Repeated Low-Level Blast Exposure: A Descriptive Human Subjects Study

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.

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Repeated Occupational Exposure to Low-level Blast in the Canadian Armed Forces: Effects on Hearing, Balance, and Ataxia

Military Medicine ◽

10.1093/milmed/usaa439 ◽

2021 ◽

Author(s):

Ann Nakashima ◽

Oshin Vartanian ◽

Shawn G Rhind ◽

Kristen King ◽

Catherine Tenn ◽

...

Keyword(s):

Hearing Loss ◽

Occupational Exposure ◽

Armed Forces ◽

Cross Sectional ◽

Low Level ◽

Additional Information ◽

Adverse Health Effects ◽

Blast Overpressure ◽

Blast Exposure

ABSTRACT Introduction Recently, there has been increasing concern about the adverse health effects of long-term occupational exposure to low-level blast in military personnel. Occupational blast exposure occurs routinely in garrison through use of armaments and controlled blast detonations. In the current study, we focused on a population of breaching instructors and range staff. Breaching is a tactical technique that is used to gain entry into closed spaces, often through the use of explosives. Materials and Methods Initial measurements of blast overpressure collected during breaching courses found that up to 10% of the blasts for range staff and up to 32% of the blasts for instructors exceeded the recommended 3 psi exposure limit. Using a cross-sectional design, we used tests of balance, ataxia, and hearing to compare a sample of breachers (n = 19) to age-and sex-matched military controls (n = 19). Results There were no significant differences between the two groups on the balance and ataxia tests, although the average scores of both groups were lower than would be expected in a normative population. The prevalence of hearing loss was low in the breacher group (4 of 19), and hearing thresholds were not significantly different from the controls. However, the prevalence of self-reported tinnitus was significantly higher in the breacher group (12 of 19) compared with the controls (4 of 19), and all breachers who were identified as having hearing loss also reported tinnitus. Conclusions Our results suggest that basic tests of balance, ataxia, and hearing on their own were not sensitive to the effects of long-term occupational exposure to low-level blast. Some of the blast exposure levels exceeded limits, and there was a significant association of exposure with tinnitus. Future studies should supplement with additional information including exposure history and functional hearing assessments. These findings should be considered in the design of future acute and longitudinal studies of low-level blast exposure.

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Repetitive low-level blast exposure improves behavioral deficits and chronically lowers Aβ42 in an Alzheimer's disease transgenic mouse model

Journal of Neurotrauma ◽

10.1089/neu.2021.0184 ◽

2021 ◽

Author(s):

Georgina Perez Garcia ◽

Rita De Gasperi ◽

Anna E Tschiffely ◽

Miguel A Gama Sosa ◽

Rania Abutarboush ◽

...

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Mouse Model ◽

Transgenic Mouse ◽

Transgenic Mouse Model ◽

Behavioral Deficits ◽

Low Level ◽

Blast Exposure

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Effects of repetitive low-level blast exposure on visual system and ocular structures

The Journal of Rehabilitation Research and Development ◽

10.1682/jrrd.2014.09.0204 ◽

2015 ◽

Vol 52 (3) ◽

pp. 273-290 ◽

Cited By ~ 6

Author(s):

José E. Capó-Aponte ◽

Gina M. Jurek ◽

David V. Walsh ◽

Leonard A. Temme ◽

William A. Ahroon ◽

...

Keyword(s):

Visual System ◽

Low Level ◽

Blast Exposure

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Development of a Portable Tool for Screening Neuromotor Sequelae From Repetitive Low-Level Blast Exposure

Military Medicine ◽

10.7205/milmed-d-16-00140 ◽

2017 ◽

Vol 182 (S1) ◽

pp. 147-154 ◽

Cited By ~ 9

Author(s):

Christopher K. Rhea ◽

Nikita A. Kuznetsov ◽

Scott E. Ross ◽

Benjamin Long ◽

Jason T. Jakiela ◽

...

Keyword(s):

Low Level ◽

Blast Exposure

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Chronic post-traumatic stress disorder-related traits in a rat model of low-level blast exposure

Behavioural Brain Research ◽

10.1016/j.bbr.2016.09.061 ◽

2018 ◽

Vol 340 ◽

pp. 117-125 ◽

Cited By ~ 13

Author(s):

Georgina Perez-Garcia ◽

Miguel A. Gama Sosa ◽

Rita De Gasperi ◽

Margaret Lashof-Sullivan ◽

Eric Maudlin-Jeronimo ◽

...

Keyword(s):

Rat Model ◽

Post Traumatic Stress Disorder ◽

Traumatic Stress ◽

Stress Disorder ◽

Post Traumatic Stress ◽

Low Level ◽

Blast Exposure ◽

Post Traumatic

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Common spatiotemporal processing of visual features shapes object representation

10.1101/459214 ◽

2018 ◽

Author(s):

Paolo Papale ◽

Monica Betta ◽

Giacomo Handjaras ◽

Giulia Malfatti ◽

Luca Cecchetti ◽

...

