Association of MOS-Based Blast Exposure With Medical Outcomes

Associations between concussion and more severe TBIs, mild cognitive impairment, and early-onset dementia among military retirees over 40 years

Background and objectives

As the population of U.S. service members (SMs) who have sustained concussions and more severe traumatic brain injuries (TBIs) during military service ages, understanding the long-term outcomes associated with such injuries will provide critical information that may promote long-term assessment, support, and rehabilitation following military service. The objective of this research was to examine whether concussion and more severe TBIs are associated with greater risk of precursors to dementia (i.e., mild cognitive impairment, memory loss), early-onset dementia, and any dementia.

Methods

This study used a retrospective cohort design wherein archival medical and career records from 1980 to 2020 identified U.S. military personnel who retired from military service and their corresponding Tricare-reimbursable medical encounters in inpatient and/or outpatient settings in military treatment facilities and/or purchased care settings both before and after retirement. All military personnel who served on active duty between 1980 and 2020 and were at least 45 years of age by 2020 were eligible for inclusion (N = 6,092,432). Those who were discharged from military service with a retirement designation, and were thus eligible for Tricare for Life, were included in the analytic sample (N = 1,211,972). Diagnoses of concussion and more severe TBI during active duty service recorded in inpatient settings between 1980 and 2020 and in outpatient settings from 2001 to 2020 were identified. Focal outcomes of interest included memory loss, mild cognitive impairment, Alzheimer's, Lewy Body dementia, frontotemporal dementia, and vascular dementia. Dementia diagnoses before age 65 were labeled early-onset.

Results

Those with (vs. without) concussion diagnoses during military service were significantly more likely to be diagnosed with memory loss and mild cognitive impairment and any of the dementias examined. However, they were not at greater risk of being diagnosed with early-onset dementia.

Discussion

Military SMs diagnosed with concussion may be at elevated risk for long-term neurodegenerative outcomes including memory loss, mild cognitive impairment, and dementia. As the population of SMs who sustained TBI during the Global War on Terror continue to age, the prevalence of dementia will increase and may bring a unique burden to the VHA.

An End-User Evaluation of Blast Overpressure and Accelerative Impact Body-Worn Sensors

INTRODUCTION

Blast overpressure and accelerative impact can produce concussive-like symptoms in service members serving both garrison and deployed environments. In an effort to measure, document, and improve the response to these overpressure and impact events, the U.S. Army Medical Material Development Activity is evaluating body-worn sensors for use by the Joint Conventional Force. In support, the WRAIR completed a qualitative end-user evaluation with service members from high-risk mission occupational specialties to determine the potential needs, benefits, and challenges associated with adopting body-worn sensors into their job duties.

MATERIALS AND METHODS

WRAIR staff led hour-long semi-structured focus groups with 156 Army, Navy, and Marine Corps participants, primarily representing infantry, combat engineer, explosive ordnance disposal, artillery, mortar, and armor job specialties. Topics included their sensor needs, concepts of operations, and recommended design features for implementing sensors into the force. Dialogue from each focus group was audio recorded and resulting transcripts were coded for thematic qualitative analysis using NVivo software.

RESULTS

Users recommended a single, unobtrusive, rugged, multi-directional sensor that could be securely mounted to the helmet and powered by a battery type (such as rechargeable lithium or disposable alkaline batteries) that was best suited for their garrison and field/deployed environments. The sensors should accurately measure low-level (∼1.0 pounds per square inch) blasts and maintain a record of cumulative exposures for each service member. Discussions supported the need for immediate, actionable feedback from the sensor with the option to view detailed blast or impact data on a computer. There were, however, divergent opinions on security issues regarding wireless versus wired data transfer methods. Participants also expressed a need for the exposure data to integrate with their medical records and were also willing to have their data shared with leadership, although opinions differed on the level of echelon and if the data should be identifiable. Regarding accountability, users did not want to be held fiscally liable for the sensors and recommended having the unit be responsible for maintenance and distribution. Concerns about being held fiscally liable, being overly burdened, and having one's career negatively impacted were listed as factors that could decrease usage. Finally, participants highlighted the importance of understanding the purpose and function of the sensors and supported a corresponding training module.

CONCLUSIONS

Participating service members were generally willing to adopt body-worn sensors into their garrison and deployed activities. To maximize adoption of the devices, they should be convenient to use and should not interfere with service members' job tasks. Providing a clear understanding of the benefits (such as incorporating exposure data into medical records) and the function of sensors will be critical for encouraging buy-in among users and leaders. Incorporating end-user requirements and considering the benefits and challenges highlighted by end users are important for the design and implementation of body-worn sensors to mitigate the risks of blast overpressure and accelerative impact on service members' health.

