Gas Exchange Mechanism in Conducting Airways of Human Lung

人肺的气道由非常复杂的分支管网组成。在每个支气管处，气道重复分支，其平均直径和长度逐渐减少。在呼吸道的末端，存在许多将二氧化碳交换为氧气的肺泡。对于气体在导气管中的输运，人们做了大量的研究。然而，在吸气过程中吸入的新鲜空气如何到达肺泡的机制尚不清楚。近年来，作者揭示了人肺系统传导气道中发生的双向轴向气体交换现象是由流动分离区的“产生-消失”引起的“捕获-释放”机制所控制的，为了进一步研究真实的人肺中发生的现象，在二维实验截面的基础上，新构建了三维实验截面。多通道内往复流动的流动显示实验与数值分析 关于我们 产生分支管网。实验结果表明：（1）即使在三维试验段，“捕获-释放”机制也起着重要作用。(2)在三维实验段中，由于原始管中的非对称流动，导致不同的路径上的轴向传质速度不同。（3）轴向传质最快路径的变化取决于相邻分支之间的旋转角所决定的几何构型。并计算了具有三个不同分支角的二维分支情况。在数值计算结果中，观察到流动分离气泡的尺寸和轴向质量传输之间的关系。该关系不是单调的，因此必须存在最佳分支角。通过对流场的详细观察，发现流动分离泡对传质的强化有两种作用：“捕获-释放”效应和通过减小流动通道的横截面积来加速流体。少

The airway of the human lung consists of a very complicated branching tube network. At each bronchus, the airways repeat branching with their average diameter and the length decreasing. At the end of airways, numerous alveoli that exchange carbon dioxide for oxygen exist. As for the gas transport in the conducting airways, a lot of researches have been done. However, the mechanism how the fresh air, which was inhaled in the inspiration process, reaches alveoli is not known well yet. Recently, the authors revealed that bi-directional axial gas-exchange phenomenon occurring in the conducting airways of human lung system was governed by "trap-and-release" mechanism caused by "generation-and-extinction" of flow-separation regions.In order to further examine the phenomena occurring in the real human lung, three-dimensional test sections were newly constructed in addition to the two-dimensional one. Flow visualization experiments and numerical analysis in reciprocating flow inside a multi-ge … More neration branching-tube network were performed. In the experiments, the followings were revealed : (1) Even in the 3-D test section, "trap-and-release" mechanism played an important role. (2) In the 3-D test section, asymmetric flow in the ancestor tube results in the different axial mass transport speed depending on the path. (3) The fastest path concerning the axial mass transport changed depending on the geometric configuration decided by the rotation angle between the successive branches.In the numerical analysis, the finite volume method was used, and a two-dimensional branching case was computed with three different branching angles. In the numerical results, the relation between the size of the flow-separation bubble and axial mass transport was observed. The relation was not monotonic, and therefore there must be an optimal branching angle. By examining the flow field in detail, it was observed that the flow-separation bubble had two effects on the mass transport enhancement : the "trap-and-release" effect and the acceleration of the fluid bv reducing the cross-sectional area of the flow passaee. Less