Pulmonary biochemical and histological alterations after repeated low-level blast overpressure exposures

Blast Waves Cause Immune System Dysfunction and Transient Bone Marrow Failure in a Mouse Model

Explosive devices, either conventional or improvised, are common sources of injuries during combat, civil unrest, and terror attacks, resulting in trauma from exposure to blast. A blast wave (BW), a near-instantaneous rise in pressure followed by a negative pressure, propagates through the body in milliseconds and can affect physiology for days/months after exposure. Epidemiological data show that blast-related casualties result in significantly higher susceptibility to wound infections, suggesting long-lasting immune modulatory effects from blast exposure. The mechanisms involved in BW-induced immune changes are poorly understood. We evaluated the effects of BW on the immune system using an established murine model. Animals were exposed to BWs (using an Advanced Blast Simulator), followed by longitudinally sampling for 14 days. Blood, bone marrow, and spleen were analyzed for changes in the 1) complete blood count (CBC), and 2) composition of bone marrow cells (BMC) and splenocytes, and 3) concentrations of systemic cytokines/chemokines. Our data demonstrate that BW results in transient bone marrow failure and long-term changes in the frequency and profile of progenitor cell populations. Viability progressively decreased in hematopoietic stem cells and pluripotent progenitor cells. Significant decrease of CD4⁺ T cells in the spleen indicates reduced functionality of adaptive immune system. Dynamic changes in the concentrations of several cytokines and chemokines such as IL-1α and IL-17 occurred potentially contributing to dysregulation of immune response after trauma. This work lays the foundation for identifying the potential mechanisms behind BW’s immunosuppressive effects to inform the recognition of this compromised status is crucial for the development of therapeutic interventions for infections to reduce recovery time of wounded patients injured by explosive devices.

Getting on the Same Page: Consolidating Terminology to Facilitate Cross-Disciplinary Health-Related Blast Research

The consequences of blast exposure (including both high-level and low-level blast) have been a focal point of military interest and research for years. Recent mandates from Congress (e.g., National Defense Authorization Act for Fiscal Year 2018, section 734) have further accelerated these efforts, facilitating collaborations between research teams from a variety of disciplinary backgrounds. Based on findings from a recent scoping review, we argue that the scientific field of blast research is plagued by inconsistencies in both conceptualization of relevant constructs and terminology used to describe them. These issues hamper our ability to interpret study methods and findings, hinder efforts to integrate findings across studies to reach scientific consensus, and increase the likelihood of redundant efforts. We argue that multidisciplinary experts in this field require a universal language and clear, standardized terminology to further advance the important work of examining the effects of blast exposure on human health, performance, and well-being. To this end, we present a summary of descriptive conventions regarding the language scientists currently use when discussing blast-related exposures and outcomes based on findings from a recent scoping review. We then provide prescriptive conventions about how these terms should be used by clearly conceptualizing and explicitly defining relevant constructs. Specifically, we summarize essential concepts relevant to the study of blast, precisely distinguish between high-level blast and low-level blast, and discuss how the terms acute, chronic, exposure, and outcome should be used when referring to the health-related consequences of blast exposure.

Potential Health and Performance Effects of High-Level and Low-Level Blast: A Scoping Review of Two Decades of Research

Although blast exposure has been recognized as a significant source of morbidity and mortality in military populations, our understanding of the effects of blast exposure, particularly low-level blast (LLB) exposure, on health outcomes remains limited. This scoping review provides a comprehensive, accessible review of the peer-reviewed literature that has been published on blast exposure over the past two decades, with specific emphasis on LLB. We conducted a comprehensive scoping review of the scientific literature published between January 2000 and 2019 pertaining to the effects of blast injury and/or exposure on human and animal health. A three-level review process with specific inclusion and exclusion criteria was used. A full-text review of all articles pertaining to LLB exposure was conducted and relevant study characteristics were extracted. The research team identified 3,215 blast-relevant articles, approximately half of which (55.4%) studied live humans, 16% studied animals, and the remainder were non-subjects research (e.g., literature reviews). Nearly all (99.49%) of the included studies were conducted by experts in medicine or epidemiology; approximately half of these articles were categorized into more than one medical specialty. Among the 51 articles identified as pertaining to LLB specifically, 45.1% were conducted on animals and 39.2% focused on human subjects. Animal studies of LLB predominately used shock tubes to induce various blast exposures in rats, assessed a variety of outcomes, and clearly demonstrated that LLB exposure is associated with brain injury. In contrast, the majority of LLB studies on humans were conducted among military and law enforcement personnel in training environments and had remarkable variability in the exposures and outcomes assessed. While findings suggest that there is the potential for LLB to harm human populations, findings are mixed and more research is needed. Although it is clear that more research is needed on this rapidly growing topic, this review highlights the detrimental effects of LLB on the health of both animals and humans. Future research would benefit from multidisciplinary collaboration, larger sample sizes, and standardization of terminology, exposures, and outcomes.

