Modelling the Brain for Rotational Loading: Shear Effects and Other Complications.

This study considers modelling the brain due to rotation of the skull where, at lower frequencies, the shear property of the material is important. Investigations reported here cover the effect of elastic and viscoelastic (lossy) cerebral material, the effect of the Falx protruding into the brain, the gap around the Falx and the brain filled with non viscous fluid in addition to different models of the Falx with bending or membrane stiffness. Analytical benchmark formulations are also described for the simple 2D plane strain in a cylinder produced by a half-sine rotation on the outer periphery which allows numerical (Finite Element) models to be validated. The results show the importance of the material properties, duration of loading and amplitude of loading as well as the influence of the partition. The results are shown for predicted maximum Principal strains in the models, as this may well be indicative of whether damage of the brain tissue occurs.

[Crista ampullaris mechanics and possibilities of regulation of the semi-circular canal]. / Mécanique ampullaire et possibilités de régulation du canal semi-circulaire.

A software using a finite element method is used to study the deformation of a bidimensional model of the human cupular diaphragm and the distribution of angular shearing of the hairs of the sensory cells located on the crista ampularis. This study shows that the hairs on the top of the crista are more sensitive to the pressure difference across the cupula due to angular acceleration of the head and those located on the sides of the crista are sensitive to the variation of the inflation pressure of the ampulla. This spatial discrimination of sensibility of the hair cells to the two types of mechanical solicitations leads us to consider the SCC as regulated sensor.

Modal and temporal analysis of head mathematical models.

The basic hypotheses used during these investigations were based on the vibration analysis of the head, which demonstrated that the head is not a solid nondeformable body, but a complex structure including deformable elements. Laboratoire des Systemes Biomecanique (LSBM) has recently proposed three mathematical models: a lumped model, a finite element model of the head in its sagittal plane, and a three-dimensional finite element model. These models were validated by their modal behavior and enabled the lesion mechanisms to be distinguished as a function of the spectral characteristics of the shock. The objective of this study is to complete these modal results by temporal analysis of the models by calculating the evolution of the intracranian mechanical parameters under shock conditions. To describe the head's dynamic behavior in the temporal domain, constant energy shocks of variable duration were simulated to evaluate their influence on different quantities as the intracerebral stresses in terms of compression, tensile, and shearing stresses, the relative brain-skull displacement, and the skull deformation. The importance of modal behavior of the head is illustrated by analyzing its temporal response to variable duration impacts, thus exciting very different frequencies. For a triangular shock, the critical duration times are between 10 and 15 x 10(-3) s, which correspond to impacts that excite the first resonance frequency of the head. Taking modal behavior into consideration in developing the finite element model leads to a harmonization of the calculated intracerebral stresses, even for short duration shocks. So, when the head is considered as a complex structure made up of several deformable elements, risk limitation is conditioned by an impact energy reduction for frequencies close to the natural frequencies of the structure. In the time field, the objective will be to avoid a number of impact shapes and durations. Therefore, the aim will not be to dampen the impact at any cost, but to damper it in an "intelligent" manner. In the future, this will allow the reduction of an injury mechanism-related risk, without increasing the risk of an injury generated by another mechanism.

The effect of epinephrine on pulpal microcirculation.

The effect of epinephrine (Epi) on the microcirculation of the pulp and its neuropharmacological mechanism has been established, as well as the existence of alpha adrenergic receptors in the blood vessels of the pulp. In addition, our results showed that local injections of Epi at doses greater than 10(-8) M produced an extreme drop in intrapulpal pressure (IPP). This effect was not obtained when Epi was injected intravenously.

[Danger of iodine drugs in the pregnant woman]. / Dangers des médicaments iodés chez la femme enceinte.

The authors draw attention to the fact that the possible effects of drugs containing iodine are often neglected during pregnancy. As an example, they report the following observation : "A young woman with benign asthma, treated for 14 years Asthmasedine and Asthmaligne, gave birth, on the 36th week of pregnancy, to a child apparenty dead but who was able to be reanimated. The child showed two types of signs : respiratory distress due to higher neurological disorders and a multinodular, non-compressing goiter. These two complications were caused by a congenital hypothyroidism corroborated by laboratory tests and due to the prolonged absorption of iodinated drugs by the mother". In conclusion, in cases of women receiving during pregnancy high doses of drugs containing iodine (250 such drugs are recorded in the Vidal), it is desirable to control the effect on the fetus and to propose an intra-amniotic therapy with L-Thyroxine, thus allowing a cerebral development close to normal.