Herbert R. Lissner: The Father of Impact Biomechanics.

Professor Herbert R. Lissner was a pioneer in impact biomechanics, having initiated research on the injury mechanisms, mechanical response, and human tolerance of the human brain to blunt impact 80 years ago-in 1939. This paper summarizes the contributions made by Professor Lissner in head injury as well as in the many areas of impact biomechanics in which he was involved. In 1977, the Bioengineering Division of ASME established the H. R. Lissner Award to recognize outstanding career achievements in the area of biomechanics. In 1987, this award was converted to a society-wide Medal, and to date it has been awarded to 44 exemplary researchers and educators. The lead author of this paper was Professor Lissner's first and only Ph.D. student, and he offers a unique insight into his research and contributions.

Concussion with primary impact to the chest and the potential role of neck tension.

OBJECTIVES: Most biomechanical research on brain injury focuses on direct blows to the head. There are a few older studies that indicate craniocervical stretch could be a factor in concussion by causing strain in the upper spinal cord and brainstem. The objectives of this study are to assess the biomechanical response and estimate the strain in the upper cervical spine and brainstem from primary impact to the chest in American football. METHODS: Impact testing was conducted to the chest of a stationary unhelmeted and helmeted anthropomorphic test device (ATD) as well as the laboratory reconstruction of two NFL game collisions resulting in concussion. A finite element (FE) study was also conducted to estimate the elongation of the cervical spine under tensile and flexion loading conditions. RESULTS: The helmeted ATD had a 40% (t=9.84, p<0.001) increase in neck tensile force and an 8% (t=7.267, p<0.001) increase in neck flexion angle when compared with an unhelmeted ATD. The case studies indicated that the neck tension in the injured players exceeded tolerable levels from volunteer studies. The neck tension was combined with flexion of the head relative to the torso. The FE analysis, combined with a spinal cord coupling ratio, estimated that the strain along the axis of the upper cervical spinal cord and brainstem was 10%-20% for the combined flexion and tension loading in the two cases presented. CONCLUSION: Strain in the upper spinal cord and brainstem from neck tension is a factor in concussion.

Neuronal Injury and Glial Changes Are Hallmarks of Open Field Blast Exposure in Swine Frontal Lobe.

With the rapid increase in the number of blast induced traumatic brain injuries and associated neuropsychological consequences in veterans returning from the operations in Iraq and Afghanistan, the need to better understand the neuropathological sequelae following exposure to an open field blast exposure is still critical. Although a large body of experimental studies have attempted to address these pathological changes using shock tube models of blast injury, studies directed at understanding changes in a gyrencephalic brain exposed to a true open field blast are limited and thus forms the focus of this study. Anesthetized, male Yucatan swine were subjected to forward facing medium blast overpressure (peak side on overpressure 224-332 kPa; n = 7) or high blast overpressure (peak side on overpressure 350-403 kPa; n = 5) by detonating 3.6 kg of composition-4 charge. Sham animals (n = 5) were subjected to all the conditions without blast exposure. After a 3-day survival period, the brain was harvested and sections from the frontal lobes were processed for histological assessment of neuronal injury and glial reactivity changes. Significant neuronal injury in the form of beta amyloid precursor protein immunoreactive zones in the gray and white matter was observed in the frontal lobe sections from both the blast exposure groups. A significant increase in the number of astrocytes and microglia was also observed in the blast exposed sections compared to sham sections. We postulate that the observed acute injury changes may progress to chronic periods after blast and may contribute to short and long-term neuronal degeneration and glial mediated inflammation.

Quantitative electroencephalography in a swine model of blast-induced brain injury.

OBJECTIVE: Electroencephalography (EEG) was used to examine brain activity abnormalities earlier after blast exposure using a swine model to develop a qEEG data analysis protocol. METHODS: Anaesthetized swine were exposed to 420-450 Kpa blast overpressure and survived for 3 days after blast. EEG recordings were performed at 15 minutes before the blast and 15 minutes, 30 minutes, 2 hours and 1, 2 and 3 days post-blast using surface recording electrodes and a Biopac 4-channel data acquisition system. Off-line quantitative EEG (qEEG) data analysis was performed to determine qEEG changes. RESULTS: Blast induced qEEG changes earlier after blast exposure, including a decrease of mean amplitude (MAMP), an increase of delta band power, a decrease of alpha band root mean square (RMS) and a decrease of 90% spectral edge frequency (SEF90). CONCLUSIONS: This study demonstrated that qEEG is sensitive for cerebral injury. The changes of qEEG earlier after the blast indicate the potential of utilization of multiple parameters of qEEG for diagnosis of blast-induced brain injury. Early detection of blast induced brain injury will allow early screening and assessment of brain abnormalities in soldiers to enable timely therapeutic intervention.

