Yamada H
Department of Anesthesiology, Keio University, School of Medicine, Tokyo.
Masui. 1990 Jan;39(1):27-38.
To clarify the enhancing effect of turbulence on gas transfer in high frequency oscillation (HFO), the role of turbulence during oscillatory flow was studied. Oscillatory flow was generated in a straight circular tube as a trachea model, over the range of Reynolds' number (Re: 2000-16000) and Stokes parameter (lambda : 3-7). This simulates clinical settings. Measurements of the axial velocity were made by means of hot wire anemometer, and turbulence intensity (I) as well as ensemble mean velocity was calculated. At the same time, 1 ml of 100% CO2 was injected into the tube, and CO2 concentration was measured by a CO2 analyzer to yield the effective diffusivity (Deff). As Re increases and lambda decreases to a certain level, "conditional turbulence" appears in the whole cross section to produce an efficient lateral mixing. Deff increases with increasing I as well as Re, and increasing lambda results in an increase in the difference of measured and theoretical Deff (Watson's prediction for laminar oscillatory flow). It is concluded that turbulence during oscillatory flow plays an important role in lateral mixing to facilitate gas transport, and decision of ventilator settings is essential so as to give rise to "conditional turbulence" for the purpose of Deff augmentation during HFO.
为阐明湍流对高频振荡（HFO）中气体传输的增强作用，研究了振荡流期间湍流的作用。在作为气管模型的直圆形管中产生振荡流，范围为雷诺数（Re：2000 - 16000）和斯托克斯参数（λ：3 - 7）。这模拟了临床情况。通过热线风速仪测量轴向速度，并计算湍流强度（I）以及总体平均速度。同时，向管中注入1 ml的100%二氧化碳，并用二氧化碳分析仪测量二氧化碳浓度以得出有效扩散率（Deff）。随着Re增加且λ减小到一定水平，“条件性湍流”出现在整个横截面上，以产生有效的横向混合。Deff随I以及Re的增加而增加，并且λ增加导致测量的Deff与理论Deff（层流振荡流的沃森预测）之间的差异增大。得出结论，振荡流期间的湍流在促进气体传输的横向混合中起重要作用，并且确定呼吸机设置对于在HFO期间产生“条件性湍流”以增加Deff至关重要。
