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.

• Blast overpressure exposure during explosive breaching training (Other): Participants are exposed to sub-concussive blast overpressure as part of the pre-existing Guild Solutions explosive breaching curriculum. The study does not assign, add, or modify exposures. It does not change the number of blast events, the charges used, or participant proximity to the breaching target. Participants rotate through standard training positions, including the three active breacher roles in each round, according to the training syllabus. Exposure is measured rather than administered. All participants wear a Blast Tracker 4 pressure sensor on the belt or helmet rail during breaching exercises to quantify the pressure and force of each nearby blast event. Individual exposure is further characterized by a self-reported count of blast overpressure events in the three months before enrollment, collected at intake.

Primary outcomes

• Feasibility of EEG data collection during active explosive breaching, measured as the proportion of AMP Neuro recordings meeting signal-quality criteria [During each breaching exercise, Days 2 through 5]: Percentage of AMP Neuro recording epochs retained after automated movement-artifact rejection, out of all epochs recorded during active breaching. Reported per session and aggregated across the cohort, with the proportion of sessions yielding analyzable data.
• Change from baseline in normalized Delta band power [Day 1 baseline; then morning, within 60 minutes before and within 60 minutes after each breaching exercise, and evening, Days 2 through 5]: Delta band power derived from 2-minute resting-state neural snapshots recorded with the MW75 Neuro headset, with eyes-open and eyes-closed segments analyzed separately. Values are expressed as a normalized index in which 100 represents the mean of a general healthy adult reference population and scores from 75 to 125 fall within one standard deviation of that mean. The index is continuous with no fixed minimum or maximum. Higher scores indicate greater Delta band power. Because the index is centered on a population mean, neither direction represents a uniformly better or worse outcome; deviation from each participant's own Day 1 baseline in either direction is the outcome of interest. The hypothesized direction following blast overpressure exposure is an increase.
• Change from baseline in normalized Theta band power [Day 1 baseline; then morning, within 60 minutes before and within 60 minutes after each breaching exercise, and evening, Days 2 through 5]: Theta band power derived from 2-minute resting-state neural snapshots recorded with the MW75 Neuro headset, with eyes-open and eyes-closed segments analyzed separately. Values are expressed as a normalized index in which 100 represents the mean of a general healthy adult reference population and scores from 75 to 125 fall within one standard deviation of that mean. The index is continuous with no fixed minimum or maximum. Higher scores indicate greater Theta band power. Because the index is centered on a population mean, neither direction represents a uniformly better or worse outcome; deviation from each participant's own Day 1 baseline in either direction is the outcome of interest. The hypothesized direction following blast overpressure exposure is an increase.
• Change from baseline in normalized Alpha band power [Day 1 baseline; then morning, within 60 minutes before and within 60 minutes after each breaching exercise, and evening, Days 2 through 5]: Alpha band power derived from 2-minute resting-state neural snapshots recorded with the MW75 Neuro headset, with eyes-open and eyes-closed segments analyzed separately. Values are expressed as a normalized index in which 100 represents the mean of a general healthy adult reference population and scores from 75 to 125 fall within one standard deviation of that mean. The index is continuous with no fixed minimum or maximum. Higher scores indicate greater Alpha band power. Because the index is centered on a population mean, neither direction represents a uniformly better or worse outcome; deviation from each participant's own Day 1 baseline in either direction is the outcome of interest. The hypothesized direction following blast overpressure exposure is a decrease.

Secondary outcomes

• Association between change in EEG band power and measured blast overpressure exposure [Days 2 through 5, pairing each pre-to-post breaching EEG change with the dosimetry recorded during that exercise]: Correlation between within-participant change in Delta, Theta, and Alpha power and blast dosimetry recorded by the Blast Tracker 4, including peak overpressure and cumulative exposure across the training day. Assessed by Pearson correlation.
• Change from baseline in Neurobehavioral Symptom Inventory (NSI) score [Day 1 intake; then morning, within 60 minutes before and within 60 minutes after each breaching exercise, and evening, Days 2 through 5]: The Neurobehavioral Symptom Inventory (NSI) is a 22-item self-report questionnaire in which each item is rated on a 5-point scale from 0 (None) to 4 (Very Severe). The total score is the sum of all 22 items and ranges from 0 to 88. Higher scores indicate greater symptom burden, so an increase represents a worse outcome. Change is calculated against each participant's Day 1 intake rating.
• Change from baseline in postural stability measured by the Sway Balance assessment [Day 1 baseline; then morning and evening, Days 2 through 5]: The Sway Balance score is generated by the Sway Concussion application (Healthy Roster) from accelerometer data collected on a mobile device held at the sternum across specified stances, including tandem stance and single-leg stance. Scores range from 0 to 100. Higher scores indicate better postural stability; a decrease from baseline represents a worse outcome. The Day 1 baseline comprises a practice round plus a minimum of two trial rounds, with a third round administered if between-round variance exceeds the vendor's preset threshold; subsequent assessments use a single round. Change is calculated against each participant's own Day 1 baseline.
• Change from baseline in the Sway Reaction Time score [Day 1 baseline; then morning and evening, Days 2 through 5]: The Sway Reaction Time score is generated by the Sway Concussion application (Healthy Roster) from a task requiring the participant to move the mobile device when the screen changes color. The score is reported as raw reaction time in milliseconds. There is no fixed maximum; the fixed minimum is 0ms. Lower values indicate faster reaction time and better performance; an increase from baseline represents a worse outcome. Change is calculated against each participant's own Day 1 baseline.
• Change from baseline in the Sway Working Memory score [Day 1 baseline; then morning and evening, Days 2 through 5]: The Sway Working Memory score is generated by the Sway Concussion application (Healthy Roster) from a 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. Scores range from 0 to 100. Higher scores indicate better working memory performance; a decrease from baseline represents a worse outcome. Change is calculated against each participant's own Day 1 baseline.
• Association between measured blast overpressure exposure and Neurobehavioral Symptom Inventory (NSI) total score [Days 2 through 5]: Correlation between cumulative blast impulse recorded by the Blast Tracker 4 and the Neurobehavioral Symptom Inventory (NSI) total score. The NSI is a 22-item self-report questionnaire, each item rated 0 (None) to 4 (Very Severe), with a total score ranging from 0 to 88; higher scores indicate greater symptom burden and a worse outcome. Assessed by Pearson correlation.

Other outcomes

• Sleep duration and substance use as covariates of EEG and symptom measures [Day 1 intake; then each morning, Days 2 through 5]: Self-reported hours of sleep and quantity of caffeine, alcohol, and nicotine consumed in the preceding 24 hours, collected each morning. Used as covariates in models of EEG band power change and symptom score change.
• Number of participants reporting discomfort or skin irritation attributable to headset wear [Day 1 through Day 5]: Count of participants who report discomfort or skin irritation attributable to wearing the MW75 Neuro or AMP Neuro headset at any point during the study, recorded by research staff. Unit of measure: participants.
• Number of sessions in which headset use was discontinued [Day 1 through Day 5]: Count of sessions in which headset use was discontinued before completion, either by the participant or at the direction of a range instructor, recorded by research staff. Unit of measure: sessions.

Sex: All, ages: 18 Years to any, accepts healthy volunteers

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

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• Alicia Howell-Munson, PhD, Principal investigator, Neurable, Inc