Traumatic brain injury and occupational risk of low-level blast exposure on adverse career outcomes: an examination of administrative and medical separations from Service (2005-2015)

Introduction

Although traumatic brain injury (TBI) has been linked with adverse long-term health, less research has examined whether TBI is linked with non-clinical outcomes including involuntary job loss. Symptoms associated with TBI may influence one's ability to maintain gainful employment including employment in the U.S. military. That influence may impact military service members with exposure to repetitive low-level blast (LLB). Understanding the association between TBI and involuntary job loss outcomes among military populations is particularly important as it may be associated with differences in eligibility for post-service benefits. The purpose of the present research was to determine whether (1) TBI and related conditions are associated with involuntary job loss (i.e., medical and administrative separations from service) among military personnel, and (2) occupational risk of LLB is associated with involuntary job loss in both the presence and absence of clinical diagnoses of TBI and related conditions.

Method

This research leveraged population-level data from the Career History Archival Medical and Personnel System for enlisted personnel who served on active duty between 2005-2015. Risk of LLB exposure was categorized using military occupational specialty as a proxy. Medical diagnoses were identified using ICD-9 codes. Separations for medical and administrative reasons were identified.

Results

Risk for administrative separation differed across medical diagnoses of interest, but those who worked in high-risk occupations were more likely to be administratively separated than those working in low-risk occupations. Risk for medical separation was associated with occupational risk of LLB and each of the diagnoses of interest, though significant interactions suggested that the effects of certain diagnoses of interest (e.g., concussion, cognitive problems, postconcussive syndrome, migraines) on medical separations was greater among those working in high-risk occupations.

Discussion

Taken together, the present research suggests that TBI and associated medical conditions, as well as occupational risk of LLB, are associated with long-term involuntary job loss for medical reasons. This study is the first to demonstrate involuntary military job loss outcomes associated with TBI, mental health conditions, and conditions associated with blast exposure using both inpatient and outpatient population-level data and may have important implications for civilian employment and post-service benefits.

Convergent and Discriminant Validity of the Blast Exposure Threshold Survey in United States Military Service Members and Veterans

The Blast Exposure Threshold Survey (BETS) is a recently developed and promising new self-report measure of lifetime blast exposure (LBE). However, there are no studies that have examined the psychometric properties of the BETS, which currently limits its clinical utility. The purpose of this study was to examine the convergent and discriminant validity of the BETS by comparing the BETS Generalized Blast Exposure Value (GBEV) to six variables hypothesized to be associated with LBE (i.e., single-item LBE, combat exposure, years in the military, number of combat deployments, and military occupation specialty [MOS]) and three variables hypothesized not to be associated with LBE (i.e., age at the time of injury, estimated pre-morbid Full-Scale Intelligence Quotient [FSIQ], and resilience). Participants were 202 United States service members and veterans prospectively enrolled from three military medical treatment facilities (68.7%) and via community recruitment initiatives (31.3%). Participants completed the BETS, Combat Exposure Scale (CES), Deployment Risk and Resiliency Inventory-2 Combat Experiences (DRRI-2 CE), Traumatic Brain Injury-Quality of Life Resilience scale, and a brief structured interview. For some analyses, participants were classified into two blast risk MOS groups: high (n = 89) and low (n = 94). The BETS GBEV was not significantly correlated with all three non-blast related variables (rs = 0.01 to rs = -0.12). In contrast, GBEV was significantly (p < 0.001) associated with all blast-related variables; single-item LBE (rs = 0.76), CES (rs = 0.58), number of combat deployments (rs = 0.53), DRRI-2 CE (rs = 0.48), and high blast risk MOS (r = 0.36, medium effect size). However, a stronger relationship was found between the blast-related variables and three modified GBEV scores when excluding some small weapons categories; single-item LBE (rs = 0.80-0.82), CES (rs = 0.64-0.67), number of combat deployments (rs = 0.56), DRRI-2 CE (rs = 0.51-0.53), and high blast risk MOS (r = 0.42-0.49, medium-large effect size). This is the first study to examine the psychometric properties of the BETS. Overall, these results offer support for the convergent and discriminant validity of the BETS. In order to ensure that the BETS can be confidently used as a valid and reliable measure of LBE, more research is needed to further examine the psychometric properties of the test, particularly with regard to the establishment of test-retest reliability.

