An unusual primary blast injury

Primary Blast Causes Delayed Effects without Cell Death in Shell-Encased Brain Cell Aggregates

Previous work in this laboratory used underwater explosive exposures to isolate the effects of shock-induced principle stress without shear on rat brain aggregate cultures. The current study has utilized simulated air blast to expose aggregates in suspension and enclosed within a spherical shell, enabling the examination of a much more complex biomechanical insult. Culture medium-filled spheres were exposed to single pulse overpressures of 15-30 psi (∼6-7 msec duration) and measurements within the sphere at defined sites showed complex and spatially dependent pressure changes. When brain aggregates were exposed to similar conditions, no cell death was observed and no changes in several commonly used biomarkers of traumatic brain injury (TBI) were noted. However, similarly to underwater blast, immediate and transient increases in the protein kinase B signaling pathway were observed at early time-points (3 days). In contrast, the oligodendrocyte marker 2',3'-cyclic nucleotide 3'-phosphodiesterase, as well as vascular endothelial growth factor, both displayed markedly delayed (14-28 days) and pressure-dependent responses. The imposition of a spherical shell between the single pulse shock wave and the target brain tissue introduces greatly increased complexity to the insult. This work shows that brain tissue can not only discriminate the nature of the pressure changes it experiences, but that a portion of its response is significantly delayed. These results have mechanistic implications for the study of primary blast-induced TBI and also highlight the importance of rigorously characterizing the actual pressure variations experienced by target tissue in primary blast studies.

The Effect of Underwater Blast on Aggregating Brain Cell Cultures

Although the deleterious effects of primary blast on gas-filled organs are well accepted, the effect of blast-induced shock waves on the brain is less clear because of factors that complicate the interpretation of clinical and experimental data. Brain cell aggregate cultures are comprised of multiple differentiated brain cell types and were used to examine the effects of underwater blast. Suspensions of these cultures encased in dialysis tubing were exposed to explosive-generated underwater blasts of low (∼300 kPa), medium (∼2,700 kPa), or high (∼14,000 kPa) intensities and harvested at 1-28 days post-exposure. No changes in gross morphology were noted immediately or weeks after blast wave exposure, and no increases in either apoptotic (caspase-3) or necrotic (lactate dehydrogenase) cell death were observed. Changes in neuronal (neurofilament H, acetylcholinesterase, and choline acetyltransferase) and glial (glial fibrillary acidic protein, glutamine synthetase) endpoints did not occur. However, significant time- and pressure-related increases in Akt (protein kinase B) phosphorylation were noted, as well as declines in vascular endothelial growth factor levels, implicating pathways involved in cellular survival mechanisms. The free-floating nature of the aggregates during blast wave exposure, coupled with their highly hydrolyzed dialysis tubing containment, results in minimized boundary effects, thus enabling accurate assessment of brain cell response to a simplified shock-induced stress wave. This work shows that, at its simplest, blast-induced shock waves produce subtle changes in brain tissue. This study has mechanistic implications for the study of primary blast-induced traumatic brain injury and supports the thesis that underwater blast may cause subtle changes in the brains of submerged individuals.

Understanding and treating blast traumatic brain injury in the combat theater

OBJECTIVES

Blast injury is a frequent cause of traumatic brain injury (TBI) in the modern combat theater. We sought to explain the research and treatment associated with this injury.

METHODS

We reviewed literature on the prevalence of blast TBI (bTBI), blast injury mechanisms, research, and perspectives on the neurosurgical experience treating bTBI.

RESULTS

A majority of combat-related casualties in recent wars are due to blast. A majority of survivors of blast injuries are diagnosed with TBI. Blast injury may induce changes in the brain not seen with non-blast-related mechanisms. However, long-term symptoms are not significantly different from non-blast mechanisms. Aggressive decompressive craniectomies are commonly performed in the combat theater.

DISCUSSION

Due to the prevalence and debilitating nature of bTBI, understanding injury mechanisms is crucial in treating the injury before symptoms become permanent. Treatment is currently limited to decompressive craniectomies, which are the most effective treatment for a relatively young and fit military population.

