Dutta-Roy Tonmoy, Wittek Adam, Miller Karol
Intelligent Systems for Medicine Laboratory, School of Mechanical Engineering MBDP: M050, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
J Biomech. 2008 Jul 19;41(10):2263-71. doi: 10.1016/j.jbiomech.2008.04.014. Epub 2008 Jun 4.
This study investigates the mechanics of normal pressure hydrocephalus (NPH) growth using a computational approach. We created a generic 3-D brain mesh of a healthy human brain and modelled the brain parenchyma as single phase and biphasic continuum. In our model, hyperelastic constitutive law and finite deformation theory described deformations within the brain parenchyma. We used a value of 155.77Pa for the shear modulus (mu) of the brain parenchyma. Additionally, in our model, contact boundary definitions constrained the brain outer surface inside the skull. We used transmantle pressure difference to load the model. Fully nonlinear, implicit finite element procedures in the time domain were used to obtain the deformations of the ventricles and the brain. To the best of our knowledge, this was the first 3-D, fully nonlinear model investigating NPH growth mechanics. Clinicians generally accept that at most 1mm of Hg transmantle pressure difference (133.416Pa) is associated with the condition of NPH. Our computations showed that transmantle pressure difference of 1mm of Hg (133.416Pa) did not produce NPH for either single phase or biphasic model of the brain parenchyma. A minimum transmantle pressure difference of 1.764mm of Hg (235.44Pa) was required to produce the clinical condition of NPH. This suggested that the hypothesis of a purely mechanical basis for NPH growth needs to be revised. We also showed that under equal transmantle pressure difference load, there were no significant differences between the computed ventricular volumes for biphasic and incompressible/nearly incompressible single phase model of the brain parenchyma. As a result, there was no major advantage gained by using a biphasic model for the brain parenchyma. We propose that for modelling NPH, nearly incompressible single phase model of the brain parenchyma was adequate. Single phase treatment of the brain parenchyma simplified the mathematical description of the NPH model and resulted in significant reduction of computational time.
本研究采用计算方法研究正常压力脑积水（NPH）的生长机制。我们创建了一个健康人脑的通用三维脑网格，并将脑实质建模为单相和双相连续体。在我们的模型中，超弹性本构定律和有限变形理论描述了脑实质内的变形。我们将脑实质的剪切模量（μ）值设为155.77Pa。此外，在我们的模型中，接触边界定义限制了颅骨内的脑外表面。我们使用跨脑压差异来加载模型。在时域中使用完全非线性、隐式有限元程序来获得脑室和脑的变形。据我们所知，这是第一个研究NPH生长机制的三维、完全非线性模型。临床医生普遍认为，与NPH病情相关的跨脑压差异最多为1mmHg（133.416Pa）。我们的计算表明，对于脑实质的单相或双相模型，1mmHg（133.416Pa）的跨脑压差异不会产生NPH。产生NPH临床症状所需的最小跨脑压差异为1.764mmHg（235.44Pa）。这表明需要修正NPH生长纯粹基于机械基础的假设。我们还表明，在相等的跨脑压差异载荷下，脑实质双相模型与不可压缩/近不可压缩单相模型的计算脑室体积之间没有显著差异。因此，使用脑实质双相模型没有明显优势。我们建议，对于NPH建模，脑实质近不可压缩单相模型就足够了。脑实质的单相处理简化了NPH模型的数学描述，并显著减少了计算时间。
