Naseri Arash, Shaghaghian Sana, Abouali Omid, Ahmadi Goodarz
School of Mechanical Engineering, Shiraz University, Shiraz, Iran.
School of Mechanical Engineering, Shiraz University, Shiraz, Iran.
Respir Physiol Neurobiol. 2017 Oct;244:56-72. doi: 10.1016/j.resp.2017.06.005. Epub 2017 Jul 1.
In the present study, unsteady airflow patterns and particle deposition in healthy human upper airways were simulated. A realistic 3-D computational model of the upper airways including the vestibule to the end of the trachea was developed using a series of CT scan images of a healthy human. Unsteady simulations of the inhaled and exhaled airflow fields in the upper airway passages were performed by solving the Navier-Stokes and continuity equations for low breathing rates corresponding to low and moderate activities. The Lagrangian trajectory analysis approach was utilized to investigate the transient particle transport and deposition under cyclic breathing condition. Particles were released uniformly at the nostrils' entrance during the inhalation phase, and the total and regional depositions for various micro-particle sizes were evaluated. The transient particle deposition fractions for various regions of the human upper airways were compared with those obtained from the equivalent steady flow condition. The presented results revealed that the equivalent constant airflow simulation can approximately predict the total particle deposition during cyclic breathing in human upper airways. While the trends of steady and unsteady model predictions for local deposition were similar, there were noticeable differences in the predicted amount of deposition. In addition, it was shown that a steady simulation cannot properly predict some critical parameters, such as the penetration fraction. Finally, the presented results showed that using a detached nasal cavity (commonly used in earlier studies) for evaluation of total deposition fraction of particles in the nasal cavity was reasonably accurate for the steady flow simulations. However, in transient simulation for predicting the deposition fraction in a specific region, such as the nasal cavity, using the full airway system geometry becomes necessary.
在本研究中，对健康人体上呼吸道内的非定常气流模式和颗粒沉积进行了模拟。利用一名健康人的一系列CT扫描图像，建立了一个逼真的上呼吸道三维计算模型，该模型包括从前庭到气管末端。通过求解对应于低强度和中等强度活动的低呼吸频率下的Navier-Stokes方程和连续性方程，对上呼吸道通道内吸入和呼出气流场进行了非定常模拟。采用拉格朗日轨迹分析方法研究了周期性呼吸条件下颗粒的瞬态输运和沉积。在吸气阶段，颗粒在鼻孔入口处均匀释放，并评估了各种微粒尺寸的总沉积和区域沉积。将人体上呼吸道不同区域的瞬态颗粒沉积分数与等效稳定流动条件下获得的分数进行了比较。结果表明，等效恒定气流模拟可以近似预测人体上呼吸道周期性呼吸过程中的总颗粒沉积。虽然稳定和非稳定模型预测局部沉积的趋势相似，但预测的沉积量存在明显差异。此外，结果表明，稳定模拟不能正确预测一些关键参数，如穿透分数。最后，结果表明，对于稳定流动模拟，使用分离的鼻腔（早期研究中常用）来评估鼻腔内颗粒的总沉积分数是相当准确的。然而，在预测特定区域（如鼻腔）的沉积分数的瞬态模拟中，使用完整的气道系统几何模型是必要的。
