Findings may help in designing more effective airbags and sports headgear
Researchers attempting to understand what happens to the brain in a car crash or sporting accident have found that a key cause of coma may be the specific angle in which a victim's head snaps at the moment of impact.
Working with miniature swine, and replicating the forces of car crashes, University of Pennsylvania researchers have discovered that loss of consciousness is related to the axis of head rotation. When the head snaps down and sideways toward either the right or left shoulder, the result is an instantaneous coma. But if the head snaps in a swiveling motion, there is no accompanying loss of consciousness.
The researchers also found that the more rapid the speed at impact, the longer the coma lasts, according to Douglas H. Smith, MD, associate professor of neurosurgery at the University of Pennsylvania School of Medicine and director of the study. The findings appear in the August issue of the Journal of Neurosurgery.
Smith said these finding could help engineers design safer airbags for automobiles, and perhaps even safer headgear for bikers, motorcyclists, roller-bladers and football players.
"There is no current treatment for brain injury, so we must focus on prevention," he said. "Now we can start supplying information to refine preventative techniques."
Doctors and scientists have long known that an automobile or sports-accident victim may have immediate loss of consciousness after sustaining head trauma. This immediate coma has previously been connected with diffuse damage to nerve fibers in the brain or "diffuse axonal injury" (DAI). It results from "acceleration-deceleration injury" -- which takes place when a high-speed impact causes the brain to reel inside the skull, stretching and tearing the nerve fibers, a mechanism that Smith calls "brainlash".
However, this new study shows that it is not the 'diffuse' aspect of DAI that is responsible for coma.
Rather, it is the extent of nerve fiber damage in the brain stem -- the region of the brain that is connected to the spinal cord -- that determines the presence of coma.
The study used two groups of anesthetized animals, subjecting the groups to accelerated head-rotation on two different planes.
Smith and his colleagues found that although DAI was produced in all injured animals, only those injured along the shoulder-to-shoulder plane, which produced high strain and damage to the nerve fibers in the brain stem, sustained immediate coma.
This finding may help doctors recognize that substantial brain injury may be present even in accident victims with no loss of consciousness or with only transient loss of consciousness.
Previous work by Smith and his colleagues at Penn demonstrated that even mild DAI that fails to register on an MRI examinations may lead to serious long-term damage. The torn or weakened axons can eventually degenerate in a pathology similar to that found in Alzheimer's disease.
"You can have almost no loss of consciousness, or very transient loss of consciousness, but still have significant axonal pathology. Although many patients expect to recover following brain injury, they may subsequently find that they have prolonged memory dysfunction," Smith said. "It's extremely common that people come back later with symptoms of cognitive dysfunction, even if their injury appeared to be minor at the time."
Smith and other researchers are working to develop an effective treatment for diffuse axonal injury, and he sees enough promise in their work to believe "there are some treatments on the horizon."
"But first you want to prevent the trauma," he said. "And if you can't prevent it, you must try to minimize it."
The research was conducted with the cooperation of Penn's departments of neurosurgery, bioengineering and radiology.
Smith's colleagues in the investigation include Masahiro Nonaka, MD; Reid Miller, PhD; Matthew Leoni, BS; Xaio-Han Chen, MD; David Alsop, PhD, and David F. Meaney, PhD. The study was funded in part by the National Institutes of Health.
Editor's Note: Dr. Smith may also be contacted directly at 215-898-0881.
Journal
Journal of Neurosurgery