Invisible Wounds

How a Thumb-Sized Gauge Is Revolutionizing Traumatic Brain Injuries

Thanks to a new invention, we’re finally learning how to diagnose and treat the lingering affects of explosive events that have led to a mass of traumatic brain injuries in veterans.


In 2011, Scott Featherman was in Kandahar, Afghanistan as a scout platoon leader with the 2nd Brigade Combat Team of the 101st Airborne Division. He patrolled on foot, and Improvised Explosive Devices (IEDs) filled the donkey paths that crisscrossed the wadis and hills.

“I was hit several times when I was over,” he says, “and you have no clue if you’re hurt. You get back up, say “Am I good? Looks good.” And then you go back out.”

Was Featherman really “good,” though? How can you tell? If he wasn’t bleeding out, had all of his fingers and toes, knew what day it was, and had no nausea or headache, was he good?

A recently released report by the Institute of Medicine (IOM) says maybe not. Surveying the current research, the IOM found large gaps in our knowledge of the medical impacts of explosive blasts. Experts continue studying the damage caused by these detonations, but the magnitude of their impact on American service members is enormous and beyond question—IEDs, small often remotely triggered bombs, have killed more troops serving overseas than any other kind of attack.

Explosive blasts have caused 75% of the injuries and deaths in Iraq and Afghanistan, and according to a 2008 RAND Corporation study (PDF), 20% of combat veterans returning from Iraq and Afghanistan have come home with some level of Traumatic Brain Injury (TBI) from these events.

In previous wars many of these soldiers would have died. Advancements in armor and medical care have saved their lives but left them struggling with these residual injuries. Just as many, however, are in Featherman’s category; their gut says the IED blast they walked away from must have cause some harm, but they have no way of knowing what hidden damage may have been done and no objective way to measure it.

To help close this knowledge gap, the IOM report recommends that the military “should develop and deploy a system that measures essential components of blast and characteristics of the exposure environment.” But that’s easier said than done, so let’s begin with a deceptively simple question: How much blast can the average soldier withstand?

If we asked the same a vehicle, developers could just blow up real trucks with real explosives to measure the effects. They could repetitively test a new design—a V-shaped hull, for example, that deflects the blast—until the armored beast survived.

Given that a ‘blow it up and measure the impact’ approach isn’t possible for testing on people, researchers have looked for other testing methods. Traditional concussions can be studied using automobile accident victims in hospitals, but the number of average citizens exposed to explosions is relatively low and doesn’t provide a large enough sample group for adequate research. The other problem is that before you can prevent the effects of blast-induced TBI you have to understand the mechanism by which blasts cause injury, and until recently scientists have not even been sure what instruments to use or which physical phenomenon was most relevant.

“To measure is to know” Lord Kelvin said in the nineteenth century, and by that analysis, our understanding of blast’s effect on human beings has been very dim.

Stories about the tragic later years of once-great sports figures have familiarized many Americans with the dangers of blunt trauma induced concussions. This kind of injury, caused when the soft brain moves quickly and then comes to a sudden stop against the hard skull, can lead to memory loss, Parkinson’s Disease, depression and suicide. Accounts of retired pro athletes who’ve suffered grim outcomes or taken their own lives after receiving TBIs have prompted the National Football League and National Hockey League to make their sports safer.

But explosive blast injuries are different. Unlike sports cases, which mimic the physics of injuries that can occur in nature, they have no corollary outside of modern combat, and thus evolution has not prepared us to endure them.

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Before researchers can decide how much blast is too much, they need to settle the basic physics of how such injuries even occur.

One organization investigating these questions is the Defense Advanced Research Projects Agency, better known as DARPA. One of only a few government agencies with a cool reputation, DARPA is famous, infamous perhaps, for funding gonzo futuristic projects, everything from plant eating robots (PDF) to flying cars (PDF) to training bees to find landmines.

But DARPA has also traditionally funded basic research and practical projects, including the internet (originally called ARPAnet, before DARPA had a “D”).

In the mid-2000’s several government agencies, including DARPA, began studying the just-emerging TBI epidemic plaguing the US military. DARPA, in collaboration with other agencies, started funding several lines of research, some technical and some medical and much of it is just now ready for official publication.

The research may have led to a breakthrough: A blast gauge. The gauge is a device small enough to be worn by a soldier in the field, and in the event of an explosion, it can register the effects of a blast event and provide critical early warning signs of injury.

