Using Wavelet Analysis to Distinguish Cavitation Acoustic Emissions From Blunt Impact Noise.

Cavitation has been shown to have implications for head injury, but currently there is no solution for detecting the formation of cavitation through the skull during blunt impact. The goal of this communication is to confirm the wideband acoustic wavelet signature of cavitation collapse, and determine that this signature can be differentiated from the noise of a blunt impact. A controlled, laser induced cavitation study was conducted in an isolated water tank to confirm the wide band acoustic signature of cavitation collapse in the absence of a blunt impact. A clear acrylic surrogate head was impacted to induce blunt impact cavitation. The bubble formation was imaged using a high speed camera, and the collapse was synched up with the wavelet transform of the acoustic emission. Wideband acoustic response is seen in wavelet transform of positive laser induced cavitation tests, but absent in laser induced negative controls. Clear acrylic surrogate tests showed the wideband acoustic wavelet signature of collapse can be differentiated from acoustic noise generated by a blunt impact. Broadband acoustic signal can be used as a biomarker to detect the incidence of cavitation through the skull as it consists of frequencies that are low enough to potentially pass through the skull but high enough to differentiate from blunt impact noise. This lays the foundation for a vital tool to conduct CSF cavitation research in-vivo.

Long-term complications of glycogen storage disease type Ia in the canine model treated with gene replacement therapy.

BACKGROUND: Glycogen storage disease type Ia (GSD Ia) in dogs closely resembles human GSD Ia. Untreated patients with GSD Ia develop complications associated with glucose-6-phosphatase (G6Pase) deficiency. Survival of human patients on intensive nutritional management has improved; however, long-term complications persist including renal failure, nephrolithiasis, hepatocellular adenomas (HCA), and a high risk for hepatocellular carcinoma (HCC). Affected dogs fail to thrive with dietary therapy alone. Treatment with gene replacement therapy using adeno-associated viral vectors (AAV) expressing G6Pase has greatly prolonged life and prevented hypoglycemia in affected dogs. However, long-term complications have not been described to date. METHODS: Five GSD Ia-affected dogs treated with AAV-G6Pase were evaluated. Dogs were euthanized due to reaching humane endpoints related to liver and/or kidney involvement, at 4 to 8 years of life. Necropsies were performed and tissues were analyzed. RESULTS: Four dogs had liver tumors consistent with HCA and HCC. Three dogs developed renal failure, but all dogs exhibited progressive kidney disease histologically. Urolithiasis was detected in two dogs; uroliths were composed of calcium oxalate and calcium phosphate. One affected and one carrier dog had polycystic ovarian disease. Bone mineral density was not significantly affected. CONCLUSIONS: Here, we show that the canine GSD Ia model demonstrates similar long-term complications as GSD Ia patients in spite of gene replacement therapy. Further development of gene therapy is needed to develop a more effective treatment to prevent long-term complications of GSD Ia.

Male and Female Cervical Spine Biomechanics and Anatomy: Implication for Scaling Injury Criteria.

There is an increased need to develop female-specific injury criteria and anthropomorphic test devices (dummies) for military and automotive environments, especially as women take occupational roles traditionally reserved for men. Although some exhaustive reviews on the biomechanics and injuries of the human spine have appeared in clinical and bioengineering literatures, focus has been largely ignored on the difference between male and female cervical spine responses and characteristics. Current neck injury criteria for automotive dummies for assessing crashworthiness and occupant safety are obtained from animal and human cadaver experiments, computational modeling, and human volunteer studies. They are also used in the military. Since the average human female spines are smaller than average male spines, metrics specific to the female population may be derived using simple geometric scaling, based on the assumption that male and female spines are geometrically scalable. However, as described in this technical brief, studies have shown that the biomechanical responses between males and females do not obey strict geometric similitude. Anatomical differences in terms of the structural component geometry are also different between the two cervical spines. Postural, physiological, and motion responses under automotive scenarios are also different. This technical brief, focused on such nonuniform differences, underscores the need to conduct female spine-specific evaluations/experiments to derive injury criteria for this important group of the population.

Pulmonary ultrasound and pulse oximetry versus chest radiography and arterial blood gas analysis for the diagnosis of acute respiratory distress syndrome: a pilot study.

