Article

Brain Injuries from Blast

Department of Biomedical Engineering, Duke University, 136 Hudson Hall, Durham, NC 27708, USA.
Annals of Biomedical Engineering (Impact Factor: 3.23). 01/2012; 40(1):185-202. DOI: 10.1007/s10439-011-0424-0
Source: PubMed

ABSTRACT Traumatic brain injury (TBI) from blast produces a number of conundrums. This review focuses on five fundamental questions including: (1) What are the physical correlates for blast TBI in humans? (2) Why is there limited evidence of traditional pulmonary injury from blast in current military field epidemiology? (3) What are the primary blast brain injury mechanisms in humans? (4) If TBI can present with clinical symptoms similar to those of Post-Traumatic Stress Disorder (PTSD), how do we clinically differentiate blast TBI from PTSD and other psychiatric conditions? (5) How do we scale experimental animal models to human response? The preponderance of the evidence from a combination of clinical practice and experimental models suggests that blast TBI from direct blast exposure occurs on the modern battlefield. Progress has been made in establishing injury risk functions in terms of blast overpressure time histories, and there is strong experimental evidence in animal models that mild brain injuries occur at blast intensities that are similar to the pulmonary injury threshold. Enhanced thoracic protection from ballistic protective body armor likely plays a role in the occurrence of blast TBI by preventing lung injuries at blast intensities that could cause TBI. Principal areas of uncertainty include the need for a more comprehensive injury assessment for mild blast injuries in humans, an improved understanding of blast TBI pathophysiology of blast TBI in animal models and humans, the relationship between clinical manifestations of PTSD and mild TBI from blunt or blast trauma including possible synergistic effects, and scaling between animals models and human exposure to blasts in wartime and terrorist attacks. Experimental methodologies, including location of the animal model relative to the shock or blast source, should be carefully designed to provide a realistic blast experiment with conditions comparable to blasts on humans. If traditional blast scaling is appropriate between species, many reported rodent blast TBI experiments using air shock tubes have blast overpressure conditions that are similar to human long-duration nuclear blasts, not high explosive blasts.

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    • "The cognitive and emotional difficulties that can result from TBI may also reduce awareness and interfere with reliability of selfreport [12]. Last, symptoms resulting from mTBI, such as headache, dizziness, depression, and anxiety, are nonspecific and, although frequently exacerbated by injury, are also common premorbidly (in the population at large). "
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    ABSTRACT: Military mild traumatic brain injury (mTBI) differs from civilian injury in important ways. Although mTBI sustained in both military and civilian settings are likely to be underreported, the combat theater presents additional obstacles to reporting and accessing care. The impact of blast forces on the nervous system may differ from nonblast mechanisms, mTBI although studies comparing the neurologic and cognitive sequelae in mTBI survivors have not provided such evidence. However, emotional distress appears to figure prominently in symptoms following military mTBI. This review evaluates the extant literature with an eye towards future research directions.
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    • "Second, with the exception of peak pressure, the waveform is relatively impervious to modulation and dependent on tube dimensions and animal placement. Third, there are important considerations with respect to the scale difference between human exposures and animal models (Bass et al. 2011). A free-field blast wave may operate at 30-cm wavelength and have significant variation within the human body, including within the head region. "
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    ABSTRACT: Though intrinsically of much higher frequency than open-field blast overpressures, high-intensity focused ultrasound (HIFU) pulse trains can be frequency modulated to produce a radiation pressure having a similar form. In this study, 1.5-MHz HIFU pulse trains of 1-ms duration were applied to intact skulls of mice in vivo and resulted in blood-brain barrier disruption and immune responses (astrocyte reactivity and microglial activation). Analyses of variance indicated that 24 h after HIFU exposure, staining density for glial fibrillary acidic protein was elevated in the parietal and temporal regions of the cerebral cortex, corpus callosum and hippocampus, and staining density for the microglial marker, ionized calcium binding adaptor molecule, was elevated 2 and 24 h after exposure in the corpus callosum and hippocampus (all statistical test results, p < 0.05). HIFU shows promise for the study of some bio-effect aspects of blast-related, non-impact mild traumatic brain injuries in animals.
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    • "While some of these symptoms could be related to comorbid states (as described by Capehart and Bass, 2012), sensitive diagnostic tests to evaluate and quantify the reported symptoms are needed. Unfortunately, the battery of neurocognitive testing performed is often normal in patients who describe this increased cognitive effort, suggesting that the tests might not be sensitive enough to detect the increased neural load requirements. "
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    ABSTRACT: This review focuses on the application of functional magnetic resonance imaging (fMRI) to the investigation of blast-related traumatic brain injury (bTBI). Relatively little is known about the exact mechanisms of neurophysiological injury and pathological and functional sequelae of bTBI. Furthermore, in mild bTBI, standard anatomical imaging techniques (MRI and computed tomography) generally fail to show focal lesions and most of the symptoms present as subjective clinical functional deficits. Therefore, an objective test of brain functionality has great potential to aid in patient diagnosis and provide a sensitive measurement to monitor disease progression and treatment. The goal of this review is to highlight the relevant body of blast-related TBI literature and present suggestions and considerations in the development of fMRI studies for the investigation of bTBI. The review begins with a summary of recent bTBI publications followed by discussions of various elements of blast-related injury. Brief reviews of some fMRI techniques that focus on mental processes commonly disrupted by bTBI, including working memory, selective attention, and emotional processing, are presented in addition to a short review of resting state fMRI. Potential strengths and weaknesses of these approaches as regards bTBI are discussed. Finally, this review presents considerations that must be made when designing fMRI studies for bTBI populations, given the heterogeneous nature of bTBI and its high rate of comorbidity with other physical and psychological injuries.
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