The Effects of Helmet Weight on Hybrid III Head and Neck Responses by Comparing Unhelmeted and Helmeted Impacts.

Most studies on football helmet performance focus on lowering head acceleration-related parameters to reduce concussions. This has resulted in an increase in helmet size and mass. The objective of this paper was to study the effect of helmet mass on head and upper neck responses. Two independent test series were conducted. In test series one, 90 pendulum impact tests were conducted with four different headform and helmet conditions: unhelmeted Hybrid III headform, Hybrid III headform with a football helmet shell, Hybrid III headform with helmet shell and facemask, and Hybrid III headform with the helmet and facemask with mass added to the shell (n = 90). The Hybrid III neck was used for all the conditions. For all the configurations combined, the shell only, shell and facemask, and weighted helmet conditions resulted in 36%, 43%, and 44% lower resultant head accelerations (p < 0.0001), respectively, when compared to the unhelmeted condition. Head delta-V reductions were 1.1%, 4.5%, and 4.4%, respectively. In contrast, the helmeted conditions resulted in 26%, 41%, and 49% higher resultant neck forces (p < 0.0001), respectively. The increased neck forces were dominated by neck tension. In test series two, testing was conducted with a pneumatic linear impactor (n = 178). Fourteen different helmet makes and models illustrate the same trend. The increased neck forces provide a possible explanation as to why there has not been a corresponding reduction in concussion rates despite improvements in helmets ability to reduce head accelerations.

Parametric analysis of the biomechanical response of head subjected to the primary blast loading--a data mining approach.

Traumatic brain injury due to primary blast loading has become a signature injury in recent military conflicts and terrorist activities. Extensive experimental and computational investigations have been conducted to study the interrelationships between intracranial pressure response and intrinsic or 'input' parameters such as the head geometry and loading conditions. However, these relationships are very complicated and are usually implicit and 'hidden' in a large amount of simulation/test data. In this study, a data mining method is proposed to explore such underlying information from the numerical simulation results. The heads of different species are described as a highly simplified two-part (skull and brain) finite element model with varying geometric parameters. The parameters considered include peak incident pressure, skull thickness, brain radius and snout length. Their interrelationship and coupling effect are discovered by developing a decision tree based on the large simulation data-set. The results show that the proposed data-driven method is superior to the conventional linear regression method and is comparable to the nonlinear regression method. Considering its capability of exploring implicit information and the relatively simple relationships between response and input variables, the data mining method is considered to be a good tool for an in-depth understanding of the mechanisms of blast-induced brain injury. As a general method, this approach can also be applied to other nonlinear complex biomechanical systems.

Development of a new biomechanical indicator for primary blast-induced brain injury.

Primary blast-induced traumatic brain injury (bTBI) has been observed at the boundary of brain tissue and cerebrospinal fluid (CSF). Such injury can hardly be explained by using the theory of compressive wave propagation, since both the solid and fuid materials have similar compressibility and thus the intracranial pressure (ICP) has a continuous distribution across the boundary. Since they have completely different shear properties, it is hypothesized the injury at the interface is caused by shear wave. In the present study, a preliminary combined numerical and theoretical analysis was conducted based on the theory of shear wave propagation/reflection. Simulation results show that higher lateral acceleration of brain tissue particles is concentrated in the boundary region. Based on this fnding, a new biomechanical vector, termed as strain gradient, was suggested for primary bTBI. The subsequent simple theoretical analysis reveals that this parameter is proportional to the value of lateral acceleration. At the boundary of lateral ventricles, high spatial strain gradient implies that the brain tissue in this area (where neuron cells may be contained) undergo significantly different strains and large velocity discontinuity, which may result in mechanical damage of the neuron cells.

Biomechanical sex differences of crewmembers during a simulated space capsule landing.