Early Peritoneal Dialysis Ameliorates Blast Lung Injury by Alleviating Pulmonary Edema and Inflammation

BACKGROUND

Blast lung injury is a high-energy trauma with high mortality for explosion victims. A treatment for blast lung injury is still lacking. The aim of this study was to observe the efficacy and mechanism of peritoneal dialysis combined with glucocorticoids (GC) in the treatment of blast lung injury in rats.

METHODS

Rats were randomly divided into five groups: control, sham, GC, peritoneal dialysis (dialysis for short), and dialysis + GC groups. All rats were injured by a biological shock tube-I.

RESULTS

The lung water levels in the dialysis group and dialysis + GC group were significantly lower than that in the control group at 6 and 24 h after blast injury. The oxygenation index, forced vital capacity, maximum midexpiratory flow, and functional residual capacity of rats in the dialysis and dialysis + GC groups were significantly higher than those in the control group. The serum levels of interleukin (IL)-1β, IL-6, tumor necrosis factor- α, monocyte chemoattractant protein-1, C-reactive protein, and IL-10 in the dialysis and dialysis + GC groups were significantly lower than those in the control group. Genome-wide mRNA microarray results showed that the aquaporin 1 level in the lung tissue of the dialysis group was 6.67 times higher than that in the control group.

CONCLUSION

Early peritoneal dialysis can attenuate pulmonary edema and inflammation, and protect acute lung injury after blast injury.

Pulmonary injury risk curves and behavioral changes from blast overpressure exposures of varying frequency and intensity in rats

At present, there are no set guidelines establishing cumulative limits for blast exposure numbers and intensities in military personnel, in combat or training operations. The objective of the current study was to define lung injury, pathology, and associated behavioral changes from primary repeated blast lung injury under appropriate exposure conditions and combinations (i.e. blast overpressure (BOP) intensity and exposure frequency) using an advanced blast simulator. Male Sprague Dawley rats were exposed to BOP frontally and laterally at a pressure range of ~ 8.5-19 psi, for up to 30 daily exposures. The extent of lung injury was identified at 24 h following BOP by assessing the extent of surface hemorrhage/contusion, Hematoxylin and Eosin staining, and behavioral deficits with open field activity. Lung injury was mathematically modeled to define the military standard 1% lung injury threshold. Significant levels of histiocytosis and inflammation were observed in pressures ≥ 10 psi and orientation effects were observed at pressures ≥ 13 psi. Experimental data demonstrated ~ 8.5 psi is the threshold for hemorrhage/contusion, up to 30 exposures. Modeling the data predicted injury risk up to 50 exposures with intensity thresholds at 8 psi for front exposure and 6psi for side exposures, which needs to be validated further.

Overpressure Exposure From .50-Caliber Rifle Training Is Associated With Increased Amyloid Beta Peptides in Serum

Background: Overpressure (OP) is an increase in air pressure above normal atmospheric levels. Military personnel are repeatedly exposed to low levels of OP caused by various weapon systems. Repeated OP may increase risk of neurological disease or psychological disorder diagnoses. A means to detect early phase effects that may be relevant to brain trauma remain elusive. Therefore, development of quantitative and objective OP-mediated effects during acute timeframes would vastly augment point-of-care or field-based decisions. This pilot study evaluated the amplitude of traumatic brain injury (TBI)–associated biomarkers in serum as a consequence of repeated OP exposure from .50-caliber rifle use over training multiple days.

Objective: To determine the acute temporal profile of TBI-associated serum biomarkers and their relationship with neurocognitive decrements or self-reported symptoms among participants exposed to low-level, repeated OP from weapons used in a training environment.

Methods: Study participants were enrolled in .50-caliber sniper rifle training and exposed to mild OP (peak pressure 3.8–4.5 psi, impulse 19.27–42.22 psi-ms per day) for three consecutive days (D1–D3). Defense automated neurobehavioral assessment (DANA) neurocognitive testing, symptom reporting, and blood collection were conducted 2–3 h before (pre-) and again 0.45–3 h after (post-) OP exposure. The TBI-associated serum biomarkers, glial fibrillary acidic protein (GFAP), ubiquitin C-terminal hydrolase-L1 (UCH-L1), neurofilament light (Nf-L), tau, and amyloid beta peptides (Aβ-40 and Aβ-42) were measured using digital ELISAs.

