"Breachers" are a unique military and law enforcement population because they are routinely exposed to low-level blast (LLB) during training and operations. This repeated exposure has been associated with symptoms similar to that of sports concussion. This study examined effects of repeated exposure to LLB during an explosive entry course. Twenty-one members of the New Zealand Defence Force volunteered for this study. Serum samples, neurocognitive performance, and self-reported symptoms were periodically measured before, during, and after a 2-week course. Serum concentrations of three biomarkers, ubiquitin C-terminal hydrolase-L1, αII-spectrin breakdown product, and glial fibrillary acidic protein, were determined with sandwich enzyme-linked immunosorbent assays, and rank scores were derived using the area under the curve (relative to baseline) for each subject. Neurocognitive performance was measured with a computer-based test battery, and symptoms were assessed by paper-based inventory. There was a significant relationship (p<0.05) between composite biomarker and neurocognitive performance and between neurocognitive performance and symptoms. The individuals with the five highest (Top 5) and lowest (Bottom 5) composite biomarker scores were identified and compared using Wilcoxon's rank-sum test. The Top 5 had significantly longer reaction times and lower percent correct on neurocognitive performance and an increase in symptom reporting. The difference between individuals expressing the highest biomarker load during breacher training (Top 5) and those with the lowest biomarker load (Bottom 5) is reflected in neurocognitive performance deficits and self-reported symptoms. This suggests a measureable degree of brain perturbation linked to LLB exposure. Follow-up studies are underway to expand upon these results.

Given the prevalence of repeated exposure to blast among some military and civilian law enforcement occupations, the results of this survey study support a role for blast surveillance programs as well as continued research on health impacts of low-level repeated blast exposure.

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Results are consistent with expectations that multiple test sessions are required to reach stable performance on some computerized tasks. These results have implications for taking ANAM4 TBI Battery practice effects into account in test administration and in data interpretation.

"Breachers" (dynamic entry personnel) are routinely exposed to low-level blast overpressure during training and occupational duties. Data were collected from 22 military breachers (mean 29.7 yr) over a 5-yr period to characterize the longitudinal effects of repeated low-level blast overpressure exposure. None of the participants reported a diagnosed concussion during the study period. Blood-based biomarker concentrations (n = 22) showed either no significant change or a significant decrease over time. Neurocognitive performance (n = 20) and symptom reporting (n = 22) did not change over time. Neuroimaging analyses resulted in no significant differences for within-subject (baseline vs follow-up, n = 8) and between-subject (naïve, n = 5 vs experienced, n = 8) comparisons. Changes to training doctrine mid-study reduced blast exposure (< 4 psi) and may have mitigated any measurable effects associated with long-term, low-level blast exposure. The results suggest that the first 5 yr of a breaching career in healthy, young individuals is unlikely to result in measurable effects when overpressure exposure is maintained within the 4 psi safe limit. The lack of any significant changes in these operators suggests that either no identifiable injuries occurred and/or measurement tools may not be sensitive enough to identify any negative subconcussive effects.