The impact of caffeine consumption during 50 hr of extended wakefulness on glucose metabolism, self-reported hunger and mood state.

Caffeine is known for its capacity to mitigate performance decrements. The metabolic side-effects are less well understood. This study examined the impact of cumulative caffeine doses on glucose metabolism, self-reported hunger and mood state during 50 hr of wakefulness. In a double-blind laboratory study, participants were assigned to caffeine (n = 9, 6M, age 21.3 ± 2.1 years; body mass index 21.9 ± 1.6 kg/m2 ) or placebo conditions (n = 8, 4M, age 23.0 ± 2.8 years; body mass index 21.8 ± 1.6 kg/m2 ). Following a baseline sleep (22:00 hours-08:00 hours), participants commenced 50 hr of sleep deprivation. Meal timing and composition were controlled throughout the study. Caffeine (200 mg) or placebo gum was chewed for 5 min at 01:00 hours, 03:00 hours, 05:00 hours and 07:00 hours during each night of sleep deprivation. Continual glucose monitors captured interstitial glucose 2 hr post-breakfast, at 5-min intervals. Hunger and mood state were assessed at 10:00 hours, 16:30 hours, 22:30 hours and 04:30 hours. Caffeine did not affect glucose area under the curve (p = 0.680); however, glucose response to breakfast significantly increased after 2 nights of extended wakefulness compared with baseline (p = 0.001). There was a significant main effect of day, with increased tiredness (p < 0.001), mental exhaustion (p < 0.001), irritability (p = 0.002) and stress (p < 0.001) on the second day of extended wake compared with day 1. Caffeine attenuated the rise in tiredness (p < 0.001), mental exhaustion (p = 0.044) and irritability (p = 0.018) on day 1 but not day 2. Self-reported hunger was not affected by sleep deprivation or caffeine. These data confirm the effectiveness of caffeine in improving performance under conditions of sleep deprivation by reducing feelings of tiredness, mental exhaustion and irritability without exacerbating glucose metabolism and feelings of hunger.

Aerobic fitness impacts sympathoadrenal axis responses to concurrent challenges.

The combination of mental and physical challenges can elicit exacerbated cardiorespiratory (CR) and catecholamine responses above that of a single challenge alone. PURPOSE: This study examined the effects of a combination of acute mental challenges and physical stress on cardiorespiratory and catecholamine responses. METHOD: Eight below-average fitness (LF VO2max = 36.58 ± 3.36 ml-1 kg-1 min-1) and eight above-average fitness (HF VO2max = 51.18 ± 2.09 ml-1 kg-1 min-1) participants completed an exercise-alone condition (EAC) session consisting of moderate-intensity cycling at 60% VO2max for 37 min, and a dual-challenge condition (DCC) that included concurrent participation in mental challenges while cycling. RESULT: The DCC resulted in increases in perceived workload, CR, epinephrine, and norepinephrine responses overall. HF participants had greater absolute CR and catecholamine responses compared to LF participants and quicker HR recovery after the dual challenge. CONCLUSION: These findings demonstrate that cardiorespiratory fitness does impact the effect of concurrent stressors on CR and catecholamine responses.

Dose-dependent model of caffeine effects on human vigilance during total sleep deprivation.

Caffeine is the most widely consumed stimulant to counter sleep-loss effects. While the pharmacokinetics of caffeine in the body is well-understood, its alertness-restoring effects are still not well characterized. In fact, mathematical models capable of predicting the effects of varying doses of caffeine on objective measures of vigilance are not available. In this paper, we describe a phenomenological model of the dose-dependent effects of caffeine on psychomotor vigilance task (PVT) performance of sleep-deprived subjects. We used the two-process model of sleep regulation to quantify performance during sleep loss in the absence of caffeine and a dose-dependent multiplier factor derived from the Hill equation to model the effects of single and repeated caffeine doses. We developed and validated the model fits and predictions on PVT lapse (number of reaction times exceeding 500 ms) data from two separate laboratory studies. At the population-average level, the model captured the effects of a range of caffeine doses (50-300 mg), yielding up to a 90% improvement over the two-process model. Individual-specific caffeine models, on average, predicted the effects up to 23% better than population-average caffeine models. The proposed model serves as a useful tool for predicting the dose-dependent effects of caffeine on the PVT performance of sleep-deprived subjects and, therefore, can be used for determining caffeine doses that optimize the timing and duration of peak performance.

