Browsing by Author "Bass, Cameron R"
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Item Open Access Assessing the Injury Tolerance of the Human Spine(2017) Schmidt, Allison LindseyChronic and acute back injuries are widespread, affecting people in environments where they are exposed to vibration and repeated shock. These issues have been widely reported among personnel on aircraft and small watercraft; operators of heavy industrial or construction equipment may also experience morbidity associated with cyclic loading. To prevent these types of injuries, an improved understanding is needed of the spine’s tolerance to fatigue injury and of the factors that affect fatigue tolerance.
These types of vibration and shock exposures are addressed by international standards that propose limitations on the length and severity of the accelerations to which an individual is subjected. However, the current standard, ISO 2631-5:2004, provides an imprecise health hazard assessment. In this dissertation, a detailed technical critique is presented to examine the assumptions on which ISO 2631-5:2004 is based. An original analysis of existing data yields an age-based regression of the ultimate strength of lumbar spinal units and demonstrates sources of error in the strength regression in the standard. This dissertation also demonstrates that, contradicting earlier assumptions, the ultimate strength of the spine does not lie on a power-law S-N curve, and fatigue tolerance cannot be extrapolated from ultimate strength tests.
An alternative approach is presented for estimating the injury risk due to repeated loading. Drawing from existing data in the literature, a large dataset of in vitro fatigue tests of lumbar spinal segments was assembled. Using this fatigue data, a survival analysis approach was used to estimate the risk of failure based on several factors. Number of cycles, load amplitude, sex, and age all were significant predictors of bony failure in the spinal column. The parameter described by ISO 2631-5:2004 to quantify repeated loading exposure was modified, and an injury risk model was developed based on this modified parameter which relates risk of vertebral failure to repeated compressive loading. Notably, the effect of sex on fatigue tolerance persisted after normalizing by area, emphasizing the need for men and women to be addressed separately in the creation of injury risk predictions and occupational guidelines.
Posture has also been implicated in altering the injury mechanisms and tolerance to fatigue loading. However, few previous investigations in cyclic loading have addressed non-neutral postures. To assess the influence of dynamic flexion on the fatigue tolerance of the lumbar spine, a series of tests were conducted which combined a cyclic compressive force with a dynamic flexing motion. A study of 17 spinal segments from six young male cadavers was conducted, with tests ranging from 1000 to 500 000 cycles. Of the 17 specimens, 7 failed during testing. These failures were analyzed using a Cox Proportional Hazards model. As in compressive fatigue behavior, significant factors were the magnitude of the applied load and the age of the specimen. However, when the dynamically flexed specimens in these tests were compared to the specimens in the axial fatigue dataset, the flexion condition did not have a detectable effect on fatigue tolerance.
The Hybrid III dummy is a critical tool the assessment of such loading. Although the Hybrid III was originally designed for automotive frontal impact testing, these dummies have since been used to measure exposures and estimate injury risks of a wide variety of scenarios. These scenarios often involve using the dummy under non-standard temperatures or with little recovery interval between tests. Series of tests were conducted on the Hybrid III neck and lumbar components to assess the effects of rest duration intervals and a range of temperatures. Variations in rest duration intervals had little effect on the response of either component. However, both components were extremely sensitive to changes in temperature. For the 50th percentile male HIII neck, the stiffness fell by 18% between 25°C and 37.5°C; at 0°C, the stiffness more than doubled, increasing by 115%. Temperature variation had an even more pronounced effect on the HIII lumbar. Compared to room temperature, the lumbar stiffness at 37.5°C fell by 40%, and at 12.5°C, the stiffness more than doubled, increasing by 115%.
This dissertation has advanced the state of knowledge about the fatigue characteristics of the spine. An injury risk function has been developed that can serve as a tool for health hazard assessment in occupational standards. It has also contributed a fatigue dataset with dynamic flexion. This work will improve the scientific community’s ability to prevent repeated loading injuries. This dissertation has also demonstrated the immense sensitivity to temperature of the Hybrid III spinal components. This finding has major implications for the interpretation of previously published work using the Hybrid III, for the conduct of future research, and for future dummy design.
Item Open Access Blast-Induced Neurotrauma and the Cavitation Mechanism of Injury(2019) Yu, Allen WeiTraumatic brain injuries (TBIs) are a major public health concern and socioeconomic burden worldwide. In recent years, brain injuries in US service personnel have focused attention on TBI affecting the military population (Bass et al., 2012). Blast injuries have become the most common cause of mortality and morbidity in soldiers returning from Iraq and Afghanistan (Owens et al., 2008, Warden, 2006). The frequency of blast-related sequelae found in allied forces has led some to call it the ‘signature wound’ of the wars abroad.
The growing incidence of TBI has spurred an increase in research efforts within the neurotrauma community to define TBI etiology. Identification of the critical injury mechanisms underlying TBI is an area of greatest need. Our understanding of TBI etiology, physical damaging mechanisms, and pathophysiology remains inadequate. The ability to design specific countermeasures and targeted prevention strategies is restricted by an incomplete understanding of the underlying damaging mechanisms.
Cavitation, the formation of vapor filled cavities in a liquid medium, has been proposed as a damaging mechanism of TBI in both blunt impacts (Ward et al., 1948, Gross, 1958) and blast-induced neurotrauma (Moore et al., 2008, Panzer et al., 2012c). The cavitation hypothesis of TBI centers on observation that high energy events such as high-explosive blast impingement onto the head generate large pressure transients in and around the brain. Localized areas of low pressure may surpass the tensile limits of the cerebrospinal fluid vaporizing the fluid and forming cavitation bubbles. These voids grow, potentially displacing surrounding tissue. When the bubbles collapse, perhaps violently, jets of liquid with potentially large localized pressures and temperatures may be created, damaging surrounding tissue.
The main objective of this dissertation was to develop an experimental foundation and provide empirical evidence for cavitation as a damaging mechanism of blast-induced TBI. This dissertation uses biofidelic surrogate head models of blast and in vivo animal models of blast injury to address the unanswered questions surrounding cavitation and blast neurotrauma. Foremost, cavitation response was observed in the surrogate head form exposed to blast conditions associated with injury. The 50% risk of cavitation occurs at a blast level of 262 kPa incident overpressure and 1.96 ms duration. This blast dosage represents a 62% chance of mild intracranial bleeding from scaled ferret experiments (Rafaels et al., 2012). Cavitation onsert, growth, and collapse were confirmed through high-speed imaging of the fluid layers of the contrecoup, while strong acoustic emission signatures associated with cavity collapse were captured and time matched with the video. Near-harmonic frequencies at 64 kHz, 126 kHz, and 267 kHz were associated with the energetic collapse of the bubbles. Our results provide compelling evidence that primary blast alone may induce cavitation that leads to TBI.
