Understanding blast-induced neurotrauma: how far have we come?

The Purple Heart and suicide risk in Post-9/11 U.S. Army Combat Veterans with a traumatic brain injury: A mixed methods study

Active service members and Veterans with a combat-related traumatic brain injury (TBI) are four times more likely to attempt suicide than those without a TBI. TBIs are the signature injuries of the Post-9/11 conflicts and Combat Veterans (i.e., current and former service members who deployed in support of a combat mission) with these injuries are entitled to receive the Purple Heart medal. However, potentially tens of thousands of Combat Veterans did not receive, or were denied the Purple Heart during the first decade of the Global War on Terrorism because a TBI was not documented during the deployment. To our knowledge, this is the first study to explore the meaning of the Purple Heart and examine the impact of the Purple Heart on Army Combat Veterans with a combat-related TBI. Findings from this mixed methods study revealed that not receiving the Purple Heart is associated with increased suicide risk and lower quality of life after a brain injury. Additionally, thwarted belongingness, perceived burdensomeness, and perceived military institutional betrayal are associated with increased suicide risk in Army Combat Veterans with a TBI. This mixed methods study provides important insights into how Army culture is perceived and the power of the Purple Heart among this high-risk group of Combat Veterans.

Individualized high-resolution analysis to categorize diverse learning and memory deficits in tau rTg4510 mice exposed to low-intensity blast

Mild traumatic brain injury (mTBI) resulting from low-intensity blast (LIB) exposure in military and civilian individuals is linked to enduring behavioral and cognitive abnormalities. These injuries can serve as confounding risk factors for the development of neurodegenerative disorders, including Alzheimer's disease-related dementias (ADRD). Recent animal studies have demonstrated LIB-induced brain damage at the molecular and nanoscale levels. Nevertheless, the mechanisms linking these damages to cognitive abnormalities are unresolved. Challenges preventing the translation of preclinical studies into meaningful findings in "real-world clinics" encompass the heterogeneity observed between different species and strains, variable time durations of the tests, quantification of dosing effects and differing approaches to data analysis. Moreover, while behavioral tests in most pre-clinical studies are conducted at the group level, clinical tests are predominantly assessed on an individual basis. In this investigation, we advanced a high-resolution and sensitive method utilizing the CognitionWall test system and applying reversal learning data to the Boltzmann fitting curves. A flow chart was developed that enable categorizing individual mouse to different levels of learning deficits and patterns. In this study, rTg4510 mice, which represent a neuropathology model due to elevated levels of tau P301L, together with the non-carrier genotype were exposed to LIB. Results revealed distinct and intricate patterns of learning deficits and patterns within each group and in relation to blast exposure. With the current findings, it is possible to establish connections between mice with specific cognitive deficits to molecular changes. This approach can enhance the translational value of preclinical findings and also allow for future development of a precision clinical treatment plan for ameliorating neurologic damage of individuals with mTBI.

Critical assessment of the effectiveness of different dust control measures in a granite quarry

The exposure to respirable crystalline silica found in granite dust presents significant health hazards to quarry workers and nearby communities, including silicosis and various respiratory ailments. This study evaluates the efficacy of various pollution control measures implemented in granite quarries. It aimed to provide a comprehensive critical assessment of the effectiveness of various dust control measures, considering their mechanisms, impact on air quality, and implications for worker health and community welfare. The strategy involved compiling and systematically analysing existing research articles, literature, and industry reports. The investigation identified three primary categories of measures: engineering controls, water-based suppression methods, and technological solutions. The study highlighted the significance of environmental impact and sustainability factors in selecting measures. These factors include water and energy consumption, production of secondary pollutants, long-term ecological effects, regulatory compliance, and cost-effectiveness. Operators and policymakers should utilize integrated, context-specific, inventive, and interdisciplinary strategies to efficiently control particle emissions from granite quarrying.

Considerations for the assessment of blast exposure in service members and veterans

Introduction

Blast exposure is an increasingly present occupational hazard for military service members, particularly in modern warfare scenarios. The study of blast exposure in humans is limited by the lack of a consensus definition for blast exposure and considerable variability in measurement. Research has clearly demonstrated a robust and reliable effect of blast exposure on brain structure and function in the absence of other injury mechanisms. However, the exact mechanisms underlying these outcomes remain unclear. Despite clear contributions from preclinical studies, this knowledge has been slow to translate to clinical applications. The present manuscript empirically demonstrates the consequences of variability in measurement and definition across studies through a re-analysis of previously published data from the Chronic Effects of Neurotrauma Study 34.

Methods

Definitions of blast exposure used in prior work were examined including Blast TBI, Primary Blast TBI, Pressure Severity, Distance, and Frequency of Exposure. Outcomes included both symptom report and cognitive testing.

Results

Results demonstrate significant differences in outcomes based on the definition of blast exposure used. In some cases the same definition was strongly related to one type of outcome, but unrelated to another.

Discussion

The implications of these results for the study of blast exposure are discussed and potential actions to address the major limitations in the field are recommended. These include the development of a consensus definition of blast exposure, further refinement of the assessment of blast exposure, continued work to identify relevant mechanisms leading to long-term negative outcomes in humans, and improved education efforts.

Effects of Low-Level Blast on Neurovascular Health and Cerebral Blood Flow: Current Findings and Future Opportunities in Neuroimaging

Low-level blast (LLB) exposure can lead to alterations in neurological health, cerebral vasculature, and cerebral blood flow (CBF). The development of cognitive issues and behavioral abnormalities after LLB, or subconcussive blast exposure, is insidious due to the lack of acute symptoms. One major hallmark of LLB exposure is the initiation of neurovascular damage followed by the development of neurovascular dysfunction. Preclinical studies of LLB exposure demonstrate impairment to cerebral vasculature and the blood-brain barrier (BBB) at both early and long-term stages following LLB. Neuroimaging techniques, such as arterial spin labeling (ASL) using magnetic resonance imaging (MRI), have been utilized in clinical investigations to understand brain perfusion and CBF changes in response to cumulative LLB exposure. In this review, we summarize neuroimaging techniques that can further our understanding of the underlying mechanisms of blast-related neurotrauma, specifically after LLB. Neuroimaging related to cerebrovascular function can contribute to improved diagnostic and therapeutic strategies for LLB. As these same imaging modalities can capture the effects of LLB exposure in animal models, neuroimaging can serve as a gap-bridging diagnostic tool that permits a more extensive exploration of potential relationships between blast-induced changes in CBF and neurovascular health. Future research directions are suggested, including investigating chronic LLB effects on cerebral perfusion, exploring mechanisms of dysautoregulation after LLB, and measuring cerebrovascular reactivity (CVR) in preclinical LLB models.