Results: Serum GFAP decreased on D1 and D3 but not D2 after OP exposure. Nf-L was suppressed on D3 alone. Aβ-40 was elevated on D2 alone while Aβ-42 was elevated each day after OP exposure. Suppression of GFAP and elevation of Aβ-42 correlated to OP-mediated impulse levels measured on D3.

Conclusions: Acute measurement of Aβ-peptides may have utility as biomarkers of subconcussive OP caused by rifle fire. Fluctuation of GFAP, Nf-L, and particularly Aβ peptide levels may have utility as acute, systemic responders of subconcussive OP exposure caused by rifle fire even in the absence of extreme operational deficits or clinically defined concussion.

Regional hypothermia attenuates secondary-injury caused by time-out application of tourniquets following limb fragments injury combined with hemorrhagic shock

Background

Tourniquet is the most widely used and effective first-aid equipment for controlling hemorrhage of injured limb in battlefield. However, time-out application of tourniquets leads to ischemic-necrosis of skeletal muscles and ischemia-reperfusion injury. Regional hypothermia (RH) on wounded limb can relieve the injury on local tissue and distant organs. We aimed to investigate the protective effects of RH on rabbits’ limbs injured by a steel-ball combined with hemorrhagic-shock, and then employed tourniquet over-time, tried to identify the optimal treatment RH.

Methods

Thirty rabbits were randomly divided into 5 groups. All rabbits were anesthetized, intubated femoral artery and vein in right-hind limbs. Sham operation group (Sham): only femoral arteriovenous cannula in right-hind limb. None RH group (NRH): rabbits were intubated as Sham group, then the soft tissues of rabbits’ left-hinds were injured by a steel-ball shooting, and were exsanguinated until shock, then bundled with rubber tourniquets for 4 h. Three RH subgroups: rabbits were injured as mentioned above, the injured limbs were bundled with rubber tourniquets and treated with different temperature (5 ± 1 °C, 10 ± 1 °C, and 20 ± 1 °C, respectively) for 4 h. The injury severity of lung and regional muscle was assessed by histologic examination. Activity of adenosine triphosphatase (ATPase) and content of malondialdehyde (MDA) in muscle, inflammatory cytokines, myoglobin, creatine kinase-MM (CK-MM), Heme, Heme oxygenase 1 (HO-1), lactic acid (Lac), and lectrolyte ion in serum were detected.

Results

Following with RH treatment, the injury of lung and local muscle tissue was alleviated evidencing by mitigation of histopathological changes, significant decrease of water-content and MDA content, and increase of ATPase activity. Lower level of Lac, Potassium (K⁺), inflammatory cytokines, Heme, CK-MM, myoglobin content, and higher level of Calcium (Ca²⁺), HO-1 content were shown in RH treatment. 10 °C was the most effective RH to increase ATPase activity, and decrease MDA, myoglobin, CK-MM content.

Conclusion

Transient RH (4 h) had a “long-term mitigation effects” (continued for 6 h) on time-out application of tourniquet with the fluid resuscitation and core temperature maintenance, and the most effective temperature for reducing the side effects on tourniquet time-out application was 10 °C.

A Comprehensive Review of Experimental Rodent Models of Repeated Blast TBI

We reviewed the relevant literature delineating advances in the development of the experimental models of repeated blast TBI (rbTBI). It appears this subject is a relatively unexplored area considering the first work published in 2007 and the bulk of peer-reviewed papers was published post-2011. There are merely 34 papers published to date utilizing rodent rbTBI models. We performed an analysis and extracted basic parameters to capture the characteristics of the exposure conditions (the blast intensity, inter-exposure interval and the number of exposures), the age and weight of the animal models most commonly used in the studies, and their endpoints. Our analysis revealed three strains of rodents are predominantly used: Sprague Dawley and Long Evans rats and wild type (C57BL/6J) mice, and young adult animals 8 to 12-week-old are a preferred choice. Typical exposure conditions are the following: (1) peak overpressure in the 27–145 kPa (4–21 psi) range, (2) number of exposures: 2 (13.9%), 3 (63.9%), 5 (16.7%), or 12 (5.6%) with a single exposure used for a baseline comparison in 41.24% of the studies. Two inter-exposure interval durations were used: (1) short (1–30 min.) and (2) extended (24 h) between consecutive shock wave exposures. The experiments included characterization of repeated blast exposure effects on auditory, ocular and neurological function, with a focus on brain etiology in most of the published work. We present an overview of major histopathological findings, which are supplemented by studies implementing MRI (DTI) and behavioral changes after rbTBI in the acute (1–7 days post-injury), subacute (7–14 days), and chronic (>14 days) phases post-injury.

