Mary Roach - Stiff

Tempered glass, the follow-up innovation, was strong enough to keep heads from smashing through, but the concern then became that striking the stiffer glass would cause brain damage. (The less a material gives, the more damaging the forces of the impact: Think ice rink versus lawn.) Neurologists knew that a concussion from a forehead impact was accompanied by some degree of skull fracture. You can’t give a dead man a concussion, but you can check his skull for hairline cracks, and this is what researchers did. At Wayne State, cadavers were leaned forward over a simulated car window and dropped from varying heights (simulating varying speeds) so that their foreheads hit the glass. (Contrary to popular impression, impact test cadavers were not typically ushered into the front seats of actual running automobiles, driving being one of the other things cadavers don’t do well. More often than not, the cadaver was either dropped or it remained still while some sort of controllable impacting device was directed at it.) The study showed that tempered glass, provided it wasn’t too thick, was unlikely to create forces strong enough to cause concussion. Windshields today have even more give, enabling the modern-day head to undergo a 30-mph unbelted car crash straight into a wall and come away with little to complain about save a welt and an owner whose driving skills are up there with the average cadaver’s.

Despite forgiving windshields and knobless, padded dashboards, brain damage is still the major culprit in car crash fatalities. Very often, the bang to the head isn’t all that severe. It’s the combination of banging it into something and whipping it in one direction and then rapidly back at high speeds (rotation, this is called) that tends to cause serious brain damage. “If you hit the head without any rotation, it takes a huge amount of force to knock you out,” says Wayne State Bioengineering Center director Albert King. “Similarly, if you rotate the head without hitting anything, it’s hard to cause severe damage.” (High-speed rear-enders sometimes do this; the brain is whipped back and forth so fast that shear forces tear open the veins on its surface.) “In the run-of-the-mill crash, there’s some of each, neither of which is very high, but you can get a severe head injury.” The sideways jarring of a side-impact crash is especially notorious for putting passengers in comas.

King and some of his colleagues are trying to get a handle on what, exactly, is happening to the brain in these banging/whipping-around scenarios. Across town at Henry Ford Hospital, the team has been filming cadavers’ heads with a high-speed X-ray video camera [12] Other lively things to do with X-ray video cameras: At Cornell University, biomechanics researcher Diane Kelley has filmed lab rats mating in X-ray, in order to shed light on the possible role of the penis bone. Humans do not have penis bones, nor have they, to the author’s knowledge, been captured having sex on X-ray videotape. They have, however, been filmed having sex inside an MRI tube, by fun-loving physiologists at the University Hospital in Groningen, Netherlands. The researchers concluded that during intercourse in the missionary position, the penis “has the shape of a boomerang.” during simulated crashes, to find out what’s going on inside the skull. So far they’re finding a lot more “sloshing of the brain,” as King put it, with more rotation than was previously thought to occur. “The brain traces out a kind of figure eight,” says King. It is something best left to skaters: When brains do this they get what’s called diffuse axonal injury—potentially fatal tears and leaks in the microtubules of the brain’s axons.

Chest injuries are the other generous contributor to crash fatalities. (This was true even before the dawn of the automobile; the great anatomist Vesalius, in 1557, described the burst aorta of a man thrown from his horse.) In the days before seat belts, the steering wheel was the most lethal item in a car’s interior. In a head-on collision, the body would slide forward and the chest would slam into the steering wheel, often with enough force to fold the rim of the wheel around the column, in the manner of a closing umbrella. “We had a guy take a tree head-on and there was the N from the steering wheel—the car was a Nash—imprinted in the center of his chest,” recalls Don Huelke, a safety researcher who spent the years from 1961 through 1970 visiting the scene of every car accident fatality in the county surrounding the University of Michigan and recording what happened and how.

Steering wheel columns up through the sixties were narrow, sometimes only six or seven inches in diameter. Just as a ski pole will sink into the snow without its circular basket, a steering column with its rim flattened back will sink into a body. In an unfortunate design decision, the steering wheel shaft of the average automobile was angled and positioned to point straight at the driver’s heart. [13] From a safety standpoint, it would have been better to skip steering wheels entirely and install a pair of rudderlike handles on either side of the driver’s seat, as was done in the “Survival Car,” a traveling demo car built by the Liberty Mutual Insurance Company in the early 1960s to show the world how to build cars that save lives (and reduce insurance company payouts). Other visionary design elements included a rear-facing front passenger seat, a feature about as likely to sell cars as, well, steering rudders. Safety did not sell automobiles in the sixties, style did, and the Survival Car failed to change the world. In a head-on, you’d be impaled in pretty much the last place you’d want to be impaled. Even when the metal didn’t penetrate the chest, the impact alone was often fatal. Despite its thickness, an aorta ruptures relatively easily. This is because every other second, it has a one-pound weight suspended from it: the human heart, filled with blood. Get the weight moving with enough force, as happened in blunt impacts from steering wheels, and even the body’s largest blood vessel can’t take the strain. If you insist on driving around in vintage cars with no seat belt on, try to time your crashes for the systole—blood-squeezed-out—portion of your heartbeat.

With all this in mind, bioengineers and automobile manufacturers (GM, notably) began ushering cadavers into the driver’s seats of crash simulators, front halves of cars on machine-accelerated sleds that are stopped abruptly to mimic the forces of a head-on collision. The goal, one of them anyway, was to design a steering column that would collapse on impact, absorbing enough of the shock to prevent serious injury to the heart and its supporting vessels. (Hoods are now designed to do this too, so that even cars in relatively minor accidents have completely jackknifed hoods, the idea being that the more the car crumples, the less you do.) GM’s first collapsible steering wheel shaft, introduced in the early 1960s, cut the risk of death in a head-on collision by half.

And so it went. The collective cadaver résumé boasts contributions to government legislation for lap-shoulder belts, air bags, dashboard padding, and recessed dashboard knobs (autopsy files from the 1950s and 1960s contain more than a few X-ray images of human heads with radio knobs embedded in them). It was not pretty work. In countless seat-belt studies—car manufacturers, seeking to save money, spent years trying to prove that seat belts caused more injuries than they prevented and thus shouldn’t be required—bodies were strapped in and crashed, and their innards were then probed for ruptures and manglings. To establish the tolerance limits of the human face, cadavers have been seated with their cheekbones in the firing lines of “rotary strikers.”