Evidence of cavitation was recorded in live porcine specimen exposed to blast. Acoustic sensors mounted to the skull of each specimen recorded acoustic emissions during blast exposure. Scaled spectral analysis revealed acoustic energy in higher frequencies bands with peaks at 64 kHz, 139 kHz, and 251 kHz, closely matching the spectral peaks associated with void collapse in surrogate experiments. To our knowledge, this study is the first to present evidence of blast-induced cavitation in a live animal model in the field of cavitation TBI research.
The results presented in this dissertation also greatly improve our understanding of how mechanical loads are imparted onto the head during a blast exposure and how this loading leads to cavitation onset. Strain analysis of the surrogate head indicates wall compliance from skull deformation and shear wave propagation through the skull as significant physical factors driving the tensile fluid responses in the head. Future design considerations for preventative measures should account for these physical mechanisms.
This dissertation also makes important contributions to blast injury research by presenting a clinically relevant murine model of blast TBI. Murine blast lethality risk and functional behavior outcomes before and after blast injury are presented. We provide guidelines for small animal blast testing, along with methodological recommendations for benchtop shock tube design and specimen placement in relation to the shock tube.
The contributions of this dissertation further serve as an important methodological guide to the neurotrauma and biomechanics community studying blast-related TBI and cavitation as a damaging mechanism. The developed surrogate head system and cavitation detection techniques provide a research template and are a springboard to future research efforts elucidating the damaging effects of cavitation during TBI.
Item Open Access Cavitation in Blunt Traumatic Brain Injury(2021) Eckersley, ChristopherTraumatic Brain Injury (TBI) has become a marquee injury of this generation, prevalent in both military and civilian populations (Meaney 2014). Blunt impacts to the head are the known cause of approximately 1.7 million of TBI hospitalizations per year (Meaney 2014), and while mild TBI has the highest incidence (approximately 75% of TBIs) the injuries range from mild concussions to life threating severe bleeding within the brain (Meaney 2014).Due to wide spread prominence, blunt impact TBI has garnered a wealth of academic research interest focusing on the full spectrum of the biological scale, from subcellular and cellular response, to global human body modeling. The foundational theory of current blunt impact TBI research is neurological tissue damage by simple shear strain caused by motion of the skull (Cullen 2016, Alshareef 2020). While this likely contributes to tissue damage, its global perspective does not provide a satisfactory solution to the focal symptomology of TBI etiology. This is most likely because there are less appreciated mechanisms of injury contributing to TBI such as shear shock formation or cerebrospinal fluid (CSF) cavitation. The focus of this dissertation is to unpack the role of CSF cavitation in blunt impact TBI and contribute an important piece missing from the mechanistic understanding of TBI. This work develops an acoustic biomarker that indicates transient cavitation collapse, uses this biomarker to investigate cavitation mechanisms, observes cavitation in fresh, non-frozen, full body pig cadaver blunt impact testing, and provides clinical implications for transient cavitation through a reanalysis of live subhuman primate seminal data. It takes advantage of the large magnitude wideband acoustic emission of transient cavitation collapse, advanced acoustic sensor technology, and novel acoustic analysis methods to uncover a piece of the mechanistic mystery surrounding blunt impact TBI. There are five major conclusions reached in this dissertation. 1: The blunt impact head kinematics that induce cavitation are not significantly influenced by neck strength or cervical muscle activation. 2: Broadband acoustic emissions can be used as an acoustic biomarker to detect the incidence of transient cavitation collapse through the skull. 3: Compliance of the vessel containing a cavitating medium significantly influences the levels at which cavitation occurs during a blunt impact. 4: Blunt impact CSF cavitation occurs in a fresh, non-frozen, uncompromised pig cadaver head at impact levels below catastrophic injury thresholds. 5: Brain contusions are a potential clinical implication of transient cavitation collapse. Due to a lack of tools and technology, previous work on blunt impact cavitation was restricted to experimentation with limitations prohibiting the direct study of intracranial transient CSF cavitation. This innovative work provides direct observation of blunt impact CSF cavitation that benefits tools, injury risk functions, safety device design, and detection methodologies.
Item Open Access Characterization of Blast-Induced Activation of Human Immune Cells(2012) Garrett, Joel FrederickBlast related injuries have become a common occurrence among soldiers and civilians serving in Iraq and Afghanistan, and minor traumatic brain injuries associated with such incidents have increased correspondingly. Advances in protection and treatment have allowed many individuals to survive what would have previously been deadly blasts but there is a concern that there are additional negative side effects associated with such exposure. This study hypothesizes that human T leukocytes and promyelocytes respond to blasts by initiating cell death processes and releasing microparticles that could lead to further systemic inflammation. It was found that there was a significant (p<0.05) increase in lactase dehydrogenase activity and microparticle release in HL-60 cells blasted using a shock tube (with an incident blast overpressure of either 1000 or 1300 kPA and a duration of 2 ms) compared to control populations after 24 hours. There were no corresponding increases in Jurkat cells exposed to similar conditions.
Item Open Access Computational Modeling of the Lumbar Spine: Active Musculature and Intra-abdominal Pressure in Compressive Loading(2020) Cox, CourtneyA current area of interest in lumbar injury is vertical impact loading. This includes effects of underbody blast (UBB), high speed planing boat impacts, and helicopter crashes. Lumbar spine fractures occur in 18% of all wounded in action injuries and 26% of soldiers killed in action exposed to UBB. Further, the US military has moving towards including women in all combat roles, including as the Special Forces beginning in January 2016. Volunteer and cadaveric data exist which suggest that male and female injury risk is not the same for equal stresses or loads. Dynamic injury mechanisms and thresholds have been extensively studied in the cervical spine, but not for the lumbar spine. While many lumbar models are available, no previously developed model is appropriate for high-rate vertical impact loading with intra-abdominal pressure and active musculature. So, the primary objective of this dissertation was to create a biofidelic hybrid multibody/finite element model to compare male and female response and assess the importance of active musculature and intra-abdominal pressure during single accelerative loading impacts (3-15g).
A 50th percentile male model was created using data from literature, experimental data, and medical imaging data. Scaling relationships for the 50th and 85th percentile female were derived, and an 85th percentile female model developed. The 85th percentile female model is mass-matched to the 50th percentile male model. An 11% increase in ischium breadth in the 85th female changes the line of action for muscles inserting on the pelvis. These changes resulted in a female model having increased axial loads over a male model when matched for mass.
