抄録
We discuss the incidence of consciousness disturbance, by converting the centripetal theory proposed by Ommaya and Gennarelli (1974) into a circular mechanical model, and comparing it with the finite element model. The centripetal theory assumes that the consciousness disturbance becomes more severe as the sequential disruption of a nerve track caused by a given shear strain becomes deeper from the periphery of the brain to the diencephalon and to the mesencephalon. By assuming that the sagittal section of the brain is circular in the mechanical model, it is possible to that the angular acceleration of the brain is a cause of traumatic unconsciousness. However, a finite element brain model has been used to reproduce the shape of a brain more precisely, since the shape of a brain is not circular. The concentration of shear stress is analyzed, where both rotational and translational impacts are applied to the model. As a result, the stress concentration is found to occur on the rostral brain stem acting as the mesencephalon, as well as on the surface of the brain, where a rotational impact is applied. This does not agree with the mechanical model representing the stress gradient from the periphery of the brain to the core of the brain. It is thus clarified that the type of impact - whether it is rotational or translational - is not related to the stress concentration in the core of the brain, as the stress concentration occurs in both rotational and translational impacts, according to the results of the analysis performed with the finite element model. It is well known among those engaged in impact biomechanics and/or neurosurgery that the angular acceleration contributes to the consciousness disturbance caused by an impact loading, and such a disturbance occurs as a result of an extensive injury of the cerebrum. The results of analysis of the impact shear stress concentration by means of the finite element model have reproduced the conditions under which the brain stem region in the core of the brain was injured primarily by external forces of rotational and translational impacts. According to the medical information that brain stem reticular formation and the ascending projectional system play important roles in maintaining consciousness, it can be deduced that the disturbance of consciousness under a given impact loading is caused by the concentration of shear stress at the core of the brain consisting of the brain stem and the diencephalon, which is caused by the complex head structure.