In October of 2012, at the annual meeting of the Neurocritical Care Society in Denver, military medical doctors and a DARPA physicist presented research involving a recently fielded blast gauge. The presentation noted that “Passage of the shock wave through the parenchymal tissue [the functional tissue of the brain] generates a combination of mechanical stresses; sheering stress, deviatoric stress, pressure, and volumetric tension.”

Blast waves are compression waves, like sound waves, and thus speed up or slow down based upon the density of the medium through which they travel. They move relatively slowly in the air, but once the waves strike a person they change speed throughout the human body. When encountering a dense organ (like a liver) or an air filled one (such as the lungs), this violent change in velocity ruptures intestines and disconnects kidneys from ureter ducts and tears air-sacks in the lungs, causing the victim to drown on their own blood.

These injuries have long been understood, but the effect is more arbitrary and subtle when the blast wave hits the brain, and here science has struggled to link the size of explosions to specific injuries. In the brain the blast wave finds a maze of nodules and gaps, ample opportunity for rapid velocity fluctuation, but what delicate structures rip and tear, what specific effect this has on a person’s health, is individual to each victim.

The DARPA scientist on that 2012 team was Dr. Jeff Rogers, a Program Manager in the Microsystems Technology office, a physicist, mathematician and surfer who had previously done research at Caltech and the HRL Labs in Malibu. His specialty is very small sensors that analyze complex systems, and in 2009 he began to take a serious look at the basic question of measurement. How does one determine the relative severity of blast? The breakthrough occurred when he realized scientists needed to make the problem simpler.

“In the past,” Rogers says, “we were trying to measure everything: the light that is thrown off, electromagnetic pulse, everything you can imagine. But you don’t need all that. What you really need to focus on is the blast overpressure because that’s what conveying all the energy you are worried about.”

This insight contradicted the approach taken by some programs in other agencies. The US Army’s Soldier Systems Center in Natick, Massachusetts had been looking at the same problem, but viewed the issue as one of accelerations, the “g-force” the brain was experiencing.

But DARPA’s research showed that acceleration in the brain didn’t reliably predict or explain specific injuries, and so Rogers led an effort to finally measure blast overpressure in a new way. The only basic research that had been done on blast itself used sheep and pigs in the 1970’s and had not been updated since. At conferences and in speeches, Rogers publicly sought an industry partner to develop the gauge.

Dr. David Borkholder at the Rochester Institute of Technology is an electrical engineer who specializes in microsystems and small electronic gauges. He had been following the on-going challenge of measuring blast effects in human brains, including the focus on over-pressure versus acceleration.

In late 2009 Borkholder wrote a white paper proposal to DARPA that pitched a disposable blast gauge using a tiny pressure sensor. Rogers bit, and by April 2010 Borkholder had one million dollars in seed money to develop the gauge from the ground up and deliver 1000 units in eleven months.

“DARPA is an incredibly dynamic place. It’s very exciting, high expectations, high pressure,” Borkholder says.

While DARPA is still the government, and so must still obey the same labyrinthine contracting rules, it does resemble the venture capital world in that, as Borkholder says, “It’s a place that moves extremely fast and is populated with insanely smart people and you’re sprinting to keep up. Borkholder’s new company, Black Box Biometrics, would ultimately produce four generations of the blast gauge in less than a year.

The gauge itself looks unremarkable: the size of your thumb, black resin body and three colored lights and a metal mesh dome that protects the microprocessor guts. It is made to be strapped to an individual soldier’s body armor, one on the chest, another on the shoulder, a third on the back of the helmet. An internal battery lasts about sixty days, so at $50 a pop, it costs $900 to outfit each soldier per average year-long tour. Cleverly (but perhaps counter-intuitively) the gauge is disposable, not only to take advantage of lighter and more energetic batteries, but also to circumvent the Army’s fiendishly long logistics tail that requires “durable goods” to be ordered to in bulk and refurbished at slow centralized depots.

When a soldier is hit by an IED the gauge records the event. Depending on the severity of the blast, a green, yellow or red light comes on, and once the soldier is back at their fire base or outpost, each gauge is plugged into a laptop via USB cable. The data available for download includes the detailed waveform of the blast overpressure with sufficient granularity to tie specific PSI (pounds per square inch, the unit of measurement of overpressure) levels to injuries.

“It tells the soldier if that was a blast I need to be worried about,” Borkholder says, “but it does more than that too. It doesn’t just give them a light, but also detailed data on the event.”

Finally, soldiers like Featherman have an objective indicator of a potential injury, a measuring tool fueled by electricity and not adrenaline, something to tell them if they were “too close.”

