Shock to the System

Ever since her pioneering study, Cernak has been trying to prove her theory that blast waves indirectly damage the brain, and to figure out how. She is now the medical director of the national-security technology department at Johns Hopkins University’s Applied Physics Laboratory. She spends much of her time working with the engineers in the APL’s Impact Biomechanics Test Facility, which houses a hydraulic impact sled for testing car seats and a 60-foot-long steel pipe called a shock tube that simulates the force of a blast wave.

From the protection of the impact lab’s control room, one of Cernak’s colleagues punches in a computer command to fill a chamber at one end of the shock tube with compressed air and then fire it down the tube at 760 miles per hour. Today’s target is a pink plastic torso complete with synthetic organs and dozens of pressure and acceleration sensors to measure the impact of the blast. But Cernak’s usual mark is a rodent.
In one of her most cited studies, Cernak compared the brains of rats whose entire bodies were exposed to the blast with another group whose heads and necks were protected with steel helmets. She found that even animals whose heads were perfectly immobilized and shielded develop the biological hallmarks of traumatic brain injury: broken-down nerve pathways, swollen brain cells, accelerated cell death, and the buildup of gunk you would expect to see in a brain-tissue sample of an Alzheimer’s patient. The findings suggest that helmets alone may fail to protect the brain from a blast. If true, then combat vests may not only need to deflect the shrapnel from an explosion but also dampen blast-wave frequencies.

How can a blast jump-start brain decay? Cernak theorizes that the rapid compression of organs and tissue in the torso sends a spike of energy rippling through the vessels, including those that loop through the brain. She envisions tiny bursts of pressure that squeeze brain cells and warp the connections between them in ways that are too subtle to show up on standard MRI scans. It’s the cumulative result of stretching nerve endings, she believes, that triggers a domino effect of chemical and molecular changes that damage brain cells and disrupt the normal flow of information. It takes time for these changes to snowball, and she thinks this explains what she calls a “slow cooking” of lab animals’ brain cells that can lead to long-term tissue degeneration. It might also explain why some soldiers’ symptoms never seem to clear up.

STRETCHED TO THE LIMIT: Shock waves can damage healthy brain cells. [left] Sometimes just lightly twisting the cell is enough to do the job.

THE DOWNWARD SPIRAL: The shearing not only causes physical damage to cells but can also unleash a biochemical cascade that eventually causes cells to self-destruct [right].

 Medi-Mation

School of Hard Knocks

Cernak’s lab is not alone in the search. Among the experiments in Darpa’s program, called PREVENT (for Preventing Violent Explosive Neurologic Trauma), researchers are exposing pigs to live munitions and then analyzing their brain tissue for damage. During the explosions, sensors record the full range of physical characteristics of the blast, including peak pressure, the frequency of the blast wave, the electromagnetic pulse (EMP) generated by the blast, the burst of light, the volume of noise, and even the gases generated.

Geoffrey Ling, who oversees PREVENT, believes that most scientists are focused too narrowly on the effects of blast pressure. He’s not at all convinced that it’s the culprit—or at least not the only one. He points out, for instance, that an electromagnetic pulse could affect electrochemical impulses in the brain, but nobody has studied this possibility. Ling notes that steel helmets worn in World War II and Vietnam reflect EMPs, whereas today’s Kevlar helmets don’t. “A 155-millimeter artillery shell sends out an EMP so strong that it will short-circuit our radios,” he says. “If there is something that could short-circuit an electrical pathway in the brain, that could disrupt function, I really want to rule that out.”

Pig data is telling, but there’s no substitute for a controlled study on humans. One of the most promising is a clinical trial involving breachers. These are the soldiers who blast down doors to storm buildings and, as a result, are guaranteed to get their bells rung on a regular basis. Lee Ann Young, a mechanical engineer who works for Albuquerque defense contractor Applied Research Associates, is studying a group of Marines as they go through breacher school at their base in Quantico, Virginia. Before, during and after their training, they will undergo MRIs and neurobehavioral testing for hearing and balance. They will be outfitted with pressure gauges to measure the strength of each of up to 40 blasts that they will be exposed to over a two-week period. “They’re very low-level blasts,” Young says. “I’ve been in the room, and it doesn’t feel that much different than the thump of a speaker at a loud rock concert. The question is whether it’s causing some sort of cumulative neurological impairments.”

As more stories like Hussey’s come out, some experts worry about fomenting fear of a mysterious widespread epidemic. Many make comparisons to the controversy over Gulf War syndrome, a much-debated affliction marked by fatigue, headache, dizziness and respiratory disorders. But although numerous questions remain about what Cernak calls blast-induced neurotrauma, she believes that if scientists accept it as a possibility, there is hope that it can be diagnosed and treated, and perhaps even prevented. “It is not a doomed message,” she says. “It is not that you were exposed to a blast, therefore you have a brain injury. But if you don’t do anything, the potentially reversible changes can become irreversible.”

It’s possible that mental exercises such as the ones Hussey practices could improve some cognitive symptoms, given the brain’s marked ability to heal itself. But the best medicine of all, Hussey says, was simply getting medical validation of his problems. “I wanted things to make sense to me,” he says. “My two weeks down in Tampa answered a lot of questions—a lot of it about my own sanity. I was wondering if it was just me. I don’t feel hopeless anymore.”