Quantifying acute changes in neurometabolism following blast-induced traumatic brain injury

Brain health is largely dependent on the metabolic regulation of amino acids. Brain injuries, diseases, and disorders can be detected through alterations in free amino acid (FAA) concentrations; and thus, mapping the changes has high diagnostic potential. Common methods focus on optimizing neurotransmitter quantification; however, recent focus has expanded to investigate the roles of molecular precursors in brain metabolism. An isocratic method using high performance liquid chromatography with electrochemical cell detection was developed to quantify a wide range of molecular precursors and neurotransmitters: alanine, arginine, aspartate, serine, taurine, threonine, tyrosine, glycine, glutamate, glutamine, and γ-Aminobutyric acid (GABA) following traumatic brain injury. First, baseline concentrations were determined in the serum, cerebrospinal fluid, hippocampus, cortex, and cerebellum of naïve male Sprague Dawley rats. A subsequent study was performed investigating acute changes in FAA concentrations following blast-induced traumatic brain injury (bTBI). Molecular precursor associated FAAs decreased in concentration at 4 h after injury in both the cortex and hippocampus while those serving as neurotransmitters remained unchanged. In particular, the influence of oxidative stress on the observed changes within alanine and arginine pathways following bTBI should be further investigated to elucidate the full therapeutic potential of these molecular precursors at acute time points.

Blast Overpressures as a Military and Occupational Health Concern

PURPOSE

This tutorial reviews effects of environmental stressors like blast overpressures and other well-known acoustic contaminants (continuous, intermittent, and impulsive noise) on hearing, tinnitus, vestibular, and balance-related functions. Based on the overall outcome of these effects, detailed consideration is given to the health and well-being of individuals.

METHOD

Because hearing loss and tinnitus are consequential in affecting quality of life, novel neuromodulation paradigms are reviewed for their positive abatement and treatment-related effects. Examples of clinical data, research strategies, and methodological approaches focus on repetitive transcranial magnetic stimulation (rTMS) and electrical stimulation of the vagus nerve paired with tones (VNSt) for their unique contributions to this area.

RESULTS

Acoustic toxicants transmitted through the atmosphere are noteworthy for their propensity to induce hearing loss and tinnitus. Mounting evidence also indicates that high-level rapid onset changes in atmospheric sound pressure can significantly impact vestibular and balance function. Indeed, the risk of falling secondary to loss of, or damage to, sensory receptor cells in otolith organs (utricle and saccule) is a primary reason for this concern. As part of the complexities involved in VNSt treatment strategies, vocal dysfunction may also manifest. In addition, evaluation of temporospatial gait parameters is worthy of consideration based on their ability to detect and monitor incipient neurological disease, cognitive decline, and mortality.

CONCLUSION

Highlighting these respective areas underscores the need to enhance information exchange among scientists, clinicians, and caregivers on the benefits and complications of these outcomes.

Double Blast Wave Primary Effect on Synaptic, Glymphatic, Myelin, Neuronal and Neurovascular Markers

Explosive blasts are associated with neurological consequences as a result of blast waves impact on the brain. Yet, the neuropathologic and molecular consequences due to blast waves vs. blunt-TBI are not fully understood. An explosive-driven blast-generating system was used to reproduce blast wave exposure and examine pathological and molecular changes generated by primary wave effects of blast exposure. We assessed if pre- and post-synaptic (synaptophysin, PSD-95, spinophilin, GAP-43), neuronal (NF-L), glymphatic (LYVE1, podoplanin), myelin (MBP), neurovascular (AQP4, S100β, PDGF) and genomic (DNA polymerase-β, RNA polymerase II) markers could be altered across different brain regions of double blast vs. sham animals. Twelve male rats exposed to two consecutive blasts were compared to 12 control/sham rats. Western blot, ELISA, and immunofluorescence analyses were performed across the frontal cortex, hippocampus, cerebellum, and brainstem. The results showed altered levels of AQP4, S100β, DNA-polymerase-β, PDGF, synaptophysin and PSD-95 in double blast vs. sham animals in most of the examined regions. These data indicate that blast-generated changes are preferentially associated with neurovascular, glymphatic, and DNA repair markers, especially in the brainstem. Moreover, these changes were not accompanied by behavioral changes and corroborate the hypothesis for which an asymptomatic altered status is caused by repeated blast exposures.

P188 Therapy in In Vitro Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is a significant cause of morbidity and mortality worldwide. Varied mechanisms of injury contribute to the heterogeneity of this patient population as demonstrated by the multiple published grading scales and diverse required criteria leading to diagnoses from mild to severe. TBI pathophysiology is classically separated into a primary injury that is characterized by local tissue destruction as a result of the initial blow, followed by a secondary phase of injury constituted by a score of incompletely understood cellular processes including reperfusion injury, disruption to the blood-brain barrier, excitotoxicity, and metabolic dysregulation. There are currently no effective pharmacological treatments in the wide-spread use for TBI, in large part due to challenges associated with the development of clinically representative in vitro and in vivo models. Poloxamer 188 (P188), a Food and Drug Administration-approved amphiphilic triblock copolymer embeds itself into the plasma membrane of damaged cells. P188 has been shown to have neuroprotective properties on various cell types. The objective of this review is to provide a summary of the current literature on in vitro models of TBI treated with P188.