The 50th percentile male osteoligamentous model was validated against developed strain energy-force corridors and T12/L1 injury risk functions. A 50th percentile risk of spinal fracture of 5237 N was reported. During failure loading (as seen from experimental tests), the osteoligamentous spine model predicts a 41% risk of failure. While the model slightly underpredicts the risk of injury, the peak compressive load in T12/L1 lies within the 95th percentile confidence intervals for the 50th percentile risk of injury.
In this dissertation, it was hypothesized that men and women do not have the same risk of injury on an effective stress basis. This hypothesis was supported by comparing mass-matched male and female hybrid multibody/finite element models during an underbody blast loading condition. Based on the comparison between the 85th percentile female model to the 50th percentile male model predicts higher axial loads due to changes in musculature. It was also hypothesized that the use of active musculature decreases injury tolerance in compressive loading. This hypothesis was supported by comparing model intervertebral axial loads to both experimental (underbody blast) and epidemiological (electroconvulsive therapy) loading conditions. This research demonstrates higher muscle activations increase risk of lumbar spine injury in vertical impact loading. A tensed activation state contributes 48 percent of the compressive load estimated to fracture the lumbar spine during underbody blast. While this corresponds to a low risk of injury (<10%), this could exacerbate risk of injury during additional compressive loading.
By better understanding the female lumbar spine response, new safety measures can be developed. This work could inform the design of new protective personal equipment, or guide permissible exposure limits and risk of injury.
Item Open Access fars_cleaner: A Python package for downloading and pre-processing vehicle fatality data in the US(Journal of Open Source Software, 2022-11-07) Abrams, Mitchell Z; Bass, Cameron RItem Open Access Female vs. male relative fatality risk in fatal motor vehicle crashes in the US, 1975-2020.(PloS one, 2024-01) Abrams, Mitchell Z; Bass, Cameron RMotor vehicle accidents are the leading cause of death for young adults 18-29 years old worldwide, resulting in nearly 1 million years of life lost annually in the United States. Despite improvements in vehicle safety technologies, young women are at higher risk of dying in car crashes compared with men in matched scenarios. Vehicle crash testing primarily revolves around test dummies representative of the 50th percentile adult male, potentially resulting in these differences in fatality risk for female occupants compared to males. Vehicle occupants involved in fatal car crashes were matched using seating location, vehicle type, airbag deployment, seatbelt usage, and age. The relative risk for fatality (R) between males and females was calculated using a Double Pair Comparison. Young women (20s-40s) are at approximately 20% higher risk of dying in car crashes compared with men of the same age in matched scenarios. In passenger cars, 25-year-old female occupants in passenger car crashes from 1975-2020 exhibit R = 1.201 (95% CI 1.160-1.250) compared to 25-year-old males, and R-1.117 (95% CI 1.040-1.207) for passenger car crashes from 2010-2020. This trend persists across vehicle type, airbag deployment, seatbelt use, and number of vehicles involved in a crash. Known sex-based differences do not explain this large risk differential, suggesting a need for expanded test methodologies and research strategies to address as-yet unexplored sex differences in crash fatalities. These differences should be further investigated to ensure equitable crash protection.Item Embargo Head Injuries in Multiple Domains(2024) Abrams, Mitchell ZacharyHead and brain injuries are significant public health issues that affect individuals worldwide and encompass a wide range of injury types and severities. Traumatic head and brain injuries are common injuries observed in sports and motor vehicle crashes (MVC). Specifically, within MVCs they are a common cause of death and disability. Despite decades of dedicated research, the fundamental underlying causes of traumatic brain injuries remain poorly understood. Studying head injuries in vivo requires reliable instrumentation systems which can accurately measure head kinematics under potentially injurious conditions. Head kinematics obtained from reliable instrumentation can be used to study brain response in silico and can support the development of improved injury criteria and injury risk functions. Additionally, with enhanced instrumentation our ability to investigate differences in TBI across different populations (e.g. biological sex or age) would also be greatly enhanced.
Head injuries were studied across multiple domains in this study. First, relative risk of fatality and injury for female vehicle occupants were examined. Data from multiple automotive safety and public health datasets (National Highway Traffic Safety Administration (NHTSA) Fatality Analysis Reporting System (FARS); Centers for Disease Control (CDC) Multiple Cause of Death (MCOD)) were linked to examine head injuries and overall differences in fatality rates in motor vehicle crashes. Matched cases were examined to determine the relative risk (R) of fatality or injury using a double pair comparison method. Young females (20s-40s) are at approximately 20% higher risk of dying in car crashes compared with males of the same age in matched scenarios. For example, 25-year-old female occupants in passenger car crashes were at 20% higher risk of fatality (R = 1.201; 95% CI 1.160–1.250) compared to 25-year-old males. This trend persisted across vehicle type, airbag deployment, seatbelt use, and number of vehicles involved in a crash. Similar trends were noted for matched crashes where head injury was the cause of death: 20-25 year old female occupants were 30% more likely to suffer fatal head injuries than males of the same age (R = 1.29; 95% CI 1.17-1.42). This increased risk was pronounced for young females in both fatal crashes and non-fatal crashes with severe injuries.
Second, the biofidelity of in vivo wearable instrumentation systems used in the study of head kinematics was tested. Instrumented mouthguard systems (iMGs) are commonly used to study rigid body head kinematics across a variety of athletic environments. While iMGs rigidly fixed to anthropomorphic test device (ATD) headforms have demonstrated good correlation with reference systems in previous work, only one validation study focused on iMG performance in human cadaver heads. To assess iMG biofidelity, three unembalmed human cadaver heads were fitted with two instrumented boil-and-bite mouthguards (Prevent Biometrics and Diversified Technical Systems (DTS)) per manufacturer instructions, and were fitted with a properly-sized Riddell SpeedFlex American football helmet. Reference sensors were rigidly fixed to each specimen. Specimens were impacted with a rigid impactor at three velocities and locations.
The Prevent iMG performed comparably to the reference system up to approximately 60g in linear acceleration, but overall had poor correlation (CCC = 0.39). The DTS iMG consistently overestimated the reference across all measures, with linear acceleration error ranging from 10-66%, and angular acceleration errors greater than 300%. Overall, neither iMG demonstrated consistent agreement with the reference system. While iMG validation efforts have utilized ATD testing, this study highlighted the need for cadaver testing and proper validation of devices intended for use in vivo, particularly when considering realistic (non-idealized) sensor-skull coupling, when accounting for interactions with the mandible and when subject-specific anatomy may affect device performance.