Neurological Effects of Repeated Blast Exposure in Special Operations Personnel

Exposure to blast overpressure has been a pervasive feature of combat-related injuries. Studies exploring the neurological correlates of repeated low-level blast exposure in career "breachers" demonstrated higher levels of tumor necrosis factor alpha (TNFα) and interleukin (IL)-6 and decreases in IL-10 within brain-derived extracellular vesicles (BDEVs). The current pilot study was initiated in partnership with the U.S. Special Operations Command (USSOCOM) to explore whether neuroinflammation is seen within special operators with prior blast exposure. Data were analyzed from 18 service members (SMs), inclusive of 9 blast-exposed special operators with an extensive career history of repeated blast exposures and 9 controls matched by age and duration of service. Neuroinflammation was assessed utilizing positron emission tomography (PET) imaging with [18F]DPA-714. Serum was acquired to assess inflammatory biomarkers within whole serum and BDEVs. The Blast Exposure Threshold Survey (BETS) was acquired to determine blast history. Both self-report and neurocognitive measures were acquired to assess cognition. Similarity-driven Multi-view Linear Reconstruction (SiMLR) was used for joint analysis of acquired data. Analysis of BDEVs indicated significant positive associations with a generalized blast exposure value (GBEV) derived from the BETS. SiMLR-based analyses of neuroimaging demonstrated exposure-related relationships between GBEV, PET-neuroinflammation, cortical thickness, and volume loss within special operators. Affected brain networks included regions associated with memory retrieval and executive functioning, as well as visual and heteromodal processing. Post hoc assessments of cognitive measures failed to demonstrate significant associations with GBEV. This emerging evidence suggests neuroinflammation may be a key feature of the brain response to blast exposure over a career in operational personnel. The common thread of neuroinflammation observed in blast-exposed populations requires further study.

Comparison of Vestibular/Ocular Motor Screening (VOMS) and Computerized Eye-tracking to Identify Exposure to Repetitive Head Impacts

INTRODUCTION

Military service members (SMs) are exposed to repetitive head impacts (RHIs) in combat and training that are purported to adversely affect brain health, including cognition, behavior, and function. Researchers have reported that RHI from blast-related exposure may affect both vestibular and ocular function, which in turn may be related to symptomology. As such, an examination of the effects of RHI on exposed military SMs should incorporate these domains. To date, researchers have not compared groups of exposed special operations forces (SOF) operators on combined clinical vestibular/ocular and eye-tracker-based outcomes. Therefore, the primary purpose of this study was to compare participant-reported symptoms and performance on the Vestibular/Ocular Motor Screening (VOMS) tool with performance on the computerized RightEye tracking system between SOF operators exposed to blast-related RHI and healthy controls without blast-related exposure. In addition, the study aimed to compare subgroups of snipers and breachers exposed to RHI to controls on the preceding metrics, as well as identify a subset of individual (demographic) factors, participant-reported symptoms, and performance metrics on VOMS and RightEye that best identify SOF operators exposed to RHI from unexposed controls.

MATERIALS AND METHODS

The study involved a cross-sectional design including 25 Canadian SOF SMs comprised of breachers (n = 9), snipers (n = 9), and healthy, unexposed controls (n = 7). The former 2 groups were combined into an RHI group (n = 18) and compared to controls (n = 7). Participants provided demographics and completed a self-reported concussion-related symptom report via the Military Acute Concussion Evaluation 2, the VOMS, and RightEye computerized eye-tracking assessments. Independent samples t-tests and ANOVAs were used to compare the groups on the outcomes, with receiver operating characteristic curve and area under the curve (AUC) analyses to identify predictors of blast exposure. This study was approved by the Defence Research Development Canada Human Research Ethics Committee and the Canadian Forces Surgeon General/Special Forces Command.

RESULTS

The results from t-tests supported group differences for age (P = .012), participant-reported symptoms (P = .006), and all VOMS items (P range = <.001-.02), with the RHI group being higher than healthy controls on all variables. ANOVA results supported group differences among snipers, breachers, and controls for age (P = .01), RightEye saccades (P = .04), participant-reported total symptom severity (P = .03), and VOMS total scores (P = .003). The results of the receiver operating characteristic curve analyses supported age (AUC = 0.81), Military Acute Concussion Evaluation 2 participant-reported total symptom severity (AUC = 0.87), and VOMS total scores (AUC = 0.92) as significant predictors of prior blast exposure.

CONCLUSIONS

Participant-reported concussion symptoms, VOMS scores, and age were useful in identifying SOF operators exposed to RHI from controls. RightEye metrics were not useful in differentiating RHI groups from controls. Differences between snipers and breachers warrant further research. Overall, the findings suggest that VOMS may be a useful tool for screening for the effects of exposure to RHI in SOF operators. Future investigations should be conducted on a larger sample of military SMs, consider additional factors (e.g., RHI exposure levels, medical history, and sex), and include additional assessment domains (e.g., balance, cognitive, and psychological).