INTRODUCTION: In low-resource settings it is not always possible to acquire the information required to diagnose acute respiratory distress syndrome (ARDS). Ultrasound and pulse oximetry, however, may be available in these settings. This study was designed to test whether pulmonary ultrasound and pulse oximetry could be used in place of traditional radiographic and oxygenation evaluation for ARDS. METHODS: This study was a prospective, single-center study in the ICU of Harborview Medical Center, a referral hospital in Seattle, Washington, USA. Bedside pulmonary ultrasound was performed on ICU patients receiving invasive mechanical ventilation. Pulse oximetric oxygen saturation (SpO2), partial pressure of oxygen (PaO2), fraction of inspired oxygen (FiO2), provider diagnoses, and chest radiograph closest to time of ultrasound were recorded or interpreted. RESULTS: One hundred and twenty three ultrasound assessments were performed on 77 consecutively enrolled patients with respiratory failure. Oxygenation and radiographic criteria for ARDS were met in 35 assessments. Where SpO2 ≤ 97%, the Spearman rank correlation coefficient between SpO2/FiO2 and PaO2/FiO2 was 0.83, p < 0.0001. The sensitivity and specificity of the previously reported threshold of SpO2/FiO2 ≤ 315 for PaO2/FiO2 ≤ 300 was 83% (95% confidence interval (CI) 68-93), and 50% (95% CI 1-99), respectively. Sensitivity and specificity of SpO2/FiO2 ≤ 235 for PaO2/FiO2 ≤ 200 was 70% (95% CI 47-87), and 90% (95% CI 68-99), respectively. For pulmonary ultrasound assessments interpreted by the study physician, the sensitivity and specificity of ultrasound interstitial syndrome bilaterally and involving at least three lung fields were 80% (95% CI 63-92) and 62% (95% CI 49-74) for radiographic criteria for ARDS. Combining SpO2/FiO2 with ultrasound to determine oxygenation and radiographic criteria for ARDS, the sensitivity was 83% (95% CI 52-98) and specificity was 62% (95% CI 38-82). For moderate-severe ARDS criteria (PaO2/FiO2 ≤ 200), sensitivity was 64% (95% CI 31-89) and specificity was 86% (95% CI 65-97). Excluding repeat assessments and independent interpretation of ultrasound images did not significantly alter the sensitivity measures. CONCLUSIONS: Pulse oximetry and pulmonary ultrasound may be useful tools to screen for, or rule out, impaired oxygenation or lung abnormalities consistent with ARDS in under-resourced settings where arterial blood gas testing and chest radiography are not readily available.

The mechanics of traumatic brain injury: a review of what we know and what we need to know for reducing its societal burden.

Traumatic brain injury (TBI) is a significant public health problem, on pace to become the third leading cause of death worldwide by 2020. Moreover, emerging evidence linking repeated mild traumatic brain injury to long-term neurodegenerative disorders points out that TBI can be both an acute disorder and a chronic disease. We are at an important transition point in our understanding of TBI, as past work has generated significant advances in better protecting us against some forms of moderate and severe TBI. However, we still lack a clear understanding of how to study milder forms of injury, such as concussion, or new forms of TBI that can occur from primary blast loading. In this review, we highlight the major advances made in understanding the biomechanical basis of TBI. We point out opportunities to generate significant new advances in our understanding of TBI biomechanics, especially as it appears across the molecular, cellular, and whole organ scale.

Significant head accelerations can influence immediate neurological impairments in a murine model of blast-induced traumatic brain injury.

