Brain Injury Risk from Primary Blast

Objectives Increased use of explosive devices in recent military conflicts have resulted in, blast overpressure is the primary cause of traumatic brain injury among combat veterans Owens, 2008. Primary blast injury has been studied extensively in air-containing organs such as the lungs, gastrointestinal tract, and ear due to their increased susceptibility to primary blast Hooker, 1924, but recent epidemiology shows an increase in the occurrence of head injuries Martin, 2008. Since there is little information on the intensity of a blast wave needed to cause blast brain injury, the goal of this study is to provide injury risk assessments for brain blast fatality, meningeal bleeding, and apnea as a function of blast intensity in a gyrencephalic animal model and to provide exposure guidelines for clinically relevant blast injuries. Materials and Methods Shock waves were generated that simulated blasts with charge sizes up to 1000 kg of high explosives. The blast exposure to a gyrencephalic animal model ferret was isolated to the head by combined abdominal and thoracic protection that reduced blast levels to an order of magnitude below pulmonary injury threshold. The results were scaled to a 70kg human using a biomechanical scaling technique. The outcomes including apnea, meningeal bleeding, and fatalities were analyzed using logistic regressions in terms of applied shock peak pressure and scaled duration. Results Increasing severity of blast exposures either by increasing peak maximum pressure and positive phase duration or both increases occurrence of injury. Gross necropsy revealed subdural, subarachnoid, and cerebral contusions typically on or around the brainstem though there were no skull fractures for any blast intensity.