Extent of Cerebrovascular Disruption Following Blast Exposure is Influenced by the Duration of the Positive Phase in Addition to Peak Overpressure

Blast-induced traumatic brain injury (bTBI) has been described as the defining injury of Operations Enduring Freedom and Iraqi Freedom (OEF/OIF). Although there has been a significant amount of research characterizing the brain injury produced by blast, greater 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 previously designed and built a multi-mode shock tube capable of utilizing air-driven membrane rupture or chemical explosives (oxyhydrogen: A 2:1 mixture of hydrogen and oxygen gasses to produce a shockwave. Compressed airdriven shockwaves exhibited longer duration positive phases than compressed oxyhydrogen-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 impacted by shockwaves of identical peak overpressures from the other sources. Animals exposed to compressed air-driven shockwaves exhibited more extensive brain surface hematoma and more blood-brain barrier compromise 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 can result in more severe bTBI. The results of this study are relevant to the design of blast wave mitigation technology and future clinical intervention