Cerebral injury mechanism in translation configuration with and without impact find different origins in the literature. In order to better understand these mechanisms, a cerebral motion analysis through the "internal impedance" study of the brain is proposed.
For the test, a bovine brain is placed in a closed water-filled plastic box fixed on a metallic support. This support is connected to a spring and the sliding frictionless motion is carried out in the spring axis direction.
The impulse force is given to the support or to the box to simulate configurations with or without impact respectively. The inputt force, as well as the support, box and brain acceleration with time are recorded. A signal processing system gives the mechanical impedance.
For a rigid mass-spring system the theoretical impedance is z= iwm + k/iw. In our test when the brain box and support show displacements similar to those of a rigid mass then the three impedances recorded can be superimposed to the theoretical model.
The first test series included a translation impulse test without impact. The three impedance curves recorded are close to the theoretical curveup to 200 Hz. Above 200Hz the two external impedances, i.e. box and support, drop and can be super imposed to a new mass-spring system where the mass value is the precedent total mass less the brain mass. Above this critical frequency the internal impedance, i.e the brain, raises but this has no physical significance as there is only a little energy in the acceleration signal above 200 Hz.
A second test series dealt with the translation impulse with impact. In spite of a force impulse twenty times lower than the previous one due to the elasticity of the box, the internal impedance recorded is very close to those masured in the configuration without impact. This means that the brain moves like the box and the support and that it is stationary at higher frequency.
Mainly three conclusions can be drawn up at this stage of the study: