Nygaard H, Giersiepen M, Hasenkam J M, Westphal D, Paulsen P K, Reul H
Engineering College, Aarhus, Denmark.
J Biomech. 1990;23(12):1231-8. doi: 10.1016/0021-9290(90)90380-l.
Measuring turbulent shear stresses is of major importance in artificial heart valve evaluation. Bi- and unidirectional fluid velocity measurements enable calculation of Reynolds shear stress [formula: see text] and Reynolds normal stress [formula: see text]. tau is important due to the relation to hemolysis and thrombus formation, but sigma is the only obtainable parameter in vivo. Therefore, determination of a correlation factor between tau and sigma is pertinent. In a pulsatile flow model, laser Doppler (LDA) and hot-film (HFA) anemometry were used for simultaneous bi- and unidirectional fluid velocity measurements downstream of a Hall Kaster and a Hancock Porcine aortic valve. Velocities were registered in two flow field locations and at four cardiac outputs. The velocity signals were subjected to analog signal processing prior to digital turbulence analysis, as a basis for calculation of tau and sigma. A correlation factor of 0.5 with a correlation coefficient of 0.97 was found between the maximum Reynolds shear stress and Reynolds normal stress, implying [formula: see text]. In vitro estimation of turbulent shear stresses downstream of artificial aortic valves, based on the axial velocity component alone, seems possible.
测量湍流剪应力在人工心脏瓣膜评估中至关重要。双向和单向流体速度测量能够计算雷诺剪应力[公式：见原文]和雷诺法向应力[公式：见原文]。由于与溶血和血栓形成有关，τ很重要，但σ是体内唯一可获取的参数。因此，确定τ和σ之间的相关因子很有必要。在一个脉动流模型中，激光多普勒（LDA）和热膜（HFA）风速仪被用于在Hall Kaster和Hancock猪主动脉瓣下游同时进行双向和单向流体速度测量。在两个流场位置和四个心输出量下记录速度。在进行数字湍流分析之前，对速度信号进行模拟信号处理，作为计算τ和σ的基础。发现最大雷诺剪应力和雷诺法向应力之间的相关因子为0.5，相关系数为0.97，这意味着[公式：见原文]。仅基于轴向速度分量对人工主动脉瓣下游的湍流剪应力进行体外估计似乎是可行的。