A biomathematical model of the restoring effects of caffeine on cognitive performance during sleep deprivation.

RATIONALE: While caffeine is widely used as a countermeasure to sleep loss, mathematical models are lacking. OBJECTIVE: Develop a biomathematical model for the performance-restoring effects of caffeine in sleep-deprived subjects. METHODS: We hypothesized that caffeine has a multiplicative effect on performance during sleep loss. Accordingly, we first used a phenomenological two-process model of sleep regulation to estimate performance in the absence of caffeine, and then multiplied a caffeine-effect factor, which relates the pharmacokinetic-pharmacodynamic effects through the Hill equation, to estimate the performance-restoring effects of caffeine. RESULTS: We validated the model on psychomotor vigilance test data from two studies involving 12 subjects each: (1) single caffeine dose of 600mg after 64.5h of wakefulness and (2) repeated doses of 200mg after 20, 22, and 24h of wakefulness. Individualized caffeine models produced overall errors that were 19% and 42% lower than their population-average counterparts for the two studies. Had we not accounted for the effects of caffeine, the individualized model errors would have been 117% and 201% larger, respectively. CONCLUSIONS: The presented model captured the performance-enhancing effects of caffeine for most subjects in the single- and repeated-dose studies, suggesting that the proposed multiplicative factor is a feasible solution.

Caffeine gum minimizes sleep inertia.

Naps are an effective strategy for maintaining alertness and cognitive performance; however, upon abrupt wakening from naps, sleep inertia (temporary performance degradation) may ensue. In the present study, attenuation of post-nap sleep inertia was attempted by administration of caffeine gum. Using a double-blind, placebo-controlled crossover design, 15 healthy, non-smoking adults were awakened at 1 hr. and again at 6 hr. after lights out (0100 and 0600, respectively) and were immediately administered a gum pellet containing 100 mg of caffeine or placebo. A 5-min. psychomotor vigilance task was administered at 0 min., 6 min., 12 min., and 18 min. post-awakening. At 0100, response speed with caffeine was significantly better at 12 min. and 18 min. post-awakening compared to placebo; at 0600, caffeine's effects were evident at 18 min. post-awakening. Caffeinated gum is a viable means of rapidly attenuating sleep inertia, suggesting that the adenosine receptor system is involved in sleep maintenance.

Low-dose caffeine administered in chewing gum does not enhance cycling to exhaustion.

Low-dose caffeine administered in chewing gum does not enhance cycling to exhaustion. The purpose of the current investigation was to examine the effect of low-dose caffeine (CAF) administered in chewing gum at 3 different time points during submaximal cycling exercise to exhaustion. Eight college-aged (26 ± 4 years), physically active (45.5 ± 5.7 ml·kg(-1)·min(-1)) volunteers participated in 4 experimental trials. Two pieces of caffeinated chewing gum (100 mg per piece, total quantity of 200 mg) were administered in a double-blind manner at 1 of 3 time points (-35, -5, and +15 minutes) with placebo at the other 2 points and at all 3 points in the control trial. The participants cycled at 85% of maximal oxygen consumption until volitional fatigue and time to exhaustion (TTE) were recorded in minutes. Venous blood samples were obtained at -40, -10, and immediately postexercise and analyzed for serum-free fatty acid and plasma catecholamine concentrations. Oxygen consumption, respiratory exchange ratio, heart rate, glucose, lactate, ratings of perceived exertion, and perceived leg pain measures were obtained at baseline and every 10 minutes during cycling. The results showed that there were no significant differences between the trials for any of the parameters measured including TTE. These findings suggest that low-dose CAF administered in chewing gum has no effect on TTE during cycling in recreational athletes and is, therefore, not recommended.

An Exploratory Comparison of Water-Tamped and -Untamped Explosive Breaches: Practical Applications for the Tactical Community via a Pilot Study.