Impact of Low-Level Blast Exposure on Brain Function after a One-Day Tactile Training and the Ameliorating Effect of a Jugular Vein Compression Neck Collar Device

Special Weapons and Tactics (SWAT) personnel who conduct breacher exercises are at risk for blast-related head trauma. We aimed to investigate the potential impact of low-level blast exposure during breacher training on the neural functioning of working memory and auditory network connectivity. We also aimed to evaluate the effects of a jugular vein compression collar, designed to internally mitigate slosh energy absorption, preserving neural functioning and connectivity, following blast exposure. A total of 23 SWAT personnel were recruited and randomly assigned to a non-collar (n = 11) and collar group (n = 12). All participants completed a 1-day breacher training with multiple blast exposure. Prior to and following training, 18 participants (non-collar, n = 8; collar, n = 10) completed functional magnetic resonance imaging (fMRI) of working memory using N-Back task; 20 participants (non-collar, n = 10; collar, n = 12) completed resting-state fMRI. Key findings from the working memory analysis include significantly increased fMRI brain activation in the right insular, right superior temporal pole, right inferior frontal gyrus, and pars orbitalis post-training for the non-collar group (p < 0.05, threshold-free cluster enhancement corrected), but no changes were noted for the collar group. The elevation in fMRI activation in the non-collar group was found to correlate significantly (n = 7, r = 0.943, p = 0.001) with average peak impulse amplitude experienced during the training. In the resting-state fMRI analysis, significant pre- to post-training increase in connectivity between the auditory network and two discrete regions (left middle frontal gyrus and left superior lateral occipital/angular gyri) was found in the non-collar group, while no change was observed in the collar group. These data provided initial evidence of the impact of low-level blast on working memory and auditory network connectivity as well as the protective effect of collar on brain function following blast exposure, and is congruent with previous collar findings in sport-related traumatic brain injury.

Shock waves increase pulmonary vascular leakage, inflammation, oxidative stress, and apoptosis in a mouse model

Severe lung damage is a major cause of death in blast victims, but the mechanisms of pulmonary blast injury are not well understood. Therefore, it is important to study the injury mechanism of pulmonary blast injury. A model of lung injury induced by blast exposure was established by using a simulation blast device. The effectiveness and reproducibility of the device were investigated. Eighty mice were randomly divided into eight groups: control group and 3 h, 6 h, 12 h, 24 h, 48 h, 7 days and 14 days post blast. The explosive device induced an explosion injury model of a single lung injury in mice. The success rate of the model was as high as 90%, and the degree of lung injury was basically the same under the same pressure. Under the same conditions, the thickness of the aluminum film can be from 0.8 mm to 1.6 mm, and the peak pressure could be from 95.85 ± 15.61 PSI to 423.32 ± 11.64 PSI. There is no statistical difference in intragroup comparison. A follow-up lung injury experiment using an aluminum film thickness of 1.4 mm showed a pressure of 337.46 ± 18.30 PSI induced a mortality rate of approximately 23.2%. Compared with the control group (372 ± 23 times/min, 85.9 ± 9.4 mmHg, 4.34 ± 0.09), blast exposed mice had decreased heart rate (283 ± 21 times/min) and blood pressure (73.6 ± 3.6 mmHg), and increased lung wet/dry weight ratio(2.67 ± 0.11), marked edematous lung tissue, ruptured blood vessels, infiltrating inflammatory cells, increased NF-κB (4.13 ± 0.01), TNF-α (4.13 ± 0.01), IL-1β (2.43 ± 0.01) and IL-6 (4.65 ± 0.01) mRNA and protein, decreased IL-10(0.18 ± 0.02) mRNA and protein ( P < 0.05). The formation of ROS and the expression of MDA5 (4.46 ± 0.01) and IREα (3.43 ± 0.00) mRNA and protein were increased and the expression of SOD-1 (0.28 ± 0.02) mRNA and protein was decreased ( P < 0.05). Increased expression of Bax (3.54 ± 0.00) and caspase 3 (4.18 ± 0.01) mRNA and protein inhibited the expression of Bcl-2 (0.39 ± 0.02) mRNA and protein. The changes of pulmonary edema, inflammatory cell infiltration, and cell damage factor expression increased gradually with time, and reached the peak at 12-24 h after the outbreak, and returned to normal at 7-14 days. Detonation injury can lead to edema of lung tissue, pulmonary hemorrhage, rupture of pulmonary vessels, induction of early inflammatory responses accompanied by increased oxidative stress in lung tissue cells and increased apoptosis in mice experiencing blast injury. The above results are consistent with those reported in other literatures. It is showed that the mouse lung blast injury model is successfully modeled, and the device can be used for the study of pulmonary blast injury. Impact statement The number of patients with explosive injury has increased year by year, but there is no better treatment. However, the research on detonation injury is difficult to carry out. One of the factors is the difficulty in making the model of blast injury. The laboratory successfully developed and produced a simulation device of explosive knocking through a large amount of literature data and preliminary experiments, and verified the preparation of the simulation device through various experimental techniques. The results showed that the device could simulate the shock wave-induced acute lung injury generated, which was similar to the actual knocking injury. The experimental process was controlled. Under the same condition, there was no statistical difference between the groups. It is possible to realize miniaturization and precision of an explosive knocking simulation device, which is a good experimental tool for further research on the mechanism of organ damage caused by detonation and the development of protective drugs.