Lifetime blast exposure is not related to cognitive performance or psychiatric symptoms in US military personnel

Objective: The present study aimed to examine the impact of lifetime blast exposure (LBE) on neuropsychological functioning in service members and veterans (SMVs). Method: Participants were 282 SMVs, with and without history of traumatic brain injury (TBI), who were prospectively enrolled in a Defense and Veterans Brain Injury Center (DVBIC)-Traumatic Brain Injury Center of Excellence (TBICoE) Longitudinal TBI Study. A cross-sectional analysis of baseline data was conducted. LBE was based on two factors: Military Occupational Speciality (MOS) and SMV self-report. Participants were divided into three groups based on LBE: Blast Naive (n = 61), Blast + Low Risk MOS (n = 96), Blast + High Risk MOS (n = 125). Multivariate analysis of variance (MANOVA) was used to examine group differences on neurocognitive domains and the Minnesota Multiphasic Personality Inventory-2 Restructured Form. Results: There were no statistically significant differences in attention/working memory, processing speed, executive functioning, and memory (Fs < 1.75, ps > .1, ηp2s < .032) or in General Cognition (Fs < 0.95, ps > .3, ηp2s < .008). Prior to correction for covariates, lifetime blast exposure was related to Restructured Clinical (F(18,542) = 1.77, p = .026, ηp2 = .055), Somatic/Cognitive (F(10,550) = 1.99, p = .033, ηp2 = .035), and Externalizing Scales (F(8,552) = 2.17, p = .028, ηp2 = .030); however, these relationships did not remain significant after correction for covariates (Fs < 1.53, ps > .145, ηp2s < .032). Conclusions: We did not find evidence of a relationship between LBE and neurocognitive performance or psychiatric symptoms. This stands in contrast to prior studies demonstrating an association between lifetime blast exposure and highly sensitive blood biomarkers and/or neuroimaging. Overall, findings suggest the neuropsychological impact of lifetime blast exposure is minimal in individuals remaining in or recently retired from military service.

Validation of Military Occupational Specialty as a Proxy for Blast Exposure Using the Salisbury Blast Interview

Abstract Evaluating large data sets precludes the ability to directly measure individual experiences, instead relying on proxies to infer certain constructs. Blast exposure is a construct of study currently in its infancy, resulting in diverse definitions and measurements across studies. The purpose of the present study was to validate military occupational specialty (MOS) as a proxy for blast exposure in combat veterans. A total of 256 veterans (86.33% male) completed the Salisbury Blast Interview (SBI) and Mid-Atlantic Mental Illness Research Education and Clinical Center (MIRECC) Assessment of Traumatic Brain Injury (MMA-TBI). MOS was collected through record review and categorized into low and high risk for blast exposure. Chi-square analyses and t tests compared SBI metrics between MOS categories. Receiver operating characteristic (ROC) analyses evaluated the diagnostic accuracy of MOS category in determining blast exposure severity. Veterans in high-risk MOS were more likely to have experienced blast and deployment TBI (ps < 0.001) than were those in low-risk MOS. ROC analyses indicated good specificity (81.29-88.00) for blast and deployment TBI outcomes, suggesting that low-risk MOS is generally associated with an absence of blast and deployment TBI outcomes. Sensitivity was low (36.46-51.14), indicating that MOS risk level was not a good predictor of the presence of these outcomes. Results demonstrate that high-risk MOSs will identify individuals with blast exposure and deployment TBI history whereas low-risk MOSs will capture a highly variable group. Accuracy of MOS categorization was not acceptable for diagnostic-level tests; however, results support its use as a screening measure for a history of exposure to blast, use in epidemiological studies, and considerations for military policy.

Occupation and Risk of Traumatic Brain Injury in the Millennium Cohort Study

INTRODUCTION

Traumatic brain injury (TBI) is an occupational health hazard of military service. Few studies have examined differences in military occupational categories (MOC) which take into consideration the physical demands and job requirements across occupational groups.