BACKGROUND: Tamping explosive charges used by breachers is an increasingly common technique. The ability to increase the directional effectiveness of the charge used, combined with the potential to reduce experienced overpressure on breachers, makes tamping a desirable tool not only from an efficacy standpoint for breachers but also from a safety standpoint for operational personnel. The long-term consequences of blast exposure are an open question and may be associated with temporary performance deficits and negative health symptomatology. PURPOSE: This work evaluates breaches of varying charge weight, material breached, and tamping device used to determine the value of tamping during various scenarios by measuring actual breaches conducted during military and law enforcement training for efficacy and blast overpressure on Operators. METHODS: Three data collections across 18 charges of various construction were evaluated with blast overpressure sensors at various distances and locations where breachers would be located, to assess explosive forces on human personnel engaged in breaching activities. RESULTS AND CONCLUSIONS: Findings indicate that water tamping in general is a benefit on moderate and heavy charges but offers less benefit at a low charge with regard to mitigating blast overpressure on breachers. Reduced overpressure allows Operators to stage closer to explosives and lowers the potential for compromised reaction time. It also reduces the likelihood of negative consequences that can result from excessive overpressure exposure and allow Operators to "do more with less" in complex environments, where resource access may be limited by logistic or other limitations. However, tamping in all instances improved blast efficacy in creating successful breaches. Future studies are planned to investigate tamping mediums beyond water and environment changes, whether tamping can be used to mitigate acoustic insult, and other explosive types.

Caffeine protects against increased risk-taking propensity during severe sleep deprivation.

Previous research suggests that sleep deprivation is associated with declines in metabolic activity within brain regions important for judgement and impulse control, yet previous studies have reported inconsistent findings regarding the effects of sleep loss and caffeine on risk-taking. In this study, 25 healthy adults (21 men, four women) completed the Balloon Analog Risk Task (BART) and Evaluation of Risks (EVAR) scale at regular intervals to examine behavioral and self-reported risk-taking propensity during 75 h of continuous sleep deprivation. Participants received either four double-blind administrations of 200 mg caffeine (n=12) or indistinguishable placebo (n=13) gum bi-hourly during each of the 3 nights of sleep deprivation. No significant effects of drug group or sleep deprivation were evident on the BART or EVAR when measured at 51 h of wakefulness. However, by 75 h, the placebo group showed a significant increase in risk-taking behavior on the cost-benefit ratio and total number of exploded balloons on the BART, whereas the caffeine group remained at baseline levels. On the EVAR, several factors of self-reported risk-taking propensity, including total risk, impulsivity and risk/thrill seeking, were reduced among subjects receiving caffeine across the 3 days of sleep deprivation, but remained at baseline levels for the placebo group. These results suggest that 3 nights of total sleep deprivation led to a significant increase in behavioral risk-taking but not self-reported perception of risk-propensity. Overnight caffeine prevented this increase in risky behavior.

Stress reactivity to repeated low-level challenges: a pilot study.

The purpose of this study was to examine the effects of a mental challenge on cardiovascular and endocrine [epinephrine (EPI), norepinephrine (NE), and cortisol (CORT)] responses to subsequent low-intensity physical exertion. Twelve males (23.25±0.45 years) completed three sessions, including a graded exercise test on a cycle ergometer and two counter-balanced mental stress trials. In the mental challenge-control condition (MC), participants sat quietly for 20 min following a 20 min mental challenge whereas in the mental challenge-exercise condition (MEC) subjects cycled at 35% of maximal oxygen consumption (VO2max) following the mental challenge. Repeated-measures ANOVAs were used to assess state anxiety (SAI), cardiovascular variables, EPI, NE, and CORT levels across time between conditions. Participants reported significantly greater increases in SAI scores immediately after the mental challenge, which then decreased post-challenge in both conditions. Neither EPI or NE demonstrated an alteration in levels in either condition, but CORT significantly increased after the mental challenge in both conditions and then maintained a significantly greater level during the MEC compared to the MC condition from midexercise through 15 min of recovery. Area-under-the-curve calculations for CORT was significantly greater in the MEC compared to the MC. Results suggest that the initial mental challenge may have acted to enhance the overall adrenal response to the subsequent anticipation of and actual participation in the low-level physical challenge.