Although blast-induced traumatic brain injury (bTBI) is well recognized for its significance in the military population, the unique mechanisms of primary bTBI remain undefined. Animate models of primary bTBI are critical for determining these potentially unique mechanisms, but the biomechanical characteristics of many bTBI models are poorly understood. In this study, we examine some common shock tube configurations used to study blast-induced brain injury in the laboratory and define the optimal configuration to minimize the effect of torso overpressure and blast-induced head accelerations. Pressure transducers indicated that a customized animal holder successfully reduced peak torso overpressures to safe levels across all tested configurations. However, high speed video imaging acquired during the blast showed significant head accelerations occurred when animals were oriented perpendicular to the shock tube axis. These findings of complex head motions during blast are similar to previous reports [Goldstein et al., 2012, "Chronic Traumatic Encephalopathy in Blast-Exposed Military Veterans and a Blast Neurotrauma Mouse Model," Sci. Transl. Med., 4(134), 134ra160; Sundaramurthy et al., 2012, "Blast-Induced Biomechanical Loading of the Rat: An Experimental and Anatomically Accurate Computational Blast Injury Model," J. Neurotrauma, 29(13), pp. 2352-2364; Svetlov et al., 2010, "Morphologic and Biochemical Characterization of Brain Injury in a Model of Controlled Blast Overpressure Exposure," J. Trauma, 69(4), pp. 795-804]. Under the same blast input conditions, minimizing head acceleration led to a corresponding elimination of righting time deficits. However, we could still achieve righting time deficits under minimal acceleration conditions by significantly increasing the peak blast overpressure. Together, these data show the importance of characterizing the effect of blast overpressure on head kinematics, with the goal of producing models focused on understanding the effects of blast overpressure on the brain without the complicating factor of superimposed head accelerations.

Female vs. male relative fatality risk in fatal motor vehicle crashes in the US, 1975-2020.

Motor 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.

Hydration State Throughout Porcine Lumbar Intervertebral Discs: Comparing Fresh and Frozen-Thawed Specimens.

Water content in intervertebral discs (IVDs) is essential for physiological and mechanical function. Freezing post-mortem tissue prior to biomechanical testing is a common practice to prevent tissue degradation, but this process has been theorized to alter hydration within IVDs. The hydration state throughout porcine lumbar IVDs, a common lumbar surrogate, is unknown as are the effects of freezing on porcine IVD hydration. Nineteen porcine lumbar spines were stored in one of the three conditions: frozen (- 20 °C) wrapped in saline-soaked gauze, frozen (- 20 °C) without saline, or fresh. Water content was measured in four disc regions within each of 89 discs: nucleus pulposus (NP), inner (AF-A), intermediate (AF-B), and outer (AF-C) annulus fibrosus. A three-factor, repeated measure analysis of variance was conducted for storage condition, spinal level, and repeated measure disc region. No significant differences were observed in spinal level or storage condition as a main effect. Mean hydration was significantly different in each disc region with mass percentage of water found to be 88.8 ± 1.7% in NP, 79.6 ± 3.8% in AF-A, 71.9 ± 3.7% in AF-B, and 62.3 ± 3.3% in AF-C. No significant differences were shown in NP and AF-C regions between storage conditions. Two significant differences in storage condition were observed in AF-A and AF-B regions, but there is likely no biological difference in these populations. Water content throughout porcine lumbar IVD was determined and results suggest one freeze-thaw cycle at - 20 °C does not alter the overall hydration within the porcine lumbar IVD.

Translating Cadaveric Injury Risk to Dummy Injury Risk at Iso-energy.

Injury risk assessment based on cadaver data is essential for informing safety standards. The common 'matched-pair' method matches energy-based inputs to translate human response to anthropometric test devices (ATDs). However, this method can result in less conservative human injury risk curves due to intrinsic differences between human and ATDs. Generally, dummies are stiffer than cadavers, so force and displacement cannot be matched simultaneously. Differences in fracture tolerance further influence the dummy risk curve to be less conservative under matched-pair. For example, translating a human lumbar injury risk curve to a dummy of equivalent stiffness using matched-pair resulted in a dummy injury risk over 80% greater than the cadaver at 50% fracture risk. This inevitable increase arises because the dummy continues loading without fracture to attenuate energy beyond the 'matched' cadaver input selected. Human injury response should be translated using an iso-energy approach, as strain energy is well associated with failure in biological tissues. Until cadaver failure, dummy force is related to cadaver force at iso-energy. Beyond cadaver failure, dummy force is related to cadaver force through failure energy. This method does not require perfect cadaver/dummy biofidelity and ensures that energy beyond cadaver failure does not influence the injury risk function.

Primary Creep Characterization in Porcine Lumbar Spine Subject to Repeated Loading.

