Exposure to blast waves is suspected to cause primary traumatic brain injury. However, existing finite-element (FE) models of the rat head lack the necessary fidelity to characterize the biomechanical responses in the brain due to blast exposure. They neglect to represent the cerebral vasculature, which increases brain stiffness, and lack the appropriate brain material properties characteristic of high strain rates observed in blast exposures. To address these limitations, we developed a high-fidelity three-dimensional FE model of a rat head. We explicitly represented the rat’s cerebral vasculature and used high-strain-rate material properties of the rat brain. For a range of blast overpressures (100 to 230 kPa) the brain-pressure predictions matched experimental results and largely overlapped with and tracked the incident pressure–time profile. Incorporating the vasculature decreased the average peak strain in the cerebrum, cerebellum, and brainstem by 17, 33, and 18%, respectively. When compared with our model based on rat-brain properties, the use of human-brain properties in the FE model led to a three-fold reduction in the strain predictions. For simulations of blast exposure in rats, our findings suggest that representing cerebral vasculature and species-specific brain properties has a considerable influence in the resulting brain strain but not the pressure predictions.

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A 3-D Rat Brain Model for Blast-Wave Exposure: Effects of Brain Vasculature and Material Properties.

Pelvic vascular injury in the casualty of an explosive insult is a principal risk factor for increased mortality. The mechanism of injury has not previously been investigated in a physical model. In this study, a small-animal model of pelvic blast injury with a shock-tube mediated blast wave was utilised and showed that lower limb flail is necessary for an unstable pelvic fracture with vascular injury to occur. One hundred and seventy-three cadaveric mice underwent shock-tube blast testing and subsequent injury analysis. Increasingly displaced pelvic fractures and an increase in the incidence of pelvic vascular injury were seen with increasing lower limb flail; the 50% risk of vascular injury was 66° of lower limb flail out from the midline (95% confidence intervals 59°–75°). Pre-blast surgical amputation at the hip or knee showed the thigh was essential to result in pelvic displacement whilst the leg was not. These findings, corroborated by clinical data, bring a paradigm shift in our understanding of the mechanism of blast injury. Restriction of lower limb flail in the human, through personal protective equipment, has the potential to mitigate the effects of pelvic blast injury.

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Restricting Lower Limb Flail is Key to Preventing Fatal Pelvic Blast Injury.

Neurologic conditions such as stroke and traumatic brain injury are challenging conditions to study in humans. Animal models are necessary to uncover disease processes and develop novel therapies. When attempting to model these or other neurologic diseases, the accompanying anesthesia and analgesia create variables that are not part of the onset of the clinical disease in the human population but are critical components of the postinjury care both in humans and animals. To maximize model validity, researchers must consider whether the disease process or a novel therapy is being studied. Damage to the neurons of the brain or the spinal cord is not painful at the neural tissue itself, but alterations to nociceptive signaling along the pain pathway can induce chronic pain. In addition, trauma or surgery leading to the event is associated with damage to peripheral tissue. Inflammation is inextricably associated with tissue injury. Inflammation is known to evoke nociception in the periphery and drive long-term changes to neurons in the CNS. Analgesics and anesthetics alter these responses yet are required as part of humane animal care. Careful planning for effective drug administration consistent with the standard of care for humans and equivalent animal care is required.

/pdf/defining-and-managing-pain-in-stroke-and-traumatic-brain-lxla6k3kie.pdf

Defining and Managing Pain in Stroke and Traumatic Brain Injury Research.

Defining blast loading 'zones of relevance' for primary blast injury research: A consensus of injury criteria for idealised explosive scenarios.

