Federspiel W J, Fredberg J J
Department of Pediatrics, Harvard University, Boston, Massachusetts 02215.
J Appl Physiol (1985). 1988 Jun;64(6):2614-21. doi: 10.1152/jappl.1988.64.6.2614.
The mixing of gases in the pulmonary acinus was characterized by analyzing axial gas dispersion during steady flow in models of respiratory bronchioles and alveolar ducts. An analysis (method of moments) developed for addressing dispersion in porous media was used to derive an integral expression for the axial dispersion coefficient (D*). Evaluation of D* required solving the Navier-Stokes equations for the flow field and a convection-diffusion type equation arising from the analysis. D* was strongly dependent on alveolar volume per central duct volume, the aperture size through which the alveoli communicate with the central duct, and the Péclet number (Pe). At smaller Pe (flow rate) D* was substantially smaller than the molecular diffusion coefficient, whereas at larger Pe (flow rate) D* was much greater than the Taylor-Aris result for flow-enhanced dispersion in straight tubes. Also, flow-enhanced dispersion became appreciable at smaller Pe than indicated by the Taylor-Aris result. These behaviors transcend both the lower and upper limits established previously for gas mixing in the pulmonary acinus.
通过分析呼吸性细支气管和肺泡管模型中稳定流动期间的轴向气体扩散，对肺腺泡内气体混合进行了表征。为解决多孔介质中的扩散问题而开发的一种分析方法（矩量法）被用于推导轴向扩散系数（D*）的积分表达式。对D的评估需要求解流场的纳维-斯托克斯方程以及分析得出的对流扩散型方程。D强烈依赖于每个中央导管体积的肺泡体积、肺泡与中央导管连通的孔径大小以及佩克莱数（Pe）。在较小的Pe（流速）下，D显著小于分子扩散系数，而在较大的Pe（流速）下，D远大于直管中流动增强扩散的泰勒-阿里斯结果。此外，流动增强扩散在比泰勒-阿里斯结果所示更小的Pe时就变得明显。这些行为超越了先前为肺腺泡内气体混合所确定的下限和上限。