The effects of low-dose caffeine on perceived pain during a grip to exhaustion task.

This double-blind, placebo-controlled, within-subject experiment examined the effects of low-dose caffeine on pain reported during an exhaustive grip task. The grip task consisted of holding a metal block attached to standard Olympic weight plates with the arm at the side until the participants could no longer maintain their grip. Apparently healthy recreationally trained college-aged adults (men, n = 5; women, n = 5) were given either a piece of Stay Alert™ gum that delivered 85% of the effective dose of 100 mg of caffeine in 5 minutes or an identical placebo gum that contained no caffeine. Subsequently, pain perception and ratings of perceived exertion were recorded during an exhaustive grip task every 15 seconds and the overall time to exhaustion. No significant difference was found in time to exhaustion between treatments. A significant main effect of treatment for reported pain (p < 0.001, Φ = 0.377) was observed. Thus, in a population of recreationally trained college-aged adults, low-dose caffeine may attenuate the individual's perception of pain during a grip to exhaustion task.

Automated Neuropsychological Assessment Metrics: repeated assessment with two military samples.

INTRODUCTION: U.S. military troops deploying to war zones are currently administered the Automated Neuropsychological Assessment Metrics (ANAM4) Traumatic Brain Injury (TBI) Battery to establish individual neurocognitive performance baselines. In part, the utility of the ANAM4 TBI Battery baseline measurement depends on test-retest reliability of this instrument. The purpose of this report was to evaluate performance following multiple administrations of the ANAM4 TBI Battery: does performance in a repeated measures paradigm constitute a stable, interpretable indication of baseline neurocognitive ability? METHODS: The data presented here are from the ANAM4 TBI Battery administered four times to a group of U.S. Marines in Study 1 and eight times to a group of New Zealand Defence Force personnel in Study 2. RESULTS: The results show practice effect in five of six performance subtests in both Study 1 and Study 2. DISCUSSION: 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.

Bisulfite Amplicon Sequencing Can Detect Glia and Neuron Cell-Free DNA in Blood Plasma.

Sampling the live brain is difficult and dangerous, and withdrawing cerebrospinal fluid is uncomfortable and frightening to the subject, so new sources of real-time analysis are constantly sought. Cell-free DNA (cfDNA) derived from glia and neurons offers the potential for wide-ranging neurological disease diagnosis and monitoring. However, new laboratory and bioinformatic strategies are needed. DNA methylation patterns on individual cfDNA fragments can be used to ascribe their cell-of-origin. Here we describe bisulfite sequencing assays and bioinformatic processing methods to identify cfDNA derived from glia and neurons. In proof-of-concept experiments, we describe the presence of both glia- and neuron-cfDNA in the blood plasma of human subjects following mild trauma. This detection of glia- and neuron-cfDNA represents a significant step forward in the translation of liquid biopsies for neurological diseases.

Neurotrauma Biomarker Levels and Adverse Symptoms Among Military and Law Enforcement Personnel Exposed to Occupational Overpressure Without Diagnosed Traumatic Brain Injury.