Low back pain (LBP) is a common medical condition worldwide, though the etiology of injuries causing most LBP is unknown. Flexion and repeated compression increase lumbar injury risk, yet the complex viscoelastic behavior of the lumbar spine has not been characterized under this loading scheme. Characterizing the non-injurious primary creep behavior in the lumbar spine is necessary for understanding the biomechanical response preceding injury. Fifteen porcine lumbar spinal units were loaded in repeated flexion-compression with peak compressive stresses ranging from 1.41 to 4.68 MPa. Applied loading simulated real loading exposures experienced by high-speed watercraft occupants. The strain response in the primary creep region was modeled for all tests using a generalized Kelvin-Voigt model. A quasilinear viscoelastic (QLV) approach was used to separate time-dependent (creep) and stress-dependent (elastic) responses. Optimizations between the models and experimental data determined creep time constants, creep coefficients, and elastic constants associated with this tissue under repeated flexion-compression loading. Average R2 for all fifteen models was 0.997. Creep time constants optimized across all fifteen models were 24 s and 580 s and contributed to 20 ± 3% and 30 ± 3% of the overall strain response, respectively. The non-transient behavior contributed to 50 ± 0% of the overall response. Elastic behavior for this porcine population had an average standard deviation of 24.5% strain across the applied stress range. The presented primary creep characterization provides the response precursor to injurious behavior in the lumbar spine. Results from this study can further inform lumbar injury prediction and kinematic models.

Shear shock wave injury in vivo: High frame-rate ultrasound observation and histological assessment.

Using high frame-rate ultrasound and ¡1µm sensitive motion tracking we previously showed that shear waves at the surface of ex vivo and in situ brains develop into shear shock waves deep inside the brain, with destructive local accelerations. However post-mortem tissue cannot develop injuries and has different viscoelastodynamic behavior from in vivo tissue. Here we present the ultrasonic measurement of the high-rate shear shock biomechanics in the in vivo porcine brain, and histological assessment of the resulting axonal pathology. A new biomechanical model of brain injury was developed consisting of a perforated mylar surface attached to the brain and vibrated using an electromechanical shaker. Using a custom sequence with 8 interleaved wide beam emissions, brain imaging and motion tracking were performed at 2900 images/s. Shear shock waves were observed for the first time in vivo wherein the shock acceleration was measured to be 2.6 times larger than the surface acceleration ( 95g vs. 36g). Histopathology showed axonal damage in the impacted side of the brain from the brain surface, accompanied by a local shock-front acceleration of >70g. This shows that axonal injury occurs deep in the brain even though the shear excitation was at the brain surface, and the acceleration measurements support the hypothesis that shear shock waves are responsible for deep traumatic brain injuries.

Cyclic Mechanism Affects Lumbar Spine Creep Response.

PURPOSE: This study aims to explore how cyclic loading influences creep response in the lumbar spine under combined flexion-compression loading. METHODS: Ten porcine functional spinal units (FSUs) were mechanically tested in cyclic or static combined flexion-compression loading. Creep response between loading regimes was compared using strain-time histories and linear regression. High-resolution computed tomography (µCT) visualized damage to FSUs. Statistical methods, ANCOVA and ANOVA, assessed differences in behavior between loading regimes. RESULTS: Cyclic and static loading regimes exhibited distinct creep response patterns and biphasic response. ANCOVA and ANOVA analyses revealed significant differences in slopes of creep behavior in both linear phases. Cyclic tests consistently showed endplate fractures in µCT imaging. CONCLUSION: The study reveals statistically significant differences in creep response between cyclic and static loading regimes in porcine lumbar spinal units under combined flexion-compression loading. The observed biphasic behavior suggests distinct phases of tissue response, indicating potential shifts in load transfer mechanisms. Endplate fractures in cyclic tests suggest increased injury risk compared to static loading. These findings underscore the importance of considering loading conditions in computational models and designing preventive measures for occupations involving repetitive spinal loading.

Matched-pair hybrid test paradigm for behind armor blunt trauma using an experimental animal model.

