Non-impact blast exposures occur when warfighters are close enough to an explosion to experience the high pressures created by the blast itself but far enough away to avoid penetrating injuries caused by fragments, and blunt impact injuries caused by debris or whole-body translation. The existence and mechanism of a non-impact, blast-induced mild traumatic brain injury continues to be a key knowledge gap in the DoD portfolio of blast injury research.

Seventy-five experts representing Canada, Japan, the Netherlands and the Departments of Defense, Transportation and Veterans Affairs, as well as academia and industry, met in Herndon, Virginia to critically examine research focused on the relationship between blast exposure and non-impact blast-induced mild traumatic brain injury and to get a clearer understanding of the current state-of-the-science on the existence and mechanisms of non-impact, blast-induced mild traumatic brain injury.

For the first half, scientists who study non-impact, blast-induced mTBI presented their research on topics ranging from blast physics and mathematical modeling to animal modeling and neurocognitive studies in humans. A four-member panel of accomplished and respected scientists listened to each of the 27 presentation and led the post-presentation discussions.

‘‘I wanted to present our research and receive feedback. I also wanted to see what others had to say. It’s important that we don’t duplicate research.” said Douglas DeWitt, professor of Anesthesiology at the University of Texas, who presented a talk on the characterization of a new rodent model of blast-induced brain injury.

‘‘No one has the answer right now and I’m looking forward to the new data and collaborating with other experts in the field. It’s nice to know if what you’ve been doing is fitting with everyone else’s research,” said Pamela VandeVord, associate professor at Wayne State University, who spoke on understanding shock wave transmission to the brain.

On the second afternoon, participants divided into workgroups to address four issues pertinent to non-impact, blast induced mTBI: the association of non-impact blast exposure with a physical mTBI; the existence of substantial evidence to support one mechanism as the most plausible explanation for how non-impact blast exposure is associated with mTBI; research gaps regarding the association between non-impact blast exposure and mTBI, and recommendations regarding how researchers could standardize research methods to facilitate research synthesis of comparable studies.

The third day was meant to distill the conclusions and recommendations made by the work groups. Based on data presented at the meeting and other published and unpublished studies, the groups concluded that there is sufficient evidence from clinical and animal studies that non-impact, blast-induced mild trauma to the brain can occur. However, the groups also determined that there is insufficient evidence to support any one mechanism of insult or any one physiological response as the most plausible explanation for the association of non-impact blast exposure with mTBI.

The groups agreed that the current working definition of mTBI does not entirely meet the needs for the clinical assessment of brain injury. Mild TBI is currently defined by exposure to a blast event and through self-reporting of symptoms. The current working definition encompasses any post-exposure alteration of mental state at the time of injury, any loss of consciousness lasting 30 minutes or less, or post-traumatic amnesia lasting less than 24 hours.

The workgroups and executive panel identified several knowledge gaps regarding the association between non-impact blast exposure and mTBI, and proposed potential research to close the knowledge gaps. The knowledge gaps concern the components of a blast responsible for the insult and injury, the clinical correlates of non-impact blast exposure, the existence of validated computational models for blast injury, an understanding of the neuropathological data surrounding blast injury in humans, the sharing of data across research entities, access to data from historical blast injury research; and scientifically-informed strategies to improve protection, prevention, and treatment for blast-related mTBI.

Recommendations on how to standardize research methods to facilitate research synthesis of comparable studies were discussed.

‘‘This meeting helped us understand what is currently known and what is not known about the existence and mechanisms of non-impact, blast-induced mTBI” said Michael J. Leggieri, Jr. director of the DoD Blast Injury Research Program Coordinating Office.