Investigation of cavitation as a possible damage mechanism in blast-induced traumatic brain injury.

Cavitation was investigated as a possible damage mechanism for war-related traumatic brain injury (TBI) due to an improvised explosive device (IED) blast. When a frontal blast wave encounters the head, a shock wave is transmitted through the skull, cerebrospinal fluid (CSF), and tissue, causing negative pressure at the contrecoup that may result in cavitation. Numerical simulations and shock tube experiments were conducted to determine the possibility of cranial cavitation from realistic IED non-impact blast loading. Simplified surrogate models of the head consisted of a transparent polycarbonate ellipsoid. The first series of tests in the 18-inch-diameter shock tube were conducted on an ellipsoid filled with degassed water to simulate CSF and tissue. In the second series, Sylgard gel, surrounded by a layer of degassed water, was used to represent the tissue and CSF, respectively. Simulated blast overpressure in the shock tube tests ranged from a nominal 10-25 pounds per square inch gauge (psig; 69-170 kPa). Pressure in the simulated CSF was determined by Kulite thin line pressure sensors at the coup, center, and contrecoup positions. Using video taken at 10,000 frames/sec, we verified the presence of cavitation bubbles at the contrecoup in both ellipsoid models. In all tests, cavitation at the contrecoup was observed to coincide temporally with periods of negative pressure. Collapse of the cavitation bubbles caused by the surrounding pressure and elastic rebound of the skull resulted in significant pressure spikes in the simulated CSF. Numerical simulations using the DYSMAS hydrocode to predict onset of cavitation and pressure spikes during cavity collapse were in good agreement with the tests. The numerical simulations and experiments indicate that skull deformation is a significant factor causing cavitation. These results suggest that cavitation may be a damage mechanism contributing to TBI that requires future study.

The facial-bone fractures among fatally injured car occupants in frontal collisions.

The retrospective study was performed of all deceased car-occupants in frontal car collisions in order to identify persons with facial-bone fractures. The sample consisted of 482 cases: 378 males and 104 females, average age of 39.59+/-16.01 years. There were 239 car-drivers, 194 front-seat passengers, and 49 rear-seat passengers. In 46 of 482 cases, single fracture of upper facial bones was established: nasal fractures were the most common, followed by zygomatic. In 118 of 482 cases, fracture of upper facial bones was established, as well as 70 cases of jawbone. The fractured facial bones either of the upper or lower face could not be a factor that predicts the position of the deceased in the motor vehicle at the moment of injury (lambda=0.989, p>0.05). The multi-fractured facial-bones were very often associated with the multi-fractured cranial bones - 85 cases (chi(2) =138.75, df=8, p<0.001), as well as jawbone fracture - 35 cases (chi(2) =20.52, df=4, p<0.001). Brain injuries were more present and more severe (coup and contrecoup-contusion and brain laceration) if more facial-bone fractures were involved (chi(2) =147.99, df=8, p<0.001). Cases with only contrecoup brain contusions, associated with multi-fractured facial-bones, were rare - 6 of 118. These fractures are very often associated with cranial fractures, as well as with brain injuries and were caused by intensive contact of the deceased's head with the car's pillar.