Jin W, Clark C
Department of Manufacturing and Engineering Systems, Brunel University, Uxbridge, Middlesex, U.K.
J Biomech. 1994 Nov;27(11):1319-29. doi: 10.1016/0021-9290(94)90041-8.
Intrinsic features of the pumping process of a pneumatically driven ventricular assist device (VAD) and the effects of different types of pneumatic drivers upon its performance were investigated in vitro by analysing the pressure distributions within the device and the motions of the prosthetic valves. It was found that the stretching of the flexible, elastic diaphragm in both late systole and diastole initiates a pressure oscillation which directly affects the timing of the pumping process. The timing was also found to be dependent on the length and stiffness of the cannulae which link the VAD to the model circulation system. During the stretch-induced oscillation in late systole, the VAD housing experiences partial collapse due to fluid momentum effects, which tends to increase the effective stroke volume of the device, and reduce the amplitude of the pressure oscillation. Reducing the rising (falling) rate of driving pressures (dpd/dt) may not necessarily reduce the maximum rate of change of the blood chamber pressure (dpch/dtmax) but may upset the stability of the pumping process. This is because a minimum dpch/dtmax exists, which is determined by the stretch-induced oscillation. In order to minimize dpch/dtmax and to provide the device with a stable working condition, dpd/dt should match the dpch/dtmax.
通过分析气动驱动心室辅助装置（VAD）内部的压力分布和人工瓣膜的运动，在体外研究了该装置泵送过程的内在特征以及不同类型气动驱动器对其性能的影响。研究发现，在收缩末期和舒张期，柔性弹性隔膜的伸展都会引发压力振荡，这直接影响泵送过程的时间。还发现该时间取决于连接VAD与模型循环系统的插管的长度和刚度。在收缩末期由伸展引起的振荡期间，由于流体动量效应，VAD外壳会部分塌陷，这往往会增加装置的有效搏出量，并减小压力振荡的幅度。降低驱动压力的上升（下降）速率（dpd/dt）不一定会降低血腔压力的最大变化速率（dpch/dtmax），但可能会破坏泵送过程的稳定性。这是因为存在一个由伸展引起的振荡所决定的最小dpch/dtmax。为了使dpch/dtmax最小化并为装置提供稳定的工作条件，dpd/dt应与dpch/dtmax相匹配。