Keyword(s):

Object Representation ◽

Temporal Dynamics ◽

Medial Axis ◽

Human Subjects ◽

Physical World ◽

Stimulus Onset ◽

Low Level ◽

Semantic Categories ◽

Spatial Frequencies ◽

Feature Processing

AbstractBiological vision relies on representations of the physical world at different levels of complexity. Relevant features span from simple low-level properties, as contrast and spatial frequencies, to object-based attributes, as shape and category. However, how these features are integrated into coherent percepts is still debated. Moreover, these dimensions often share common biases: for instance, stimuli from the same category (e.g., tools) may have similar shapes. Here, using magnetoencephalography, we revealed the temporal dynamics of feature processing in human subjects attending to pictures of items pertaining to different semantic categories. By employing Relative Weights Analysis, we mitigated collinearity between model-based descriptions of stimuli and showed that low-level properties (contrast and spatial frequencies), shape (medial-axis) and category are represented within the same spatial locations early in time: 100-150ms after stimulus onset. This fast and overlapping processing may result from independent parallel computations, with categorical representation emerging later than the onset of low-level feature processing, yet before shape coding. Categorical information is represented both before and after shape also suggesting a role for this feature in the refinement of categorical matching.

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Binocular disparity-based learning is retinotopically specific and independent of sleep

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2019.0463 ◽

2020 ◽

Vol 375 (1799) ◽

pp. 20190463 ◽

Cited By ~ 2

Author(s):

Jens G. Klinzing ◽

Lena Herbrik ◽

Hendrikje Nienborg ◽

Karsten Rauss

Keyword(s):

Visual Field ◽

Discrimination Task ◽

Binocular Disparity ◽

Human Subjects ◽

Stereoscopic Vision ◽

Memory Encoding ◽

Retention Period ◽

Low Level ◽

Neuronal Ensemble ◽

Ensemble Activity

Sleep supports the consolidation of recently encoded declarative and procedural memories. An important component of this effect is the repeated reactivation of neuronal ensemble activity elicited during memory encoding. For perceptual learning, however, sleep benefits have only been reported for specific tasks and it is not clear whether sleep targets low-level perceptual, higher-order temporal or attentional aspects of performance. Here, we employed a coarse binocular disparity discrimination task, known to rely on low-level stereoscopic vision. We show that human subjects improve over training and retain the same performance level across a 12-h retention period. Improvements do not generalize to other parts of the visual field and are unaffected by whether the retention period contains sleep or not. These results are compatible with the notion that behavioural improvements in binocular disparity discrimination do not additionally benefit from sleep when compared with the same time spent awake. We hypothesize that this might generalize to other strictly low-level perceptual tasks. This article is part of the Theo Murphy meeting issue ‘Memory reactivation: replaying events past, present and future'.

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Repetitive Low-level Blast Exposure and Neurocognitive Effects in Army Ranger Mortarmen

Military Medicine ◽

10.1093/milmed/usab394 ◽

2021 ◽

Author(s):

Julia l.a Woodall ◽

Jordyn a Sak ◽

Kyle R Cowdrick ◽

Brady m Bove Muñoz ◽

Jessica h McElrath ◽

...

Keyword(s):

Military Training ◽

Pupillary Light Reflex ◽

Cumulative Exposure ◽

Weapon Systems ◽

Light Reflex ◽

Low Level ◽

Reflex Responses ◽

Blast Exposure ◽

Pupillary Light ◽

Subconcussive Injury

ABSTRACT Introduction Occupational exposure to repetitive, low-level blasts in military training and combat has been tied to subconcussive injury and poor health outcomes for service members. Most low-level blast studies to date have focused on explosive breaching and firing heavy weapon systems; however, there is limited research on the repetitive blast exposure and physiological effects that mortarmen experience when firing mortar weapon systems. Motivated by anecdotal symptoms of mortarmen, the purpose of this paper is to characterize this exposure and its resulting neurocognitive effects in order to provide preliminary findings and actionable recommendations to safeguard the health of mortarmen. Materials and Methods In collaboration with the U.S. Army Rangers at Fort Benning, blast exposure, symptoms, and pupillary light reflex were measured during 3 days of firing 81 mm and 120 mm mortars in training. Blast exposure analysis included the examination of the blast overpressure (BOP) and cumulative exposure by mortarman position, as well as comparison to the 4 psi safety threshold. Pupillary light reflex responses were analyzed with linear mixed effects modeling. All neurocognitive results were compared between mortarmen (n = 11) and controls (n = 4) and cross-compared with blast exposure and blast history. Results Nearly 500 rounds were fired during the study, resulting in a high cumulative blast exposure for all mortarmen. While two mortarmen had average BOPs exceeding the 4 psi safety limit (Fig. 2), there was a high prevalence of mTBI-like symptoms among all mortarmen, with over 70% experiencing headaches, ringing in the ears, forgetfulness/poor memory, and taking longer to think during the training week (n ≥ 8/11). Mortarmen also had smaller and slower pupillary light reflex responses relative to controls, with significantly slower dilation velocity (P < 0.05) and constriction velocity (P < 0.10). Conclusion Mortarmen experienced high cumulative blast exposure coinciding with altered neurocognition that is suggestive of blast-related subconcussive injury. These neurocognitive effects occurred even in mortarmen with average BOP below the 4 psi safety threshold. While this study was limited by a small sample size, its results demonstrate a concerning health risk for mortarmen that requires additional study and immediate action. Behavioral changes like ducking and standing farther from the mortar when firing can generally help reduce mortarmen BOP exposure, but we recommend the establishment of daily cumulative safety thresholds and daily firing limits in training to reduce cumulative blast exposure, and ultimately, improve mortarmen’s quality of life and longevity in service.

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