Computational Modeling of Causal Mechanisms of Blast Wave Induced Traumatic Brain Injury - A Potential Tool for Injury Prevention PDF Download

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Category :
Languages : en
Pages : 17

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The finite element simulation of blast wave formation, wave interactions with the head and subsequent response in the brain to blast exposure various conditions were carried out. Based on Bowen's curve, the maximum peak pressure transmitted to the scalp, skull and brain were about 3, 12 and 4 times respectively higher than the blast pressure received by the head. Increasing levels of overpressure produced higher intracranial pressure and strain. In contrast, increasing levels of impulse had adverse effects on the brain pressure. A person in a prone head-on position subjected to the ground explosion would sustain a greater damage in the brain as compared to one standing in a free blast condition. The effects of being adjacent to a reflecting wall were noticeable only on the region of the brain closer to the wall. The blast threats based on Bowen iso-damage curve of short duration regimen do not always produce the same level of compressive stress responses in the brain. These variations in tissue response predict potential multi-level damage outcomes rather than the same level estimated using the blast input-based tolerance curve of Bowen.

Author: Michelle Kyaw Nyein
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Category :
Languages : en
Pages : 113

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Blast-induced TBI has gained prominence in recent years due to the conflicts in Iraq and Afghanistan, yet little is known about the mechanical effects of blasts on the human head; no injury thresholds have been established for blast effects on the head, and even direct transmission of the shock wave to the intracranial cavity is disputed. Still less is known about how personal protective equipment such as the Advanced Combat Helmet (ACH) affect the brain's response to blasts. The goal of this thesis is to investigate the mechanical response of the human brain to blasts and to study the effect of the ACH on the blast response of the head. To that end, a biofidelic computational model of the human head consisting of 11 distinct structures was developed from high-resolution medical imaging data. The model, known as the DVBIC/MIT Full Head Model (FHM), was subjected to blasts with incident overpressures of 6 atm and 30 atm and to a 5 m/s lateral impact. Results from the simulations demonstrate that blasts can penetrate the intracranial cavity and generate intracranial pressures that exceed the pressures produced during impact; the results suggest that blasts can plausibly directly cause traumatic brain injury. Subsequent investigation of the effect of the ACH on the blast response of the head found that the ACH provided minimal mitigation of blast effects. Results from the simulations conducted with the FHM extended to include the ACH suggest that the ACH can slightly reduce peak pressure magnitudes and delay peak pressure arrival times, but the benefits are minimal because the ACH does not protect the main pathways of load transmission from the blast to brain tissue. A more effective blast mitigation strategy might involve altering the helmet design to more completely surround the head in order to protect it from direct exposure to blast waves.

Author: David Ira Shreiber
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ISBN:
Category :
Languages : en
Pages : 188

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Author: Michelle Kyaw Nyein
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ISBN:
Category :
Languages : en
Pages : 167

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Since the beginning of the military conflicts in Iraq and Afghanistan, there have been over 250,000 diagnoses of traumatic brain injury (TBI) in the U.S. military, with the majority of incidents caused by improvised explosive devices (IEDs). Despite the urgent need to understand blast-induced TBI in order to devise strategies for protection and treatment, much remains unknown about the mechanism of injury, the effects of personal protective equipment (PPE) such as helmets, and injury metrics and thresholds. In order to help address these gaps, this thesis has four objectives: 1) to present a comprehensive computational framework for investigating the mechanical response of the human head to blasts that includes blast-structure interaction codes, a detailed, three-dimensional model of a human head generated from high-resolution medical imaging data, and an experimentally-validated constitutive model for brain tissue; 2) to validate the framework against a broad range of experiments, including free-field blast tests involving physical human head surrogates and laboratory-scale shock tube tests involving animals and human cadavers; 3) to use the computational framework to investigate the effect of PPE on the propagation of stress waves within the brain following blast events and evaluate their blast protection performance; and 4) to develop interspecies scaling laws for the blast response of the brain that would allow translation of injury metrics from animals to humans.

