ZHANG YUELIN

Many patients are unable to recover completely their social function follow­ing head trauma caused by traffic accidents. Prediction on occur­rence of higher brain dys­function is important for those who will be able to return home after head trauma. In this study we tried to reproduce injury condition in cases with traumatic higher brain dysfunction caused by traffic accidents and discussed the relationship between the mecha­nical impact to brain and higher brain dysfunction. We reproduced 6 cases using combination of multi­body analysis and finite element (FE) head modeling. As a result, the strain on the frontal lobe caused by an injury condition was suggested to contribute to the onset of attention disturbance during the chronic phase of treatment. This method has the possibility to predict the onset and severity of traumatic higher brain dys­function.

In this study, a method for determining the viscoelastic material properties from displacement fields is proposed. Stress-strain relationship represented by the superposition integral is employed as the viscoelastic constitutive equation. Thus, the unknown properties are bulk and shear relaxation moduli. The virtual fields method based on the principle of virtual work is used as a method for the inverse analysis. The unknown material properties are determined by solving nonlinear simultaneous equations of the virtual work containing the constitutive equations. The validity of the proposed method is demonstrated by identifying the viscoelastic properties of a soft epoxy resin. Results show that the two independent viscoelastic material properties can be identified by proposed method.

Many accidents in which head trauma is caused by falling indoors have been reported. In this study, numerical simulation was used to quantitatively evaluate the protective effect of carpet against head trauma caused by fall accident. Four postures （faint, slip, trip, step down） of falling were assumed and simulated. The collision motion between the head and the floor was reproduced by using a whole body numerical model, then the obtained mechanical response of the head was input to a finite element human head model. The posture, translational and rotational velocity before the collision, translational and rotational acceleration of the heads during the collision were input. Injury risks of skull fracture, cerebral contusion, concussion are evaluated by using the calculated mechanical parameter. For each posture of falling, three types of floor structures （flooring, carpet and flooring, underfelt and carpet） were simulated. The results showed that in all injury risk, falling to the flooring was the highest and falling to the combination with underfelt and carpet was the lowest. By comparing the results of the various head injury risks, the use of carpets has the effect of reducing the risk of head injury and carpets with high cushioning properties have high protection performance.

Head trauma accidents caused by falling indoors have been reported. The purpose of this study is to evaluate quantitatively the protective effect of a headband against head impact caused by falls by using computer simulation. Firstly, four types of movements of falls resulting from faint, slip, trip and step down were simulated by using a whole body numerical model and four regions of bruises on the frontal, parietal, temporal, and occipital region were chosen as the impact condition of the head. Secondly, the posture, translational and rotational velocity just before the collision of the head were input to a finite element human head model to simulate the collision motion of the head against the floor. A headband model made from EVA （ ethylene-vinyl acetate） foam is constructed, and two kinds of floor （ tile and wooden flooring ） are assumed and modeled. For each scenario of falls, head collisions with and without headband were simulated and the risk of fracture, cerebral contusion and concussion was calculated from the obtained mechanical responses during head collision. As a result, the use of the headband generally reduced the risk of head injury in indoor fall accidents, even though there are differences in protection effect depending on the postures of falling and the type of floor.

Effects of relative positions of the random pattern and the imaging sensor for measurement error in digital image correlation method are investigated. In order to take account of the effect of the relative position of microlens array on the imaging sensor and the speckle image formed on the image plane, simulations of imaging processes are carried out. Errors of DIC measurement are evaluated using the simulated images having several displacements and initial gap between the center of the pixel and the speckle. As a result, relationships between the error and the displacements for each center gap show various profiles. The average profile of them shows a sinusoidal curve with a relatively low amplitude. Since various error profiles of each speckle in the random pattern are averaged in the subset area in DIC measurement of translation displacements, the error profile of the subset approaches the average sinusoidal curve.

<p> The aim of this study is to visualize Judo accident using the reconstruction analysis for the medical field, and propose an injury risk assessment system based on detailed statistical analysis of the past cases for calling medical field's attention. In the assessment system, the mechanical input caused by the accident is obtained from replication of the motion called as Waza in Judo based on game video by using whole body numerical simulation, then the obtained acceleration response of the head was input to a human head finite element model to evaluate the injury risk by using the calculated mechanical parameter inside the skull. In this study, the replicated motion based on the video was verified by comparing the movement loci of the player's head analyzed by a three-dimensional motion analysis system experimentally. In this paper, two concussion suspected accident cases were analyzed by using the purposed evaluation system, and the concussion was evaluated by seven mechanical parameters generated inside the skull caused by the collision. The injury risk evaluated by the parameters belonged to the dangerous range that may cause concussion. The brain injury risk can be successfully estimated by the reconstructed simulation of the game video and FE analysis.</p>

