Blast-induced Brain Injury: Influence of Shockwave Components

OF DISSERTATION BLAST-INDUCED TRAUMATIC BRAIN INJURY: INFLUENCE OF SHOCKWAVE COMPONENTS Blast-induced traumatic brain injury (bTBI) has been described as the defining injury of Operations Enduring Freedom and Iraqi Freedom (OEF/OIF). Previously, most blast injury research has focused on the effects of blast on internal, gas filled organs due to their increased susceptibility. However, due to a change in enemy tactics combined with better armor and front-line medical care, bTBI has become one of the most common injuries due to blast. Though there has been a significant amount of research characterizing the brain injury produced by blast, a sound understanding of the contribution of each component of the shockwave to the injury is needed. Large animal models of bTBI utilize chemical explosives as their shockwave source while small animal models predominantly utilize compressed air-driven membrane rupture as their shockwave source. We designed and built a multi-mode shock tube capable of utilizing compressed gas (air or helium)-driven membrane rupture or chemical explosives (oxyhydrogen – a 2:1 mixture of hydrogen and oxygen gasses, or RDX – high order explosive) to produce a shockwave. Analysis of the shockwaves produced by each mode of the McMillan Blast Device (MBD) revealed that compressed air-driven shockwaves exhibited longer duration positive phases than compressed helium-, oxyhydrogen-, or RDX-driven shockwaves of similar peak overpressure. The longer duration of compressed air-driven shockwaves results in greater energy being imparted on a test subject than would be imparted by shockwaves of identical peak overpressures from the other sources. Animals exposed to compressed air-driven shockwaves exhibited more extensive brain surface hematoma, more blood-brain barrier compromise, more extensive reactive astrocytosis, and greater numbers of activated microglia in their brains than did animals exposed to oxyhydrogen-driven shockwaves of even greater peak overpressure. Taken together, these data suggest that compressed air-driven shockwaves contain more energy than their chemical explosive-derived counterparts of equal peak overpressure and can result in greater injury in an experimental animal model. Additionally, these data suggest that exposure to longer duration shockwaves, which is common in certain realworld scenarios, can result in more severe bTBI. The results of this study can be used to aid design of blast wave mitigation technology and future clinical intervention.