INTRODUCTION: The objective of this study was to observe the differences in the biodynamic responses of male and female crewmembers during a simulated Soyuz spacecraft (short-duration flights) impact landing. METHODS: There were 16 volunteers (8 men and 8 women) recruited to sit in a pseudo-supine position and be exposed to several impact acceleration pulses. The acceleration peaks ranged from 7.7 to 11.8 g with a duration of around 50 ms. Acceleration responses from the drop platform and seat, and at the volunteers' head, shoulder, chest, and ilium were measured. RESULTS: Results indicated that there were significant gender-based differences in the peak acceleration measured from volunteers' shoulders and iliums. The peak decelerations measured at the head and ilium were relatively higher than those measured at other levels on the seat. DISCUSSION: It was recommended that more attention be focused on the sex differences of biodynamic responses of crews in the study of new protective designs for space capsule and personal life support equipment.

Development of a 10-year-old full body geometric dataset for computational modeling.

The objective of this study was to create a computer-aided design (CAD) geometric dataset of a 10-year-old (10 YO) child. The study includes two phases of efforts. At Phase One, the 10 YO whole body CAD was developed from component computed tomography and magnetic resonance imaging scans of 12 pediatric subjects. Geometrical scaling methods were used to convert all component parts to the average size for a 10 YO child, based on available anthropometric data. Then the component surfaces were compiled and integrated into a complete body. The bony structures and flesh were adjusted as symmetrical to minimize the bias from a single subject while maintaining anthropometrical measurements. Internal organs including the liver, spleen, and kidney were further verified by literature data. At Phase Two, internal characteristics for the cervical spine disc, wrist, hand, pelvis, femur, and tibia were verified with data measured from additional 94 10 YO children. The CAD dataset developed through these processes was mostly within the corridor of one standard deviation (SD) of the mean. In conclusion, a geometric dataset for an average size 10 YO child was created. The dataset serves as a foundation to develop computational 10 YO whole body models for enhanced pediatric injury prevention.

A theoretical analysis of stress wave propagation in the head under primary blast loading.

Traumatic brain injury due to primary blast loading has become a signature injury in recent military conflicts. Efforts have been made to study the stress wave propagation in the head. However, the relationship of incident pressure, reflected pressure and intracranial pressure is still not clear, and the experimental findings reported in the literature are contradictory. In this article, an analytical model is developed to calculate the stress wave transfer through a multiple-layered structure which is used to mimic the head. The model predicts stress at the scalp-skull and skull-brain interfaces as the functions of reflected pressure, which is further dependent on incident pressure. A numerical model is used to corroborate the theoretical predictions. It is concluded that scalp has an amplification effect on intracranial pressure. If scalp is absent, there exists a critical incident pressure, defined as P cr at approximately 16 kPa. When peak incident pressure σ in is higher than 16 kPa, the pressure at the skull-brain interface is greater than σ in; otherwise, it is lower than σ in.

Dynamic changes of macaque cancellous bone following head-down bed rest.

INTRODUCTION: Skeletal unloading during a spaceflight could result in bone loss and osteopenia, ultimately leading to poor bone strength. The purpose of the present study was to investigate the influence of bone loss on the dynamic behavior of cancellous bone. METHODS: Microgravity-induced bone loss and osteopenia were simulated in a macaque head-down bed rest (HDBR) model, in which 20 macaques were laid on a bed tilted by -6 degrees from the horizontal. These macaques were randomly divided into control (Con) and head down bed rest (HDBR) groups. After 28 d, 5 macaques chosen at random from each group were tested for bone density and mechanical properties, and the obtained data was used to develop a density-based constitutive equation; the remaining animals were tested only for bone density in order to attain statistical power. A split Hopkinson bar was used to monitor the dynamic response of cancellous bone. Cancellous bone deformation under high strain rate conditions was recorded by high-speed videos. RESULTS: Compared with the Con group, the Young's modulus of cancellous bone from HDBR macaque lumbar vertebrae were decreased by 6.03%. Based on the static and dynamic experimental results, parameters in the Maxwell nonlinear viscoelasticity material model were estimated. DISCUSSION: This model of cancellous bone under high strain rate was useful to establish the medical tolerance and evolution criteria of impact-related trauma by finite element method calculations.

Constitutive modeling of pia-arachnoid complex.