Damage of vascular endothelial barrier induced by explosive blast and its clinical significance

In recent years, injuries induced by explosive blast have got more and more attention owing to weapon development and frequent terrorist activities. Tear, bleeding and edema of tissues and organs are the main manifestations of blast shock wave damage. Vascular endothelial barrier is the main defense of tissues and organs' integrity. This article aims to discuss possible mechanisms of endothelial barrier damage induced by explosive blast and main manifestations of blood brain barrier, bloodeair barrier, and intestinal vascular barrier impairments. In addition, the main regulatory factors of vascular permeability are also summarized so as to provide theoretical basis for prevention and cure of vascular endothelial barrier damage resulting from explosive blast.

Steroid-Loaded Hemostatic Nanoparticles Combat Lung Injury after Blast Trauma

In response to the lack of therapeutics for internal bleeding following a traumatic event, we synthesized hemostatic dexamethasone nanoparticles (hDNP) to help alleviate internal hemorrhaging. hDNP consist of a block copolymer, poly(lactic-co-glycolic acid)-poly(l-lysine)-poly(ethylene glycol) conjugated to a peptide, glycine-arginine-glycine-aspartic acid-serine (GRGDS). These particles were evaluated as treatment for primary blast lung injury in a rodent model. Animals were randomly placed into test and control groups, exposed to blast and given immediate injection. Recovery was assessed using physiological parameters and immunohistochemistry. We found that dexamethasone-loaded hemostatic nanoparticles alleviate physiological deprivation caused by blast injury and reduce lung injury damage.

Blast-induced color change in photonic crystals corresponds with brain pathology

A high incidence of blast exposure is a 21st century reality in counter-insurgency warfare. However, thresholds for closed-head blast-induced traumatic brain injury (bTBI) remain unknown. Moreover, without objective information about relative blast exposure, warfighters with bTBI may not receive appropriate medical care and may remain in harm's way. Accordingly, we have engineered a blast injury dosimeter (BID) using a photonic crystalline material that changes color following blast exposure. The photonic crystals are fabricated using SU-8 via multi-beam interference laser lithography. The final BID is similar in appearance to an array of small colored stickers that may be affixed to uniforms or helmets in multiple locations. Although durable under normal conditions, the photonic crystalline micro- and nano-structure are precisely altered by blast to create a color change. These BIDs were evaluated using a rat model of bTBI, for which blast shockwave exposure was generated via a compressed air-driven shock tube. With prototype BID arrays affixed to the animals, we found that BID color changes corresponded with subtle brain pathologies, including neuronal degeneration and reactive astrocytosis. These subtle changes were most notable in the dentate gyrus of the hippocampus, cerebral cortex, and cerebellum. These data demonstrate the feasibility of using a materials-based, power-free colorimetric BID as the first self-contained blast sensor calibrated to correspond with brain pathology.

Local pulmonary administration of factor VIIa (rFVIIa) in diffuse alveolar hemorrhage (DAH) - a review of a new treatment paradigm

Background

Diffuse alveolar hemorrhage (DAH) is a clinical syndrome with typical symptoms dyspnea and hemoptysis. DAH is a complication of specific diseases, in some cases with acute catastrophic hemoptysis, while other patients present low grade alveolar bleeding with a need of chronic transfusion as in pulmonary hemosiderosis.