Importance: There is a scientific and operational need to define objective measures of exposure to low-level overpressure (LLOP) and concussion-like symptoms among persons with specialized occupations. Objective: To evaluate serum levels of neurotrauma biomarkers and their association with concussion-like symptoms reported by LLOP-exposed military and law enforcement personnel who are outwardly healthy and cleared to perform duties. Design, Setting, and Participants: This retrospective cohort study, conducted from January 23, 2017, to October 21, 2019, used serum samples and survey data collected from healthy, male, active-duty military and law enforcement personnel assigned to operational training at 4 US Department of Defense and civilian law enforcement training sites. Personnel aged 18 years or older with prior LLOP exposure but no diagnosed traumatic brain injury or with acute blast exposure during sampling participated in the study. Serum samples from 30 control individuals were obtained from a commercial vendor. Main Outcomes and Measures: Serum levels of glial fibrillary acidic protein, ubiquitin carboxyl hydrolase (UCH)-L1, neurofilament light chain, tau, amyloid ß (Aß)-40, and Aß-42 from a random sample (30 participants) of the LLOP-exposed cohort were compared with those of 30 age-matched controls. Associations between biomarker levels and self-reported symptoms or operational demographics in the remainder of the study cohort (76 participants) were assessed using generalized linear modeling or Spearman correlations with age as a covariate. Results: Among the 30 randomly sampled participants (mean [SD] age, 32 [7.75] years), serum levels of UCH-L1 (mean difference, 4.92; 95% CI, 0.71-9.14), tau (mean difference, 0.16; 95% CI, -0.06 to 0.39), Aß-40 (mean difference, 138.44; 95% CI, 116.32-160.56), and Aß-42 (mean difference, 4.97; 95% CI, 4.10-5.83) were elevated compared with those in controls. Among the remaining cohort of 76 participants (mean [SD] age, 34 [7.43] years), ear ringing was reported by 44 (58%) and memory or sleep problems were reported by 24 (32%) and 20 (26%), respectively. A total of 26 participants (34%) reported prior concussion. Amyloid ß-42 levels were associated with ear ringing (F1,72 = 7.40; P = .008) and memory problems (F1,72 = 9.20; P = .003). Conclusions and Relevance: The findings suggest that long-term LLOP exposure acquired during occupational training may be associated with serum levels of neurotrauma biomarkers. Assessment of biomarkers and concussion-like symptoms among personnel considered healthy at the time of sampling may be useful for military occupational medicine risk management.

Fast-Running Tools for Personalized Monitoring of Blast Exposure in Military Training and Operations.

INTRODUCTION: During training and combat operations, military personnel may be exposed to repetitive low-level blast while using explosives to gain entry or by firing heavy weapon systems such as recoilless weapons and high-caliber sniper rifles. This repeated exposure, even within allowable limits, has been associated with cognitive deficits similar to that of accidental and sports concussion such as delayed verbal memory, visual-spatial memory, and executive function. This article presents a novel framework for accurate calculation of the human body blast exposure in military heavy weapon training scenarios using data from the free-field and warfighter wearable pressure sensors. MATERIALS AND METHODS: The CoBi human body model generator tools were used to reconstruct multiple training scenes with different weapon systems. The CoBi Blast tools were used to develop the weapon signature and estimate blast overpressure exposure. The authors have used data from the free-field and wearable pressure sensors to evaluate the framework. RESULTS: Carl-Gustav and 0.50 caliber sniper training scenarios were used to demonstrate and validate the developed framework. These simulations can calculate spatially and temporally resolved blast loads on the whole human body and on specific organs vulnerable to blast loads, such as head, face, and lungs. CONCLUSIONS: This framework has numerous advantages including easier model setup and shorter simulation times. The framework is an important step towards developing an advanced field-applicable technology to monitor low-level blast exposure during heavy weapon military training and combat scenarios.

Stress hormone responses to an ultraendurance race in the cold.

OBJECTIVE: Physical stress (exercise and/or environmental) activates the sympathetic-adrenal-medullary (SAM) and hypothalamic-pituitary-adrenocortical (HPA) axes. The combination of ultraendurance exercise in the cold presents a unique summated stress to the body. The purpose of this study was to assess the stress hormone response in runners, cyclists, and skiers participating in a 161-km ultraendurance race on a snow-packed course in the Alaskan wilderness. METHODS: Forty-four athletes (20 runners, 17 cyclists, 7 skiers) competed on the same course of snow-machine trails and ice roads with each athlete carrying 7 kg of mandatory equipment. Pre-race weight and blood samples were collected 2 days prior to the race start. Post-race measurements were made within 15 minutes of race finish. Hematocrit was measured, and blood samples were analyzed for levels of norepinephrine, epinephrine, adrenocorticotropic hormone, and cortisol. RESULTS: Runners lost significant weight (-1.74 kg +/- 1.29) pre-race to post-race. Hematocrit was maintained, and plasma volume increased minimally. Norepinephrine increased significantly pre-race (279.9 pg/mL +/- 356.9) to post-race (691.7 pg/mL +/- 422.6) with no difference among divisions. Epinephrine did not change significantly during the race. Adrenocorticotropic hormone (2.40 pg/mL +/- 2.40 to 19.04 pg/mL +/- 45.38) increased significantly with no difference among divisions. Cortisol increased significantly pre-race (12.03 microg/dL +/- 5.66) to post-race (26.69 microg/dL +/- 5.77), and post-race cortisol was significantly higher in runners vs skiers. CONCLUSIONS: These data suggest activation of both the SAM and HPA axes from an ultraendurance race in the cold and reveal the degree of stress hormone responses to this exhausting bout of exercise.