Mechanisms and treatment of blast induced hearing loss

The main objective of this study is to provide an overview of the basic mechanisms of blast induced hearing loss and review pharmacological treatments or interventions that can reduce or inhibit blast induced hearing loss. The mechanisms of blast induced hearing loss have been studied in experimental animal models mimicking features of damage or injury seen in human. Blast induced hearing loss is characterized by perforation and rupture of the tympanic membrane, ossicular damage, basilar membrane damage, inner and outer hair cell loss, rupture of round window, changes in chemical components of cochlear fluid, vasospasm, ischemia, oxidative stress, excitotoxicity, hematoma, and hemorrhage in both animals and humans. These histopathological consequences of blast exposure can induce hearing loss, tinnitus, dizziness, and headache. The pharmacological approaches to block or inhibit some of the auditory pathological consequences caused by blast exposure have been developed with antioxidant drugs such as 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HXY-059, now called HPN-07) and N-acetylcysteine (NAC). A combination of antioxidant drugs (HPN-07 and NAC) was administered to reduce blast induced cochlear damage and hearing loss. The combination of the antioxidant drugs can prevent or treat blast induced hearing loss by reducing damage to the mechanical and neural component of the auditory system. Although information of the underlying mechanisms and treatment of blast induced hearing loss are provided, further and deep research should be achieved due to the limited and controversial knowledge.

A case of frontal neuropsychological and neuroimaging signs following multiple primary-blast exposure

Blast-related traumatic brain injury (TBI) from the Afghanistan and Iraq wars represents a significant medical concern for troops and veterans. To better understand the consequences of primary-blast injury in humans, we present a case of a Marine exposed to multiple primary blasts during his 14-year military career. The neuropsychological profile of this formerly high-functioning veteran suggested primarily executive dysfunction. Diffusion-tensor imaging revealed white-matter pathology in long fiber tracks compared with a composite fractional-anisotropy template derived from a veteran reference control group without TBI. This study supports the existence of primary blast-induced neurotrauma in humans and introduces a neuroimaging technique with potential to discriminate multiple-blast TBI.

Neuropsychological outcome from blast versus non-blast: mild traumatic brain injury in U.S. military service members

The purpose of this study was to compare the neuropsychological outcome from blast-related versus non-blast related mild traumatic brain injury (MTBI). Participants were 56 U.S. military service members who sustained an MTBI, divided into two groups based on mechanism of injury: (a) non-blast related (Non-blast; n = 21), and (b) blast plus secondary blunt trauma (Blast Plus; n = 35). All participants had sustained their injury in theatre whilst deployed during Operation Iraqi Freedom or Operation Enduring Freedom. Patients had been seen for neuropsychological evaluation at Walter Reed Army Medical Center on average 4.4 months (SD = 4.1) post-injury. Measures included 14 clinical scales from the Personality Assessment Inventory (PAI) and 12 common neurocognitive measures. For the PAI, there were no significant differences between groups on all scales (p > .05). However, medium effect sizes were found for the Depression (d = .49) and Stress (d = .47) scales (i.e., Blast Plus > Non-blast). On the neurocognitive measures, after controlling for the influence of psychological distress (i.e., Depression, Stress), there were no differences between the Non-blast and Blast Plus groups on all measures. These findings provide little evidence to suggest that blast exposure plus secondary blunt trauma results in worse cognitive or psychological recovery than blunt trauma alone. (JINS, 2012, 18, 595-605).