Third, a population of Muay Thai martial arts athletes were instrumented with an in-ear wearable sensor system (DASHR) to better understand the epidemiology of head impact exposure during active sparring training. Martial arts athletes sustain many head impacts in a short period of time, and many martial arts forms focus competition victories on knock outs – the loss of consciousness or observable deficits in cognition and motor function due to repetitive impacts to the head. In this study, Muay Thai athletes were found to sustain 2.3 ± 1.8 head impacts per minute while sparring. Impact magnitudes were significantly higher during sessions when athletes wore headgear than during sessions that they did not, with linear accelerations 5.6g higher with headgear (Hodges-Lehman estimate of difference between medians; Mann-Whitney U-test p < 0.0001), angular velocities 1.6 rad/sec higher (p < 0.0001), and angular accelerations 710 rad/s^2 higher (p < 0.0001). While the use of headgear in martial arts has been shown to reduce accelerations during ATD drop testing, and to reduce the incidence of facial lacerations and contusions in competition settings, there is no consensus on the degree to which they protect against concussions and brain injuries. This study showed that during low magnitude impacts in a training setting, head kinematics are higher when headgear is worn than when it is not, potentially suggesting behavioral differences which offset any impact attenuation benefits the headgear offers. A large percentage of the impacts observed in this study (28%) fell below established recording thresholds used by most field-deployable wearables, suggesting a need for triggerless, continuous field recording systems.
Finally, the efficacy of existing injury metrics and risk functions were tested assessed using 731 non-injurious impacts recorded in the Muay Thai population. Head impacts were assessed with 14 injury metrics and 30 injury risk functions. Injury risks were summed across all impacts for each metric to determine the number of expected injury events. Risk functions developed from reconstructed impact events overpredicted injury rates more than risk functions developed from field data. For example, Head Injury Criterion risk functions developed from reconstructed American football events predicted 45-126 concussions, compared to 0 concussions predicted by risk functions developed from collegiate football field data. While cumulative impact exposure may be an important factor in individual risk tolerances, only one measure (RWE) was related to injury outcomes, and predicted concussions for seven of nine athletes in this study where no concussions were observed.
Overall, these studies highlight areas where injury biomechanics research has attempted to move forward without a reliable foundation to build upon. A lack of equitable cadaver testing has led to a gap in the biomechanical understanding of potentially fundamental underlying differences between males and females, reflected in sex differences in injury and fatality rates in motor vehicle crashes. Wearable head instrumentation systems which appear to perform well in controlled laboratory conditions are deployed without validation against biofidelic boundary conditions, significantly limiting their trustworthiness and usability. A large proportion of recorded head acceleration events using an in-ear sensing system fell below established trigger thresholds, suggesting a need for expanded data collection and continuous recording. The lack of cumulative exposure measures correlating to injury outcomes may, in part, be due to a lack of information in this low-level regime. Finally, established injury risk functions incorrectly classified many non-injurious head acceleration events, suggesting a need for new approaches to injury risk assessment using accurate in vivo kinematics as their basis.
Item Open Access Injury Detection and Localization in the Spine using Acoustic Emission(2016) Shridharani, Jay KetanThe National Spinal Cord Injury Statistical Center estimates there are 12,500 new cases of spinal cord injury (SCI) in the United States every year (www.nscisc.uab.edu, 2014) and vehicular crashes are the leading cause. Spinal injuries can have extensive long term consequences leading to widespread social and economic costs as well as the human cost of living with chronic, sometimes debilitating, pain (Côté et al. 1998, Côté et al. 2001, Daffner et al. 2003, Harrop et al. 2001, Sekhon et al. 2001). Within the military population, spinal injuries are a common result of repeated loading from high-speed planing watercraft (Bass et al. 2005, Gollwitzer et al. 1995, Schmidt et al. 2012), high performance aircraft (Coakwell et al. 2004, de Oliviera et al. 2005), and underbody blast exposure (Vasquez et al. 2011, Wilson 2006). Therefore, there is interest within the automotive, military, and clinical communities to understand the biomechanics the failure mechanics of the osteoligamentous structures in the spine.
Acoustic emissions have been shown to be produced during micro-cracking of cortical bone (Kohn 1995). However, there has been minimal work utilizing acoustic emission to detect cortical and trabecular bone damage. The research in this dissertation developed experimental and analytic methods of sensitively assessing when failure (both micro-cracks and more extensive failures) occurs in the cervical spine using acoustic emissions.
The acoustic emissions from cortical and trabecular bone failure were characterized using a Welch power spectrum density estimate and continuous wavelet transform. The power spectrum density results showed both cortical bone and trabecular bone failure produced wideband acoustic emission signals with spectral peaks between from 20 kHz to 1380 kHz and 24 kHz to 1382 kHz respectively. The continuous wavelet transform showed the spectral content begins with high frequency content followed quickly by low frequency content, but the low frequency lasts for a longer time causing it to dominate the response in the Welch power spectrum density. The first frequency component in the continuous wavelet transform was used to characterize the signals and was found to form three distinct bands in the cortical bone tests (166 ± 52.6 kHz, 379 ± 37.2 kHz, and 668 ± 63.4 kHz) and one band in the trabecular bone tests (185 ± 37.9 kHz). Therefore, observing spectral content within these bands suggests failure of the respective bone.
This dissertation also uses continuous wavelet transform to identify failure in whole cervical spine compression tests. Whole cervical spines placed in a pre-flexed and pre-extended posture were compressed to induce failure while being monitored for acoustic emissions. Cortical bone failure was identified in the acoustic emissions when local maxima in the continuous wavelet transform fell within the spectral bands associated with cortical bone failure previously identified. The timing of these failures was matched to the force-displacement response to identify the initiation of failure and the major failure. Cortical bone failure was detected at 70-90% of the failure load suggesting that the failure occurs as an evolution from micro-cracks to the eventual major failure. Locating these micro-cracks before the major failure forms may be useful in the prediction of the location of failure.
This dissertation also presents a technique to calculate the AE source location for AEs generated from fracture. The primary obstacle for AE source localization in the spine is that the speed of sound is different in cortical bone (Prevrhal et al. 2001), trabecular bone (Cardoso et al. 2003), intervertebral disc (Pluijm et al. 2004), ligaments (Kijima et al. 2009), and also differs based on its direction of travel in cortical bone (Kann et al. 1993) and likely in the other materials. Any algorithm must account for these differences to obtain any useful level of accuracy. The algorithm presented in this dissertation is based on hyperbolic source location algorithms (De Ronde et al. 2007, O'Toole et al. 2012, Salinas et al. 2010) except that it iterates on the speed of sound over a specified range, and convergence is defined as when the solution change is minimized. This procedure calculated the AE source location with a mean error of 5.7 mm and a standard deviation of 3.8 mm.
