A traumatic brain injury (TBI) is defined by the Centers for Disease Control and Prevention (CDC) as a “disruption in the normal function of the brain that can be caused by a bump, blow, or jolt to the head, or a penetrating head injury.”

Symptoms can include headaches, nausea, vomiting, sleep disturbances, physical weakness, problems with memory and attention, anxiety, and depression. TBI can be challenging to diagnose because symptoms can appear immediately or not for days or months after an injury.

TBIs can range from mild to severe. Severe TBI can result in death or permanent physical, mental, or emotional impairment. However, the most common form of TBI is mild TBI (mTBI), also known as concussion. While symptoms can be distressing, most people typically recover well and estimates suggest that 90 percent of people with concussions recover fully within 3 months. However, the more concussions a person has, the longer it may take to recover.

The CDC considers TBI to be a serious public health problem-a leading cause of death and disability each year. In 2010, the CDC says there were 2.5 million TBIs in the United States.

Within the military, more than 375,000 service members have been diagnosed with a TBI between 2000 and 2017, according to the Defense and Veteran Brain Injury Center. Most-just over 308,000-were concussions diagnosed outside of combat, caused primarily by falls and motor vehicle crashes.

The annual rate of TBIs among military personnel increased from 2000 to 2011, when the number of service members deployed to Iraq and Afghanistan also grew. During this time, most of the TBIs sustained during combat operations were caused by blasts from improvised explosive devices (IED).

TBI has become known as one of the signature injuries from these recent conflicts and between 10 and 20 percent of military personnel who served in these conflicts have been diagnosed with this injury.

The need to better understand TBI-how to diagnose it, treat it, and prevent it-has spurred researchers throughout the military medical community to study this condition that can impair the short- and long-term health and readiness of service members.

Most research on military TBI to date has focused on injuries resulting from a single trauma, such as an IED or motor vehicle crash, but few studies have examined the relationship between chronic exposure to low-level blast waves (also referred to as overpressure exposure) and the development of TBI.

Researchers at the Naval Health Research Center (NHRC) aim to change that. A recent study examined whether personnel in military occupational specialties (MOS) that regularly expose them to overpressure are at increased risk of sustaining an mTBI.

“There’s a lot of great research about the consequences of TBIs, but relatively little has focused on who is at risk for developing a TBI,” Research Psychologist at NHRC Lt. Uade Olaghere da Silva said. “Not everyone who experiences a car crash, for example, will develop a TBI or, if they do, experience negative outcomes. Our intent was to identify factors that may put service members at higher risk for developing a TBI.”

One potential risk factor is the chronic low-level overpressure exposure, such as firing heavy caliber weapons, which certain service members experience as part of their regular, job-related duties. When service members are near a heavy caliber weapon being fired or an explosive detonating, they are subject to a blast/overpressure wave.

“With my colleague Jennifer Belding, a behavioral health researcher at NHRC, and the rest of our team, I am examining whether service members who work in occupations with more frequent exposure to low-level overpressure, such as artillery and infantry, are more likely to develop a TBI if they are exposed to a major blast during deployment,” da Silva said.

To begin answering these questions, the research team examined the records of enlisted active duty Marines who had completed post-deployment health assessments between 2005 and 2012. Researchers identified nearly 23,000 Marines who experienced an event that may have put them at risk for an mTBI, including falls, blasts, and vehicle accidents.

Researchers then grouped the Marines by MOS-one group included jobs with high risk for chronic overpressure exposure, such as artillery and infantry, and the second group included low risk occupations, such as administration or communications. The team analyzed the relationship between MOS risk (high or low), exposure to a major blast event, and self-reported mTBI to determine if Marines in certain MOSs are more susceptible to mTBI after blast exposure.

“After our analysis, we found that Marines in high-risk occupations were substantially more likely to develop an mTBI after a major blast exposure than Marines in low-risk jobs,” da Silva said. “We also found that Marines whose concussions were associated with a blast experienced significantly more symptoms than Marines who reported a concussion from another cause, such as a fall or car accident. Blast-related mTBIs may be fundamentally different from non-blasted related mTBIs in terms of symptoms and how the injury develops and progresses.”

With these initial findings under their belt, NHRC researchers are already looking ahead.

“There’s really much more research to do as we increase what we know about TBI,” da Silva adds. “For instance, do service members in high-risk MOSs develop more severe TBIs after a blast? Does chronic exposure to low-level overpressure result in the same symptoms and medical outcomes over time as acute high-level overpressure exposure? As we work to answer these questions, we’d like to expand the study to all services-overpressure exposure isn’t limited to a single branch of the military. And, to better understand the long-term health outcomes for those diagnosed with TBI, studying our veteran population would be crucial.”

There are many avenues to pursue for future research, including one that da Silva is passionate about-studying TBI-related stigma.

“We need to consider the different health risks associated with TBI, including stigma and other factors that influence whether service members seek care and treatment,” da Silva said. “Increasing our understanding of why people avoid getting help for TBI symptoms can inform targeted interventions to encourage service members and veterans to seek treatment and get the help they need.”

By its very nature, military service comes with risk. While it’s not possible to eliminate all risk to service members, researchers can identify those risks and find ways to reduce their impact on service members. There’s much more work to be done before TBIs are fully understood, but the team at NHRC is hopeful the research they’re doing to identify risk factors for developing TBI could lead to improved preventive and screening measures. The earlier TBI is detected, the sooner care and treatment can begin, which can improve recovery, health, and readiness.

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