Biomarkers of Brain Health in Blast Overpressure Exposure

Background and rationale

Tactical operators are repeatedly exposed to sub-concussive blast overpressure during breaching training. Current safety standards rely primarily on distance-based calculations and subjective symptom reporting, which may fail to capture acute neural strain. Prior work in mild traumatic brain injury suggests quantitative EEG is sensitive to changes in Delta, Theta, and Alpha power spectra. This observational study investigates whether non-invasive EEG acquired with dry-electrode, EEG-integrated personal protective equipment can detect pre-symptomatic physiological deviation from an individual baseline in an operational training environment.

Specific aims

Validate the feasibility of collecting high-fidelity EEG during active breaching using EEG-integrated tactical hearing protection (AMP Neuro).

Identify EEG biomarkers associated with acute blast overpressure exposure, specifically Delta and Theta power increases and Alpha suppression.

Correlate objective measures of physiological change and blast dosimetry with subjective symptom report using the Neurobehavioral Symptom Inventory (NSI).

Design

Observational, longitudinal, within-subject cohort study conducted alongside a pre-scheduled tactical training curriculum. Participants serve as their own controls, with post-exposure data compared against each participant's Day 1 baseline. Approximately 12 participants will enroll. Study duration per participant is five days.

The study is non-interventional and introduces no new physical maneuvers; it does not alter the frequency, intensity, or proximity of blast exposures already required by the training syllabus. All participants provide neural snapshot EEG data and wear a blast sensor during breaching exercises. All participants also wear the AMP Neuro headset during active breaching at some point during the training week: because each breaching round involves three active breachers, AMP Neuro wear rotates in groups of three in step with the training rotation.

Data collection modalities

• Neural snapshot: a 3-minute resting-state EEG recording in which the participant sits still and alternates between eyes closed and eyes open, collected via the MW75 Neuro headset.
• Cognitive assessment: two tasks administered on a mobile device through the Sway Concussion application (Healthy Roster) - a reaction-time task requiring the participant to move the device when the screen changes color, and a working-memory task in which three letters are presented for three seconds, followed by a block-tapping sequence that lengthens each round until an error occurs, after which the participant recalls the three letters. The Day 1 assessment establishes an individual baseline; subsequent assessments are abbreviated.
• Balance assessment: a postural assessment administered on a mobile device through the Sway Concussion application (Healthy Roster), in which the participant holds specified stances such as tandem stance and single-leg stance.
• Questionnaires: sleep, stress, and habitual-pattern items; a daily 24-hour sleep and substance-use log (caffeine, alcohol, nicotine); a 3-month retrospective count of blast overpressure exposures at intake; and the NSI covering sensory (hearing, vision), physical (headache, dizziness), and cognitive (disorientation, mental sharpness, mental fatigue, concentration) items.
• Blast dosimetry: Blast Tracker 4 pressure sensor worn during breaching exercises to quantify the pressure and force of each nearby blast event.

Schedule of assessments

Recruitment and consent occur on Day 1 via a verbal briefing led by the Principal Investigator, with a private room available for individual review and signing of the informed consent form. No research procedures begin before the form is signed by both the participant and study personnel.

Day 1 - intake and baseline:

• Questionnaires on sleep, stress, and habitual patterns
• Current symptom assessment
• Retrospective 3-month blast overpressure exposure history
• Combined balance and cognitive baseline, approximately 15 minutes total (approximately 7 minutes each)
• Neural snapshot (3 minutes)

Days 2-5 - training days with potential blast overpressure exposure:

• Morning: 24-hour sleep, stress, and habit questionnaire; current symptom assessment; balance assessment (approximately 2 minutes); cognitive assessment (approximately 2 minutes); neural snapshot (3 minutes)
• Before and after each breaching exercise: current NSI symptom assessment and neural snapshot (3 minutes)
• During each breaching exercise: Blast Tracker 4 worn by all participants; AMP Neuro hearing protection headset worn by the three active breachers for that round, with signal-quality checks by research staff before training begins
• Evening: current symptom assessment; balance assessment (approximately 2 minutes); cognitive assessment (approximately 2 minutes); neural snapshot (3 minutes)

Participation requires approximately 5 to 10 minutes per session, apart from the Day 1 baseline session.

Devices

Both EEG systems use passive dry-electrode sensors and deliver no energy or electrical stimulation to the participant. The MW75 Neuro is a commercial-form-factor over-ear headphone used for stationary neural snapshots. The AMP Neuro integrates EEG sensing into tactical hearing protection for recording during active breaching. The Blast Tracker 4 is a passive pressure monitor mounted to existing gear. The devices have not been approved by Health Canada and are used solely as non-invasive research data collection tools; they are not the subject of investigation and will not be evaluated for medical safety or effectiveness.

Statistical analysis

Repeated-measures design. Paired t-tests and linear mixed-effects models will test for significant deviation in EEG power bands from individual baseline. Pearson correlations will assess associations between EEG power bands and NSI scores, and between Blast Tracker 4 dosimetry and both EEG perturbation and NSI scores.

Data management and privacy

Participant names and dates of birth are replaced with a coded participant ID at intake, and participants state this ID when completing daily questionnaires. A single password-protected file linking names to codes is held by the Principal Investigator and deleted at the completion of data collection. Individual results are not shared with Guild Solutions leadership or trainers in any way that would identify a participant. All data are held on locked systems or encrypted cloud servers. Source records may be reviewed by sponsor representatives, the Advarra IRB, and regulatory authorities including Health Canada and the US FDA for monitoring, auditing, and data verification.

Risks, benefits, and withdrawal

Risks are minimal: mild discomfort from extended sensor wear, comparable to wearing headphones, and a small risk of privacy breach, mitigated by the safeguards above. The AMP Neuro is not expected to affect hearing protection; a participant who judges its use unsafe on the range may stop using it, coordinating first with an onsite instructor. There is no intended clinical benefit to participants and no monetary compensation. Participation is voluntary, may be discontinued at any time without penalty, and participants who withdraw may request destruction of data already collected.

Inclusion criteria

• Currently enrolled participant in the Guild Solutions explosive breaching training course
• At least 18 years of age
• Fluent in English, sufficient to understand the consent form and study instructions
• Able and willing to provide written informed consent
• Willing to wear the study EEG headsets during assigned portions of the study

Exclusion criteria

(all criteria are self-reported; medical records are not reviewed):

• Major head injury within the past 6 months
• Regular use of anti-seizure or sedative (sleep) medication
• Known skin allergy or sensitivity to headset materials, including silver, silver-chloride, or vinyl