METHODS

This study was approved by the University of Texas Health Science Center at Houston Institutional Review Board. Data for this cross-sectional study were obtained from the Naval Health Research Center's Millennium Cohort Study, an ongoing DoD study. Univariate analyses were employed to calculate frequencies and proportions for all variables. Bivariate analyses included unadjusted odds ratios (OR) and 95% CI for the association between all variables and TBI. Multivariable logistic regression was used to calculate adjusted ORs and 95% CIs to assess the association between MOC and TBI, adjusted for potential confounders: sex, race/ethnicity, rank, military status, branch of service, before-service TBI, and panel. Logistic regression models estimated odds of TBI for each MOC, and stratified models estimated odds separately for enlisted and officer MOCs.

RESULTS

Approximately 27% of all participants reported experiencing a service-related TBI. All MOCs were statistically significantly associated with increased odds of service-related TBI, with a range of 16 to 45%, except for "Health Care" MOCs (OR: 1.01, 95% CI 0.91-1.13). Service members in "Infantry/Tactical Operations" had the highest odds (OR: 1.45, 95% CI 1.31-1.61) of service-related TBI as compared to "Administration & Executives." Among enlisted service members, approximately 28% reported experiencing a service-related TBI. Among enlisted-specific MOCs, the odds of TBI were elevated for those serving in "Infantry, Gun Crews, Seamanship (OR: 1.79, 95% CI 1.58-2.02)," followed by "Electrical/Mechanical Equipment Repairers (OR: 1.23, 95% CI 1.09-1.38)," "Service & Supply Handlers (OR 1.21, 95% CI 1.08-1.37)," "Other Technical & Allied Specialists (OR 1.21, 95% CI 1.02-1.43)," "Health Care Specialists (OR 1.19, 95% CI 1.04-1.36)," and "Communications & Intelligence (OR: 1.16, 95% CI 1.02-1.31)," compared to "Functional Support & Administration." Among officer service members, approximately 24% reported experiencing a service-related TBI. After adjustment the odds of TBI were found to be significant for those serving as "Health Care Officers" (OR: 0.65, 95% CI: 0.52-0.80) and "Intelligence Officers" (OR: 1.27, 95% CI: 1.01-1.61).

CONCLUSIONS

A strength of this analysis is the breakdown of MOC associations with TBI stratified by enlisted and officer ranks, which has been previously unreported. Given the significantly increased odds of service-related TBI reporting within enlisted ranks, further exploration into the location (deployed versus non-deployed) and mechanism (e.g., blast, training, sports, etc.) for these injuries is needed. Understanding injury patterns within these military occupations is necessary to increase TBI identification, treatment, and foremost, prevention.Results highlight the importance of examining specific occupational categories rather than relying on gross categorizations, which do not account for shared knowledge, skills, and abilities within occupations. The quantification of risk among enlisted MOCs suggests a need for further research into the causes of TBI.

Partial Depletion of Microglia Attenuates Long-Term Potentiation Deficits following Repeated Blast Traumatic Brain Injury in Organotypic Hippocampal Slice Cultures

Blast-induced traumatic brain injury (bTBI) has been a health concern in both military and civilian populations due to recent military and geopolitical conflicts. Military service members are frequently exposed to repeated bTBI throughout their training and deployment. Our group has previously reported compounding functional deficits as a result of increased number of blast exposures. In this study, we further characterized the decrease in long-term potentiation (LTP) by varying the blast injury severity and the inter-blast interval between two blast exposures. LTP deficits were attenuated with increasing inter-blast intervals. We also investigated changes in microglial activation; expression of CD68 was increased and expression of CD206 was decreased after multiple blast exposures. Expression of macrophage inflammatory protein (MIP)-1α, interleukin (IL)-1β, monocyte chemoattractant protein (MCP)-1, interferon gamma-inducible protein (IP)-10, and regulated on activation, normal T cell expressed and secreted (RANTES) increased, while expression of IL-10 decreased in the acute period after both single and repeated bTBI. By partially depleting microglia prior to injury, LTP deficits after injury were significantly reduced. Treatment with the novel drug, MW-189, prevented LTP deficits when administered immediately following a repeated bTBI and even when administered only for an acute period (24 h) between two blast injuries. These findings could inform the development of therapeutic strategies to treat the neurological deficits of repeated bTBI suggesting that microglia play a major role in functional neuronal deficits and may be a viable therapeutic target to lessen the neurophysiological deficits after bTBI.