The contributions and conclusions of this dissertation provide methodology and results to evaluate the failure mechanics in the spine. Although these procedures were developed for use in the spine, they are of great value to the biomechanics community because they are applicable to every body region. The recommendations presented will serve to better understand the failure mechanics of the human body and will likely lead to better defined and safer standards for protective equipment. It also provides data for the generation of finite element models that require failure criteria.
Item Embargo Injury Risks in Behind Armor Blunt Trauma(2024) Op 't Eynde, JoostBody armor protects law enforcement and military personnel from gunshot wounds to the thorax. However, even when a round is stopped, armor can deform into the thorax at high rate and produce injuries. To evaluate armor protection against this behind armor blunt trauma (BABT), an outdated standard developed in the 1970s is currently used. The applicability of the standard to modern design and its biofidelity are questionable. There is a need for biofidelic models and accurate injury criteria for BABT.
To support numerical modeling of high rate insults, material property characterizations are essential. Pure shear tests at high rate and high shear strain were performed on porcine dorsal skin, ventral skin, liver, and lung tissue post-mortem. Synthetic gelatin was subjected to the same shear tests, to evaluate its validity as a tissue surrogate. Instantaneous elastic shear properties of the tissues were determined, and their stress relaxation over short and long timescales. Dorsal skin tissue was found to have the highest shear stiffness, followed by ventral skin, liver, and lung. Synthetic 10-20% gelatin approximates the instantaneous elastic shear properties of porcine dorsal skin but does not show the same viscoelastic relaxation behavior. Synthetic 10% gelatin behaved similarly to 20% gelatin in stress relaxation, but with significantly reduced shear stiffness. Shear moduli of biological tissues increase with increased shear strain, suggesting a non-linear model is appropriate for computational purposes.
To recreate BABT in an experimental setting, a 3D-printed acrylic indenter was developed. This indenter replicates the backface deformation of the body armor into the chest, matching velocity and aerial density of hard body armor. The performance of the indenter was evaluated using the current clay testing standard (n = 52). The obtained deformations in clay match those from previous hard armor experiments. The limitations of using clay as a surrogate for behind armor blunt trauma are discussed in relation to the indenter performance: clay is inconsistent and produces and unpredictable elastic rebound obfuscating the final deformation measurement used in the standard. Equivalent exposures comparing indenter velocity to rifle round velocity are used to translate indenter impacts to in-field scenarios.
Indenter BABT impacts (n = 117) were performed on porcine (n = 16) and human (n = 18) cadavers to establish injury scaling from pig to human. Impactor dynamics were determined using an onboard accelerometer and high-speed video, and rib fractures were assessed using post-test micro-CT imaging and necropsy. Regional injury risk curves were developed for different impact locations on the human cadaver (n = 6) thorax and different injury severity levels, indicating the risk might not be uniform. The injury threshold for anterior ribcage injuries is lower than for the posterior ribcage. The kinetic energy of the impact was scaled according to body mass based on equal velocity scaling, widely used in injury biomechanics. Confidence intervals of injury risk curves substantially overlap for the human and swine cadavers, suggesting that this scaling is appropriate for transferring risk across these species. Residual energy differences of 20 to 30% for similar injury risk between the human and swine cadavers suggest an additional bone quality scaling is desirable since the swine cadavers are generally at an earlier developmental age than available human cadavers. The structural scaling relationships between the human and swine cadavers are valuable in interpreting injury results from live animal BABT tests.
In vivo swine (n = 18) were subjected to BABT impacts to the ribcage. Chest wall and lung injuries were assessed using necropsy and histology, and injury risk curves were developed for different severity injuries based on the kinetic energy of the impact. The resulting injury risks are compared to those obtained for human cadavers. Chest wall injury risk corresponds closely with lung injury risk severity. Injury risks for lateral ribcage impacts in the live swine are close to posterior ribcage impact injury risks in the human cadaver, but injury risks are lower than for frontal impacts in human cadavers. Acoustic emissions of rib fractures were non-invasively detected during BABT impact with the use of hydrophones. Obtained injury risks and fracture detection may guide future armor design and injury monitoring.
A novel modality of lung injury was observed in the live swine impacts. Advancement of the chest wall into the lung tissue at high velocity produces a local compressive shock that can damage alveolar walls and cause bleeding within the lung tissue. A theoretical basis for shock development, experimental shock pressure measurements, and characteristic injuries are presented.
Item Open Access Interspecies Scaling in Blast Neurotrauma(2015) Wood, Garrett WayneBetween October 2001 and May 2012 approximately 70% of U.S. military personnel killed in action and 75% wounded in action were the direct result of exposure to an explosion. As of 2008, it was estimated that close to 20% of all Operation Iraqi Freedom and Operation Enduring Freedom (OIF/OEF) veterans had sustained some form of traumatic brain injury (TBI). Further, blast exposure is also a civilian problem due to the increased usage of explosives in terrorist attacks. Blast injury research has historically focused on the pulmonary system and the other air-containing organs which have been shown through extensive experimentation to be susceptible to blast overpressure injury. A shift in injury pattern during recent conflicts is characterized by decreased incidence of pulmonary injuries with an increase in TBI thought to be associated with blast exposure. This increase in observation of blast TBI has resulted in a large research effort to understand mechanisms and thresholds. However, due to the relatively sudden shift, much of this research is being conducted without a proper understanding and consideration of blast mechanics and interspecies scaling effects.
This dissertation used experimental and computational finite element (FE) analysis to investigate some large questions surrounding blast TBI research. An experimental investigation was conducted to determine the effects of modern thoracic body armor usage on blast pressure exposure seen by the body. To improve FE modeling capabilities, brain tissue mechanics in common blast TBI animal model species were investigated experimentally and computationally to determine viscoelastic constitutive behavior and measure interspecies variation. Meta-analysis of blast pulmonary literature was conducted to update interspecies scaling and injury risk models. To derive interspecies scaling and injury risk models for blast neurotrauma endpoints a meta-analysis of existing experimental data was used.
