上气道内流动现象与压力分布模拟

目的用计算流体力学模拟的方法和体外模型实验的手段,研究呼吸时真实结构的上气道内的流动状态和压力分布,同时验证数值模拟模型的准确性。方法首先基于磁共振图像,借助Mimics软件重建上气道三维结构。在此真实几何结构基础上,建立上呼吸道内流动的有限元分析模型,以及制作相应的实体模型。模拟并测量呼吸流量为200、400和600 m L/s时的情况,并将数值模型预测的壁面压力分布与实测结果比较。结果如果气道内气流流量相同,吸气时气道两端的压差比呼气时大,即吸气时气道阻力比呼气时大。不同点压力分布的数值计算结果与实体模型测量结果一致。数值模拟结果表明,吸气时气道悬雍垂以及会厌后的舌后区域流动速度较高,悬雍垂下舌后区有涡旋产生。呼气时矢状位鼻咽顶端靠近后壁处,冠状位鼻咽、会厌下口咽处均有涡旋产生。结论数值模型可以准确地模拟上气道的流动状态和压力分布,直观地反映上气道内流动特点。作为非侵入式的工具,气道模型和数值模拟可以在探索阻塞性睡眠呼吸暂停(obstructive sleep apnea,OSA)的发病机制和有效治疗方法的过程中发挥重要作用。

Simulations of flow and pressure distribution in the upper airway

Objective The alm of this study was to investigate the flow and pressure distributions in the upper alrway during respiration using computational fluid dynamics methods and in vitro experiments,and to test the accuracy of the numerical models. Methods An anatomically accurate finite element model of the human upper alrway was constructed from magnetic resonance images,and an identical physical model of the same alrway was built. Numerical simulations and experimental measurements were performed at flow rates of 200 ml/s,400 ml/s,and 600 ml/s,and the model-predicted distributions of the wall static pressure were compared with measured results. Results When the flow flux was the same,a larger pressure drop between the two ends of the upper alrway was required during inspiration compared to expiration. That means a larger flow resistance during inspiration compared to expiration. The numerical predictions of the wall pressure at different locations of the upper alrway were consistent with the measured data from the physical model. Numerical results showed high velocities in the retropalatal and retroglossal regions near the epiglottis during inspiration. Vortex flows occurred at the region below the uvula. During expiration, vortex flows could be observed at the region near the posterior top of the nasopharynx wall in the midsagittal plane,and in the nasopharynx and the oropharynx below the uvula in the coronal plane. Conclusions Numerical models can be used to simulate the flow field and pressure distribution accurately,as well as to show the flow characteristics in the upper alrway intuitively. As noninvasive methods,in vitro models and numerical simulations could play an important role in the study on the pathogenesis and effective treatment methods of obstructive sleep apnea.