Author: Sowmya N. Sundaresh
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Category :
Languages : en
Pages : 0

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Together, this illustrated the ability of these two enzymes to regulate the response to exposure of bTBI-induced pathogenic forms of tau. This study indicates the potential of targeting PP2A activity as a viable strategy for therapeutic intervention. In conclusion, this research expands our understanding of the complexity of brain tissue injury mechanics to inform computational models of TBI, illustrates the deleterious effect of pathogenic forms of tau induced by blast injury on cognitive function, and presents a potential target mechanism for the investigation of therapeutic strategies.

Author: Tyler Haladuick
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Category :
Languages : en
Pages :

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In Operations Enduring Freedom and Iraqi Freedom, explosions accounted for 81% of all injuries; this is a higher casualty percentage than in any previous wars. Blast wave overpressure has recently been associated with varying levels of traumatic brain injury in soldiers exposed to blast loading. Presently, the injury mechanism behind primary blast brain injury is not well understood due to the complex interactions between the blast wave and the human body. Despite these limitations in the understanding of head injury thresholds, head kinematics are often used to predict the overall potential for head injury. The purpose of this study was to investigate head kinematics, and predict injury from a range of simulated blast loads at varying standoff distances and differing heights of bursts. The validated Generator of body data multi-body human surrogate model allows for numerical kinematic data simulation in explicit finite element method fluid structure interaction blast modeling. Two finite element methods were investigated to simulate blast interaction with humans, an enhanced blast uncoupled method, and an Arbitrary Lagrangian Eularian fully coupled method. The enhanced blast method defines an air blast function through the application of a blast pressure wave, including ground reflections, based on the explosives relative location to a target; the pressures curves are based on the Convention Weapons databases. LBE model is efficient for parametric numerical studies of blast interaction where the target response is the only necessary result. The ALE model, unlike classical Lagrangian methods, has a fixed finite element mesh that allows material to flow through it; this enables simulation of large deformation problems such as blast in an air medium and its subsequent interaction with structures. The ALE model should be used when research into a specific blast scenario is of interest, since this method is more computationally expensive. The ALE method can evaluate a blast scenario in more detail including: explosive detonation, blast wave development and propagation, near-field fireball effects, blast wave reflection, as well as 3D blast wave interaction, reflection and refraction with a target. Both approaches were validated against experimental blast tests performed by Defense Research and Development Valcartier and ConWep databases for peak pressure, arrival time, impulse, and curve shape. The models were in good agreement with one another and follow the experimental data trend showing an exponential reduction in peak acceleration with increasing standoff distance until the Mach stem effect reached head height. The Mach stem phenomenon is a shock front formed by the merging of the incident and reflected shock waves; it increases the applied peak pressure and duration of a blast wave thus expanding the potential head injury zone surrounding a raised explosive. The enhanced blast model was in good agreement with experimental data in the near-field, and mid-field; however, overestimated the peak acceleration, and head injury criteria values in the far-field due to an over predicted pressure impulse force. The ALE model also over predicted the response based on the head injury criteria at an increased standoff distance due to smearing of the blast wave over several finite elements leading to an increased duration loading. According to the Abbreviated Injury Scale, the models predicted a maximal level 6 injury for all explosive sizes in the near-field, with a rapid acceleration of the head over approximately 1 ms. There is a drastic exponential reduction in the insult force and potential injury received with increasing standoff distance outside of the near-field region of an explosive charge.

