research psychologist Walter Reed Army Institute of Research
Abstract Text: Investigating blast effects during military training helps to understand and mitigate risk. There have been a variety of outcomes used to assess effects including hearing assessments, neurocognitive performance, neurotrauma biomarkers, and symptom reporting. Identifying a blast-dose relationship or exposure threshold associated with the onset of outcomes is paramount but complex. A complementary approach is identifying to what extent various outcome measures associate with each other. In a previous study, a sample of 270 breachers was used to investigate multiple symptom reporting combinations and neurocognitive performance patterns which revealed individuals reporting an increase in three specific symptoms, headache, taking longer to think, and tinnitus, had slower neurocognitive performance after blast exposure. This study is an extension of that previous work to see if results, reporting three specific symptoms associated with slower neurocognitive performance after blast exposure, can be replicated in other training settings (indirect fire weapons and shoulder-launched munitions).
Individuals participating in the study took a 32-item symptom inventory based on the Rivermead Post Concussion Symptoms Questionnaire and a 5-minute neurocognitive assessment called the Defense Automated Neurobehavioral Assessment (DANA) Rapid. DANA Rapid has three subtasks: Simple Reaction Time (SRT), Procedural Reaction Time (PRT), and Go/No-Go (GNG). The symptom inventory and DANA were administered before and after blast exposure. Change scores from baseline were analyzed using mixed-effect model to investigate differences in neurocognitive performance and increased symptom reporting from three symptoms: headache, long think (“Taking longer to think”), and tinnitus. Individuals wore blast gauges to measure blast exposure and all environments resulted in peak overpressure exposures that exceeded 4 psi.
In the original study, the top symptoms reported were headache (38%), long think (20%), tinnitus (16%). Multiple symptom combinations were tested and the model with the lowest Akaike information criterion was selected (headache, long think, and tinnitus). Comparing DANA performance from individuals reporting all three, combination of two, one, or zero symptoms resulted in slower DANA performance as the number of symptoms reported increased (SRT: zero versus three symptoms reported diff = 48 ms, p<.001; PRT: zero versus three symptoms reported diff = 107 ms, p<.001). For the indirect fire weapons environment (n = 38), using the same three symptoms, more symptoms reported also resulted in slower DANA performance (PRT: zero versus three symptoms reported diff = 113 ms, p=.038; GNG: zero versus three symptoms reported diff = 129 ms, p=.032). In this environment, the top reported symptoms included poorer concentration (66%), long think (65%), dizziness (60%). For the third replication, shoulder-launched munitions (n = 17), symptom reporting was spare where four (of the 32) symptoms were reported by four subjects; top symptom was headache (18%). Given the symptom reporting pattern, the model only included headache and tinnitus and resulted in slower DANA performance as the number of symptoms reported increased (PRT: zero versus two symptoms reported diff = 260 ms, p<.001; GNG: zero versus two symptoms reported diff = 257 ms, p=.002).
Testing the relationship between symptom reporting and neurocognitive performance has resulted in similar results in multiple training environments involving blast exposure where reporting three specific symptoms was associated with slower neurocognitive performance. Common to all three replicates are the findings in the DANA PRT subtask. Further, reaction time differences in PRT in the two environments with larger sample sizes are consistent (breachers: 107 ms and indirect fire weapons: 113 ms). The top symptoms reported between the different cohorts do differ, yet the model replicated findings in separate settings. The additional data could help confirm or re-evaluate the three-symptom model. There is a need for tools that measure and monitor blast exposure effects. The results here, coupled with existing blast level associations, give opportunity for more complex analyses which can assist with monitoring exposure, health status, and performance. It is likely that a multi-modal tool would be an asset to the DoD in identifying individuals that may need support and explain why some individuals have impairments and others don’t within the same environment. It is unlikely that any one factor alone is enough to sufficiently explain blast effects as they relate to outcomes.
Keywords: symptomology, neurocognitive, performance, blast, military