This dissertation makes major contributions to the field of injury biomechanics and blast injury research. Research presented in this dissertation showed that modern thoracic body armor has the ability to lower the risk of pulmonary injury from blast exposure by attenuating and altering blast overpressure. The study shows that the use of soft body armor results in the pulmonary injury threshold being similar to that for neurotrauma. The use of hard body armor results in the threshold for pulmonary injury occurring at higher levels than that of neurotrauma. This finding is important, as it helps to explain the recent shift in injury types observed and highlights the importance of continued widespread usage of body armor not only for ballistic protection but for protection from blast as well.
This dissertation also shows the importance of interspecies scaling for investigation of blast neurotrauma. This work looks at existing in vivo animal model data to derive appropriate scaling across a wide range of brain size. Appropriate scaling for apnea occurrence and fatality for blast isolated to the head was found to be approximately equal to a characteristic length scaling of brain size, assuming similar brain geometry. By combining the interspecies scaling developed and existing tests data, injury risk models were derived for short duration blast exposures.
The contributions and conclusions of this dissertation serve to inform the injury biomechanics field and to improve future research efforts. The consideration by researchers of the recommendations presented in this dissertation for in vivo animal model testing will serve to maximize the value gained from experimentation and improve our understanding of blast injury mechanisms and thresholds. The injury risk models presented in this work help to improve our ability to prevent, diagnose, and treat blast neurotrauma.
Item Open Access Lumbar Spinal Injury Under Dynamic Compression(2022) Ortiz Paparoni, Maria AndreinaSpinal trauma is a major issue with considerable societal, economic and physical consequences. Lumbar spine injuries during dynamic compression have been highly prevalent in recent American military conflicts in part due to the increased use of improvised explosive devices. The susceptibility of the lumbar spine during these scenarios can reduce functional capacity of soldiers and result in disability and morbidity in the military population. Characterizing the spine response during dynamic compression scenarios is essential in understanding injury risk in military personnel from underbody blast. Further, translating the experimental response to real world applications is crucial in developing future vehicle designs and mitigation strategies to reduce the incidence of these injuries.To advance the understanding of lumbar spine injury tolerance an axial loading lumbar spine vertebral body fracture injury criterion (Lic) across a range of three postures was established from 75 tests performed on instrumented cadaveric lumbar spine specimens. The spines were predominantly exposed to dynamic axial compressive forces from an upward vertical thrust with 64 of the tests resulting in at least one vertebral body fracture and 11 in no vertebral body injury. A loglogistic parametric survival analysis determined that the tolerance of the lumbar spine was 5569 N, 4618 N, and 4493 N for the tested nominal, pre-flexed, and pre-extended postures respectively. The differences in tolerance across the tested posture suggests that the injury probability is not captured by axial data alone. Therefore, a combined loading injury criteria was developed to provide an improved assessment. The susceptibility of the lumbar spine during underbody blast loading scenarios could also be exacerbated by coupled moments that act with the rapid compressive force depending on the occupant’s seated posture. The influence of the bending moment on the injury tolerance of the lumbar spine was evaluated using a combined metric that considers both the axial force and bending moment of the loading event. This combined loading lumbar spine vertebral body fracture injury criterion (CLic) across a range of postures was established from 75 cadaveric lumbar spine tests. The proposed CLic utilizes a metric (κ), based on prismatic beam failure theory, resulting from the combination of the T12-L1 resultant sagittal force and the decorrelated bending moment with optimized critical values of Fr,crit = 5824N and My,crit = 1155Nm. The 50% risk of lumbar spine vertebral body fracture corresponded to a combined metric of 1, with the risk decreasing with the combined metric value. At 50% injury risk the Normalized Confidence Interval Size improved from 0.24 of a force-based injury reference curve to 0.17 for the combined loading metric. At this point the injury tolerance for the lumbar spine during UBB events to the axial force and a combined loading metric was investigated for a limited range of occupant’s seated postures. However, it is highly desirable to expand the criterion to consider postures and dynamically evolved positions for a wider range of compression and bending moments in the lumbar spine. Therefore, the established lumbar combined injury criterion (CLic) was expanded to a wider range of initial and dynamically evolved postures and account for a higher contribution of the bending moment to the loading scenario. An expanded combined loading injury criterion (ECLic) was developed by testing an additional 15 specimens for initial and dynamically evolving postures that further increased the extension or flexion of the lumbar spine. These were combined with the 75 previously tested specimens in the nominal posture range. The injury criterion established from 90 cadaveric tests, produced a resultant sagittal force and decorrelated bending moment critical values of Fr,crit = 6011N and My,crit = 904 Nm. Out of the 90 specimens tested 77 had at least one vertebral body fracture, with 13 specimens having minor injuries or no injuries. The 50% risk of lumbar spine vertebral body fracture was normalized to a combined metric of 1, with the risk decreasing with the combined metric value. Finally, translating cadaver injury risk to equivalent anthropometric test devices measurements is a vital step for effective injury mitigation efforts. The commonly used matched-pair approach to translate these data consistently overestimates dummy injury risk, which then exaggerates human injury tolerance. A novel translation method based on energy equivalency was proposed to avoid these errors by matching strain energy between cadaver and dummy. To translate a single metric, say force, to an ATD risk assessment (IARC), the force-energy responses for both cadaver and simulated dummy measurements were used to determine the transfer function from cadaver measurement to ATD measurements at iso-energy. Similarly, a generic a combined metric, similar to the combined loading injury criterion (CLic) developed, was used to illustrate the translation of a complex loading scenario by characterizing the energy response of both cadaver and ATD in the corresponding force/moment duplets that define the CLic.
