Military and law-enforcement personnel repeatedly exposed to low-level blasts have significant brain changes – including an increased level of brain injury and inflammation – compared with a control group, according to a study in the Journal of Neurotrauma.
Led by University of Virginia School of Medicine researcher James Stone, MD, PhD, the study compared the brains of 20 “breachers” – specialists who use explosives to enter buildings and other structures – with a 14-person, age-matched control group. The breachers had been exposed to an average of 4,628 blasts, while the control group had been exposed to an average of three.
Blood measurements and neuropsychological assessments suggest that the breachers have increased levels of brain injury and inflammation, which the researchers wrote is “consistent with the theory that exposure to breaching-related blasts leads to system-wide effects in the brain.”
The study also found that the breachers had statistically significant differences in blood flow, brain structure and brain activity.
“This study is the first to comprehensively assess military and law enforcement personnel to better understand whether repetitive blast exposure over a career can lead to changes within the brain,” Stone said. “This is an area of high importance to military and law enforcement communities, as it is becoming increasingly clear there may be occupational health considerations related to repetitive low-level blast exposure in training and operations over the career of an exposed individual.”
The researchers wrote that further studies will be needed to determine more precisely what level and frequency of blast exposure may result in the observed brain changes.
Stone and his colleagues have two additional studies underway to further examine the effects of blasts on the brains of military personnel. The first – backed by a three-year, $2.1 million grant from the US Department of Defense – is researching the effects of regular exposure to artillery blasts. The second is examining whether special operations forces are at risk for brain injury over their career.
“These additional studies will allow us to better understand whether the observations made in breachers are also seen in other blast-exposed populations, such as those that operate heavy weapons,” Stone said. “We also hope to be able to shed light on how the brain responds to repetitive blasts on a molecular level.”
Combat military and civilian law enforcement personnel may be exposed to repetitive low-intensity blast events during training and operations. Persons who use explosives to gain entry (i.e., breach) into buildings are known as “breachers” or dynamic entry personnel. Breachers operate under the guidance of established safety protocols, but despite these precautions, breachers who are exposed to low-level blast throughout their careers frequently report performance deficits and symptoms to healthcare providers. Although little is known about the etiology linking blast exposure to clinical symptoms in humans, animal studies demonstrate network-level changes in brain function, alterations in brain morphology, vascular and inflammatory changes, hearing loss, and even alterations in gene expression after repeated blast exposure. To explore whether similar effects occur in humans, we collected a comprehensive data battery from 20 experienced breachers exposed to blast throughout their careers and 14 military and law enforcement controls. This battery included neuropsychological assessments, blood biomarkers, and magnetic resonance imaging measures, including cortical thickness, diffusion tensor imaging of white matter, functional connectivity, and perfusion. To better understand the relationship between repetitive low-level blast exposure and behavioral and imaging differences in humans, we analyzed the data using similarity-driven multi-view linear reconstruction (SiMLR). SiMLR is specifically designed for multiple modality statistical integration using dimensionality-reduction techniques for studies with high-dimensional, yet sparse, data (i.e., low number of subjects and many data per subject). We identify significant group effects in these data spanning brain structure, function, and blood biomarkers.
The researchers published their findings in the Journal of Neurotrauma. The UVA research team included Stone, Brian B. Avants, Nicholas J. Tustison, Meghan O’Brien and Natalie Domeisen. They were joined by colleagues from the National Institute of Neurological Disorders and Stroke, National Institute of Nursing Research, University of Florida, Pennsylvania State University, Oak Ridge Institute for Science and Education, Uniformed Services University, Walter Reed Army Institute of Research, the Department of Defense Joint Artificial Intelligence Center, University of Glasgow and the Naval Medical Research Center.
The work was supported by Joint Program Committee-5 Development of Exposure Standards to Repeated Blast Exposure program, work unit 603115HP-3730-001-A1118; Office of Naval Research (ONR) award N00014-18-1-2440, with supplemental funding to the ONR award provided by Cohen Veterans Bioscience; imaging resources from the Center for Neuroscience and Re-generative Medicine; the Clinical Neurosciences Program of the National Institute of Neurological Disorders and Stroke, project 1ZIANS002977-21; and the Research Participation Program at the Walter Reed Army Institute of Research.
Full Journal of Neurotrauma study (Open access) report