Blast in Context: The Neuropsychological and Neurocognitive Effects of Long-Term Occupational Exposure to Repeated Low-Level Explosives on Canadian Armed Forces' Breaching Instructors and Range Staff

Abstract

Currently, there is strong interest within the military to better understand the effects of long-term occupational exposure to repeated low-level blast on health and performance. To gain traction on the chronic sequelae of blast, we focused on breaching-a tactical technique for gaining entry into closed/blocked spaces by placing explosives and maintaining a calculated safe distance from the detonation. Using a cross-sectional design, we compared the neuropsychological and neurocognitive profiles of breaching instructors and range staff to sex- and age-matched Canadian Armed Forces (CAF) controls. Univariate tests demonstrated that breaching was associated with greater post-concussive symptoms (Rivermead Post Concussion Symptoms Questionnaire) and lower levels of energy (RAND SF-36). In addition, breaching instructors and range staff were slower on a test that requires moving and thinking simultaneously (i.e., cognitive-motor integration). Next, using a multivariate approach, we explored the impact of other possible sources of injury, including concussion and prior war-zone deployment on the same outcomes. Concussion history was associated with higher post-concussive scores and musculoskeletal problems, whereas deployment was associated with higher post-concussive scores, but lower energy and greater PTSD symptomatology (using PCL-5). Our results indicate that although breaching, concussion, and deployment were similarly correlated with greater post-concussive symptoms, concussion history appears to be uniquely associated with altered musculoskeletal function, whereas deployment history appears to be uniquely associated with lower energy and risk of PTSD. We argue that the broader injury context must, therefore, be considered when studying the impact of repetitive low-level explosives on health and performance in military members.

Keywords: TBI; blast; cognitive motor integration; concussion; military personnel.

Figure 1

Canadian Forces School of Military Engineering personnel participating in breaching exercises. Photo courtesy of Haley Voutour (5th Canadian Division Support Group).

Figure 2

Schematic of experimental conditions for BrDI. BrDI, Brain Dysfunction Indicator. Visual stimuli were presented either directly on the computer tablet (same plane; Direct) or on the attached monitor (plane change). Light gray eye and hand indicate the start position. The dark gray eye and hand symbols depict the movement from start position toward the target. The target was presented in one of four locations (right, left, up or down).

Figure 3

Examples of hand movement trajectories for BrDI. BrDI, Brain Dysfunction Indicator. Examples of hand movement trajectories (green) in the Direct condition (i.e., movements in target direction and in the same plane) and in the Plane change feedback reversal condition (i.e., movements in the opposite direction of the presented target and in a different plane) from one control participant (left side of each condition panel) and from one breaching instructor or range staff (right side of each condition panel). Magenta circles represent the location of targets. Red dots indicate the starting position of the finger for each trial. Blue ellipses represent the 95% confidence intervals for the final endpoint positions of movements (blue dots).

Figure 4

Mean Reaction time under 4 different conditions for BrDI. BrDI, Brain Dysfunction Indicator. (A) Same plane with veridical (left panel) or reversed (right panel) visual feedback to move the cursor into the target. (B) Different plane with veridical (left panel) or reversed (right panel). Error bars represent ± SD. Significant difference between breaching instructors and range staff vs. controls (see text) *p < 0.01.

Figure 5

Psychological and cognitive test profiles of military personnel. PProb, posterior probability; Accur, accuracy; RT, reaction time; dMTS, delayed matching-to-sample task; BrDI, brain dysfunction indicator; SMFA, selective functional movement assessment; PCL-5, Posttraumatic stress disorder (PTSD) checklist for diagnostic and statistician's manual (DSM-5); RPQ, Rivermead post-concussion symptoms questionnaire. Plots show the contributions of psychological and cognitive measures toward class separation in (A) breachers/range staff (n = 19) vs. CAF controls (n = 19), (B) personnel with (n = 13) vs. without (n = 24) a history of concussion, and (C) personnel deployed to a war zone (n = 11) vs. never deployed (n = 25), by partial least squares discriminant analysis (PLSDA). Bars represent biomarker loadings and the standard error derived from bootstrapped resampling (1,000 samples). Colored bars = significant at a false discovery rate (FDR) < 0.05.