解稳态运动方程和连续性方程，以确定安静呼吸流速下有气味空气的层流模式。进入鼻孔腹侧尖端的气流流向嗅觉裂隙，然后几乎以直线路径穿过裂隙，不形成分离的再循环区域。通过嗅觉气道的体积流量分数约为10%，并且随着流速变化基本保持恒定。在求解非耦合稳态对流扩散方程时，使用三维吸气速度场来确定气道中的浓度场和鼻壁处的气味剂质量通量。鼻腔壁处使用的传质边界条件包括气味剂在粘膜衬里中的溶解度和扩散率以及粘液层厚度的影响。在我们的模型中，与感知到的气味强度高度相关的气味剂总嗅觉通量被确定为所有传输参数的函数。在入口浓度恒定的情况下，鼻流速增加导致所有气味剂的总嗅觉摄取量增加。然而，随着流速增加，分数摄取量，即通过入口处对流通量归一化的总嗅觉通量，对于难溶性气味剂会降低，而对于高溶性气味剂会增加。跨越嗅觉粘膜的通量模式（或施加的模式），它携带有关气味特征的信息，也被确定为传输参数的函数。随着嗅觉表面上的位置从前向后以及从下向上变化，气味剂通量总体上会降低。随着气味剂的粘液溶解度降低，通量模式变得更加均匀，即跨越嗅觉表面的通量梯度的陡度降低。不同的气味剂在嗅觉粘膜上产生明显不同的通量模式，这可能有助于气味质量的编码。通过求解气相中的非稳态扩散方程，确定了气流停止后总嗅觉通量随时间的变化。通量随时间近似呈指数下降。衰减速率随着溶解度和扩散率降低而降低，但在很宽的参数范围内非常迅速，大多数气味剂的时间常数小于0.5秒，这意味着随着鼻气流停止，感知到的气味强度会迅速下降。