The pia-arachnoid complex (PAC) covering the brain plays an important role in the mechanical response of the brain during impact or inertial loading. Recent studies have revealed the complicated material behavior of the PAC. In this study, the nonlinear viscoelastic, transversely isotropic material properties of the PAC were modeled as Mooney-Rivlin ground substance with collagen fibers strengthening within the meningeal plane through an exponential model. The material constants needed were determined using experimental data from in-plane tension, normal traction, and shear tests conducted on bovine specimens. Results from this study provide essential information to properly model the PAC membrane, an important component in the skull/brain interface, in a computational brain model. Such an improved representation of the skull/brain interface will enhance the accuracy of finite element models used in brain injury mechanism studies under various loading conditions.

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets.

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturer's fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.

Biomechanical responses of a pig head under blast loading: a computational simulation.

A series of computational studies were performed to investigate the biomechanical responses of the pig head under a specific shock tube environment. A finite element model of the head of a 50-kg Yorkshire pig was developed with sufficient details, based on the Lagrangian formulation, and a shock tube model was developed using the multimaterial arbitrary Lagrangian-Eulerian (MMALE) approach. These two models were integrated and a fluid/solid coupling algorithm was used to simulate the interaction of the shock wave with the pig's head. The finite element model-predicted incident and intracranial pressure traces were in reasonable agreement with those obtained experimentally. Using the verified numerical model of the shock tube and pig head, further investigations were carried out to study the spatial and temporal distributions of pressure, shear stress, and principal strain within the head. Pressure enhancement was found in the skull, which is believed to be caused by shock wave reflection at the interface of the materials with distinct wave impedances. Brain tissue has a shock attenuation effect and larger pressures were observed in the frontal and occipital regions, suggesting a greater possibility of coup and contrecoup contusion. Shear stresses in the brain and deflection in the skull remained at a low level. Higher principal strains were observed in the brain near the foramen magnum, suggesting that there is a greater chance of cellular or vascular injuries in the brainstem region.

Finite element aortic injury reconstruction of near side lateral impacts using real world crash data.

Traumatic rupture of the aorta (TRA) remains the second most common cause of death associated with motor vehicle crashes, only less prevalent than brain injury. On average, nearly 8000 people die annually in the United States due to blunt injury to the aorta. It is observed that over 80% of occupants who suffer an aortic injury die at the scene due to exsanguination into the chest cavity. In the current study, eight near side lateral impacts, in which TRA occurred, were reconstructed using a combination of real world crash data reported in the Crash Injury Research and Engineering Network (CIREN) database, finite element (FE) models of vehicles, and the Wayne State Human Body Model - II (WSHBM). For the eight CIREN cases reconstructed, the high strain regions in the aorta closely matched with the autopsy data provided. The peak average maximum principal strains in all of the eight CIREN cases were localized in the isthmus region of the aorta, distal to the left subclavian artery, and averaged at 22 ± 6.2% while the average maximum pressure in the aorta was found to be 117 ± 14.7 kPa.

Using a gel/plastic surrogate to study the biomechanical response of the head under air shock loading: a combined experimental and numerical investigation.

A combined experimental and numerical study was conducted to determine a method to elucidate the biomechanical response of a head surrogate physical model under air shock loading. In the physical experiments, a gel-filled egg-shaped skull/brain surrogate was exposed to blast overpressure in a shock tube environment, and static pressures within the shock tube and the surrogate were recorded throughout the event. A numerical model of the shock tube was developed using the Eulerian approach and validated against experimental data. An arbitrary Lagrangian-Eulerian (ALE) fluid-structure coupling algorithm was then utilized to simulate the interaction of the shock wave and the head surrogate. After model validation, a comprehensive series of parametric studies was carried out on the egg-shaped surrogate FE model to assess the effect of several key factors, such as the elastic modulus of the shell, bulk modulus of the core, head orientation, and internal sensor location, on pressure and strain responses. Results indicate that increasing the elastic modulus of the shell within the range simulated in this study led to considerable rise of the overpressures. Varying the bulk modulus of the core from 0.5 to 2.0 GPa, the overpressure had an increase of 7.2%. The curvature of the surface facing the shock wave significantly affected both the peak positive and negative pressures. Simulations of the head surrogate with the blunt end facing the advancing shock front had a higher pressure compared to the simulations with the pointed end facing the shock front. The influence of an opening (possibly mimicking anatomical apertures) on the peak pressures was evaluated using a surrogate head with a hole on the shell of the blunt end. It was revealed that the presence of the opening had little influence on the positive pressures but could affect the negative pressure evidently.