Multiple caffeine doses maintain vigilance, attention, complex motor sequence expression, and manual dexterity during 77 hours of total sleep deprivation.

Sleep deprivation (SD) and fatigue have detrimental effects on performance in operational settings. Few studies have investigated the cumulative effects of SD and fatigue on performance under heavy workload demands. Therefore, we investigated the efficacy of multiple repeated doses of caffeine as a countermeasure to SD and fatigue during 77 h total SD (TSD) during the early morning hours. Twenty-three males and females, 18 - 35 years of age, who identified as moderate caffeine consumers completed the Psychomotor Vigilance Task (PVT) 141 times during the experimental test period. Caffeine was administered in a multi-dose paradigm over three nights without sleep. Participants received either caffeine (200 mg) or placebo at the beginning of each 2-h test block from 0100 - 0900 (800 mg total per night). While PVT speed declined for both groups across all 3 nights, the caffeine group consistently out-performed the placebo group. Caffeine maintained attentiveness (1-5 s lapses) on night 1, but this advantage was lost on nights 2 and 3. Caffeine outperformed placebo for responsive lapses (5-9 s lapses) across all three nights, but caffeine performance was still notably worse than at baseline. Prolonged non-responsive lapses (beyond 10 s) were only reduced by caffeine on night 2. Caffeine was more effective than placebo across all nights at sustaining completion speed of a complex motor sequence task and a manual coordination task. Essentially, caffeine is an effective countermeasure for SD, as it mitigates declines in speed and failures to respond, and sustains motor planning and coordination. However, caffeine does not restore normal functioning during SD and cannot be considered as a replacement for sleep.

Sensor orientation and other factors which increase the blast overpressure reporting errors.

This study compared the response of the wearable sensors tested against the industry-standard pressure transducers at blast overpressure (BOP) levels typically experienced in training. We systematically evaluated the effects of the sensor orientation with respect to the direction of the incident shock wave and demonstrated how the averaging methods affect the reported pressure values. The evaluated methods included averaging peak overpressure and impulse of all four sensors mounted on a helmet, taking the average of the three sensors, or isolating the incident pressure equivalent using two sensors. The experimental procedures were conducted in controlled laboratory conditions using the shock tube, and some of the findings were verified in field conditions with live fire charges during explosive breaching training. We used four different orientations (0°, 90°, 180°, and 270°) of the headform retrofitted with commonly fielded helmets (ACH, ECH, Ops-Core) with four B3 Blast Gauge sensors. We determined that averaging the peak overpressure values overestimates the actual dosage experienced by operators, which is caused by the reflected pressure contribution. This conclusion is valid despite the identified limitation of the B3 gauges that consistently underreport the peak reflected overpressure, compared to the industry-standard sensors. We also noted consistent overestimation of the impulse. These findings demonstrate that extreme caution should be exercised when interpreting occupational blast exposure results without knowing the orientation of the sensors. Pure numerical values without the geometrical, training-regime specific information such as the position of the sensors, the distance and orientation of the trainee to the source of the blast wave, and weapon system used will inevitably lead to erroneous estimation of the individual and cumulative blast overpressure (BOP) dosages. Considering that the 4 psi (~28 kPa) incident BOP is currently accepted as the threshold exposure safety value, a misinterpretation of exposure level may lead to an inaccurate estimation of BOP at the minimum standoff distance (MSD), or exclusion criteria.

Dataset of Rat and Human Serum Proteomes Derived from Differential Depletion Strategies prior to Mass Spectrometry.