In order to predict how much the human ligamentum flavum (LF) will be deformed during insertion of an epidural needle, the elastic modulus of a porcine LF was determined with a tensile test. LF specimens collected from porcine spines in a slaughterhouse were prepared into a rectangular shape with connecting vertebral bones. Preconditioning was repeated 20 times up to 0.1 MPa before the porcine LF specimens were tested. Strain rate was set at 0.03 and 0.5 s^-1, in reference to previous studies. To calculate strain, we divided elongation length, measured with a laser distance sensor, by the initial length of each specimen. The stress-strain diagram exhibited a linear relation up to 30% strain. When tensile test stopped at 30% strain, force maintained a constant value without stress relaxation, which meant the specimen was exhibiting an elastic property only. Average Young's modulus was 0.13 ± 0.054 MPa (mean ± SD) for 0.03 s^-1, and 0.14 ± 0.055 MPa (mean ± SD) for 0.5 s^-1. Effect of strain rate was not statistically significant. Elastica-von-Gison stained image of the specimens revealed that they consisted of the LF and adipose, and that the average thickness of the porcine LF was thinner than that of specimens. Young's modulus of the porcine LF was estimated as 0.21 MPa in the thoracic and 0.19 MPa in the lumbar.

Diffuse axonal injury (DAI), a major component of traumatic brain injury, has been suggested to result from inertial forces applied on the head. DAI is a manifestation of microstructural cellular trauma and is accompanied by distinct morphological changes. Focal axonal swellings are the morphological hallmarks of DAI pathology and lead to the disconnection of neurons from target tissues resulting in neuronal death. Our goal is the understanding of the quantitative relation between strain acting on the axons and generation of axonal swellings. In present study, we developed an in vitro two dimensional stretch device that reproduced axonal swellings of in vivo DAI, and verified the input-output relation of the device. Then using this device, we exposed PC12 cells, which extend structurally axon-like cylindrical protrusions in culture, to 10% or 20% strains and measured the length of neurites and number of swellings in PC12 cells until 48 hours after the exposure to stretch by microscope observation. As a result, the length of neurites transiently shortened at 5 minutes and 1 hour after exposure to strain compared to those before exposure to strain. On the other hand, swellings were generated at 5minutes after exposure to strain and were the most in number at 1 hour after exposure to strain compared to swellings in normal neurites. Moreover, the number of swellings in neurites exposed to 20% strain was significantly larger than that exposed to 10% strain at 5 minutes after exposure to strain. These results suggest that production of axonal swellings correlate with strain magnitude acting on the axons.

Human umbilical veinendothelial cells (HUVECs) were exposed to an impact pressure of -100 kPa and changes in morphology of HUVECs and expression of vascular entodhelial (VE)-cadherin were examined in order to investigate effect of exposure to impact pressure on endothelial permeability. In the results, HUVECs exposed to impact pressure were absent locally. VE-cadherin in control were continuously expressed along peripheral region of cells. However, VE-cadherin in HUVECs exposed to impact pressure were sparsely expressed along peripheral region of cells and partly distributed in cells. These findings suggest that the exposure to impact pressure may change the expression and the distribution of VE-cadherin, influencing endothelial permeability.

When the human head is loaded by the rotational impact, a diffuse axonal injury (DAI) is caused in human brain. DAI is caused by the shear strain and shear strain rate that arises at the brain stem when the head does the rotation movement by the angular acceleration. However, the influences on the shear strain and shear strain rate by the change in parameters of the angular acceleration were not described. In this study, various accelerations that differs parameters were given to a human head finite element model, the influence on the shear strain and shear strain rate caused on the brain stem was considered. In this report, rise time of angular acceleration was focused on. As the result, the change in rise time did not influence the shear strain so much. But the change in the rise time greatly influenced the shear strain rate.

When a human receives a heavy impact on the head, a focal brain injury and/or a diffuse axonal injury (DAI) are caused. The focal brain injury is caused by partial strain of a brain and/or rapid pressure fluctuation inside the skull. DAI is widespread damage to the white matter of the brain and caused by the shear stress. A focal brain injury is usually associated with brain tissue damage visible to the naked eye. However, the pathological basis of DAI can be observed only under the limited condition, and the bases are very difficult to be found in morbid anatomy. DAI may be unnoticed when focal brain injury concurs. In this study, various impacts were given to a finite element human head model, the condition of causing the focal brain injury and DAI was evaluated using average acceleration and the duration of the head which obtained from the computer simulations, and the possibility of concurrence of both damages was verified. As a result of computer simulation which is based on judicial autopsy report, it was shown the possibility of concurrence of DAI and focal brain injury was high, even though the cause of death was judged as focal brain injury.

The mechanism of coup contusion and contrecoup contusion was studied by impact experiment and finite element analysis. The finite element analysis of the cerebral contusion was carried out by taking skull fracture into consideration to show the relationship of the force duration, pressure fluctuation inside the human head model and the coup contusion, contrecoup contusion. The threshold of the skull fracture was evaluated by using Japan Head Tolerance Curve as -10MPa. The result showed coup contusion would occur when impacted by light weight impactor with high velocity which yields short force duration, and contrecoup contusion would occur when impacted by heavy weight impactor with low velocity which yields long force duration. The result showed on 5 second or less of the force duration, coup contusion occurs dominantly, and contrecoup contusion occurs dominantly over 5 second.