Item Embargo Lumbar Spine Behavior and Injury Due to Cyclic Loading(2024) Morino, ConcettaLow back pain (LBP) is one of the most prevalent conditions worldwide, estimated to affect 50-80% of adults at some point in their lifetime. However, up to 90% of patients that suffer from LBP do not receive a specific diagnosis. The etiology of injury that leads to pain in most LBP cases is largely unknown, though there are some known risk factors. Those regularly exposed to repeated lumbar flexion and compression (i.e., helicopter pilots, high-speed boat operators, truck drivers) are more likely to sustain lumbar injury and to experience LBP. There is a critical need to understand low-level injuries contributing to LBP and how they develop. The primary objectives for this project were to determine lumbar spine properties, behavior, and injury risk to elucidate factors contributing to low-level, pain-inducing injuries.Water content within the intervertebral discs (IVDs) plays a crucial role in the mechanical function of the lumbar spine. Common experimental tissue storage practices involve freezing tissue prior to mechanical testing to avoid degradation. However, it has been theorized that this practice may alter the in vivo hydration state of the lumbar spine IVDs. Additionally, porcine lumbar spine is a common animal surrogate for lumbar spine investigations, yet the hydration content in the porcine discs has not been established throughout both the nucleus pulposus (NP) and annulus fibrosus (AF). Intact porcine spines (89 IVDs) were stored in three different conditions (fresh, frozen with a saline-soaked wrap, frozen without saline) to establish the effects of freezing on IVD water content. IVD tissue from the NP, and three progressive AF regions from inner to outer AF were measured for mass percentage of water. Mean hydration values were found to be 88.8 ± 1.7% in the NP, and 79.6 ± 3.8%, 71.9 ± 3.7%, and 62.3 ± 3.3% from inner to outer AF. Hydration in all four disc regions were significantly different from one another and there were no significant differences in storage condition as a main effect. No meaningful trends were observed for the interaction between storage condition and disc region, suggesting freezing porcine lumbar spine does not affect the hydration within the IVDs. The lumbar spine is viscoelastic, so its behavior under load is complex and nonlinear. Under a constant load, a viscoelastic material will exhibit both time-dependent (creep) and stress-dependent (elastic) behavior. There is a critical need to characterize this complex lumbar spine behavior prior to injury to understand how injuries develop. Porcine lumbar spinal units (n=15) were loaded in repeated flexion-compression to characterize the non-injurious primary creep behavior inherent to viscoelastic tissues. Using a quasilinear viscoelasticity (QLV) approach, a computational optimization model determined two creep time constants suitable for all fifteen tests (β1 = 24s, β2 = 580s), then determined the creep and elastic parameters optimal for each individual specimen. Each model had high model accuracy (average R2=0.997) to the experimental data. The overall behavior was found to be 50% non-transient, with the transient contributions to the overall behavior to be 30% due to the long creep time constant (β2) and 20% due to the short creep time constant (β1). Results suggest lumbar spine behavior is highly time-dependent prior to injury and the QLV approach, deemed suitable for individual spinal components in previous work, is also a suitable approach for the complete lumbar functional spinal unit loaded in combined flexion-compression. Studies suggest some LBP could originate from lumbar endplate damage. Cadaveric human (n=16) and porcine (n=20) lumbar functional spinal units were loaded in long durations of repeated flexion-compression to observe endplate failure. Both human and porcine specimens were used to establish interspecies differences in injury between human and a common lumbar animal surrogate. Five human and twelve porcine specimens experienced at least one endplate fracture. Accelerated life analyses were preformed to produce the 50% endplate fracture risk curves based on compressive stress and cycles for both human and pig. The 95% confidence intervals overlapped, suggesting the pig was a suitable model for endplate failure, however, porcine specimens demonstrated an increased tolerance for endplate fracture compared to human. For the same compressive stress, human specimens fractured at approximately 25% of the duration that porcine specimens experienced fracture at 50% risk. The human injury risk curve can be immediately used for injury mitigation efforts in those exposed to this combined loading. The human and porcine injury risk curves provide necessary interspecies scaling information for interpreting human lumbar injury risk using past and future porcine experimental results. Finally, there is a need to capture soft tissue changes in the lumbar spine prior to endplate failure. Preliminary post-test microCT images from specimens loaded in repeated flexion-compression without endplate damage revealed that there may be changes in the IVD tissue prior to endplate failure due to repeated loading. Because the outer AF in healthy IVDs is innervated and degenerated discs have increased nerve density sometimes propagating as far into the disc as the NP, tissue damage in the IVD may be inducing pain. A novel microCT imaging technique was created to resolve individual NP and AF components within porcine IVDs, with resolutions up to 43 voxels/mm. This high-resolution, non-destructive imaging technique was then used to capture how NP and AF components change and potentially fail prior to endplate failure. Porcine lumbar spinal units (n=9) were loaded in repeated flexion-compression at a peak compressive stress of 2.75 MPa for loading durations below the 50% endplate fracture threshold developed previously. For specimens that were loaded the longest (15 minutes, 45 minutes, 60 minutes), post-test images revealed a smaller NP, a less distinct NP-AF boundary, and separation between lamellae compared to pre-test imaging and the control specimen. Small tissue changes captured with the presented high-resolution, high-quality, and non-destructive microCT imaging technique could have substantial implications for understanding low-level injuries contributing to low back pain. The studies presented in the following dissertation determine critical lumbar spine properties and behaviors that precede injury while directly assessing injury risk and injury patterns in the lumbar spine after repeated flexion and compression. These results improve our understanding of lumbar injury initiation and development, with a substantial impact on future prediction modeling, live animal studies, soft tissue imaging, and injury mitigation efforts.
Item Open Access Molecular and Functional Changes of Dorsal Root Ganglion Neurons in a Rodent Model of Intervertebral Disc Degeneration(2017) Leimer, Elizabeth MarieLow back pain affects up to 85% of the population in their lifetime and is strongly associated with degeneration of the intervertebral disc (IVD). Surgical lumbar disc puncture (LDP) in rodents is a widely used model of IVD degeneration due to the development of morphologic changes and evidence of altered pain-related functional measures. LDP models of IVD degeneration also show molecular changes in the dorsal root ganglia (DRGs) at less than 9 weeks post-injury, including alterations to markers of nerve growth factor (NGF)-dependent neurons. Lumbar disc puncture-induced inflammation can lead to local release of NGF, which acts on NGF receptors (TrkA, p75NTR) on the central terminals of DRG neurons innervating the IVD to play a role in pain development. TRPV1 function can be potentiated through NGF binding to these receptors, a mechanism often assessed in vitro via capsaicin challenge. The goal of this dissertation was to develop and characterize a surgical model of painful IVD degeneration in the rat, including a behavioral phenotype as well as NGF-related molecular and functional DRG neuron changes.
In the first part of this dissertation, the L5-L6 IVD in rats was surgically punctured and the behavioral phenotype was characterized until post-operative week 20 to assess development of discogenic pain. Secondly, capsaicin challenge experiments were performed in vitro to examine the functional implications of an NGF-related mechanism in discogenic pain. Finally, IVD degeneration was confirmed and immunostaining for NGF receptors was done to further investigate the involvement of NGF-related molecular mechanisms in painful IVD degeneration.