Author: Mark D. Skopin
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Category : Blood-brain barrier
Languages : en
Pages : 164

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Animal models of traumatic brain injury (TBI) are utilized for the study of underlying mechanisms and for the development of potential therapeutics. Traditional TBI models apply concussive forces to the cranium or provide a direct injury to neuronal tissue to model penetrating head wounds. The observation of mild to moderate TBI symptoms in personnel exposed to blast waves has led to the hypothesis that the disruption of the blood-brain barrier (BBB) can cause the symptoms commonly associated with TBI. Using intracarotid injection of hyperosmotic fluid, we assessed the histological and behavioral consequences of a transient disruption of the BBB and compared the results to the classical controlled-cortical impact (CCI) model of penetrating head injuries in rats. Our results demonstrate that the disruption of the BBB causes similar deficits in spatial memory as measured by the Barnes maze compared to other classical TBI models. Furthermore, a computational model was developed to investigate how different types of neural injuries affect a biological network capable of neurogenesis. These findings suggest that a disruption of the BBB can contribute to the neuronal dysfunction associated with brain injury and novel treatments that prevent plasma extravasation during BBB disruption could have therapeutic benefits.

Author:
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ISBN:
Category :
Languages : en
Pages : 25

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The objective of this modeling and simulation study was to establish the role of stress wave interactions in the genesis of traumatic brain injury (TBI) from exposure to explosive blast. A high resolution (1 mm3 voxels), 5 material model of the human head was created by segmentation of color cryosections from the Visible Human Female dataset. Tissue material properties were assigned from literature values. The model was inserted into the shock physics wave code, CTH, and subjected to a simulated blast wave of 1.3 MPa (13 bars) peak pressure from anterior, posterior and lateral directions. Three dimensional plots of maximum pressure, volumetric tension, and deviatoric (shear) stress demonstrated significant differences related to the incident blast geometry. In particular, the calculations revealed focal brain regions of elevated pressure and deviatoric (shear) stress within the first 2 milliseconds of blast exposure. Calculated maximum levels of 15 KPa deviatoric, 3.3 MPa pressure, and 0.8 MPa volumetric tension were observed before the onset of significant head accelerations. Over a 2 msec time course, the head model moved only 1 mm in response to the blast loading. Doubling the blast strength changed the resulting intracranial stress magnitudes but not their distribution. We conclude that stress localization, due to early time wave interactions, may contribute to the development of multifocal axonal injury underlying TBI. We propose that a contribution to traumatic brain injury from blast exposure, and most likely blunt impact, can occur on a time scale shorter than previous model predictions and before the onset of linear or rotational accelerations traditionally associated with the development of TBI.

Author: Joseph Augustus Kerwin
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ISBN:
Category : Electronic dissertations
Languages : en
Pages : 193

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Traumatic brain injury (TBI) is an endemic problem in both civilian and military populations. In the United States, the incidence of civilian TBI is over a million cases annually, with some years (2014) reaching over 2.5 million TBI-related emergency department visits. In recent decades, a new category of TBI has emerged - primary blast loading or otherwise known as, blast-induced traumatic brain injuries (bTBI). bTBI has become the "signature wound'' of the Iraq (Operation Iraqi Freedom [OIF]) and Afghanistan (Operation Enduring Freedom [OEF]) conflicts as it has accounted for nearly 70% of all of the injuries to military service members. Until recently, bTBI has been almost entirely isolated to conflict regions. In August 2020, a catastrophic detonation accidentally occurred in Beirut, Lebanon that instantly affected over 300,000 people.The high prevalence of TBIs in both the civilian and military communities has led to a significant societal burden and is one of the leading public health problems we face today. The treatment and prevention of TBIs has become a major focus within the past decade for all of the United States military branches. The increased awareness of TBI/bTBI has brought about great understanding in both the medical and research fields of neurology; however, it has also shed light on just how little we previously understood about this injury. TBI is a multifaceted problem that encompasses multiple length scales, complex anatomical geometries, and nonlinear biological responses and has various time-scales depending on the severity of the injury. The objective of this research is to investigate the potential injury-causing mechanisms present during the biomechanical loading of TBI events. More specifically, it focuses on the parallels between TBI and bTBI. The bTBI community is actively debating several potential damage-causing primary mechanisms: direct cranial transmission, skull flexure, skull orifices, and thoracic surge. To this end, a brain-tissue phantom was created to investigate its response to different biomechanical loading scenarios. The phantom was fabricated into a three-dimensional extruded ellipsoid geometry made out of Polyacrylamide gelatin that incorporated gyri-sulci interaction. Additionally, the dominant length scales of the sulci, gyri, gray matter thickness, and overall brain dimensions were incorporated into the gelatin brain phantom. The phantom was assembled into a polylactic acid 3D-printed skull, surrounded with deionized water, and enclosed between two optical windows to create a human head surrogate.In this work, the response of the human-head surrogate was evaluated under two biomechanical loading conditions: blunt-force impacts and blast loading. A custom-built drop-tower apparatus was used for the blunt-force impacts and a state-of-the-art blast chamber was employed to characterize the human-head surrogate under blast conditions. These two experimental apparatuses aided in the investigation into the potential damage-causing mechanisms associated with TBI/bTBI. A noninvasive high-speed imaging system was used to capture the surrogate-head response from each biomechanical loading condition. Finally, digital image processing techniques were used to evaluate the kinematic motion of the entire surrogate head, but more importantly the direct response of the gelatin-brain phantom itself.

