Neurovascular Coupling in Special Operations Forces Combat Soldiers.

The purpose of this study was to investigate how concussion history affects neurovascular coupling in Special Operations Forces (SOF) combat Soldiers. We studied 100 SOF combat Soldiers [age = 33.5 ± 4.3 years; height = 180.4 ± 6.0 cm; 55 (55.0%) with self-reported concussion history]. We employed transcranial Doppler (TCD) ultrasound to assess neurovascular coupling (NVC) via changes in posterior cerebral artery (PCA) velocity in response to a reading and a visual search task. Baseline TCD data were collected for 2 min. NVC was quantified by the percent change in overall PCA response curves. We employed linear mixed effect models using a linear spline with one knot to assess group differences in percent change observed in the PCA velocity response curves between SOF combat Soldiers with and without a concussion history. Baseline PCA velocity did not significantly differ (t98 = 1.28, p = 0.20) between those with and without concussion history. Relative PCA velocity response curves did not differ between those with and without a concussion history during the reading task (F1,98 = 0.80, p = 0.37) or the visual search task (F1,98 = 0.52, p = 0.47). When assessing only SOF combat Soldiers with a concussion history, differential response to task was significantly greater in those with 3 or more concussions (F1,4341 = 27.24, p < 0.0001) relative to those with 1-2 concussions. Despite no main effect of concussion history on neurovascular coupling response in SOF combat Soldiers, we observed a dose-response based on lifetime concussion incidence. While long-term neurophysiological effects associated with head impact and blast-related injury are currently unknown, assessing NVC response may provide further insight into cerebrovascular function and overall physiological health.

Neuroinflammatory Biomarkers Associated With Mild Traumatic Brain Injury History in Special Operations Forces Combat Soldiers.

BACKGROUND: Special Operations Forces (SOF) combat soldiers are frequently exposed to blast and blunt neurotrauma, most often classified as mild traumatic brain injury (mTBI). Repetitive mTBI may increase the risk of developing long-term neurological sequelae. Identifying changes in neuroinflammatory biomarkers before chronic conditions emerge could serve as preliminary evidence of developing neuropathology. OBJECTIVE: To determine the effects of mTBI history, lifetime mTBI incidence, and recency on blood biomarker concentrations of axonal protein neurofilament light (NfL), glycolytic enzyme neuron-specific enolase (NSE), astrocyte-expressed S100 calcium-binding protein B (S100B), and neurotrophic cytokine interleukin-6 (IL-6) in healthy, active duty SOF combat soldiers. METHODS: Self-reported mTBI history/recency and fasted blood samples were collected in this cross-sectional study of 104 asymptomatic SOF combat soldiers. Biomarker concentrations were quantified using commercial enzyme-linked immunosorbent assays. Mann-Whitney U and Kruskal-Wallis tests were used to compare groups. Post hoc tests with appropriate corrections were conducted as warranted. RESULTS: Soldiers with mTBI history had higher NSE concentrations than those without (z = -2.60, P = .01). We also observed significant main effects of lifetime mTBI incidence on NSE (χ(3) = 9.52, P = .02) and S100B (χ(3) = 8.21, P = .04) concentrations and a significant main effect of mTBI recency on NfL concentration (χ(2) = 6.02, P = .049). CONCLUSION: The SOF combat soldiers with mTBI history had increased NSE. Longitudinal studies in this population are needed due to between-subject heterogeneity in biomarker concentrations. The NfL concentrations in our SOF combat soldiers-regardless of mTBI history or recency-were similar to values previously reported in civilian acute TBI patients.

The relationship between neurovascular coupling, vision and sensory performance, and concussion history in Special Operations Forces combat soldiers.

OBJECTIVE: To determine the relationship between neurovascular coupling (NVC), vision and sensory performance in Special Operations Forces (SOF) combat soldiers with and without concussion history. METHODS: We studied 61 SOF combat soldiers (male, age = 33.8 ± 3.7 years, n = 40 with concussion history [Median = 3; range = 1-10+]). We instrumented our participants with transcranial Doppler to quantify NVC response during reading and visual search tasks. All participants completed vision and sensory performance testing (Senaptec Sensory Station). We performed separate multiple regressions to determine if relationships between NVC and vision and sensory performance testing existed while controlling for concussion history, and to investigate the interaction between NVC and concussion history. RESULTS: Those with higher visual search NVC response magnitudes demonstrated significantly worse contrast sensitivity when controlling for concussion history (F1,60=4.57, ß = 0.03, p = .04, R2 = 12.6%). We did not observe any other significant relationships between NVC and visual and sensory performance tests nor did we observe any significant interactions between NVC and concussion history (p > .05). CONCLUSIONS: Heightened NVC response magnitudes are related to reduced contrast sensitivity in SOF combat soldiers. Because concussion history does not impact the relationships between outcomes, these measures may be utilized for performance evaluation at any point in a soldier's career. The lack of relationships between NVC response magnitude and some of the other vision and sensory performance outcomes suggests that implementing NVC assessment may add unique information and enable clinicians to detect physiological deficits that may otherwise go undetected.

Cerebrovascular Reactivity in Special Operations Forces Combat Soldiers.

The purpose of this study was to investigate how concussion history affects cerebrovascular reactivity (CVR) in Special Operations Forces (SOF) combat soldiers. We studied 104 SOF soldiers [age = 33.5 ± 4.3 years; height = 179.7 ± 6.3 cm; 59 (56.7%) with self-reported concussion history]. We employed transcranial Doppler (TCD) ultrasound to measure middle cerebral artery (MCA) velocity. Baseline TCD data were collected for 2 min. Changes in MCA velocity were measured in response to five breath-holding trials and five hyperventilation trials. Cerebrovascular reactivity was quantified by the breath-holding index (BHI), vasomotor reactivity reserve (VMRr), and percent change in overall response curves. Independent t tests were employed to assess group differences in BHI, and VMRr values. We employed mixed effects models with quadratic mean structures to assess group differences in percent change MCA velocity response curves. There were no significant group differences in BHI (t102 = 0.04, p = 0.97) or VMRr (t102 = -0.33, p = 0.75). There were no group differences in relative MCA velocity response curves during the breath-holding task (F1,5092 = 0.19, p = 0.66) or during the hyperventilation task (F1,5092 = 0.41, p = 0.52) between SOF soldiers with and without a self-reported concussion history. If CVR deficits exist immediately post-concussion, our study suggests that these deficits recover over time in this population. While long-term neurophysiological effects of blast-related injury are currently unknown, assessing CVR response may provide further insight into cerebrovascular function and overall physiological health following blast exposure.

Military static line parachuting injuries seen by the airborne battalion provider.

Military static line parachuting exposes jumpers to a variety of novel methods of injury. Providers assigned to Airborne units need to develop and maintain a high index of suspicion when dealing with jump-related injuries. Understanding the incident rate and the mechanism of injury can help a provider better identify injuries based on the history of the incidence and develop that index of suspicion. Injuries can happen at almost any point during the jump process and each step has both common and unique injuries associated with it. In addition to identifying, managing, and treating the injuries involved, providing information on estimated time until return to duty can be beneficial for the commander. In the end, a provider's best tools for managing Airborne-related injuries are an understanding of Airborne operations, quality orthopedic skills, and a high index of suspicion.