Blast effects on post-concussive and mental health outcomes: Data from Canadian Armed Forces breachers and snipers

Abstract

LAY SUMMARY There has been increasing interest in understanding the impact of blast exposure on health and performance in military members and Veterans. This phenomenon has proven difficult to study because personnel diagnosed with blast-induced mild traumatic brain injury (mTBI) typically also exhibit emotional difficulties such as posttraumatic stress disorder (PTSD), likely because the events that led to mTBI in theatre were also emotionally traumatic. In turn, this comorbidity makes it difficult to tease apart symptoms uniquely due to blast-induced mTBI or PTSD. Researchers have therefore explored surrogate settings wherein the effects of blast exposure can be assessed in an operationally realistic, yet scientifically more controlled manner, such as breacher and sniper training. To that aim, researchers administered a measure of post-concussive symptomatology and two mental health scales to breachers and snipers, as well as sex- and age-matched military controls. The breachers and snipers reported greater levels of post-concussive symptoms, but not poorer mental health outcomes. Therefore, post-concussive symptoms and mental health outcomes might be dissociable when the impact of repetitive exposure to low-level blast is assessed in the context of training and operations, rather than following warzone deployment involving primarily high-level blast exposure.

Association of Blast Exposure in Military Breaching with Intestinal Permeability Blood Biomarkers Associated with Leaky Gut

“…This suggests that injuries from subconcussive blast exposures may contribute to evolving brain injury pathology that manifests in a range of clinical symptoms [ 60 ] including chronic headaches [ 61 , 62 , 63 ] and cognitive impairment [ 60 , 64 , 65 ]. These are also reflective of symptoms of headache and cognitive problems reported acutely by military service members exposed to blast in operational settings, and specifically by participants in the present study with similar exposures to blast, which are consistent with concussion symptomology [ 66 , 67 , 68 ]. The elevated reporting of symptoms by these participants was related to headache, dizziness, concentration, and taking longer to think acutely following blast that dissipated 12 h following and was in line with constellations of symptoms typically reported by individuals experiencing mTBI [ 13 , 14 ].…”

“…Items on the symptom survey were the same as those of the Rivermead Post Concussion Symptoms Questionnaire [70,71], with additional items included relevant to capture additional effects previously observed as reported in blast exposure environments [67]. These items are consistent with concussion symptomology present in current clinical and research findings [67,68]. Items on this survey are on a 5-point Likert scale (0 "not experienced at all", 1 "no more of a problem than before training", 2 "mild problem-present but don't really notice and doesn't concern me", 3 "moderate problem-I can continue what I am doing but I notice the problem", 4 "severe problem-constantly present, feels like it could affect my performance").…”

Repetitive subconcussion results in disrupted neural activity independent of concussion history

“…1 Repetitive subconcussions were thought to be less serious, and have been largely overlooked up until recently [2][3][4] but are now considered insidious, and occur from repetitive head impacts (RHI) common in contact sports 5,6 and in military settings with occupational repetitive blast overpressure (ReBOP) exposure (e.g., explosions, small arms, heavy weapons). [7][8][9][10][11] Postmortem studies in athletes reveal that the accumulated duration of play 5,6 and total force 6 are better predictors than concussion history for the presence and severity of chronic traumatic encephalopathy (CTE), a progressive and fatal neurodegenerative tauopathy, which is distinct from concussions and persistent postconcussion symptoms (PPCS). Yet, the pathogenic mechanisms of CTE are not well understood, 12 although histopathology suggests that expression of glial fibrillary acidic proteins at the cortical grey-white matter interface are a neuropathological hallmark of cumulative mild blast or impact neurotrauma.…”

“…38 Such a model can inform basic science and provide translatable paths to refine training procedures and improve overall health outcomes for operational readiness. [7][8][9][10]30,36,37 There is evidence that repetitive blast damages the central nervous system and/or the central or peripheral vestibular system due to blast waves entering the ear canal and subsequently causing mechanical reverberations throughout the brain. 39,40 However, other studies argue that the mechanism extends beyond acceleration-deceleration injuries, due to the effect of blast waves on both air-filled organs and/or organs surrounded by fluid-filled cavities within the body.…”

“…These include somatic, cognitive, and emotional symptoms and mental health issues (e.g., anxiety, depression). 7–10 Also, higher lifetime subconcussive blast exposure is associated with poorer brain-related outcomes, including worse neurobehavioural symptoms (e.g., sleep, fatigue). 30…”