Background: The current behind armor blunt trauma (BABT) injury criterion uses a single penetration limit of 44 mm in Roma Plastilina clay and is not specific to thoracoabdominal regions. However, different regions in the human body have different injury tolerances. This manuscript presents a matched-pair hybrid test paradigm with different experimental models and candidate metrics to develop regional human injury criteria. Methods: Live and cadaver swine were used as matched pair experimental models. An impactor simulating backface deformation profiles produced by body armor from military-relevant ballistics was used to deliver BABT loading to liver and lung regions in cadaver and live swine. Impact loading was characterized using peak accelerations and energy. For live swine, physiological parameters were monitored for 6 hours, animals were euthanized, and a detailed necropsy was done to identify injuries to skeletal structures, organs and soft tissues. A similar process was used to identify injuries to the cadaver swine for targeted thoracoabdominal regions. Results: Two cadavers and one live swine were subjected to BABT impacts to the liver. One cadaver and one live swine were subjected to BABT impacts to the left lung. Injuries to both regions were similar at similar energies between the cadaver and live models. Conclusions: Swine is an established animal for thoracoabdominal impact studies in automotive standards, although at lower insult levels. Similarities in BABT responses between cadaver and live swine allow for extending testing protocols to human cadavers and for the development of scaling relationships between animal and human cadavers, acting as a hybrid protocol between species and live and cadaver models. Injury tolerances and injury risk curves from live animals can be converted to human tolerances via structural scaling using these outcomes. The present experimental paradigm can be used to develop region-based BABT injury criteria, which are not currently available.

Accuracy of Instrumented Mouthguards During Direct Jaw Impacts Seen in Boxing.

PURPOSE: Measuring head kinematics data is important to understand and develop methods and standards to mitigate head injuries in contact sports. Instrumented mouthguards (iMGs) have been developed to address coupling issues with previous sensors. Although validated with anthropomorphic test devices (ATDs), there is limited post-mortem human subjects (PMHS) data which provides more accurate soft tissue responses. This study evaluated two iMGs (Prevent Biometrics (PRE) and Diversified Technical Systems (DTS) in response to direct jaw impacts. METHODS: Three unembalmed male cadaver heads were properly fitted with two different boil-and-bite iMGs and impacted with hook (4 m/s) and uppercut (3 m/s) punches. A reference sensor (REF) was rigidly attached to the base of the skull, impact kinematics were transformed to the head center of gravity and linear and angular kinematic data were compared to the iMGs including Peak Linear Acceleration, Peak Angular Acceleration, Peak Angular Velocity, Head Injury Criterion (HIC), HIC duration, and Brain Injury Criterion. RESULTS: Compared to the REF sensor, the PRE iMG underpredicted most of the kinematic data with slopes of the validation regression line between 0.72 and 1.04 and the DTS overpredicted all the kinematic data with slopes of the regression line between 1.4 and 8.7. CONCLUSION: While the PRE iMG was closer to the REF sensor compared to the DTS iMG, the results did not support the previous findings reported with use of ATDs. Hence, our study highlights the benefits of using PMHS for validating the accuracy of iMGs since they closely mimic the human body compared to any ATD's mandible.

Biofidelity and Limitations of Instrumented Mouthguard Systems for Assessment of Rigid Body Head Kinematics.

Instrumented mouthguard systems (iMGs) are commonly used to study rigid body head kinematics across a variety of athletic environments. Previous work has found good fidelity for iMGs rigidly fixed to anthropomorphic test device (ATD) headforms when compared to reference systems, but few validation studies have focused on iMG performance in human cadaver heads. Here, we examine the performance of two boil-and-bite style iMGs in helmeted cadaver heads. Three unembalmed human cadaver heads were fitted with two instrumented boil-and-bite mouthguards [Prevent Biometrics and Diversified Technical Systems (DTS)] per manufacturer instructions. Reference sensors were rigidly fixed to each specimen. Specimens were fitted with a Riddell SpeedFlex American football helmet and impacted with a rigid impactor at three velocities and locations. All impact kinematics were compared at the head center of gravity. The Prevent iMG performed comparably to the reference system up to ~ 60 g in linear acceleration, but overall had poor correlation (CCC = 0.39). Prevent iMG angular velocity and BrIC generally well correlated with the reference, while underestimating HIC and overestimating HIC duration. The DTS iMG consistently overestimated the reference across all measures, with linear acceleration error ranging from 10 to 66%, and angular acceleration errors greater than 300%. Neither iMG demonstrated consistent agreement with the reference system. While iMG validation efforts have utilized ATD testing, this study highlights the need for cadaver testing and 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.