Mathematical model of mechanobiology of acute and repeated synaptic injury and systemic biomarker kinetics

Background

Blast induced Traumatic Brain Injury (bTBI) has become a signature casualty of military operations. Recently, military medics observed neurocognitive deficits in servicemen exposed to repeated low level blast (LLB) waves during military heavy weapons training. In spite of significant clinical and preclinical TBI research, current understanding of injury mechanisms and short- and long-term outcomes is limited. Mathematical models of bTBI biomechanics and mechanobiology of sensitive neuro-structures such as synapses may help in better understanding of injury mechanisms and in the development of improved diagnostics and neuroprotective strategies.

Methods and results

In this work, we formulated a model of a single synaptic structure integrating the dynamics of the synaptic cell adhesion molecules (CAMs) with the deformation mechanics of the synaptic cleft. The model can resolve time scales ranging from milliseconds during the hyperacute phase of mechanical loading to minutes-hours acute/chronic phase of injury progression/repair. The model was used to simulate the synaptic injury responses caused by repeated blast loads.

Conclusion

Our simulations demonstrated the importance of the number of exposures compared to the duration of recovery period between repeated loads on the synaptic injury responses. The paper recognizes current limitations of the model and identifies potential improvements.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

Gas bubbles present in liquids underpin many natural phenomena and human-developed technologies that improve the quality of life. Since all living organisms are predominantly made of water, they may also contain bubbles—introduced both naturally and artificially—that can serve as biomechanical sensors operating in hard-to-reach places inside a living body and emitting signals that can be detected by common equipment used in ultrasound and photoacoustic imaging procedures. This kind of biosensor is the focus of the present article, where we critically review the emergent sensing technologies based on acoustically driven oscillations of bubbles in liquids and bodily fluids. This review is intended for a broad biosensing community and transdisciplinary researchers translating novel ideas from theory to experiment and then to practice. To this end, all discussions in this review are written in a language that is accessible to non-experts in specific fields of acoustics, fluid dynamics and acousto-optics.

Resilience of females to acute blood–brain barrier damage and anxiety behavior following mild blast traumatic brain injury

Low-level blast exposure can result in neurological impairment for military personnel. Currently, there is a lack of experimental data using sex as a biological variable in neurovascular outcomes following blast exposure. To model mild blast traumatic brain injury (mbTBI), male and female rats were exposed to a single 11 psi static peak overpressure blast wave using the McMillan blast device and cohorts were then euthanized at 6 h, 24 h, 7 d and 14 d post-blast followed by isolation of the amygdala. After mbTBI, animals experience immediate bradycardia, although no changes in oxygen saturation levels or weight loss are observed. Male mbTBI animals displayed significantly higher levels of anxiety-like behavior (open field and elevated plus maze) compared to male sham groups; however, there was no anxiety phenotype in female mbTBI animals. Blast-induced neurovascular damage was explored by measuring expression of tight junction (TJ) proteins (zonula occludens-1 (ZO-1), occludin and claudin-5), glial fibrillary acidic protein (GFAP) and astrocyte end-feet coverage around the blood–brain barrier (BBB). Western blot analysis demonstrates that TJ protein levels were significantly decreased at 6 h and 24 h post-mbTBI in male rats, but not in female rats, compared to sham. Female animals have decreased GFAP at 6 h post-mbTBI while male animals display decreased GFAP expression at 24 h post-mbTBI. By 7 d post-mbTBI, there were no significant differences in TJ or GFAP levels between groups in either sex. At 24 h post-mbTBI, vascular integrity and astrocytic end-feet coverage around the BBB was significantly decreased in males following mbTBI. These results demonstrate that loss of GFAP expression may be due to astrocytic damage at the BBB. Our findings also demonstrate sex differences in acute vascular and behavioral outcomes after single mbTBI. Female animals display a lack of BBB pathology after mbTBI corresponding to improved acute neuropsychological outcomes as compared to male animals.

A Retrospective Study of the Effects of Traumatic Brain Injury on Auditory Function: From a Clinical Perspective

Purpose: The main purpose of this retrospective study was to identify auditory dysfunctions related to traumatic brain injury (TBI) in individuals evaluated in an Audiology clinic. Method: Peripheral and central auditory evaluations were performed from March 2014 to June 2018 in 26 patients (14 males) with TBI. The age of the participants ranged from 9 to 59 years old (34.24 ± 15.21). Six participants had blast-related TBI and 20 had blunt force TBI. Sixteen experienced a single TBI event whereas ten experienced several. Correlation analyses were performed to verify the relationship, if any, between the number of auditory tests failed and the number, type, and severity of TBIs. Result: All participants failed at least one auditory test. Nearly 60% had abnormal results on degraded speech tests (compressed and echoed, filtered or in background noise) and 25% had a high frequency hearing loss. There was no statistically significant correlation between the number of auditory tests failed and the number, type, and severity of TBIs. Conclusion: Results indicated negative and heterogenous effects of TBI on peripheral and central auditory function and highlighted the need for a more extensive auditory assessment in individuals with TBI.

A Brief Review of In Vitro Models for Injury and Regeneration in the Peripheral Nervous System

Nerve axonal injury and associated cellular mechanisms leading to peripheral nerve damage are important topics of research necessary for reducing disability and enhancing quality of life. Model systems that mimic the biological changes that occur during human nerve injury are crucial for the identification of cellular responses, screening of novel therapeutic molecules, and design of neural regeneration strategies. In addition to in vivo and mathematical models, in vitro axonal injury models provide a simple, robust, and reductionist platform to partially understand nerve injury pathogenesis and regeneration. In recent years, there have been several advances related to in vitro techniques that focus on the utilization of custom-fabricated cell culture chambers, microfluidic chamber systems, and injury techniques such as laser ablation and axonal stretching. These developments seem to reflect a gradual and natural progression towards understanding molecular and signaling events at an individual axon and neuronal-soma level. In this review, we attempt to categorize and discuss various in vitro models of injury relevant to the peripheral nervous system and highlight their strengths, weaknesses, and opportunities. Such models will help to recreate the post-injury microenvironment and aid in the development of therapeutic strategies that can accelerate nerve repair.

