Overdrainage in upright position is one of the most prevalent issues in treating hydrocephalus with a cerebrospinal fluid (CSF) shunt. Anti-siphon devices (ASDs) are employed to reduce this problem. A novel microelectromechanical system (MEMS)-based valve, termed Chronoflow device, aims to regulate CSF drainage indifferently of the body posture. With this study, the suitability of this MEMS-based valve is evaluated regarding its use for the treatment of hydrocephalus, particularly for the prevention of overdrainage and blockage. In total, four Chronoflow devices were tested. An established in-vitro hardware-in-the-loop (HIL) test bed was used to investigate the valves regarding their pressure-flow characteristics, their behaviors towards CSF dynamics, and their capabilities to prevent CSF overdrainage in upright position. Additionally, a contamination test was conducted to evaluate the susceptibility of the device to blockage due to particles. All valves tested regulated the drainage rate at similar nominal flows and independently of posture. The pressure-flow relation measured, however, was notably higher than numerically calculated. Regarding the CSF dynamics, the first three valves tested led to a decreased steady-state intracranial pressure in supine position and showed stable drainage rate in upright position. During the transitional phase from supine to upright and vice versa, the valves continuously adjusted the outflow resistance, which resulted in a stable transitional phase preventing overdrainage. Yet, the fourth valve showed continuous overdrainage in upright position due to an increased nominal flow. However, after several test iterations the nominal flow decreased and stabilized at a level similar to that of the first three valves tested. The contamination test showed that most particles initially adhere to the pillars and spread throughout the cavity of the valve as the concentration of particles increases, thereby affecting the displacement of the membrane. The devices generally provide a stable flow regulation and prevent overdrainage in upright position. Specifically, their drainage behaviors during the posture changes are very effective. However, they also showed high hysteresis and sensitivity towards particle contamination, which resulted in initial increased and altering nominal flows after many test iterations. This result suggests that the MEMS design presented lacks robustness. Yet, an upstream filter and specific coatings on the fluid pathway may increase significantly its reliability.

中文翻译：

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流量相关的MEMS CSF阀的姿势相关体外表征

在脑脊液（CSF）分流器治疗脑积水中，直立式过度排水是最普遍的问题之一。使用防虹吸设备（ASD）可以减少此问题。一种新型的基于微机电系统（MEMS）的阀，称为Chronoflow装置，旨在无差别地调节CSF引流。通过这项研究，评估了基于MEMS的瓣膜在治疗脑积水方面的适用性，尤其是在预防过度引流和阻塞方面。总共测试了四个Chronoflow设备。成熟的体外硬件在环（HIL）测试床用于研究阀门的压力流量特性，对CSF动态的行为以及防止CSF在垂直位置过度排水的能力。此外，还进行了污染测试，以评估设备因颗粒堵塞的敏感性。所有测试的阀门均以相似的标称流量调节排水速率，并且不受姿态影响。但是，测得的压力-流量关系明显高于数值计算。关于脑脊液动力学，测试的前三个瓣膜导致仰卧位稳态颅内压降低，直立位显示稳定的引流速率。在从仰卧到竖立（反之亦然）的过渡阶段，阀门会不断调节流出阻力，这导致了一个稳定的过渡阶段，防止了过度排水。但是，由于增加了标称流量，第四个阀在直立位置显示出持续的超排水状态。但是，经过几次测试迭代后，标称流量下降并稳定在与测试的前三个阀相似的水平。污染测试表明，大多数颗粒最初会粘附在支柱上，并随着颗粒浓度的增加而散布在整个阀腔中，从而影响膜的位移。该设备通常提供稳定的流量调节，并防止在竖立位置过度排水。具体而言，它们在姿势改变期间的排水行为非常有效。但是，它们也表现出很高的磁滞性和对颗粒污染的敏感性，经过多次测试，最终导致初始流量增加和名义流量改变。该结果表明所提出的MEMS设计缺乏鲁棒性。然而，上游过滤器和流体通道上的特定涂层可能会大大提高其可靠性。