The Macabre Science Of Blast-Induced Brain Injury
In 1865, the French chemist and microbiologist, was asked to find the cause of a disease that was killing great numbers of silkworms and devastating the French silkworm industry.
After a year of diligent research, he correctly identified the culprit, a parasite called pebrine, and worked out how to kill it. But when he tested his method for producing a healthy population of silkworms, he discovered the disease was still present.
It turned out that the problem was caused by two parasites. Only when Pasteur had identified the second, a parasite called flacherie, could he finally solve the problem.
Today, Michael Courtney at the US Air Force Academy in Colorado and Amy Courtney, cite this episode as a warning to researchers involved in the causes of traumatic brain injury.
Improvements in armour technology and battlefield medical techniques mean that greater numbers of soldiers are surviving injuries that not so long ago would have killed them.
But this improvement has an insidious side-effect. Having survived, many veterans are left with previously rare injuries to the brain caused by blast waves.
That has triggered a major research effort to understand, treat and prevent these kinds of injuries.
The Courtneys are at the front line of this research. Today they reveal a new, table top machine for producing blast waves that mimic the profiles of real explosions. The small size and controllability of this device makes it much more useful than tradition blast tubes, they say.
And they have used it to begin investigating the causes the traumatic brain injury. It turns out that there are three mechanisms that can cause damage to the brain. In the first, a blast waves enters the body via the chest area and then travels up the neck and into the brain.
The second is caused by a rapid acceleration of the head which can tear the brain tissue inside. This can also cause the head to bang against any nearby armour causing blunt force trauma.
The final mechanism is the direct entry of blast force waves through the cranium. In rats, blast waves travel almost unabated through the cranium and through pig craniums, they retain about two thirds of their magnitude. Tests to see how blast waves are attenuated by the human skull are ongoing.
The ultimate goal of the Courtneys research is to establish an exposure threshold for blast induced brain injury using their own and others’ work in this area. That should allow better diagnosis of blast induced brain injuries and should hopefully allow engineers to design better armour, say the Courtneys.
So far, an exposure threshold has eluded them. And it looks like the problem may be complicated by their discovery that the injury mechanisms are not mutually exclusive: more than one mechanism seems to be at play in many instances of injury. So protecting against one will be of little use if it leaves open the possibility of injury by another.
That’s the link with Pasteur’s conundrum back in the 19th century.
There may be another problem: that having established exposure thresholds, nobody takes any notice of them. Exactly this happened after extensive work in the 60s and 70s on blast exposure thresholds for lung injuries. “Despite the research effort and useful findings, no lung injury threshold has proven widely applicable,” they say.
But there is one group of people who are likely to study blast injury thresholds in detail. What the Coutneys don’t mention is that while this kind of data is useful for preventing injuries, it is also handy for weapons designers wanting to make their products more “effective”.
And by effective, they don’t mean weapons better able to kill; quite the opposite.
Military strategists have long known that weapons that injure, but don’t kill, can be much more effective because they demoralise an army and tie up valuable resources in caring for the injured. That’s why many armies find it so hard to give up land mines, many of which are specifically designed not to kill.
Just how the Courtneys work will be used, probably even they don’t know for sure. The terrible truth about research into blast injuries, like many areas of science, is that it can be used for good or ill.
arxiv.org/abs/1102.1508: Working Toward Exposure Thresholds For Blast-Induced Traumatic Brain Injury: Thoracic And Acceleration Mechanisms
arxiv.org/abs/1102.1614: A Table-top Blast Driven Shock Tube
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