The Viscoelasticity of Normal and Hydrocephalic Brain Tissue

Abstract

Many studies have investigated the role of brain compliance and the pressure volume index (PVI) in the hydrocephalic process (Shulman and Marmarou 1971, Guinane 1974, Shapiro et al. 1985, Shapiro and Fried 1986). However, very little is known about the changes in the brain tissue characteristics which take place during hydrocephalus. These properties are of interest because, although the PVI has been shown to increase with hydrocephalus and does describe changes in brain compliance, it does not explain what occurs during the disease process to account for these changes. In hydrocephalus, the brain tissue can be severely deformed. Therefore, it is probable that the mechanical properties of the brain tissue are compromised and weakened. This may be a cause for the increased brain compliance associated with hydrocephalus and may facilitate ventricular enlargement. Knowledge of brain tissue properties is essential in the understanding of ICP dynamics and pathologies. Yet, despite their importance, few studies have been performed to look at these properties (Keonman 1966; Ommaya 1968; Fallenstein et al. 1969; Metz et al. 1970, Marmarou et al. 1980). This is because there are many problems associated with studying brain tissue due to its highly compliant nature. We have developed a system using a gas bearing electrodynamometer, GBE, which addresses many of these problems and allows the direct determination of the viscoelastic properties of brain tissue. In this study the viscoelastic properties of normal and hydrocephalic brain tissue were evaluated in vivo using the GBE.