CONTRA-COUP HEAD INJURIES- An interesting little article
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Get to the tallest staircase you can find, in the upper reaches of a
stadium, maybe. Blindfold yourself and stand at the top. Now, hop down
the steps, one by one. All ... the ... way ... down. But don't just
jump. At the same time, try to feel your brain smushing around inside
your skull.
Researchers at Washington University in St. Louis have done the
equivalent. To study the elastic properties of the brain, they lay a
volunteer face down inside an MRI chamber and strap his head into a
black harness that covers the eyes and forehead. A researcher pulls a
string, a supporting lever kicks free, and the volunteer's skull
plunges. After a few centimeters, the harness catches. Then they
repeat. Almost 150 times.
The resulting acceleration on the brain roughly equals that of jumping
off a step, said researcher and mechanical engineering professor
Philip Bayly. And yes, Bayly has submitted to the routine himself.
The research should help build better computer models to simulate what
happens to the brain during a car accident, a concussion on the
football field or a slip at a construction site.
With more accurate models, doctors can make better diagnoses in the
crucial moments after trauma occurs. The research also could lead to
more realistic crash-test dummies.
The inch or so free fall in this experiment generates an acceleration
of 2 g, or twice that caused by gravity. In the past, Bayly used
special headgear to study the impact on the brain of a soccer ball
hitting the head at 40 mph, a typical speed in a high school game. He
found these headers produce 15-20 g. Concussions occur around 80, and
striking a windshield produces 150. Bayly said he doesn't have plans
to exceed 3 or 4 g in his MRI studies.
Eric Leuthardt, a neurosurgeon resident at Barnes-Jewish Hospital,
collaborated with Bayly on a paper released last week in Journal of
Neurotrauma. Leuthardt said three areas of the brain are most
susceptible to high-speed concussive damage: the frontal lobe, the tip
of the temporal lobe and the occipital lobe. Pictures from the head-
bobbing experiment reveal that at low speeds, the brain twists and
bends the most in those same areas.
Therefore, it seems the nodding and dropping provides a good, if
tentative, model for more severe trauma.
After volunteers unstrap themselves, their noses might be squished,
but they reported no dizziness, partly because the head drops straight
down and partly because of a lack of visual references.
It is a rather mild experience. But that doesn't mean things weren't
happening up in their brains.
This is obvious on video. After the MRI collects an image of a brain,
a computer paints digital stripes on it.
A slow-motion replay of the drop shows the stripes bending and bowing
as the head drops and the brain settles back into its normal state.
Data so far indicate standard models of brain movement during trauma
may need revision. Leuthardt explained the classic view of head trauma
by imagining someone slipping and hitting the back of his head on a
table.
"What people classically think happens is the skull hits first, and
then the back part of your brain hits the skull, (and) bounces off of
it," causing it to smack the front of the skull.
This is known as a coup-contra-coup brain injury. It's how a ball
would act in a fluid-filled container.
But "the brain doesn't bounce backwards and forwards - what actually
happens is we found some tether points there," said Leuthardt.
Tether points restrain the brain's motion. It's like shaking a branch
with leaves: The leaves move, but the branch restricts how far. The
spinal cord tethers the brain at one point, and blood vessels at
another.
As one part of the brain is stretched, another part can be compressed
simultaneously.
The trials, however repetitious, are safe because the brain is
elastic: It jiggles, but it regains its original shape quickly. In
another analogy, Bayly compared his study to shaking a bowl of Jell-O.
"Try to compress Jell-O - it won't," he said. But, like your brain,
it's easy to make it wriggle around.
Washington University study puts brains under 2 g of acceleration,
twice the acceleration of gravity.
15 to 20 g - Amount of acceleration generated by a header in a high
school soccer game.
80 g - Acceleration generally required to cause a concussion.
150 g - Acceleration produced by striking a windshield.