Blast-induced axonal degeneration in the rat cerebellum in the absence of head movement

Blast exposure can injure brain by multiple mechanisms, and injury attributable to direct effects of the blast wave itself have been difficult to distinguish from that caused by rapid head displacement and other secondary processes. To resolve this issue, we used a rat model of blast exposure in which head movement was either strictly prevented or permitted in the lateral plane. Blast was found to produce axonal injury even with strict prevention of head movement. This axonal injury was restricted to the cerebellum, with the exception of injury in visual tracts secondary to ocular trauma. The cerebellar axonal injury was increased in rats in which blast-induced head movement was permitted, but the pattern of injury was unchanged. These findings support the contentions that blast per se, independent of head movement, is sufficient to induce axonal injury, and that axons in cerebellar white matter are particularly vulnerable to direct blast-induced injury.

A systematic review and data synthesis of longitudinal changes in white matter integrity after mild traumatic brain injury assessed by diffusion tensor imaging in adults

PURPOSE

This study aimed to review diffusion tensor imaging studies of mild traumatic brain injury (mTBI) in adults with longitudinal acquisition of data and investigate the variability of findings in association with related factors, such as the time post-injury.

METHODS

Eligible studies from PubMed and EMBASE were searched to identify relevant studies for review. Of the 540 studies, 23 observational studies without intervention and with the following characteristics were included: original research in which adults with mTBI were examined, diffusion tensor imaging was acquired at least twice, white matter integrity was investigated by estimating diffusion metrics, and mode of injury was not restricted to sport- or blast-related mTBI.

RESULTS

Baseline scans were acquired within 3 weeks post-injury, followed by longitudinal scans within 3 months and at 12 months post-injury. During the acute/subacute period, mixed results (increase, decrease, or no significant change) of fractional anisotropy (FA) were observed compared to those in controls. Some studies reported increased FA during the acute/subacute period compared to controls, followed by normalization of FA. Decreased FA was also reported during the acute/subacute period, which lasted long into the chronic phase. In the acute phase, the mean diffusivity (MD) was greater than that in the controls. Compared to the early phase of injury, MD was reduced in the follow-up phase in most studies in the mTBI group. Insignificant differences in FA and MD have been reported in several studies. Such variability limits the clinical usefulness of diffusion tensor metrics.

CONCLUSIONS

There was a high variability in reported changes in white matter integrity. Decreased FA not only in acute/subacute but also in long-term period after injury may indicate long-term neurodegenerative processes after mTBI. Nevertheless, longitudinal changes in MD towards normalization suggest possible recovery. Long-term cohort studies with research initiatives should be considered to elucidate brain changes after mTBI.

Correlation of Histomorphometric Changes with Diffusion Tensor Imaging for Evaluation of Blast-Induced Auditory Neurodegeneration in Chinchilla

In the present study, we have evaluated the blast-induced auditory neurodegeneration in chinchilla by correlating the histomorphometric changes with diffusion tensor imaging. The chinchillas were exposed to single unilateral blast-overpressure (BOP) at ∼172dB peak sound pressure level (SPL) and the pathological changes were compared at 1 week and 1 month after BOP. The functional integrity of the auditory system was assessed by auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE). The axonal integrity was assessed using diffusion tensor imaging at regions of interests (ROIs) of the central auditory neuraxis (CAN) including the cochlear nucleus (CN), inferior colliculus (IC), and auditory cortex (AC). Post-BOP, cyto-architecture metrics such as viable cells, degenerating neurons, and apoptotic cells were quantified at the CAN ROIs using light microscopic studies using cresyl fast violet, hematoxylin and eosin, and modified Crossmon's trichrome stains. We observed mean ABR threshold shifts of 30- and 10-dB SPL at 1 week and 1 month after BOP, respectively. A similar pattern was observed in DPAOE amplitudes shift. In the CAN ROIs, diffusion tensor imaging studies showed a decreased axial diffusivity in CN 1 month after BOP and a decreased mean diffusivity and radial diffusivity at 1 week after BOP. However, morphometric measures such as decreased viable cells and increased degenerating neurons and apoptotic cells were observed at CN, IC, and AC. Specifically, increased degenerating neurons and reduced viable cells were high on the ipsilateral side when compared with the contralateral side. These results indicate that a single blast significantly damages structural and functional integrity at all levels of CAN ROIs.

Beirut Ammonium Nitrate Blast: Analysis, Review, and Recommendations

A massive chemical detonation occurred on August 4, 2020 in the Port of Beirut, Lebanon. An uncontrolled fire in an adjacent warehouse ignited ~2,750 tons of Ammonium Nitrate (AN), producing one of the most devastating blasts in recent history. The blast supersonic pressure and heat wave claimed the lives of 220 people and injured more than 6,500 instantaneously, with severe damage to the nearby dense residential and commercial areas. This review represents one of the in-depth reports to provide a detailed analysis of the Beirut blast and its health and environmental implications. It further reviews prior AN incidents and suggests actionable recommendations and strategies to optimize chemical safety measures, improve emergency preparedness, and mitigate the delayed clinical effects of blast and toxic gas exposures. These recommended actionable steps offer a starting point for government officials and policymakers to build frameworks, adopt regulations, and implement chemical safety protocols to ensure safe storage of hazardous materials as well as reorganizing healthcare system disaster preparedness to improve emergency preparedness in response to similar large-scale disasters and promote population safety. Future clinical efforts should involve detailed assessment of physical injuries sustained by blast victims, with systemic mitigation and possible treatment of late blast effects involving individuals, communities and the region at large.

