Laboratory of Thermodynamics in Emerging Technologies;
J Neurosurg. 2013 Dec;119(6):1511-9. doi: 10.3171/2013.8.JNS122497. Epub 2013 Sep 6.
The treatment of hydrocephalus requires insight into the intracranial dynamics in the patient. Resistance to CSF outflow (R0) is a clinically obtainable parameter of intracranial fluid dynamics that quantifies the apparent resistance to CSF absorption. It is used as a criterion for the selection of shunt candidates and serves as an indicator of shunt performance. The R0 is obtained clinically by performing 1 of 3 infusion tests: constant flow, constant pressure, or bolus infusion. Among these, the bolus infusion method has the shortest examination times and provides the shortest time of exposure of patients to artificially increased intracranial pressure (ICP) levels. However, for unknown reasons, the bolus infusion method systematically underestimates the R0. Here, the authors have tested and verified the hypothesis that this underestimation is due to lack of accounting for viscoelasticity of the craniospinal space in the calculation of the R0.
The authors developed a phantom model of the human craniospinal space in order to reproduce in vivo pressure-volume (PV) relationships during infusion testing. The phantom model followed the Marmarou exponential PV equation and also included a viscoelastic response to volume changes. Parameters of intracranial fluid dynamics, such as the R0, could be controlled and set independently. In addition to the phantom model, the authors designed a computational framework for virtual infusion testing in which viscoelasticity can be turned on or off in a controlled manner. Constant flow, constant pressure, and bolus infusion tests were performed on the phantom model, as well as on the virtual computational platform, using standard clinical protocols. Values for the R0 were derived from each infusion test by using both a standard method based on the Marmarou PV equation and a novel method based on a system identification approach that takes into account viscoelastic behavior.
Experiments with the phantom model confirmed clinical observations that both the constant flow and constant pressure infusion tests, but not the bolus infusion test, yield correct R0 values when they are determined with the standard method according to Marmarou. Equivalent results were obtained using the computational framework. When the novel system identification approach was used to determine the R0, all of the 3 infusion tests yielded correct values for the R0. CONCLUSIONS" The authors' investigations demonstrate that intracranial dynamics have a substantial viscoelastic component. When this viscoelastic component is taken into account in calculations, the R0, is no longer underestimated in the bolus infusion test.
脑积水的治疗需要深入了解患者颅内动力学。脑脊液流出阻力（R0）是颅内流体动力学的一个临床可获得的参数，它量化了脑脊液吸收的明显阻力。它被用作分流候选者选择的标准，并作为分流器性能的指标。R0 通过执行 3 种输注测试之一来临床获得：恒流、恒压或弹丸输注。在这些方法中，弹丸输注法的检查时间最短，患者暴露于人为增加的颅内压（ICP）水平的时间最短。然而，由于未知原因，弹丸输注法系统地低估了 R0。在这里，作者已经验证了假设，即这种低估是由于在 R0 的计算中没有考虑到颅脊空间的粘弹性。
作者开发了一个人类颅脊空间的体模模型，以在输注测试期间再现体内压力-体积（PV）关系。体模模型遵循 Marmarou 指数 PV 方程，并且还包括对体积变化的粘弹性响应。颅内流体动力学的参数，如 R0，可以独立控制和设置。除了体模模型，作者还设计了一个虚拟输注测试的计算框架，其中粘弹性可以以受控的方式打开或关闭。恒流、恒压和弹丸输注测试在体模模型上以及在虚拟计算平台上都使用标准的临床方案进行。通过使用 Marmarou PV 方程的标准方法和考虑粘弹性行为的系统识别方法，从每个输注测试中推导出 R0 值。
体模模型的实验证实了临床观察结果，即恒流和恒压输注测试，但不是弹丸输注测试，当根据 Marmarou 使用标准方法确定 R0 时，会产生正确的 R0 值。使用计算框架获得了等效的结果。当使用新的系统识别方法确定 R0 时，所有 3 种输注测试都产生了正确的 R0 值。结论：作者的研究表明，颅内动力学具有显著的粘弹性成分。当在计算中考虑到这种粘弹性成分时，弹丸输注测试中的 R0 不再被低估。
