Yuko Nakahira

Analysis of traumatic brain injury due to primary head contact during vehicle-to-pedestrian impact

We developed a 50th-percentile American male pedestrian model including a detailed brain, and the mechanical responses and kinematic biofidelity predicted by this model were validated against the available cadaveric test data. Vehicle-to-pedestrian impact simulations were then performed to investigate a potential mechanism for traumatic brain injury resulting from a lateral blunt impact to the head. Due to inertia of the brain mass, it was found that the average traction force produced in the cervical spinal cord exceeded 50 N in the impact involving a sport utility vehicle and 25 N in the impact involving a sedan, when the striking vehicle was travelling at 40 km/h. This inertial loading may play a key role in a brainstem, or upper-cervical-cord, lesion occurring before head strike. Results of this study suggest that close attention should be paid to pedestrian kinematics during free flight even before the head makes primary contact with the striking vehicle.

Development and validation of a head/brain FE model and investigation of influential factor on the brain response during head impact

Higher brain dysfunction due to traumatic brain injury (TBI) caused by head rotational impact in traffic accidents is one of the most serious automotive safety problems. However, the injury mechanism still remains unclear. In this study, we developed two human head finite element (FE) models based on THUMS for further understanding of TBI mechanism. Parametric studies were performed to investigate the factors affecting brain tissue displacements and intracranial pressures during head impact by using these models. The mesh fineness, material properties of cerebrospinal fluid (CSF) and contact conditions between brain parenchyma and surrounding external organisation had little influence on validation accuracy against test data on brain responses of post mortem human subjects (PMHS). However, there were significant differences in the values of cumulative strain damage measure (CSDM) and the contours of strain distribution between these models. These findings have the potential for better understanding of TBI mechanism.

Effects of pre-impact body orientation on traumatic brain injury in a vehicle?pedestrian collision

A series of minivan-pedestrian collisions was simulated, and pre-impact body orientation was found to considerably affect the mechanical responses of injury predictors for traumatic brain injury (TBI). The maximum average traction force generated in the cervical spinal cord prior to head strike took its peak value when the pedestrian was subjected to purely lateral head rotation in a sideways collision and decreased by up to one-half in a symmetric manner as the pedestrian changed his direction toward or away from the vehicle. The intracranial strain concentration and the cumulative strain damage measure following the head strike increased by more than 60% as the initial pedestrian configuration changed from the backward to frontal collision. Since the outcome of injury predictors is closely associated with an initial body facing angle to the striking vehicle, regulatory impactor tests should consider the effects of pre-impact body orientation for accurately assessing real-world TBIs in the future.

Human Brain Modeling with Its Anatomical Structure and Realistic Material Properties for Brain Injury Prediction

Impairments of executive brain function after traumatic brain injury (TBI) due to head impacts in traffic accidents need to be obviated. Finite element (FE) analyses with a human brain model facilitate understanding of the TBI mechanisms. However, conventional brain FE models do not suitably describe the anatomical structure in the deep brain, which is a critical region for executive brain function, and the material properties of brain parenchyma. In this study, for better TBI prediction, a novel brain FE model with anatomical structure in the deep brain was developed. The developed model comprises a constitutive model of brain parenchyma considering anisotropy and strain rate dependency. Validation was performed against postmortem human subject test data associated with brain deformation during head impact. Brain injury analyses were performed using head acceleration curves obtained from reconstruction analysis of rear-end collision with a human whole-body FE model. The difference in structure was found to affect the regions of strain concentration, while the difference in material model contributed to the peak strain value. The injury prediction result by the proposed model was consistent with the characteristics in the neuroimaging data of TBI patients due to traffic accidents.

Development and validation of THUMS version 5 with 1D muscle models for active and passive automotive safety research

Accurately predicting the occupant kinematics is critical to better understand the injury mechanisms during an automotive crash event. The objectives of this study were to develop and validate a finite element (FE) model of the human body integrated with an active muscle model called Total HUman Model for Safety (THUMS) version 5, which has the body size of the 50th percentile American adult male (AM50). This model is characterized by being able to generate a force owing to muscle tone and to predict the occupant response during an automotive crash event. Deformable materials were assigned to all body parts of THUMS model in order to evaluate the injury probabilities. Each muscle was modeled as a Hill-type muscle model with 800 muscle-tendon compartments of 1D truss and seatbelt elements covering whole joints in the neck, thorax, lumbar region, and upper and lower extremities. THUMS was validated against 36 series of post-mortem human surrogate (PMHS) and volunteer tests on frontal, lateral, and rear impacts. The muscle architectural and kinetic properties for the hip, knee, shoulder, and elbow joints were validated in terms of the moment arms and maximum isometric joint torques over a wide range of joint angles. The muscular moment arms and maximum joint torques estimated from THUMS occupant model with 1D muscles agreed with the experimental data for a wide range of joint angles. Therefore, this model has the potential to predict the occupant kinematics and injury outcomes considering appropriate human body motions associated with various human body postures, such as sitting or standing.