Drug Repurposing: Promises of Edaravone Target Drug in Traumatic Brain Injury

Edaravone is a potent free-radical scavenger that has been in the market for more than 30 years. It was originally developed in Japan to treat strokes and has been used there since 2001. Aside from its anti-oxidative effects, edaravone demonstrated beneficial effects on proinflammatory responses, nitric oxide production, and apoptotic cell death. Interestingly, edaravone has shown neuroprotective effects in several animal models of diseases other than stroke. In particular, edaravone administration was found to be effective in halting amyotrophic lateral sclerosis (ALS) progression during the early stages. Accordingly, after its success in Phase III clinical studies, edaravone has been approved by the FDA as a treatment for ALS patients. Considering its promises in neurological disorders and its safety in patients, edaravone is a drug of interest that can be repurposed for traumatic brain injury (TBI) treatment. Drug repurposing is a novel approach in drug development that identifies drugs for purposes other than their original indication. This review presents the biochemical properties of edaravone along with its effects on several neurological disorders in the hope that it can be adopted for treating TBI patients.

Guidelines to inform the generation of clinically relevant and realistic blast loading conditions for primary blast injury research

'Primary' blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. With continued experimental focus on PBI mechanisms, recently on blast traumatic brain injury, meaningful test outcomes rely on appropriate simulated conditions. Selected PBI predictive criteria (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) are combined and plotted to provide rationale for generating clinically relevant loading conditions. Using blast engineering theory, explosion characteristics including blast wave parameters and fireball dimensions were calculated for a range of charge masses assuming hemispherical surface detonations and compared with PBI criteria. While many experimental loading conditions are achievable, this analysis demonstrated limits that should be observed to ensure loading is clinically relevant, realistic and practical. For PBI outcomes sensitive only to blast overpressure, blast scaled distance was demonstrated to be a useful parameter for guiding experimental design as it permits flexibility for different experimental set-ups. This analysis revealed that blast waves should correspond to blast scaled distances of 1.75<Z<6.0 to generate loading conditions found outside the fireball and of clinical relevance to a range of PBIs. Blast waves with positive phase durations (2-10 ms) are more practical to achieve through experimental approaches, while representing realistic threats such as improvised explosive devices (ie, 1-50 kg trinitrotoluene equivalent). These guidelines can be used by researchers to inform the design of appropriate blast loading conditions in PBI experimental investigations.

Behavioral and Histopathological Impairments Caused by Topical Exposure of the Rat Brain to Mild-Impulse Laser-Induced Shock Waves: Impulse Dependency

Although an enormous number of animal studies on blast-induced traumatic brain injury (bTBI) have been conducted, there still remain many uncertain issues in its neuropathology and mechanisms. This is partially due to the complex and hence difficult experimental environment settings, e.g., to minimize the effects of blast winds (tertiary mechanism) and to separate the effects of brain exposure and torso exposure. Since a laser-induced shock wave (LISW) is free from dynamic pressure and its energy is spatially well confined, the effects of pure shock wave exposure (primary mechanism) solely on the brain can be examined by using an LISW. In this study, we applied a set of four LISWs in the impulse range of 15–71 Pa·s to the rat brain through the intact scalp and skull; the interval between each exposure was ~5 s. For the rats, we conducted locomotor activity, elevated plus maze and forced swimming tests. Axonal injury in the brain was also examined by histological analysis using Bodian silver staining. Only the rats with exposure at higher impulses of 54 and 71 Pa·s showed significantly lower spontaneous movements at 1 and 2 days post-exposure by the locomotor activity test, but after 3 days post-exposure, they had recovered. At 7 days post-exposure, however, these rats (54 and 71 Pa·s) showed significantly higher levels of anxiety-related and depression-like behaviors by the elevated plus maze test and forced swimming test, respectively. To the best of the authors' knowledge, there have been few studies in which a rat model showed both anxiety-related and depression-like behaviors caused by blast or shock wave exposure. At that time point (7 days post-exposure), histological analysis showed significant decreases in axonal density in the cingulum bundle and corpus callosum in impulse-dependent manners; axons in the cingulum bundle were found to be more affected by a shock wave. Correlation analysis showed a statistically significant correlation between the depression like-behavior and axonal density reduction in the cingulum bundle. The results demonstrated the dependence of behavior deficits and axonal injury on the shock wave impulse loaded on the brain.

Visual Outcomes in Experimental Rodent Models of Blast-Mediated Traumatic Brain Injury

Blast-mediated traumatic brain injuries (bTBI) cause long-lasting physical, cognitive, and psychological disorders, including persistent visual impairment. No known therapies are currently utilized in humans to lessen the lingering and often serious symptoms. With TBI mortality decreasing due to advancements in medical and protective technologies, there is growing interest in understanding the pathology of visual dysfunction after bTBI. However, this is complicated by numerous variables, e.g., injury location, severity, and head and body shielding. This review summarizes the visual outcomes observed by various, current experimental rodent models of bTBI, and identifies data showing that bTBI activates inflammatory and apoptotic signaling leading to visual dysfunction. Pharmacologic treatments blocking inflammation and cell death pathways reported to alleviate visual deficits in post-bTBI animal models are discussed. Notably, techniques for assessing bTBI outcomes across exposure paradigms differed widely, so we urge future studies to compare multiple models of blast injury, to allow data to be directly compared.