Military personnel sustain head and brain injuries as a result of ballistic, blast, and blunt impact threats. Combat helmets are meant to protect the heads of these personnel during injury events. Studies show peak kinematics and kinetics are attenuated using protective headgear during impacts; however, there is limited experimental biomechanical literature that examines whether or not helmets mitigate peak mechanics delivered to the head and brain during blast. While the mechanical links between blast and brain injury are not universally agreed upon, one hypothesis is that blast energy can be transmitted through the head and into the brain. These transmissions can lead to rapid skull flexure and elevated pressures in the cranial vault, and, therefore, may be relevant in determining injury likelihood. Therefore, it could be argued that assessing a helmet for the ability to mitigate mechanics may be an appropriate paradigm for assessing the potential protective benefits of helmets against blast. In this work, we use a surrogate model of the head and brain to assess whether or not helmets and eye protection can alter mechanical measures during both head-level face-on blast and high forehead blunt impact events. Measurements near the forehead suggest head protection can attenuate brain parenchyma pressures by as much as 49% during blast and 52% during impact, and forces on the inner table of the skull by as much as 80% during blast and 84% during impact, relative to an unprotected head.

/pdf/protective-headgear-attenuates-forces-on-the-inner-table-and-3fvlvsyy27.pdf

Protective Headgear Attenuates Forces on the Inner Table and Pressure in the Brain Parenchyma During Blast and Impact: An Experimental Study Using a Simulant-Based Surrogate Model of the Human Head

Injuries sustained due to attacks from explosive weapons are multiple in number, complex in nature, and not well characterised. Blast may cause damage to the human body by the direct effect of overpressure, penetration by highly energised fragments, and blunt trauma by violent displacements of the body. The ability to reproduce the injuries of such insults in a well-controlled fashion is essential in order to understand fully the unique mechanism by which they occur, and design better treatment and protection strategies to alleviate the resulting poor long-term outcomes. This paper reports a range of experimental platforms that have been developed for different blast injury models, their working mechanism, and main applications. These platforms include the shock tube, split-Hopkinson bars, the gas gun, drop towers and bespoke underbody blast simulators.

https://militaryhealth.bmj.com/content/jramc/165/1/33.full.pdf

Experimental platforms to study blast injury

Introduction Death as a consequence of underbody blast (UBB) can most commonly be attributed to central nervous system injury. UBB may be considered a form of tertiary blast injury but is at a higher rate and somewhat more predictable than injury caused by more classical forms of tertiary injury. Recent studies have focused on the transmission of axial load through the cervical spine with clinically relevant injury caused by resultant compression and flexion. This paper seeks to clarify the pattern of head and neck injuries in fatal UBB incidents using a pragmatic anatomical classification. Methods This retrospective study investigated fatal UBB incidents in UK triservice members during recent operations in Afghanistan and Iraq. Head and neck injuries were classified by anatomical site into: skull vault fractures, parenchymal brain injuries, base of skull fractures, brain stem injuries and cervical spine fractures. Incidence of all injuries and of each injury type in isolation was compared. Results 129 fatalities as a consequence of UBB were identified of whom 94 sustained head or neck injuries. 87 casualties had injuries amenable to analysis. Parenchymal brain injuries (75%) occurred most commonly followed by skull vault (55%) and base of skull fractures (32%). Cervical spine fractures occurred in only 18% of casualties. 62% of casualties had multiple sites of injury with only one casualty sustaining an isolated cervical spine fracture. Conclusion Improvement of UBB survivability requires the understanding of fatal injury mechanisms. Although previous biomechanical studies have concentrated on the effect of axial load transmission and resultant injury to the cervical spine, our work demonstrates that cervical spine injuries are of limited clinical relevance for UBB survivability and that research should focus on severe brain injury secondary to direct head impact.

https://militaryhealth.bmj.com/content/jramc/165/1/18.full.pdf

Fatal head and neck injuries in military underbody blast casualties.

IntroductionThe temporal patterns and unit-based distributions of trauma patients requiring surgical intervention are poorly described in the UK. We describe the distribution of trauma patients in ...

https://publishing.rcseng.ac.uk/doi/pdf/10.1308/rcsann.2019.0135

A. P. Pearce

Papers

Experimental platforms to study blast injury

Fatal head and neck injuries in military underbody blast casualties.

Trends in admission timing and mechanism of injury can be used to improve general surgical trauma training.