Does normal pressure hydrocephalus have mechanistic causes?

Tonmoy Dutta Roy

    Research output: ThesisDoctoral Thesis

    211 Downloads (Pure)

    Abstract

    [Truncated abstract] This thesis studies the biomechanics of Normal Pressure Hydrocephalus (NPH) growth using fully non-linear Finite Element procedures. A generic 3-D brain mesh of a healthy human brain was created. The brain parenchyma was modelled as single phase and biphasic continuum. In the computational model, hyperelastic constitutive law and finite deformation theory described deformations within the brain parenchyma. A value of 155.77 Pa for the shear modulus (μ∞) of the brain parenchyma was used. Additionally, contact boundary definitions constrained the brain outer surface inside the skull. A transmantle pressure difference was used to load the model. Fully non-linear, implicit finite element procedures in the time domain were used to obtain the deformations of the ventricles and the brain. Clinicians generally accept that at most 1 mm of Hg transmantle pressure difference (133.416 Pa) is associated with the condition of NPH. The computations showed that transmantle pressure difference of 1 mm of Hg (133.416 Pa) did not produce NPH for either single phase or biphasic model of the brain parenchyma. A minimum transmantle pressure difference of 1.764 mm of Hg (235.44 Pa) 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. The computational results 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 advantage gained by using a biphasic model for the brain parenchyma. It is proposed that for modelling NPH, nearly incompressible single phase model of the brain parenchyma was adequate.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2011

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