Hsu S H, Hou C M
Department of Chemical Engineerng, National Chung Hsing University, Taichung, Taiwan, PR China.
Med Eng Phys. 1998 Nov;20(8):558-64. doi: 10.1016/s1350-4533(98)00068-x.
In this model study, we simulated the initial airway reopening event in a rigid tube model. The air-liquid interface during airway reopening was assumed to be a simple axisymmetric meniscus similar to that of a two-phase flow in a rigid tube (radius R), where the applied pressures and the meniscus velocities were measured experimentally for fluids of different viscosities and surface tensions (gamma). Bulk flow contribution was deducted from the applied pressure to obtain the pressure accounting for interfacial movement (P*(int)). A semi-empirical formula for the interface was generated by dimensional analysis. The dimensionless interfacial pressure (P(int) = P*(int),R/gamma) was found to approach 2 for sufficiently small velocities, consistent with Bretherton's theoretical prediction. This formula also resembles that previously obtained in collapsible tubes simulating airways. The result suggests that the critical pressures required to reopen a collapsible airway and a non-collapsible one with the same radius are similar in magnitude (approximately 2 - 3gamma/R). However, in a collapsible airway, no significant bulk flow of lining fluids would develop while the interface proceeds, leading to a much smaller overall pressure for further reopening. Airway wall collapsibility thus could play a crucial role in maintaining proper ventilation through rapid reopening of the airway.
在这项模型研究中，我们在刚性管模型中模拟了气道初始 reopening 事件。气道 reopening 期间的气液界面被假定为类似于刚性管（半径为 R）中两相流的简单轴对称弯月面，其中针对不同粘度和表面张力（γ）的流体通过实验测量了施加压力和弯月面速度。从施加压力中扣除总体流动贡献以获得考虑界面运动的压力（P*(int)）。通过量纲分析生成了界面的半经验公式。发现对于足够小的速度，无量纲界面压力（P(int) = P*(int),R/γ）接近 2，这与布雷瑟顿的理论预测一致。该公式也类似于先前在模拟气道的可塌陷管中获得的公式。结果表明，重新打开具有相同半径的可塌陷气道和不可塌陷气道所需的临界压力在大小上相似（约为 2 - 3γ/R）。然而，在可塌陷气道中，当界面推进时不会产生显著的衬里流体总体流动，导致进一步重新打开所需的总压力要小得多。因此，气道壁的可塌陷性在通过气道的快速重新打开维持适当通气方面可能起关键作用。