Author: Frank David Corwin
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ISBN:
Category :
Languages : en
Pages :

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Blast wave induced traumatic brain injury (bTBI) is a modality of injury that has come into prominence at the current time due to the large number of military and civilian personnel who have experienced the localized shock wave produced by explosive devices. The shock wave will travel concentrically outward from the explosive center, being absorbed and transmitted thru soft objects, such as tissue, and reflecting off stationary obstructions. Transmission and absorption in tissues can result in a number of physiological measureable injuries, the most common of which being what is frequently called "blast lung". Blast lung involves the spalling effect at air-tissue interfaces. Another documented effect involves the asynchronous motion of tissue, particularly in the cranium, as the shock wave passes by. This predominately manifests itself in what is believed to be diffuse axonal injury and initiation of secondary injury mechanism. This study is designed to explore the relationship between shock waves and bTBI. A blast device was constructed for generating a free field shock wave through the high pressure rupture of a polycarbonate membrane. Air pressure in a small chamber is increased to a value several orders of magnitude greater than ambient air pressure and is held in place with the polycarbonate member. At the rupture of this membrane a shock wave is created. Measurements of this blast event, carried out with a piezoelectric pressure transducer, have shown that this shock wave is reproducible for the different membrane materials tested and is symmetrical with respect to the central axis of the high pressure chamber and exit nozzle. Having characterized the shock wave properties in the blast field, a location was chosen at which maximum shock wave pressure could be applied to the cranium for inducing bTBI. Experiments involving blast wave exposure were performed on two separate groups of animals in an attempt at establishing injury. One group was placed at a fixed distance directly below the blast nozzle, thereby experiencing both the shock wave and the associated air blast from the residual air in the chamber, and one placed at a defined distance off-axis to avoid the air blast, yet receiving two sequential blast exposures. All animal studies were approved by the VCU Institutional Animal Care and Use Committee. The degree of injury was then assessed with the use of magnetic resonance imaging (MRI) and spectroscopy (MRS). Image Data was acquired on a 2.4 Tesla magnet for assessing changes in either the total percent water concentration or the apparent diffusion coefficients (ADC) of selected regions of interest in the brain of rats. Localized proton spectroscopic data was acquired from a voxel placed centrally in the brain. The baseline values of these parameters were established before the induction of bTBI. After the blast exposure, the animals were followed up with MRI and MRS at defined intervals over a period of one week. The first group of animals received blast exposure directly underneath the blast device nozzle and the MR data does suggest changes in some of the measureable parameters from baseline following blast exposure. This blast wave data though is confounded with additional and undesirable characteristics of the blast wave. The second group of animals that received a pure shock wave blast exposure revealed no remarkable changes in the MR data pre- to post- blast exposure. The percent water concentration, ADC and spectroscopic parameters were for statistical purposes identical before and after the blast. The resolution of this negative result will require reconsideration of the free field blast exposure concept.