Findings revealed a timeline of pain-related behavioral changes, with evidence of LDP-related behavioral and gait changes at 16-18 weeks post-surgery. Additionally, this model produced a phenotype of clinically relevant, bilateral behavioral changes, including decreased overall activity as well as decreased hind limb stride frequency. Finally, DRG neurons showed NGF-related molecular and functional differences 20 weeks post-surgery. Ipsilateral DRG neurons showed impaired functionality of TRPV1 receptors and impaired TRPV1 receptor insertion into the cell membrane, as well as increased p75NTR expression. Contralateral neurons showed impaired TRPV1 functionality only. Bilateral DRGs showed increased transcriptional activity of both TRPV1-positive and TRPV1-negative neurons.
The studies in this dissertation support involvement of an NGF-related mechanism in painful IVD degeneration and establish the importance of utilizing a clinically relevant and longer-term model of IVD degeneration to investigate the specific mechanisms of pain generation.
Item Open Access Numerical Simulation of Primary Blast Brain Injury(2012) Panzer, Matthew BrianExplosions are associated with more than 80% of the casualties in the Iraq and Afghanistan wars. Given the widespread use of thoracic protective armor, the most prevalent injury for combat personnel is blast-related traumatic brain injury (TBI). Almost 20% of veterans returning from duty had one or more clinically confirmed cases of TBI. In the decades of research prior to 2000, neurotrauma was under-recognized as a blast injury and the etiology and pathology of these injuries remains unclear.
This dissertation used the finite element (FE) method to address many of the biomechanics-based questions related to blast brain injuries. FE modeling is a powerful tool for studying the biomechanical response of a human or animal body to blast loading, particularly because of the many challenges related to experimental work in this field. In this dissertation, novel FE models of the human and ferret head were developed for blast and blunt impact simulation, and the ensuing response of the brain was investigated. The blast conditions simulated in this research were representative of peak overpressures and durations of real-world explosives. In general, intracranial pressures were dependent on the peak pressure of the impinging blast wave, but deviatoric responses in the brain were dependent on both peak pressure and duration. The biomechanical response of the ferret brain model was correlated with in vivo injury data from shock tube experiments. This accomplishment was the first of its kind in the blast neurotrauma field.
This dissertation made major contributions to the field of blast brain injury and to the understanding of blast neurotrauma. This research determined that blast brain injuries were brain size-dependent. For example, mouse-sized brains were predicted to have approximately 7 times larger brain tissue strains than the human-sized brains for the same blast exposure. This finding has important implications for in vivo injury model design, and a scaling model was developed to relate animal experimental models to humans via scaling blast duration by the fourth-root of the ratio of brain masses.
This research also determined that blast neurotrauma is correlated to deviatoric metrics of the brain tissue rather than dilatational metrics. In addition, strains in the blasted brain were an order-of-magnitude lower than expected to produce injury with traditional closed-head TBI, but an order-of-magnitude higher in strain rate. The 50th percentile peak principle strain metric of values of 0.6%, 1.8%, and 1.6% corresponded to the 50% risk of mild brain bleeding, moderate brain bleeding, and apnea respectively. These findings imply that the mechanical thresholds for brain tissue are strain-based for primary blast injury, and different from the thresholds associated with blunt impact or concussive brain injury because of strain rate effects.
The conclusions in this dissertation provide an important guide to the biomechanics community for studying neurotrauma using in vivo, in vitro, and in silico models. Additionally, the injury risk curves developed in this dissertation provide an injury risk metric for improving the effectiveness of personal protective equipment or evaluating neurotrauma from blast.
Item Open Access Shock Propagation in Mechanical Models of Traumatic Brain Injury(2020) Bigler, BrianTraumatic brain injury represents one of the largest health crises worldwide. In the United States alone, the Centers for Disease Control and Prevention (CDC) indicates 2.87 million traumatic brain injuries resulting in emergency room visits, hospitalization, or death were recorded in 2014. The World Health Organization (WHO) places traumatic brain injury as the leading cause of death and disability for children and young adults, and estimates it to be involved in approximately half of all trauma-related deaths. The brain is likely one of the most mechanically complex materials known and, even after decades of study, robust estimates of material properties remain elusive. In order to predict brain response, develop tolerance curves, and apply injury criteria, the use of macroscopic computational brain models has become ubiquitous in the biomechanics community. There is growing concern that these models may not be sufficiently accurate across the range of scenarios for which they are often employed, and recent research across several groups has sought to quantify the variability both within and across computational brain models.
This dissertation identified deficiencies in current brain models across geometry, material formulation, numerical scheme, and experimental validation. In order to provide a tractable path forward for the biomechanics community, several of these deficiencies are addressed. In particular, the presence and propagation of shear nonlinearity has been underappreciated within the literature, despite wide acknowledgement of the importance of shear response in the brain for predicting and modeling injury. Recently it was experimentally demonstrated that the brain is capable of developing and propagating shear shock waves within physiological distances and kinematic inputs. This dissertation developed an optical method for visualizing and quantifying the propagation of nonlinear shear waves in spacetime. This study demonstrated the coalescence of shear waves during loading, a necessary precursor to shock formation. Furthermore, this dissertation presents and derives a numerical method for Eulerian nonlinear elasticity based on the conservation element solution element method, including a corresponding Mach-insensitive scheme, and eliminates several common deficiencies of traditional finite element –based brain models including large deformation instability, excessive hourglass energy, and locking phenomenon. Additionally, this dissertation demonstrated deficiencies with several common techniques used to scale responses to and from generic finite element brain models. This study recommended the cautious use of moment of inertia scaling or, preferably, subject-specific models and kinematic inputs.
The contributions in this dissertation further call into question many of the assumptions present across the mechanical computational brain modeling community. The present work both informs and supports future research with the goal of developing biofidelic brain injury models. These contributions improve the recognition of deficiencies in these models and their use to both understand and mitigate traumatic brain injury throughout the population. The presented recommendations and avenues for future work will aid researchers in obtaining accurate and robust solutions for the continued study of injurious brain mechanics
Item Open Access Underwater Blast Injuries, and the Sinking of the Submarine HL Hunley(2016) Lance, RachelUnderwater blasts travel further and injury more easily than blasts in air. However, because of a relative lack of data and study dedicated to the subject, the tolerances of personnel in the water to blast exposures have historically been poorly quantified. This dissertation presents an analysis of underwater blast exposures that have resulted in injuries and fatalities. Previously known standards for risk were evaluated and determined to be insufficient. Historical medical reports of exposed divers in the water were then evaluated and reconstructed to form the first known curves to prescribe a quantitative risk of injury or fatality.
The mystery of the submarine HL Hunley is an historical underwater blast exposure that has puzzled generations of enthusiasts. The tools for evaluating blast transmission through the water were applied to this puzzle, and data were gathered to support a theory of why the famous submarine sank.