For Featherman himself this is more than an academic concern. He saw friends die next to him, had his own head rocked by blasts. “I heard about the device while I was still in,” Featherman says, “and I knew when I got out I needed to do something I was passionate about, and this device can really help save lives and improve lives.”

Featherman left the Army when his contract was up and went to work for Black Box Biometrics as their technical sales rep. He still looks more infantry than MBA or PhD, appropriate since his job is now training soldiers to use the blast gauge to protect themselves and their buddies. Officially, the blast gauge has been fielded to 11,000 US troops and 1000 Australian soldiers in Afghanistan, mostly to Special Forces units who often serve as the military’s early adopters.

While the gauge doesn’t replace the normal medical care system (and Borkholder is quick to point out that a soldier should seek treatment if they think they are injured, no matter the color of the light), it does help doctors at field hospitals perform triage. Those who receive a traumatic brain injury are often poor historians, and may not remember what happened to them. The gauge changes that.

Featherman’s eventual goal is to get the data applied to the individual soldier’s medical file and then transferred to the VA when they leave the military. This permanent record of their trauma exposure may help them get treatment or benefits if injuries that were triggered by blasts show up years after they leave the service. The plan seems sound and it’s starting to happen, but not always and not automatically.

Science is showing humans are vulnerable to even minor amounts of blast, and it can difficult for a soldier or medical doctor to correctly link a specific IED detonation to a specific set of symptoms. A whole spectrum of injuries are associated with blast-induced TBI. Some are obvious and immediate: headache, double vision, ringing in the ears, difficulty thinking or forming coherent words and phrases. But what about the general symptoms that can come later? Difficulty making decisions, short and long term memory loss, insomnia, lingering fatigue, or an inability to control emotions. This last one is a medical euphemism for “crying in public for no reason.” Scientists are still researching the link between TBI and PTSD, and without the data from the blast gauge, the veteran is left asking if his struggles are emotional or physical or both.

The gauge helps diagnose and treat individual soldiers, but it is doing far more than that. The information collected by each sensor feeds into a massive DARPA database that officials hope will eventually detail every detonation sustained by US forces. This resource has never before been available, and could revolutionize our understanding of how blast works and how it affects humans.


So, to return to our original question, how much blast can the average soldier endure?

“It’s a very complex problem,” says Borkholder, “and the variables include the details of the explosive event, how it impacts the body, what protective gear you have on, plus individual differences.”

Blast and the TBI it causes remain complex problems, but the data gathered from gauges have already begin pointing to possible answers.

The database DARPA is building records more than just information about the blast waves. It also includes information about the terrain where the detonation happen, the presence of walls or ditches and their size, the height and orientation of the soldier, the presence of vehicles and whether their doors are open or not, and the size and type of explosive based upon the post-blast investigation of the bomb technicians on the ground. Then, like checking your algebra homework in math class, DARPA creates an independent computer simulation of each explosive event, verifying each reading and detail.

“When you measure the right things on the ground you can really reconstruct what happened, and you can see all the dynamics that are going on in three dimensions,” says Rogers.

“DARPA has been taking the data from every explosive event in theater,” says Borkholder. “They are yielding new insights into the way the shock front propagates in these really complex environments.”

We are learning lessons in the simulations that would have been difficult to discover otherwise. For example, scientists have long known that blast reflects off of walls, sometimes multiplying in strength rather than simply doubling. But DARPA has learned that wavefronts move tangentially along walls as well. Grunts can tell you that bullets also tend to travel down walls, so now there are two reasons for soldiers to avoid taking cover directly against them.

What comes next, as DARPA continues to improve the sensor, crunches the big data in their new database, runs simulations and develops injury models? The practical results of these new technologies aren’t settled yet, but consider the case of radiation exposure gives a sense of one possible future.

People who work in nuclear power plants, around nuclear weapons, or even run x-ray machines must wear dosimeters to track their lifetime exposure, to keep it within certain limits. After a nuclear accident occurs, workers are monitored to ensure they don’t exceed particular emergency daily limits of radiation. One day soldiers may be tracked similarly, monitored to ensure they don’t exceed training and wartime blast standards, and if they pass the safety threshold, reassigned into positions where they’re no longer at risk of being exposed to detonations.

“I think that’s where we’re headed,” says Borkholder, “but I don’t think you get there until you have the data on humans. You need enough data on humans so you can really determine what those impacts are. The technology is ready, the only barrier is the complexity of the biological response.”

That the technology is finally ready is no small step. As Rogers noted, “We’ve known about concussions from hitting your head for a very long time, and yet there aren’t any ways to sense those yet either. They are trying now, in football, but that comes about because of the military focus on TBI.”