Human and Porcine Lumbar Endplate Injury Risk in Repeated Flexion-Compression.

Low back pain (LBP) affects 50-80% of adults at some point in their lifetime, yet the etiology of injury is not well understood. Those exposed to repeated flexion-compression are at a higher risk for LBP, such as helicopter pilots and motor vehicle operators. Animal injury models offer insight into in vivo injury mechanisms, but interspecies scaling is needed to relate animal results to human. Human (n = 16) and porcine (n = 20) lumbar functional spinal units (FSUs) were loaded in repeated flexion-compression (1 Hz) to determine endplate fracture risk over long loading exposures. Flexion oscillated from 0 to 6° and peak applied compressive stress ranged from 0.65 to 2.38 MPa for human and 0.64 to 4.68 MPa for porcine specimens. Five human and twelve porcine injuries were observed. The confidence intervals for human and porcine 50% injury risk curves in terms of stress and cycles overlapped, indicating similar failure behavior for this loading configuration. However, porcine specimens were more tolerant to the applied loading compared to human, demonstrated by a longer time-to-failure for the same applied stress. Optimization revealed that time-to-failure in human specimens was approximately 25% that of porcine specimens at a given applied stress within 0.65-2.38 MPa. This study determined human and porcine lumbar endplate fracture risks in long-duration repeated flexion-compression that can be directly used for future equipment and vehicle design, injury prediction models, and safety standards. The interspecies scale factor produced in this study can be used for previous and future porcine lumbar injury studies to scale results to relevant human injury.

Attenuation of blast pressure behind ballistic protective vests.

BACKGROUND: Clinical studies increasingly report brain injury and not pulmonary injury following blast exposures, despite the increased frequency of exposure to explosive devices. The goal of this study was to determine the effect of personal body armour use on the potential for primary blast injury and to determine the risk of brain and pulmonary injury following a blast and its impact on the clinical care of patients with a history of blast exposure. METHODS: A shock tube was used to generate blast overpressures on soft ballistic protective vests (NIJ Level-2) and hard protective vests (NIJ Level-4) while overpressure was recorded behind the vest. RESULTS: Both types of vest were found to significantly decrease pulmonary injury risk following a blast for a wide range of conditions. At the highest tested blast overpressure, the soft vest decreased the behind armour overpressure by a factor of 14.2, and the hard vest decreased behind armour overpressure by a factor of 56.8. Addition of body armour increased the 50th percentile pulmonary death tolerance of both vests to higher levels than the 50th percentile for brain injury. CONCLUSIONS: These results suggest that ballistic protective body armour vests, especially hard body armour plates, provide substantial chest protection in primary blasts and explain the increased frequency of head injuries, without the presence of pulmonary injuries, in protected subjects reporting a history of blast exposure. These results suggest increased clinical suspicion for mild to severe brain injury is warranted in persons wearing body armour exposed to a blast with or without pulmonary injury.

Facial Fracture Injury Criteria from Night Vision Goggle Impact.

INTRODUCTION: Military personnel extensively use night vision goggles (NVGs) in contemporary scenarios. Since NVGs may induce or increase injuries from falls or vehicular accidents, biomechanical risk assessments would aid design goal or mitigation strategy development.METHODS: This study assesses injury risks from NVG impact on cadaver heads using impactors modeled on the PVS-14 NVG. Impacts to the zygoma and maxilla were performed at 20° or 40° angles. Risks of facial fracture, neurotrauma, and neck injury were assessed. Acoustic sensors and accelerometers assessed time of fracture and provided input variables for injury risk functions. Injuries were assessed using the Abbreviated Injury Scale (AIS); injury severity was assessed using the Rhee and Donat scales. Risk functions were developed for the input variables using censored survival analyses.RESULTS: The effects of impact angle and bone geometry on injury characteristics were determined with loading area, axial force, energy attenuation, and stress at fracture. Probabilities of facial fracture were quantified through survival analysis and injury risk functions. These risk functions determined a 50% risk of facial bone fracture at 1148 N (axial force) at a 20° maxillary impact, 588 N at a 40° maxillary impact, and 677 N at a 20° zygomatic impact. A cumulative distribution function indicates 769 N corresponds to 50% risk of fracture overall.DISCUSSION: Results found smaller impact areas on the maxilla are correlated with higher angles of impact increasing risk of facial fracture, neck injuries are unlikely to occur before fracture or neurotrauma, and a potential trade-off mechanism between fracture and brain injury.Davis MB, Pang DY, Herring IP, Bass CR. Facial fracture injury criteria from night vision goggle impact. Aerosp Med Hum Perform. 2023; 94(11):827-834.