Methods

Current literature in the PubMed database and other sources was reviewed in order to evaluate the current treatment recommendations, efficacy of this treatment, and finally the risk of complications after off-label use of rFVIIa in respect to DAH.

Objectives

(i) To elucidate the clinical aspects of alveolar hemorrhage, (ii) to develop a simple diagnostic algorithm in order to separate DAH from other important pulmonary diseases with similar clinical picture and comparably high mortality. Such an algorithm has important therapeutic consequences because these diseases: acute lung injury (ALI), acute respiratory distress syndrome (ARDS) and bronchiolitis obliterans organizing pneumonia (BOOP) have different therapies, (iii) to evaluate and discuss whether local pulmonary administration may improve outcome and reduce mortality in DAH, and (iv) to suggest a treatment schedule.

Results

Hitherto the diagnosis and treatment of DAH has been based on anecdotal reports. The treatment has relied on different unspecific treatment modalities based on a mixture of treatment of the underlying disease and treatment without evidence targeted to stop the alveolar bleeding. However, recently a number of publications have advocated the use of intrapulmonary rFVIIa. Even in severe bleeding DAH has been shown to respond promptly without thromboembolic complication when FVIIa was administered locally via the air side, because the FVIIa does not penetrate the alveolo-capillary membrane to the blood-side. The incidence of DAH (in the US and Europe is 100,000–150,000, and 50,000 patients annually are at risk of developing DAH following hematopoietic stem cell transplant (HSCT) and autoimmune diseases. Finally 50,000–100,000 patients may be falsely categorized as having acute respiratory distress syndrome/acute lung injury (ARDS/ALI) because DAH and ARDS cannot be separated clinically. A new treatment paradigm of DAH is proposed as no other intervention has been able to ensure pulmonary hemostasis in DAH. The diagnosis of DAH is simple, a series of broncho-alveolar washes which become increasingly bloody. This test should be performed in all patients with pulmonary opacities in order to separate ARDS/ALI from DAH. FVIIa administrated via pulmonary route is “drug of choice”, because it stops bleeding in the life-threatening syndrome DAH. Hemostasis is obtained after only one to two small doses of FVIIa (50 μg/kg body weight per dose) and after hemostasis the oxygen transport quickly improves.

Conclusion

Intrapulmonary administration of rFVIIa is recommended as the treatment of choice for DAH and blast lung injury (BLI) because the treatment has been shown to be successful and uncomplicated in spite of the fact that only a small series of DAH has been documented.

Effect of blast exposure on the brain structure and cognition in Macaca fascicularis

Blast injury to the brain is one of the major causes of death and can also significantly affect cognition and physical and psychological skills in survivors of blast. The complex mechanisms via which blast injury causes impairment of cognition and other symptoms are poorly understood. In this study, we investigated the effects of varying degrees of primary blast overpressure (BOP; 80 and 200 kPa) on the pathophysiological and magnetic resonance imaging (MRI) changes and neurocognitive performance as assessed by the monkey Cambridge Neuropsychological Test Automated Battery (mCANTAB) in non-human primates (NHP). The study aimed to examine the effects of neurobehavioral and histopathological changes in NHP. MRI and histopathology revealed ultrastructural changes in the brain, notably in the Purkinje neurons in the cerebellum and pyramidal neurons in the hippocampus, which were most vulnerable to the blast. The results correlated well with the behavioral changes and changes in motor coordination and working memory of the affected monkeys. In addition, there was white matter damage affecting myelinated axons, astrocytic hypertrophy, and increased aquaporin-4 (AQP-4) expression in astrocytes, suggesting cerebral edema. Increased apoptosis appeared to involve astrocytes and oligodendrocytes in the animals following blast exposure. The small sample size could have contributed to the non-significant outcome in cognitive performance post-blast and limited quantitative analyses. Nevertheless, the study has provided initial descriptive changes for establishing a primary BOP threshold for brain injury to serve as a useful platform for future investigations that aim to estimate brain injury potential and set safe limits of exposure.