Inhibition of cyclooxygenase and EP3 receptor improved long term potentiation in a rat organotypic hippocampal model of repeated blast traumatic brain injury

Blast-induced traumatic brain injury (bTBI) is a health concern in military service members who are exposed to multiple blasts throughout their training and deployment. Our group has previously reported decreased long term potentiation (LTP) following repeated bTBI in a rat organotypic hippocampal slice culture (OHSC) model. In this study, we investigated changes in inflammatory markers like cyclooxygenase (COX) and tested the efficacy of COX or prostaglandin EP3 receptor (EP3R) inhibitors in attenuating LTP deficits. Expression of COX-2 was increased 48 h following repeated injury, whereas COX-1 expression was unchanged. EP3R expression was upregulated, and cyclic adenosine monophosphate (cAMP) concentration was decreased after repeated blast exposure. Post-traumatic LTP deficits improved after treatment with a COX-1 specific inhibitor, SC-560, a COX-2 specific inhibitor, rofecoxib, a pan-COX inhibitor, ibuprofen, or an EP3R inhibitor, L-798,106. Delayed treatment with ibuprofen and L-798,106 also prevented LTP deficits. These findings suggest that bTBI induced neuroinflammation may be responsible for some functional deficits that we have observed in injured OHSCs. Additionally, COX and EP3R inhibition may be viable therapeutic strategies to reduce neurophysiological deficits after repeated bTBI.

Field assessment of acute auditory responses to environmental exposures in close quarters tactics training

OBJECTIVE

The purpose of this study was to evaluate auditory performance of military instructors as part of a training course involving noise and blast exposure. Boothless audiometry was used to estimate the test-retest reliability of the auditory measures under realistic field conditions and to determine risk of acute auditory injury during standard training practices.

DESIGN AND STUDY SAMPLE

Thirteen U.S. Marine instructors participated in study activities. An audiologic testing suite embedded in a noise-attenuating headset was used to test various tone detection tasks on subjects after exposure. Acoustic exposures were captured with sound level meters.

RESULTS

Boothless audiometry provide highly repeatable results for various tests of auditory performance in the field environment. In this test population, changes in auditory performance pre- and post-noise exposure were minimal for most measures. The notable exception was binaural (NoSπ) tone detection, which showed significant degradations both as a function of pre- and post-noise exposure on the same day and as a result of cumulative noise exposure over the period of the study.

CONCLUSIONS

Study outcomes are consistent with prior laboratory and epidemiological work and suggest a link between the binaural processes required for NoSπ detection and the hearing-related issues reported by blast-exposed service members.

Single and repeated high-level blast, low-level blast, and new-onset self-reported health conditions in the U.S. Millennium Cohort Study: An exploratory investigation

Introduction

Although previous research suggests that overpressure exposure from either high-level blast (HLB) or low-level blast (LLB) are harmful to health, to date no large-scale studies with representative samples of military personnel have utilized prospective designs and self-reported measures to examine the relationships between blast exposure and health conditions. To address these limitations, this analysis of data from the Millennium Cohort Study (MCS), the largest and longest running study of U.S. service members and veterans, examined (1) whether single or repeated HLB exposure is associated with self-reported diagnoses of illness and injury, (2) whether repeated HLB is associated with greater risk than single HLB, (3) potential adverse consequences of LLB exposure using military occupation as a proxy, and (4) the combined effects of single or repeated HLB and LLB exposure.

Method

MCS participants who completed the 2011-2013 survey (N = 138,949) were classified as having been exposed to "no," "single," or "repeated" HLB exposure, and into low or high risk of exposure to LLB based on occupation. Participants self-reported diagnosis of 45 medical conditions; newly reported diagnoses were regressed on single and repeated (vs. no) HLB, occupational risk of LLB, and relevant interactions using logistic regression.

Results

Single and repeated HLB were associated with new onset of 25 and 29 diagnoses, respectively; repeated HLB exposure was associated with greater risk than single HLB exposure for five diagnoses (e.g., PTSD, depression). Occupational risk of LLB was associated with 11 diagnoses (e.g., PTSD, significant hearing loss). Additionally, 14 significant interactions were detected across 11 diagnoses.

Discussion

Findings suggest that overpressure exposure (including single HLB, repeated HLB, and occupational risk of LLB) may increase the risks of self-reporting clinical diagnoses of PTSD, hearing loss, chronic fatigue syndrome, neuropathy-caused reduced sensation in the hands and feet, depression, vision loss, sinusitis, reflux, and anemia. Furthermore, the combination of HLB and LLB exposure may be associated with greater risk of migraines, PTSD, and impaired fecundity. These findings provide further evidence of the potential adverse consequences associated with overpressure exposure and underscore the necessity of public health surveillance initiatives for blast exposure and/or safety recommendations for training and operational environments.