A Novel Paradigm to Develop Regional Thoracoabdominal Criteria for Behind Armor Blunt Trauma Based on Original Data.

INTRODUCTION: For behind armor blunt trauma (BABT), recent prominent BABT standards for chest plate define a maximum deformation distance of 44 mm in clay. It was developed for soft body armor applications with limited animal, gelatin, and clay tests. The legacy criterion does not account for differing regional thoracoabdominal tolerances to behind armor-induced injury. This study examines the rationale and approaches used in the legacy BABT clay criterion and presents a novel paradigm to develop thoracoabdominal regional injury risk curves. MATERIALS AND METHODS: A review of the original military and law enforcement studies using animals, surrogates, and body armor materials was conducted, and a reanalysis of data was performed. A multiparameter model analysis describes survival-lethality responses using impactor/projectile (mass, diameter, and impact velocity) and specimen (weight and tissue thickness) variables. Binary regression risk curves with ±95% confidence intervals (CIs) and peak deformations from simulant tests are presented. RESULTS: Injury risk curves from 74 goat thorax tests showed that peak deflections of 44.7 mm (±95% CI: 17.6 to 55.4 mm) and 49.9 mm (±95% CI: 24.7 to 60.4 mm) were associated with the 10% and 15% probability of lethal outcomes. 20% gelatin and Roma Plastilina #1 clay were stiffer than goat. The clay was stiffer than 20% gelatin. Penetration diameters showed greater variations (on a test-by-test basis, difference 36-53%) than penetration depths (0-12%) across a range of projectiles and velocities. CONCLUSIONS: While the original authors stressed limitations and the importance of additional tests for refining the 44 mm recommendation, they were not pursued. As live swine tests are effective in developing injury criteria and the responses of different areas of the thoracoabdominal regions are different because of anatomy, structure, and function, a new set of swine and human cadaver tests are necessary to develop scaling relationships. Live swine tests are needed to develop incapacitation/lethal injury risk functions; using scaling relationships, human injury criteria can be developed.

Acoustic emissions in vertebral cortical shell failure.

Understanding the initiation of bony failure is critical in assessing the progression of bone fracture and in developing injury criteria. Detection of acoustic emissions in bone can be used to identify fractures more sensitively and at an earlier inception time compared to traditional methods. However, high rate loading conditions, complex specimen-device interaction or geometry may cause other acoustic signals. Therefore, characterization of the isolated local acoustic emission response from cortical bone fracture is essential to distinguish its characteristics from other potential acoustic sources. This work develops a technique to use acoustic emission signals to determine when cortical bone failure occurs by characterization using both a Welch power spectral density estimate and a continuous wavelet transform. Isolated cortical shell specimens from thoracic vertebral bodies with attached acoustic sensors were subjected to quasistatic loading until failure. The resulting acoustic emissions had a wideband frequency response with peaks from 20 to 900 kHz, with the spectral peaks clustered in three bands of frequencies (166 ± 52.6 kHz, 379 ± 37.2 kHz, and 668 ± 63.4 kHz). Using these frequency bands, acoustic emissions can be used as a monitoring tool in biomechanical spine testing, distinguishing bone failure from structural response. This work presents a necessary set of techniques for effectively utilizing acoustic emissions to determine the onset of cortical bone fracture in biological material testing. Acoustic signatures can be developed for other cortical bone regions of interest using the presented methods.