Tightly coupled repetitive blast-induced traumatic brain injury: development and characterization in mice

A mouse model of repeated blast exposure was developed using a compressed air-driven shock tube, to study the increase in severity of traumatic brain injury (bTBI) after multiple blast exposures. Isoflurane anesthetized C57BL/6J mice were exposed to 13.9, 20.6, and 25 psi single blast overpressure (BOP1) and allowed to recover for 5 days. BOP1 at 20.6 psi showed a mortality rate of 2% and this pressure was used for three repeated blast exposures (BOP3) with 1 and 30 min intervals. Overall mortality rate in BOP3 was increased to 20%. After blast exposure, righting reflex time and body-weight loss were significantly higher in BOP3 animals compared to BOP1 animals. At 4 h, brain edema was significantly increased in BOP3 animals compared to sham controls. Reactive oxygen species in the cortex were increased significantly in BOP1 and BOP3 animals. Neuropathological analysis of the cerebellum and cerebral cortex showed dense silver precipitates in BOP3 animals, indicating the presence of diffuse axonal injury. Fluoro-Jade B staining showed increased intensity in the cortex of BOP3 animals indicating neurodegeneration. Rota Rod behavioral test showed a significant decrease in performance at 10 rpm following BOP1 or BOP3 at 2 h post-blast, which gradually recovered during the 5 days. At 20 rpm, the latency to fall was significantly decreased in both BOP1 and BOP3 animals and it did not recover in the majority of the animals through 5 days of testing. These data suggest that repeated blast exposures lead to increased impairment severity in multiple neurological parameters of TBI in mice.

Computational modelling of lung injury: is there potential for benefit?

State-of-the-art medical care of the victims of current conflicts is generating large quantities of quality clinical data as a by-product. Observational research based on these data is beginning to have a profound influence on the clinical management of both military and civilian trauma patients. Computational modelling based on these datasets may offer the ability to investigate clinical treatment strategies that are practically, ethically or scientifically impossible to investigate on the front line. This article reviews the potential of this novel technology to aid development of treatment for blast lung and other unresolved medical scenarios.

Increase in blood-brain barrier permeability, oxidative stress, and activated microglia in a rat model of blast-induced traumatic brain injury

Traumatic brain injury (TBI) as a consequence of exposure to blast is increasingly prevalent in military populations, with the underlying pathophysiological mechanisms mostly unknown. In the present study, we utilized an air-driven shock tube to investigate the effects of blast exposure (120 kPa) on rat brains. Immediately following exposure to blast, neurological function was reduced. BBB permeability was measured using IgG antibody and evaluating its immunoreactivity in the brain. At 3 and 24 hr postexposure, there was a transient significant increase in IgG staining in the cortex. At 3 days postexposure, IgG immunoreactivity returned to control levels. Quantitative immunostaining was employed to determine the temporal course of brain oxidative stress following exposure to blast. Levels of 4-hydroxynonenal (4-HNE) and 3-nitrotyrosine (3-NT) were significantly increased at 3 hr postexposure and returned to control levels at 24 hr postexposure. The response of microglia to blast exposure was determined by autoradiographic localization of (3) H-PK11195 binding. At 5 days postexposure, increased binding was observed in the contralateral and ipsilateral dentate gyrus. These regions also displayed increased binding at 10 days postexposure; in addition to these regions there was increased binding in the contralateral ventral hippocampus and substantia nigra at this time point. By using antibodies against CD11b/c, microglia morphology characteristic of activated microglia was observed in the hippocampus and substantia nigra of animals exposed to blast. These results indicate that BBB breakdown, oxidative stress, and microglia activation likely play a role in the neuropathology associated with TBI as a result of blast exposure.

Drosophila melanogaster larvae as a model for blast lung injury

BACKGROUND

Primary blast injuries, specifically lung injuries, resulting from blast overpressure exposures are a major source of mortality for victims of blast events. However, existing pulmonary injury criteria are inappropriate for common exposure environments. This study uses Drosophila melanogaster larvae to develop a simple phenomenological model for human pulmonary injury from primary blast exposure.

METHODS

Drosophila larvae were exposed to blast overpressures generated by a 5.1-cm internal diameter shock tube and their mortality was observed after the exposure. To establish mortality thresholds, a survival analysis was conducted using survival data and peak incident pressures. In addition, a histologic analysis was performed on the larvae to establish the mechanisms of blast injury.

RESULTS

The results of the survival analysis suggest that blast overpressure for 50% Drosophila survival is greater than human threshold lung injury and is similar to human 50% survival levels, in the range of overpressure durations tested (1-5 ms). A "parallel" analysis of the Bass et al. 50% human survival curves indicates that 50% Drosophila survival is equivalent to a human injury resulting in a 69% chance of survival. Histologic analysis of the blast-exposed larvae failed to demonstrate damage to the dorsal trunk of the tracheal system; however, the presence of flocculent material in the larvae body cavities and tracheas suggests tissue damage.

CONCLUSIONS

This study shows that D. melanogaster survival can be correlated with large animal injury models to approximate a human blast lung injury tolerance. Within the range of durations tested, Drosophila larvae may be used as a simple model for blast injury.