Axonal damage and behavioral deficits in rats with repetitive exposure of the brain to laser-induced shock waves: Effects of inter-exposure time

Much attention has been given to effects of repeated exposure to a shock wave as a possible factor causing severe higher brain dysfunction and post-traumatic stress disorder (PTSD)-like symptoms in patients with mild to moderate blast-induced traumatic brain injury (bTBI). However, it is unclear how the repeated exposure and the inter-exposure time affect the brain. In this study, we topically applied low-impulse (∼54 Pa·s) laser-induced shock waves (LISWs; peak pressure, ∼75.7 MPa) to the rat brain once or twice with the different inter-exposure times (15 min, 1 h, 3 h, 24 h and 7 days) and examined anxiety-related behavior and motor dysfunction in the rats as well as expression of β-amyloid precursor protein (APP) as an axonal damage marker in the brains of the rats. The averaged APP expression scores for the rat brains doubly-exposed to LISWs with inter-exposure times from 15 min to 24 h were significantly higher than those for rats with a single exposure (P < 0.0001). The rats with double exposure to LISWs showed significantly more frequent anxiety-related behavior (P < 0.05) and poorer motor function (P < 0.01) than those of rats with a single exposure. When the inter-exposure time was extended to 7 days, however, the rats showed no significant differences either in axonal damage score or level of motor dysfunction. The results suggest that the cumulative effects of shock wave-related brain injury can be avoided with an appropriate inter-exposure time. However, clinical bTBI occurs in much more complex environments than those in our model. Further study considering other factors, such as the effects of acceleration, is needed to know the clinically-relevant, necessary inter-exposure time.

Cerebrospinal Fluid Cavitation as a Mechanism of Blast-Induced Traumatic Brain Injury: A Review of Current Debates, Methods, and Findings

Cavitation has gained popularity in recent years as a potential mechanism of blast-induced traumatic brain injury (bTBI). This review presents the most prominent debates on cavitation; how bubbles can form or exist within the cerebrospinal fluid (CSF) and brain vasculature, potential mechanisms of cellular, and tissue level damage following the collapse of bubbles in response to local pressure fluctuations, and a survey of experimental and computational models used to address cavitation research questions. Due to the broad and varied nature of cavitation research, this review attempts to provide a necessary synthesis of cavitation findings relevant to bTBI, and identifies key areas where additional work is required. Fundamental questions about the viability and likelihood of CSF cavitation during blast remain, despite a variety of research regarding potential injury pathways. Much of the existing literature on bTBI evaluates cavitation based off its prima facie plausibility, while more rigorous evaluation of its likelihood becomes increasingly necessary. This review assesses the validity of some of the common assumptions in cavitation research, as well as highlighting outstanding questions that are essential in future work.

Efficacy of Body Armor in Protection Against Blast Injuries Using a Swine Model in a Confined Space with a Blast Tube

The purpose of this study was to clarify whether or not body armor would protect the body of a swine model using a blast tube built at National Defense Medical College, which is the first such blast tube in Japan. Seventeen pigs were divided into two groups: the body armor group and the non-body armor group. Under intravenous anesthesia, the pigs were tightly fixed in the left lateral position on a table and exposed from the back neck to the upper lumbar back to the blast wave and wind with or without body armor, with the driving pressure of the blast tube set to 3.0 MPa. When the surviving and dead pigs were compared, blood gas analyses revealed significant differences in PaO2, PaCO2, and pH in the super-early phase. All pigs injured by the blast wave and wind had lung hemorrhage. All 6 animals in the body armor group and 6 of the 11 animals in the control group survived for 3 hours after injury. Respiratory arrest immediately after exposure to the blast wave was considered to influence the mortality in our pig model. Body armor may have a beneficial effect in protecting against respiratory arrest immediately after an explosion.

Simulation of Cumulative Exposure Statistics for Blast Pressure Transmission Into the Brain

INTRODUCTION

This study develops and demonstrates an analysis approach to understand the statistics of cumulative pressure exposure of the brain to repetitive blasts events.

MATERIALS AND METHODS

A finite element model of blast loading on the head was used for brain model biomechanical responses. The cumulative pressure exposure fraction (CPEF), ranging from 0.0 to 1.0, was used to characterize the extent and repetition of high pressures. Monte Carlo simulations were performed to generate repetitive blast cumulative exposures.

RESULTS

The blast orientation effect is as influential as the blast overpressure magnitudes. A 75° (from the side) blast orientation can produce CPEF values exceeding traumatic brain injury pressure thresholds >0.95 while, for the same blast overpressure, a 0° (front) blast orientation results in a CPEF <0.25. Monte Carlo results for different sequences reflecting notional operational and training environments show that both mean values and standard deviations of CPEF reach the statistically equilibrium state at a finite value of n exposures for each sequence.

CONCLUSIONS

Statistical convergence of the brain pressure response metrics versus number of blasts for different exposures characterizes the transitions from "low" to "high" number of blasts and quantitatively highlights the differences between operational and training exposures.

Explosive-driven double-blast exposure: molecular, histopathological, and behavioral consequences

Traumatic brain injury generated by blast may induce long-term neurological and psychiatric sequelae. We aimed to identify molecular, histopathological, and behavioral changes in rats 2 weeks after explosive-driven double-blast exposure. Rats received two 30-psi (~ 207-kPa) blasts 24 h apart or were handled identically without blast. All rats were behaviorally assessed over 2 weeks. At Day 15, rats were euthanized, and brains removed. Brains were dissected into frontal cortex, hippocampus, cerebellum, and brainstem. Western blotting was performed to measure levels of total-Tau, phosphorylated-Tau (pTau), amyloid precursor protein (APP), GFAP, Iba1, αII-spectrin, and spectrin breakdown products (SBDP). Kinases and phosphatases, correlated with tau phosphorylation were also measured. Immunohistochemistry for pTau, APP, GFAP, and Iba1 was performed. pTau protein level was greater in the hippocampus, cerebellum, and brainstem and APP protein level was greater in cerebellum of blast vs control rats (p < 0.05). GFAP, Iba1, αII-spectrin, and SBDP remained unchanged. No immunohistochemical or neurobehavioral changes were observed. The dissociation between increased pTau and APP in different regions in the absence of neurobehavioral changes 2 weeks after double blast exposure is a relevant finding, consistent with human data showing that battlefield blasts might be associated with molecular changes before signs of neurological and psychiatric disorders manifest.

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

[A human body simulator as an input parameter of ballistic experiment]

The purpose of the work is a comparative analysis of objects used in forensic ballistics as imitators of the human body for the formation of gunshot injuries, based on literature data and the results of our own experimental studies. A classification of objects of biological and non-biological origin, used to simulate the human body during the experimental simulation of a gunshot injury, is proposed. A set of advantages and disadvantages was studied, a critical assessment of the objects of each group was given, recommendations were made on their rational use in ballistic research.

