Shahed Syeda Reham, Dong Jingliang, Tu Jiyuan, Tian Lin
School of Engineering - Mechanical, Manufacturing and Mechatronic Engineering, RMIT University, Bundoora, VIC, Australia.
Institute for Sustainable Industries & Liveable Cities, Victoria University, PO Box 14428, Melbourne, VIC, 8001, Australia; First Year College, Victoria University, Footscray Park Campus, Footscray, VIC, 3011, Australia.
Comput Biol Med. 2025 Jun;191:110136. doi: 10.1016/j.compbiomed.2025.110136. Epub 2025 Apr 7.
Nasal cavity is the first line of defence against toxicants and pollutants. A deep understanding of the realistic airflow in the complex geometry is crucial to evaluate pollution impact and initiation of various respiratory diseases. Human respiration by nature is unsteady, having two phases - inhalation and exhalation. While prior studies are predominantly on the steady state considering only the inhalation phase, we are curious to understand and investigate the unsteady nature of human respiration.
A sinusoidal unsteady profile simulating a complete breathing cycle at a flow rate of 10 L/min is considered in this study. We have reconstructed a realistic human nasal cavity model from CT scans and with Ansys Fluent we have analysed the flow field. The time-evolving flow patterns and wall shear stress, in particular during the distinctive accelerating and decelerating breathing phases, are extracted. Critical transient insight to the unsteady breathing which is largely unknown in a steady simulation is revealed. Finally, the breathing air flux in the olfactory region are calculated under the transient breathing condition.
Evolving flow pattern at different time instants gives a significant variation of the flow dynamics which would not be understood in a steady study. The main differences in inhalation and exhalation are the regions where the main flow is dominant, the location of the vortices around the olfactory and wall shear stress patterns. In addition, past history of peak flow has noticeable effects on flow fields during the deceleration phase, especially when the breathing rate is low. Finally, flow pathways into the olfactory region varies during inhalation and exhalation phases.
The cyclic information provides critical transient insight to the unsteady breathing which is largely unknown in a steady study. In the context of a fast-growing interest in nasal transport to accurately evaluate pollution impact and pathogen deposition, investigation on the flow and particle depositions under unsteady condition is valuable and highly desired.
鼻腔是抵御毒物和污染物的第一道防线。深入了解复杂几何结构中的实际气流对于评估污染影响和各种呼吸道疾病的发病机制至关重要。人类呼吸本质上是不稳定的，包括吸气和呼气两个阶段。虽然先前的研究主要集中在仅考虑吸气阶段的稳态情况，但我们好奇于了解和研究人类呼吸的不稳定特性。
本研究考虑了一个正弦不稳定剖面，模拟了流速为10升/分钟的完整呼吸周期。我们从CT扫描重建了一个真实的人类鼻腔模型，并使用Ansys Fluent分析了流场。提取了随时间演变的流动模式和壁面剪应力，特别是在独特的加速和减速呼吸阶段。揭示了在稳态模拟中基本未知的不稳定呼吸的关键瞬态洞察。最后，计算了瞬态呼吸条件下嗅觉区域的呼吸气流通量。
不同时刻演变的流动模式显示出流动动力学的显著变化，这在稳态研究中是无法理解的。吸气和呼气的主要差异在于主流占主导的区域、嗅觉周围的涡旋位置和壁面剪应力模式。此外，峰值流量的过往历史对减速阶段的流场有显著影响，尤其是在呼吸频率较低时。最后，吸气和呼气阶段进入嗅觉区域的流动路径有所不同。
循环信息为不稳定呼吸提供了关键的瞬态洞察，这在稳态研究中基本未知。在对鼻腔传输以准确评估污染影响和病原体沉积的兴趣迅速增长的背景下，对不稳定条件下的流动和颗粒沉积进行研究是有价值且非常必要的。
