Lutz R J, Hsu L, Menawat A, Zrubek J, Edwards K
J Biomech. 1983;16(9):753-66. doi: 10.1016/0021-9290(83)90084-2.
Data are presented to compare fluid flow parameters for steady flow with those for time-varying flow in a simplified two branch model which simulates the region of the abdominal aorta near the celiac and superior mesenteric branches of the dog. Measurements in the model included laser doppler anemometry velocity profiles during steady flow, sinusoidal flow with a superimposed mean flow (referred to as simple oscillatory flow) and arterial pulsatile flow. Shear rate measurements were made by an electrochemical technique during steady flow. Flow visualization studies were done during steady and pulsatile flow. Fluid flow effects in the simplified model during steady flow showed many similarities to the results from previous steady flow studies in a canine aortic cast. Shear rates in the region of the proximal (first, or celiac) branch were independent of flow rates in the distal (second, or mesenteric) branch, but the shear pattern within the proximal branch changed significantly as flow in the proximal branch increased. Shear rates on the proximal flow divider (leading edge into the distal branch) depended primarily on the flow rate to the proximal branch, but not on flow to the distal branch. At certain daughter branch flow ratios (approximately 2:1, proximal to distal), flow separation was promoted at the outer wall of the second branch, but flow separation did not occur in the first branch. In contrast to the canine aortic case results, flow separation was never detected on the distal (mesenteric) flow divider of the simplified model. This observation reflects the subtle effects of geometry on flow since the mesenteric flow divider in the canine cast protrudes into the main flow whereas the distal flow divider in the simplified model does not. There were distinct differences in the flow phenomena between steady, simple oscillatory and arterial pulsatile flow. Peak shear rates during pulsatile flow were as much as 10--100 times greater than steady flow shear rates at comparable mean flow rates. Particularly noteworthy for the pulsatile flow with a Womersley parameter of sixteen were very blunt velocity profiles throughout systole, and the absence of flow separation or reversal in those regions of the model that exhibited flow separation during steady flow. The shape of the waveform influences the nature of the flow during time-varying flows. Future studies of fluid dynamics in model systems must consider the pulsatile nature of the flow if a true interpretation of arterial flow phenomena is to be made.
本文呈现了在一个简化的双分支模型中，将稳定流的流体流动参数与随时间变化的流动参数进行比较的数据，该模型模拟了犬类腹腔干和肠系膜上动脉分支附近的腹主动脉区域。模型中的测量包括稳定流、叠加平均流的正弦流（称为简单振荡流）和动脉搏动流期间的激光多普勒测速速度剖面。在稳定流期间，通过电化学技术进行剪切速率测量。在稳定流和搏动流期间进行了流动可视化研究。简化模型在稳定流期间的流体流动效应与先前在犬主动脉铸型中进行的稳定流研究结果有许多相似之处。近端（第一，即腹腔干）分支区域的剪切速率与远端（第二，即肠系膜）分支的流速无关，但随着近端分支流量的增加，近端分支内的剪切模式发生了显著变化。近端分流器（进入远端分支的前缘）上的剪切速率主要取决于近端分支的流速，而不取决于远端分支的流速。在某些子分支流量比（近端与远端约为2:1）下，第二分支外壁处促进了流动分离，但第一分支中未发生流动分离。与犬主动脉病例结果相反，在简化模型的远端（肠系膜）分流器上从未检测到流动分离。这一观察结果反映了几何形状对流动的微妙影响，因为犬铸型中的肠系膜分流器突出到主流中，而简化模型中的远端分流器则没有。稳定流、简单振荡流和动脉搏动流之间的流动现象存在明显差异。在可比平均流速下，搏动流期间的峰值剪切速率比稳定流剪切速率大10至100倍。对于沃默斯利参数为16的搏动流，特别值得注意的是整个收缩期非常钝的速度剖面，以及在稳定流期间出现流动分离的模型区域中没有流动分离或反向流动。波形的形状会影响随时间变化的流动期间的流动性质。如果要对动脉流动现象进行真正的解释，未来模型系统中的流体动力学研究必须考虑流动的搏动性质。