Long-Term Effects of Repeated Blast Exposure in United States Special Operations Forces Personnel: A Pilot Study Protocol

Emerging evidence suggests that repeated blast exposure (RBE) is associated with brain injury in military personnel. United States (U.S.) Special Operations Forces (SOF) personnel experience high rates of blast exposure during training and combat, but the effects of low-level RBE on brain structure and function in SOF have not been comprehensively characterized. Further, the pathophysiological link between RBE-related brain injuries and cognitive, behavioral, and physical symptoms has not been fully elucidated. We present a protocol for an observational pilot study, Long-Term Effects of Repeated Blast Exposure in U.S. SOF Personnel (ReBlast). In this exploratory study, 30 active-duty SOF personnel with RBE will participate in a comprehensive evaluation of: 1) brain network structure and function using Connectome magnetic resonance imaging (MRI) and 7 Tesla MRI; 2) neuroinflammation and tau deposition using positron emission tomography; 3) blood proteomics and metabolomics; 4) behavioral and physical symptoms using self-report measures; and 5) cognition using a battery of conventional and digitized assessments designed to detect subtle deficits in otherwise high-performing individuals. We will identify clinical, neuroimaging, and blood-based phenotypes that are associated with level of RBE, as measured by the Generalized Blast Exposure Value. Candidate biomarkers of RBE-related brain injury will inform the design of a subsequent study that will test a diagnostic assessment battery for detecting RBE-related brain injury. Ultimately, we anticipate that the ReBlast study will facilitate the development of interventions to optimize the brain health, quality of life, and battle readiness of U.S. SOF personnel.

Perspectives on Development of Measures to Estimate Career Blast Exposure History in Service Members and Veterans

The Department of Defense (DOD) has recently prioritized the investigation of the acute and chronic adverse brain health and performance effects of low-level blast (LLB) generated by the use of weapons systems. While acute exposure can be quantified by sensor technology, career exposure has no widely accepted and validated measure for characterization. Currently, distinct research groups are developing and validating four promising measures to estimate career blast exposure history: the Salisbury Blast Interview, Blast Exposure Threshold Survey, Blast Ordnance and Occupational Exposure Measure, and the Blast Frequency and Symptom Severity. Each measure offers an assessment of blast history that is uniquely beneficial to addressing specific research questions. However, use of divergent strategies is not efficient to accelerate the field's understanding of the impact of career exposure and Service-connected health outcomes. As a DOD-wide solution, collaboration across these groups is required to develop a tool(s) that can be standardized across research studies and, ultimately, pared down to be implemented in clinical settings. Here, we overview the current four measures and provide a perspective on the way forward for optimization and/or combination in support of this solution.

Occupational Risk of Low-Level Blast Exposure and TBI-Related Medical Diagnoses: A Population-Based Epidemiological Investigation (2005-2015)

Because traumatic brain injury (TBI)—most often caused by exposure to high-level blast (HLB)—is a leading cause of medical evacuations of deployed U.S. service members in recent conflicts, researchers seek to identify risk factors for TBI. Previous research using self-reported data has identified low-level blast (LLB) as one such risk factor and suggests an association with susceptibility to and symptoms associated with TBI. This article presents a population-based study of all branches of military service that examines the association between occupational risk for LLB and both clinically diagnosed TBIs—from concussions to severe and penetrating TBIs—and conditions commonly comorbid with concussion. Using archival medical and career records from >2 million service members between 2005–2015, this work demonstrates that occupational risk of LLB is associated with any TBI, mild TBI, moderate TBI, cognitive problems, communication problems, hearing problems, headaches, any behavioral health condition, anxiety, drug abuse/dependence, alcohol abuse/dependence, delirium/dementia, posttraumatic stress disorder, post-concussive syndrome, tinnitus, fatigue, and migraines. Understanding the full scope of the effects of LLB on service members will help ensure the health and readiness of service members and may influence both military policy and clinical practice guidelines for blast-induced injuries.

Neuronally-derived tau is increased in experienced breachers and is associated with neurobehavioral symptoms

Military and law enforcement breachers are exposed to many low-level blasts during their training and occupational experiences in which they detonate explosives to force entry into secured structures. There is a concern that exposure to these repetitive blast events in career breachers could result in cumulative neurological effects. This study aimed to determine concentrations of neurofilament light (NF-L), tau, and amyloid-beta 42 (Aβ42) in serum and in neuronal-derived extracellular vesicles (EVs) in an experienced breacher population, and to examine biomarker associations with neurobehavioral symptoms. Thirty-four participants enrolled in the study: 20 experienced breachers and 14 matched military or civilian law enforcement controls. EV tau concentrations were significantly elevated in experienced breachers (0.3301 ± 0.5225) compared to controls (-0.4279 ± 0.7557; F = 10.43, p = 0.003). No statistically significant changes were observed in EV levels of NF-L or Aβ42 or in serum levels of NF-L, tau, or Aβ42 (p's > 0.05). Elevated EV tau concentrations correlated with increased Neurobehavioral Symptom Inventory (NSI) score in experienced breachers (r = 0.596, p = 0.015) and predicted higher NSI score (F(1,14) = 7.702, p = 0.015, R² = 0.355). These findings show that neuronal-derived EV concentrations of tau are significantly elevated and associated with neurobehavioral symptoms in this sample of experienced breachers who have a history of many low-level blast exposures.