Traumatic brain injury: an overview of pathobiology with emphasis on military populations

This review considers the pathobiology of non-impact blast-induced neurotrauma (BINT). The pathobiology of traumatic brain injury (TBI) has been historically studied in experimental models mimicking features seen in the civilian population. These brain injuries are characterized by primary damage to both gray and white matter and subsequent evolution of secondary pathogenic events at the cellular, biochemical, and molecular levels, which collectively mediate widespread neurodegeneration. An emerging field of research addresses brain injuries related to the military, in particular blast-induced brain injuries. What is clear from the effort to date is that the pathobiology of military TBIs, particularly BINT, has characteristics not seen in other types of brain injury, despite similar secondary injury cascades. The pathobiology of primary BINT is extremely complex. It comprises systemic, local, and cerebral responses interacting and often occurring in parallel. Activation of the autonomous nervous system, sudden pressure-increase in vital organs such as lungs and liver, and activation of neuroendocrine-immune system are among the most important mechanisms significantly contributing to molecular changes and cascading injury mechanisms in the brain.

Biomarkers of blast-induced neurotrauma: profiling molecular and cellular mechanisms of blast brain injury

The nature of warfare in the 21st century has led to a significant increase in primary blast or over-pressurization injuries to the whole body and head, which manifest as a complex of neuro-somatic damage, including traumatic brain injury (TBI). Identifying relevant pathogenic pathways in reproducible experimental models of primary blast wave exposure is therefore vital to the development of biomarkers for diagnostics of blast brain injury. Comparative analysis of mechanisms and putative biomarkers of blast brain injury is complicated by a deficiency of experimental studies. In this article, we present an overview of current TBI biomarkers, as well as outline experimental strategies to investigate molecular signatures of blast neurotrauma and to develop a pathway network map for novel biomarker discovery. These biomarkers will be effective for triaging and managing both combat and civilian casualities.

Blast injuries

Health-care providers are increasingly faced with the possibility of needing to care for people injured in explosions, but can often, however, feel undertrained for the unique aspects of the patient's presentation and management. Although most blast-related injuries (eg, fragmentation injuries from improvised explosive devices and standard military explosives) can be managed in a similar manner to typical penetrating or blunt traumatic injuries, injuries caused by the blast pressure wave itself cannot. The blast pressure wave exerts forces mainly at air-tissue interfaces within the body, and the pulmonary, gastrointestinal, and auditory systems are at greatest risk. Arterial air emboli arising from severe pulmonary injury can cause ischaemic complications-especially in the brain, heart, and intestinal tract. Attributable, in part, to the scene chaos that undoubtedly exists, poor triage and missed diagnosis of blast injuries are substantial concerns because injuries can be subtle or their presentation can be delayed. Management of these injuries can be a challenge, compounded by potentially conflicting treatment goals. This Seminar aims to provide a thorough overview of these unique primary blast injuries and their management.

Neuropathology and pressure in the pig brain resulting from low-impulse noise exposure

Military personnel are exposed to occupational levels of blast overpressure during training. This study characterizes the pressure-time histories of air, underwater, and localized blast, and correlates blast parameters with neuropathology. Blast overpressure was produced by a howitzer, a bazooka, an automatic rifle, underwater explosives, or a shock tube. Anesthetized pigs were exposed in positions that simulated real training scenarios. Underwater exposures were performed using explosives at distances recommended by safety requirements. In other experiments, rats were exposed via a shock tube. The pressure changes were recorded with a hydrophone sensor in the brain of the pig and in rats with an optical fiber sensor. Histological examination of porcine brains revealed small parenchymal and subarachnoid hemorrhages, predominately in the occipital lobe, cerebellum, and medulla oblongata. Relative to the peak pressure in air, that in porcine brain (Pmax brain/air) was 0.7 for the bazooka and 0.5 and 0.7, respectively, for the 9- and 30-kPa howitzer. The attenuation was stronger in water: the detonation pulse had a brain/water ratio of 0.1, and the secondary pulses had ratios of 0.3-0.4. The results indicate that low-frequency spectra penetrate easily from air or water into the brain, but high-frequency spectra appear to be filtered by body structures. In addition, blast waves were recorded in the brain and abdomen of pigs after local exposure via shock tube to either the abdomen or the top of the skull. When the abdomen was exposed, the maximal peak value in the brain was only 3% of that in the abdomen. Moreover, part of this pressure could have been derived from the air outside the head. The results gave little support to significant transmission of pressure within the body.