A Decade of mTBI Experience: What Have We Learned? A Summary of Proceedings From a NATO Lecture Series on Military mTBI

Mild traumatic brain injury (mTBI, also known as a concussion) as a consequence of battlefield blast exposure or blunt force trauma has been of increasing concern to militaries during recent conflicts. This concern is due to the frequency of exposure to improvised explosive devices for forces engaged in operations both in Iraq and Afghanistan coupled with the recognition that mTBI may go unreported or undetected. Blasts can lead to mTBI through a variety of mechanisms. Debate continues as to whether exposure to a primary blast wave alone is sufficient to create brain injury in humans, and if so, exactly how this occurs with an intact skull. Resources dedicated to research in this area have also varied substantially among contributing NATO countries. Most of the research has been conducted in the US, focused on addressing uncertainties in management practices. Development of objective diagnostic tests should be a top priority to facilitate both diagnosis and prognosis, thereby improving management. It is expected that blast exposure and blunt force trauma to the head will continue to be a potential source of injury during future conflicts. An improved understanding of the effects of blast exposure will better enable military medical providers to manage mTBI cases and develop optimal protective measures. Without the immediate pressures that come with a high operational tempo, the time is right to look back at lessons learned, make full use of available data, and modify mitigation strategies with both available evidence and new evidence as it comes to light. Toward that end, leveraging our cooperation with the civilian medical community is critical because the military experience over the past 10 years has led to a renewed interest in many similar issues pertaining to mTBI in the civilian world. Such cross-fertilization of knowledge will undoubtedly benefit all. This paper highlights similarities and differences in approach to mTBI patient care in NATO and partner countries and provides a summary of and lessons learned from a NATO lecture series on the topic of mTBI, demonstrating utility of having patients present their experiences to a medical audience, linking practical clinical care to policy approaches.

Sequelae of Blast Events in Iraq and Afghanistan War Veterans using the Salisbury Blast Interview: A CENC Study

Objective: To comprehensively characterize blast exposure across the lifespan and relationship to TBI.Participants: Post-deployment veterans and service members (N = 287).Design: Prospective cohort recruitment.Main Measures: Salisbury Blast Interview (SBI).Results: 94.4% of participants reported at least one blast event, 75% reported a pressure gradient during a blast event. Participants reported an average of 337.7 (SD = 984.0) blast events (range 0-4857), 64.8% occurring during combat. Across participants, 19.7% reported experiencing a traumatic brain injury (TBI) during a blast event. Subjective ratings of blast characteristics (wind, debris, ground shaking, pressure, temperature, sound) were significantly higher when TBI was experienced and significantly lower when behind cover. Pressure had the strongest association with resulting TBI (AUC = 0.751). Pressure rating of 3 had the best sensitivity (.54)/specificity (.87) with TBI. Logistic regression demonstrated pressure, temperature and distance were the best predictors of TBI, and pressure was the best predictor of primary blast TBI.Conclusion: Results demonstrate the ubiquitous nature of blast events and provide insight into blast characteristics most associated with resulting TBI (pressure, temperature, distance). The SBI provides comprehensive characterization of blast events across the lifespan including the environment, protective factors, blast characteristics and estimates of distance and munition.

Types of Disasters

Disasters are increasing around the world. Children are greatly impacted by both natural disasters (forces of nature) and man-made (intentional, accidental) disasters. Their unique anatomical, physiological, behavioral, developmental, and psychological vulnerabilities must be considered when planning and preparing for disasters. The nurse or health care provider (HCP) must be able to rapidly identify acutely ill children during a disaster. Whether it is during a natural or man-made event, the nurse or HCP must intervene effectively to improve survival and outcomes. It is extremely vital to understand the medical management of these children during disasters, especially the use of appropriate medical countermeasures such as medications, antidotes, supplies, and equipment.

Interests and concerns of the Army Medical Services as reflected by the publications in the Journal of the Royal Army Medical Corps 1903-2019

INTRODUCTION

The Journal of the Royal Army Medical Corps (JRAMC) is published with the aim of propagating current knowledge and expertise while also acting as institutional memory for the practice of medicine within the military. This work aimed to examine how the interests of the JRAMC, and by inference the Army Medical Services, have changed over time as reflected by the articles published in the journal.

METHODS

A text mining analysis of the titles of all published articles in the JRAMC between 1903 and 2019 was performed. The most commonly used terms were identified and their relative frequency over the decades analysed to identify trends. Article content and contemporary events were compared with the observed trends to identify explanatory events and themes of interest.

RESULTS

Medical topics of interest centred around specific infectious diseases, particularly during the early/mid-20th century, and trauma and battle injury. The medical specialties of surgery, anaesthetics and mental health were all well represented in nearly all decades, while primary care only came to prominence as a named specialty from the 1960s onwards. India, France, Egypt and wider Africa were the most commonly cited geographical regions, although there were spikes of interest associated with specific conflicts in the Falklands, Bosnia, Afghanistan and Iraq.

CONCLUSION

The interests of the JRAMC have changed considerably over the years primarily driven by the geopolitical interests of Britain-in particular its colonial interests and the conflicts it has been involved in, but also by medical advances seen in contemporary society.

Blast-Related Traumatic Brain Injury: Current Concepts and Research Considerations

Traumatic brain injury (TBI) is a well-known consequence of participation in activities such as military combat or collision sports. But the wide variability in eliciting circumstances and injury severities makes the study of TBI as a uniform disease state impossible. Military Service members are under additional, unique threats such as exposure to explosive blast and its unique effects on the body. This review is aimed toward TBI researchers, as it covers important concepts and considerations for studying blast-induced head trauma. These include the comparability of blast-induced head trauma to other mechanisms of TBI, whether blast overpressure induces measureable biomarkers, and whether a biodosimeter can link blast exposure to health outcomes, using acute radiation exposure as a corollary. This examination is contextualized by the understanding of concussive events and their psychological effects throughout the past century’s wars, as well as the variables that predict sustaining a TBI and those that precipitate or exacerbate psychological conditions.