Neurotrauma Biomarker Levels and Adverse Symptoms Among Military and Law Enforcement Personnel Exposed to Occupational Overpressure Without Diagnosed Traumatic Brain Injury

IMPORTANCE

There is a scientific and operational need to define objective measures of exposure to low-level overpressure (LLOP) and concussion-like symptoms among persons with specialized occupations.

OBJECTIVE

To evaluate serum levels of neurotrauma biomarkers and their association with concussion-like symptoms reported by LLOP-exposed military and law enforcement personnel who are outwardly healthy and cleared to perform duties.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study, conducted from January 23, 2017, to October 21, 2019, used serum samples and survey data collected from healthy, male, active-duty military and law enforcement personnel assigned to operational training at 4 US Department of Defense and civilian law enforcement training sites. Personnel aged 18 years or older with prior LLOP exposure but no diagnosed traumatic brain injury or with acute blast exposure during sampling participated in the study. Serum samples from 30 control individuals were obtained from a commercial vendor.

MAIN OUTCOMES AND MEASURES

Serum levels of glial fibrillary acidic protein, ubiquitin carboxyl hydrolase (UCH)-L1, neurofilament light chain, tau, amyloid β (Aβ)-40, and Aβ-42 from a random sample (30 participants) of the LLOP-exposed cohort were compared with those of 30 age-matched controls. Associations between biomarker levels and self-reported symptoms or operational demographics in the remainder of the study cohort (76 participants) were assessed using generalized linear modeling or Spearman correlations with age as a covariate.

RESULTS

Among the 30 randomly sampled participants (mean [SD] age, 32 [7.75] years), serum levels of UCH-L1 (mean difference, 4.92; 95% CI, 0.71-9.14), tau (mean difference, 0.16; 95% CI, -0.06 to 0.39), Aβ-40 (mean difference, 138.44; 95% CI, 116.32-160.56), and Aβ-42 (mean difference, 4.97; 95% CI, 4.10-5.83) were elevated compared with those in controls. Among the remaining cohort of 76 participants (mean [SD] age, 34 [7.43] years), ear ringing was reported by 44 (58%) and memory or sleep problems were reported by 24 (32%) and 20 (26%), respectively. A total of 26 participants (34%) reported prior concussion. Amyloid β-42 levels were associated with ear ringing (F1,72 = 7.40; P = .008) and memory problems (F1,72 = 9.20; P = .003).

CONCLUSIONS AND RELEVANCE

The findings suggest that long-term LLOP exposure acquired during occupational training may be associated with serum levels of neurotrauma biomarkers. Assessment of biomarkers and concussion-like symptoms among personnel considered healthy at the time of sampling may be useful for military occupational medicine risk management.

Hearing Loss and Irritability Reporting Without Vestibular Differences in Explosive Breaching Professionals

Background: Blast exposure is a potential hazard in modern military operations and training, especially for some military occupations. Helmets, peripheral armor, hearing protection, and eye protection worn by military personnel provide some acute protection from blast effects but may not fully protect personnel against cumulative effects of repeated blast overpressure waves experienced over a career. The current study aimed to characterize the long-term outcomes of repeated exposure to primary blast overpressure in experienced career operators with an emphasis on the assessment of hearing and vestibular outcomes.

Methods: Participants included experienced “breachers” (military and law enforcement explosives professionals who gain entry into structures through controlled detonation of charges) and similarly aged and experienced “non-breachers” (non-breaching military and law enforcement personnel). Responses to a clinical interview and performance on audiological and vestibular testing were compared.

Results: Hearing loss, ringing in the ears, irritability, and sensitivity to light or noise were more common among breachers than non-breachers. Breachers reported more combat exposure than non-breachers, and subsequently, memory loss and difficulty concentrating were associated with both breaching and combat exposure. Vestibular and ocular motor outcomes were not different between breachers and non-breachers.

Conclusion: Hearing-related, irritability, and sensitivity outcomes are associated with a career in breaching. Future studies examining long-term effects of blast exposure should take measures to control for combat exposure.