[Compliance of brain--Part 2 Approach from the local elastic and viscous moduli (author's transl)]

Abstract

It is important to have information about physical property of the brain in order to elucidate both the physical changes of the morbid brain and the physical mechanism of the traumatic brain injury. Under the hypothesis that reaction of the active brain to the dynamic load can be compared to the Maxwell-Voigt three dimensional model, elastic property of the brain was obtained as the Young's modulus (E: 10(-2) Kgf/cm2) of which error was less than 10%, and viscous property of the brain as the Viscous modulus (eta: 10(-2) Kgf.sec/cm2). And it was confirmed that the reactive pressure of the brain to dynamic load came from the surface to about 15 mm depth of the brain. In this report, experiments were done on the alive normal brains, the edematous ones nd necrotic ones which were produced by the cold injury (dry ice-aceton) in dogs (9.0--16.0 Kg). In the normal brain, E = 3.24 +/- 0.25, eta = 1.10 +/- 0.37 and these moduli were also stable when the physical conditions of the brain were stable. Under the dehydration by 20% mannitol, E increased in its value (p less than 0.01). But under the hydration by 5% glucose, E did not change at all. In the edematous brain, E = 3.28 +/- 0.44, eta = 1.74 +/- 0.06 and E of the edematous brain was almost same as that of normal ones, but under the dehydration, E of the edematous brain decreased (p less than 0.10), on the other hand it increased in its value under the hydration (p less than 0.05). In the necrotic brain, E = 1.60 +/- 0.14, eta = 0.82 +/- 0.28. Both moduli were of lower values and moreover they did not change its values at all under dehydration and hydration. As Young's modulus is the elastic index of the brain, the converse (1/E) should be compliance of the brain, that is to say, buffer effect of the brain. As for the compliance, the necrotic brain has maximum buffer effect and the over-hydrated edematous brain and the dehydrated normal ones have minimum buffer effect. From analysing the changes of the viscous moduli, it became clear that the viscous moduli took quite different functions in alive brains and in fatal ones, and it was suspected that the alive brain might not be so simple in its viscoelastic property.