Neuro-glial and systemic mechanisms of pathological responses in rat models of primary blast overpressure compared to "composite" blast

A number of experimental models of blast brain injury have been implemented in rodents and larger animals. However, the variety of blast sources and the complexity of blast wave biophysics have made data on injury mechanisms and biomarkers difficult to analyze and compare. Recently, we showed the importance of rat position toward blast generated by an external shock tube. In this study, we further characterized blast producing moderate traumatic brain injury and defined "composite" blast and primary blast exposure set-ups. Schlieren optics visualized interaction between the head and a shock wave generated by external shock tube, revealing strong head acceleration upon positioning the rat on-axis with the shock tube (composite blast), but negligible skull movement upon peak overpressure exposure off-axis (primary blast). Brain injury signatures of a primary blast hitting the frontal head were assessed and compared to damage produced by composite blast. Low to negligible levels of neurodegeneration were found following primary blast compared to composite blast by silver staining. However, persistent gliosis in hippocampus and accumulation of GFAP/CNPase in circulation was detected after both primary and composite blast. Also, markers of vascular/endothelial inflammation integrin alpha/beta, soluble intercellular adhesion molecule-1, and L-selectin along with neurotrophic factor nerve growth factor-beta were increased in serum within 6 h post-blasts and persisted for 7 days thereafter. In contrast, systemic IL-1, IL-10, fractalkine, neuroendocrine peptide Orexin A, and VEGF receptor Neuropilin-2 (NRP-2) were raised predominantly after primary blast exposure. In conclusion, biomarkers of major pathological pathways were elevated at all blast set-ups. The most significant and persistent changes in neuro-glial markers were found after composite blast, while primary blast instigated prominent systemic cytokine/chemokine, Orexin A, and Neuropilin-2 release, particularly when primary blast impacted rats with unprotected body.

Biomechanics of single cortical neurons

This study presents experimental results and computational analysis of the large strain dynamic behavior of single neurons in vitro with the objective of formulating a novel quantitative framework for the biomechanics of cortical neurons. Relying on the atomic force microscopy (AFM) technique, novel testing protocols are developed to enable the characterization of neural soma deformability over a range of indentation rates spanning three orders of magnitude, 10, 1, and 0.1 μm s(-1). Modified spherical AFM probes were utilized to compress the cell bodies of neonatal rat cortical neurons in load, unload, reload and relaxation conditions. The cell response showed marked hysteretic features, strong non-linearities, and substantial time/rate dependencies. The rheological data were complemented with geometrical measurements of cell body morphology, i.e. cross-diameter and height estimates. A constitutive model, validated by the present experiments, is proposed to quantify the mechanical behavior of cortical neurons. The model aimed to correlate empirical findings with measurable degrees of (hyper)elastic resilience and viscosity at the cell level. The proposed formulation, predicated upon previous constitutive model developments undertaken at the cortical tissue level, was implemented in a three-dimensional finite element framework. The simulated cell response was calibrated to the experimental measurements under the selected test conditions, providing a novel single cell model that could form the basis for further refinements.

The use of silver-impregnated dressings in blast injuries

This article aims to critically examine the management of military patients who have been the victims of thermal injuries, which have become infected resulting from their inoculation with dirt and foreign bodies during blasts and explosions. In the interests of maintaining confidentiality, the names of NHS trusts, military hospitals and specific military operations have been omitted. This action has been taken in accordance with guidelines from the Nursing and Midwifery Council (2008).

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.

Case report of a soldier with primary blast brain injury

Primary blast injury of the central nervous system is described in a service-member exposed to a large ordinance explosion. Neuroimaging abnormalities are described together with normalization of the fractional anisotrophy on diffusion tensor imaging after follow-up imaging studies.

Blast physics and central nervous system injury

The effect of blast on biological tissue is well documented for particular organ systems such as the lung. This is not the case for the CNS, where the mechanism of CNS injury following a detonation and blast wave is unclear. The effect of blast on traumatic brain injury (TBI) has come into particular focus with the Global War on Terror and Operation Iraqi Freedom, and Operation Enduring Freedom where TBI has become known as the signature injury of these conflicts. The reason for the prominence of TBI in these particular conflicts as opposed to others is unclear, but may result from the increased survivability of blast due to improvements in body armor. In this review, we trace the historical context of blast injury and develop current concepts from this framework, in addition to highlighting many remaining unsolved questions.