Disclaimer: The views expressed in this article are solely the views of the authors and not those of the Department of Defense Blast Injury Research Coordinating Office, US Army Medical Research and Development Command, US Army Futures Command, US Army, or the Department of Defense.

Viscoelastic properties of shock wave exposed brain tissue subjected to unconfined compression experiments

Traumatic brain injuries (TBI) affect millions of people each year. While research has been dedicated to determining the mechanical properties of the uninjured brain, there has been a lack of investigation on the mechanical properties of the brain after experiencing a primary blast-induced TBI. In this paper, whole porcine brains were exposed to a shock wave to simulate blast-induced TBI. First, ten (10) brains were subjected to unconfined compression experiments immediately following shock wave exposure. In addition, 22 brains exposed to a shock wave were placed in saline solution and refrigerated between 30 minutes and 6.0 hours before undergoing unconfined compression experiments. This study aimed to investigate the effect of a time delay on the viscoelastic properties in the event that an experiment cannot be completed immediately. Samples from both soaked and freshly extracted brains were subjected to compressive rates of 5, 50, and 500 mm/min during the unconfined compression experiments. The fractional Zener (FZ) viscoelastic model was applied to obtain the brain's material properties. The length of time in the solution statistically influenced three of the four FZ coefficients, E₀ (instantaneous elastic response), τ₀ (relaxation time), and α (fractional order). Further, the compressive rate statistically influenced τ₀ and α.

Gross and histopathologic diagnoses from North Atlantic right whale Eubalaena glacialis mortalities between 2003 and 2018

Seventy mortalities of North Atlantic right whales Eubalaena glacialis (NARW) were documented between 2003 and 2018 from Florida, USA, to the Gulf of St. Lawrence, Canada. These included 29 adults, 14 juveniles, 10 calves, and 17 of unknown age class. Females represented 65.5% (19/29) of known-sex adults. Fourteen cases had photos only; 56 carcasses received external examinations, 44 of which were also necropsied. Cause of death was determined in 43 cases, of which 38 (88.4%) were due to anthropogenic trauma: 22 (57.9%) from entanglement, and 16 (42.1%) from vessel strike. Gross and histopathologic lesions associated with entanglement were often severe and included deep lacerations caused by constricting line wraps around the flippers, flukes, and head/mouth; baleen plate mutilation; chronic extensive bone lesions from impinging line, and traumatic scoliosis resulting in compromised mobility in a calf. Chronically entangled whales were often in poor body condition and had increased cyamid burden, reflecting compromised health. Vessel strike blunt force injuries included skull and vertebral fractures, blubber and muscle contusions, and large blood clots. Propeller-induced wounds often caused extensive damage to blubber, muscle, viscera, and bone. Overall prevalence of NARW entanglement mortalities increased from 21% (1970-2002) to 51% during this study period. This demonstrates that despite mitigation efforts, entanglements and vessel strikes continue to inflict profound physical trauma and suffering on individual NARWs. These cumulative mortalities are also unsustainable at the population level, so urgent and aggressive intervention is needed to end anthropogenic mortality in this critically endangered species.

The mechanical behavior of brain surrogates manufactured from silicone elastomers

The ongoing conflict against terrorism has resulted in an escalation of blast-induced traumatic brain injuries (bTBI) caused by improvised explosive devices (IEDs). The destructive IEDs create a blast wave that travels through the atmosphere. Blast-induced traumatic brain injuries, attributed to the blast wave, can cause life-threatening injuries and fatalities. This study aims to find a surrogate brain material for assessing the effectiveness of head protection systems designed to mitigate bTBI. Polydimethylsiloxane (PDMS) is considered as the surrogate brain material. The stiffness of PDMS (Sylgard 184, Dow Corning Corp.) can be controlled by varying the ratio of base and curing agent. Cylindrical PDMS specimen with ratios of 1:10, 1:70, and 1:80 were subjected to unconfined compression experiments at linear rates of 5 mm/min, 50 mm/min, and 500 mm/min. A ramp-hold strain profile was used to simulate a stress relaxation experiment. The fractional Zener viscoelastic model was used to describe the stress relaxation response, after optimization of the material constants for the brain surrogate and shock wave exposure brain tissue. The results show that the low cost PDMS can be used as a surrogate brain material to study the dynamic brain response to blast wave exposure.

Longitudinal changes in neuroimaging and neuropsychiatric status of post-deployment veterans: a CENC pilot study

PRIMARY OBJECTIVE

The purpose of this study was to evaluate preliminary data on longitudinal changes in psychiatric, neurobehavioural, and neuroimaging findings in Iraq and Afghanistan combat veterans following blast exposure.

RESEARCH DESIGN

Longitudinal observational analysis.

METHODS AND PROCEDURES

Participants were invited to participate in two research projects approximately 7 years apart. For each project, veterans completed the Structured Clinical Interview for DSM-IV Disorders and/or the Clinician-Administered PTSD Scale, Neurobehavioral Symptom Inventory, and magnetic resonance imaging (MRI).

MAIN OUTCOMES AND RESULTS

Chi-squared tests indicated no significant changes in current psychiatric diagnoses, traumatic brain injury (TBI) history, or blast exposure history between assessment visits. Wilcoxon signed-rank tests indicated significant increases in median neurobehavioural symptoms, total number of white matter hyperintensities (WMH), and total WMH volume between assessment visits. Spearman rank correlations indicated no significant associations between change in psychiatric diagnoses, TBI history, blast exposure history, or neurobehavioural symptoms and change in WMH.

CONCLUSION

MRI WMH changes were not associated with changes in psychiatric diagnoses or symptom burden, but were associated with severity of blast exposure. Future, larger studies might further evaluate presence and aetiology of long-term neuropsychiatric symptoms and MRI findings in blast-exposed populations.