Stronger and tougher body armor to shield the chest, abdomen and back may better protect soldiers in Afghanistan and Iraq from mild traumatic brain injury (TBI) tied to so-called "shell shock," a new study suggests [Journal of Neuropathology and Experimental Neurology, 70 (5): 399-416].
The mild trauma - resulting from the initial shock of exploding mines, grenades and improvised explosive devices (IEDs) - now accounts for more than 80 percent of all brain injuries among U.S. troops. Approximately 160,000 veterans are estimated to have sustained this kind of trauma.
"Protecting the body is absolutely essential to protecting the brain," said senior study investigator Vassilis Koliatsos, MD, a neuropathologist at Johns Hopkins University School of Medicine. "Blast-related injuries, including what we call blast-induced neurotrauma, are the signature medical events of current wars, and improvements to body armor in addition to wearing helmets are likely going to be needed if we want to minimize their threat to our soldiers' health."
Dr. Koliatsos and his research team used a metal shock tube specially designed at the Applied Physics Laboratory at Hopkins to isolate the effects of the primary blast wave of an explosion on mice.
A plastic glass covering around the torso of shocked mice fully protected them from any axonal nerve cell damage in critical parts of the brain responsible for body movement, including the cerebellum and the corticospinal tract, which links nerves in the brain to those in the spinal cord. Body armor also shielded mice from more than 80 percent of the axonal damage observed in the visual pathways of the brain when compared to mice wearing no body armor.
The study also found that wearing similarly secured plastic glass helmets conferred no greater protection from neurological damage from the initial, overpressure wave than in mice shocked without protective headgear.
These results do not undermine the need for soldiers to wear a helmet to shield their head from flying shrapnel and other bomb debris and protect them from secondary blast waves, some of which are strong enough to throw bodies more than 100 feet, Dr. Koliatsos emphasized.
The study is believed to be the first to show widespread axonal damage in the brain from mild blast explosions. It was designed specifically to investigate the ill effects on the body of the primary blast, of extremely fast-moving, high-pressure air, researchers say.
Researchers also found that unprotected mice took twice as long as those that wore a body shield to socialize with mice newly introduced to their surroundings. Unprotected mice also fell off a mock log-rolling test a minute earlier than shielded mice, who stood up just as long as unshocked mice who heard the blast from outside the tube.
The lungs were the chest organ most likely to be marred by a blast wave, but the absence of any respiratory injury did not mean the brain was safeguarded. Brain injuries were evident in both mice with lung damage and those without.
"Our results should put military physicians in the field on notice that they need to closely monitor veterans for mild traumatic brain injuries even in the absence of any lung injury," said Dr. Koliatsos. "Regardless of what you call it - shell shock, mild traumatic brain injury, or mild traumatic brain injury combined with post-traumatic stress disorder - it may hide a serious neurological condition."
He and colleagues will analyze brain tissue samples from recently deceased veterans who suffered mild TBI for any permanent signs of axonal damage.
Study co-investigator Ibolja Cernak, MD, PhD, medical director of the biomedicine business area in the Department of National Security Technology of the Applied Physics Laboratory, led development of the shock tube used in the study.
Researchers used a known experimental model, called the Pathology Scoring System for Blast Injuries, to help set the strength of the helium blast needed to induce a mild TBI. Blast pressure was set at roughly 10 pound-force per square inch.
Other Hopkins researchers involved in the study, conducted from 2007 to 2010, were Leyan Xu, PhD; Yeajin Song; Alena Savonenko, MD, PhD; Barbara Crain, MD, PhD; Charles Eberhart, MD, PhD; Constantine Frangakis, PhD; Tatiana Melnikova, MD, PhD; Hyunsu Kim; and Deidre Lee, MPH.
Study support was provided solely by Johns Hopkins University.