Chang H K
Department of Biomedical Engineering, University of Southern California, Los Angeles 90089-1451.
Adv Exp Med Biol. 1988;227:39-52. doi: 10.1007/978-1-4684-5481-9_4.
The bronchial tree is an asymmetric multi-generation conduit for air to pass through. Breathing is a time-varying, cyclic process. Therefore, gas transport in the bronchial tree during breathing is a problem with both spatial and temporal complexities. However, it is possible to gain a fair understanding of this complex process by examining the roles of bulk convection, molecular diffusion and the various modes of their interaction. Convection brings the inspired gas into the peripheral region of the lung and removes the mixed inspired-resident gas from the lung. During the post-inspiratory and post-expiratory pauses and in the very distal regions of the lung, molecular diffusion alone is responsible for the mixing process. Convection and diffusion together are responsible for establishing a quasi-steady front of the inspired gas in the peripheral lung region. The position of the front depends on lung volume, tidal volume, inspiratory flow-rate as well as diffusivity of the inspired gas. Taylor-type dispersion, while certainly existing in the lung, and despite its gas mixing potentials, is of questionable effectiveness in the overall gas transport process in the bronchial tree. The various modes of interaction between convection and diffusion are likely to improve gas mixing in the bronchial tree and have an effect on the phase II of the single-breath washout curve.
支气管树是空气通过的不对称多代管道。呼吸是一个随时间变化的循环过程。因此，呼吸过程中支气管树内的气体传输是一个具有空间和时间复杂性的问题。然而，通过研究体对流、分子扩散及其各种相互作用模式的作用，可以对这个复杂过程有一个较为全面的理解。对流将吸入的气体带到肺的外周区域，并将混合的吸入气体和驻留气体从肺中排出。在吸气后和呼气后的暂停期间以及肺的非常远端区域，仅分子扩散负责混合过程。对流和扩散共同负责在肺外周区域建立吸入气体的准稳态前沿。前沿的位置取决于肺容积、潮气量、吸气流量以及吸入气体的扩散率。泰勒型弥散虽然肯定存在于肺中，并且尽管具有气体混合潜力，但在支气管树的整体气体传输过程中的有效性值得怀疑。对流和扩散之间的各种相互作用模式可能会改善支气管树中的气体混合，并对单次呼吸冲洗曲线的第二阶段产生影响。