This article provides information regarding the effect of four common high abundant protein (albumin and immunoglobulins (Ig)) depletion strategies upon serum proteomics datasets derived from normal, non-diseased rat or human serum. After tryptic digest, peptides were separated using C18 reverse phase liquid chromatography-tandem mass spectrometry (rpLC-MS/MS). Peptide spectral matching (PSM) and database searching was conducted using MS Amanda 2.0 and Sequest HT. Peptide and protein false discovery rates (FDR) were set at 0.01%, with at least two peptides assigned per protein. Protein quantitation and the extent of albumin and Ig removal was defined by PSM counts. Venn diagram analysis of the core proteomes, derived from proteins identified by both search engines, was performed using Venny. Ontological characterization and gene set enrichment were performed using WebGestalt. The dataset resulting from each depletion column is provided.

Case Study of a Breacher: Investigation of Neurotrauma Biomarker Levels, Self-reported Symptoms, and Functional MRI Analysis Before and After Exposure to Measured Low-Level Blast.

We report a case study on a single military member who received moderate blast overpressure (OP) exposure during routine breacher training. We extend previous research on blast exposure during training, which lacked sufficient data to assess symptom profiles and OP exposure. The present work was conducted because a subjective symptom profile similar to that seen in sports concussion has been reported by military personnel exposed to blast. Data collection for this study was carried out under a research protocol approved by the relevant Human Subjects Review Committees on one subject, who received the highest OP exposure during training. The volunteer was a 20-year-old male with no prior history of traumatic brain injury (TBI) or blast exposure. The volunteer was part of a breacher training team that completed a 2-week explosive entry course. The course included 3 classroom days and 9 days of practical training, held in the morning, afternoon, and evening sessions. Blast exposure occurred on five of the nine practical training days, with multiple exposures over the course of each day. Assessments of serum, self-reported symptoms, magnetic resonance imaging, and blast characterization were conducted. Results indicated changes in glial fibrillary acidic protein and ubiquitin C-terminal hydrolase-L1 postblast exposure but did not manifest changes in spectrin-derived breakdown product 150 or magnetic resonance imaging. No additional symptoms were reported by the subject. Objective markers of mild TBI remain elusive, but support for serum biomarkers as an early detection mechanism is promising. Additionally, this case study demonstrated an association between OP and high level of neurotrauma biomarker in an individual.

Role of Interfacial Conditions on Blast Overpressure Propagation Into the Brain.

The complex interfacial condition between the human brain and the skull has been difficult to emulate in a surrogate system. Surrogate head models have typically been built using a homogeneous viscoelastic material to represent the brain, but the effect of different interfacial conditions between the brain and the skull on pressure transduction into the brain during blast has not been studied. In the present work, three interfacial conditions were generated in physical surrogate human head models. The first surrogate consisted of a gel brain separated from the skull by a layer of saline solution similar in thickness to the cerebrospinal fluid (CSF) layer in the human head: the fluid interface head model. The second surrogate head had the entire cranial cavity filled with the gel: the fixed interface head model. The third surrogate head contained a space-filling gel brain wrapped in a thin plastic film: the stick-slip interface head model. The human head surrogates were evaluated in a series of frontal blast tests to characterize the effect of skull-brain interfacial conditions on overpressure propagation into the gel brains. The fixed and the stick-slip interface head models showed nearly equal peak brain overpressures. In contrast, the fluid interface head model had much higher in-brain peak overpressures than the other two models, thus representing the largest transmission of forces into the gel brain. Given that the elevated peak overpressures occurred only in the fluid interface head model, the presence of the saline layer is likely responsible for this increase. This phenomenon is hypothesized to be attributed to the incompressibility of the saline and/or the impedance differences between the materials. The fixed interface head model showed pronounced high frequency energy content relative to the other two models, implying that the fluid and the stick-slip conditions provided better dampening. The cumulative impulse energy entering the three brain models were similar, suggesting that the interface conditions do not affect the total energy transmission over the positive phase duration of a blast event. This study shows that the fidelity of the surrogate human head models would improve with a CSF-emulating liquid layer.