Published March 09, 2011
Traumatic brain injury (TBI) caused by explosions has produced a high incidence of casualties among U.S. troops fighting in Iraq and Afghanistan. The propensity of this injury and the damaging, long-term chronic consequences experienced by the soldiers on these fronts has led to TBI being labeled a signature injury of these recent wars.
According to U.S. Department of Defense Military Health System, 202,281 U.S. military service members were diagnosed with traumatic brain injury in the period from 2000 through fourth quarter 2010. But improved body armor and helmets, evacuation techniques and much enhanced combat care have reduced mortality rates.
Blast injuries and the explosions that cause them are not a new phenomenon, but in the recent wars, the presence of several additional factors has changed the TBI landscape and the focus of the medical practitioners and researchers who treat and study it.
Not the Typical Head Injury
The complex properties of a blast react with the body and brain in a unique way to cause injury. This refutes the long-held theory that neurological impairments caused by blast injury are rare since the skull provides excellent protection to the brain.
Even in the absence of life-threatening injuries, explosions heat and accelerate air molecules, causing a rapid milli-second increase in air pressure; this combination makes blast-induced neurotrauma (BINT) so insidious.
“It is not the classical way most people envision a brain injury as a direct impact to the head,” says Dr. Ibolja Cernak, medical director, biomedicine business area Johns Hopkins University Applied Physics Laboratory. “Rather, in the acceleration of blast injury the whole body is exposed to huge amount of kinetic energy.”
In BINT, other injuries can be caused by fragments of other things hit by the explosions and the impact of the body being propelled through the air and hitting the ground.
Blast Properties Unique
According to Cernak, an injury sustained through a blast is unique: The shock wave or blast wave comprises a high-pressure front that compresses the surrounding air and is followed by a negative pressure phase. This is the major factor of primary blast-induced injury, she says.
“Primary blast envelopes the whole body, and interacts with all organs and organ systems, including the brain. The resulting rippling effect generates oscillating waves in the blood that spread throughout the body, delivering the kinetic energy of the blast wave to organs including the brain which are different from and remote form the initial point of contact.
Once delivered, this kinetic energy initiates organic changes; brain cells die, and initiate functional changes in deep brain structures that control things like balance, blood pressure and speech. The blast can also compromise the blood-brain barrier, which typically protects the central nervous system from substances that could cause dangerous inflammation. It is the inflammation or inflammatory molecules that work to create irreversible brain damage; it’s as if the body is engaged in a tug of war.
The brain tries desperately to right itself and regain functions of other organs. Working on overload, its metabolism increases, the brain’s attempt to compensate is ultimately overrun and the deleterious effects of the blast take over.
“Bottom line,” says Dr. James Kelly, a neurologist and director of the National Intrepid Center of Excellence, “the brain’s function of what is necessary to preserve life comes first and the basic fight or flight reflex takes over seconds following a blast. But the residual effects and the metabolic changes that occur days later when the brain’s metabolism has slowed down reflect what the individual is really feeling.”
It’s at that point, according to Dr. David Hovda, director of the Brain Injury Research Center at UCLA in Los Angeles, “that the brain is in energy crisis and the brain is starved for energy.”
Oxymoron of 'Mild TBI'
Experts agree that proper management immediately following injury is key to recovery. But this leads to another TBI paradox: In the range of injuries from mild, through moderate to severe, it is the mild TBI that often is the greatest culprit.
With a moderate TBI, a soldier will typically be dazed and confused or unconscious. In severe TBI, a soldier could manifest symptoms that include visibly serious external injury to the head. But it is the mild TBI, essentially a concussion that can easily go undetected. Of the blast injuries reported, 151,623 cause mild TBI.
“The military has always done a good job with severe head injury like a hole in the face,” says Hovda. “It’s always been mild TBI that the military has had a difficult time recognizing”—troublesome because what is needed by the victim of a mild TBI is the opportunity for the brain to rest completely. With adequate rest following the injury, 80% of soldiers afflicted with mild TBI experience normal recovery.
Immediate Injury Management Needed
Up until the last two years, a soldier might not have been red flagged as having a worrisome injury and would not have been required to take a time out from combat. Also, a soldier with a mindset to support comrades, might be inclined to withhold information about his symptoms.
The problem is that from the first impact, the mild TBI starts to cascade, especially if the soldier is exposed to more blast injuries and sustains subsequent mild TBI’s until he or she reaches what Cernak terms “a point of no return.” Even two or three years post-deployment, a soldier could go to the VA complaining of problems with speech, balance or motor control. Cernak says that there was a time when practitioners would say that the soldier developed symptoms “overnight.” Today, because of increased understanding of the complicated phenomenon of blast injury, and the work of both military and civilian researchers, protocols are constantly being developed for the prompt and accurate detection of brain injury and for immediate and ongoing management and treatment.