Between October 2001 and May 2012 approximately 70% of U.S. military personnel killed in action and 75% wounded in action were the direct result of exposure to an explosion. As of 2008, it was estimated that nearly 20% of all Operation Iraqi Freedom and Operation Enduring Freedom (OIF/OEF) veterans had sustained some form of traumatic brain injury (TBI). Blast exposure is also a civilian problem due to widespread availability of explosives and the increased usage of explosives in terrorist attacks on civilians. Before 2005, blast injury research focused on the pulmonary system and the other air-containing organs which have been shown to be susceptible to blast overpressure injury. A shift in injury pattern during recent conflicts is characterized by decreased incidence of pulmonary injuries relative to TBI thought to be associated with blast exposure. This increase in observation of blast TBI has resulted in a large research effort to understand mechanisms and thresholds. However, due to the relatively sudden shift, much of this research is being conducted without a proper understanding and consideration of blast mechanics and interspecies scaling effects.

This dissertation used experimental and computational finite element (FE) analysis to investigate some of the important questions surrounding blast TBI research. These key issues include the effects of body armor usage on blast trauma risk, the effect of interspecies differences on in vivo animal model research, and the effects of interspecies scaling on current and future in vivo animal model experimentation for blast trauma. An experimental investigation was conducted to determine the effects of modern thoracic body armor usage on blast pressure exposure seen in the lungs and gut. To improve FE modeling capabilities, brain tissue mechanics in common blast TBI animal model species were investigated experimentally and computationally to determine viscoelastic constitutive behavior and measure interspecies variation of the brain properties. To improve our understanding of blast pulmonary trauma risk and appropriate interspecies scaling a meta-analysis of blast pulmonary literature was conducted to update interspecies scaling and injury risk models. Finally, to derive interspecies scaling and injury risk models for blast neurotrauma endpoints a meta-analysis of existing experimental data was used.

This dissertation makes major contributions to the field of injury biomechanics and blast injury research. Research presented in this dissertation showed that modern thoracic body armor can lower the risk of pulmonary injury from blast exposure by attenuating and altering blast overpressure. The study shows that the use of soft body armor can attenuate peak overpressure levels by a factor of up to 14 in the tested range and results in the pulmonary injury threshold being similar to that for neurotrauma. The use of hard body armor can attenuate peak overpressure levels by a factor of up to 57 in the tested range and results in the threshold for pulmonary injury occurring at higher levels than that of neurotrauma. This finding is important, as it helps to explain the recent shift in injury types observed and highlights the importance of continued widespread usage of body armor not only for ballistic protection but for protection from blast as well.

This dissertation also shows the importance of interspecies scaling for investigation of blast neurotrauma. This work looks at existing in vivo animal model data to derive appropriate scaling across a wide range of brain size. Appropriate scaling for apnea occurrence and fatality for blast isolated to the head was found to be approximately equal to a characteristic length scaling of brain size, assuming spherical brain shape. Power law scaling for overpressure duration, based on a ratio of brain mass to a human brain mass, was found to have a scaling exponent, α, of 0.336 for apnea risk. Similarly, for neurotrauma fatality risk, scaling exponents were found to be 0.316 and 0.080 for overpressure duration and and peak overpressure scaling, respectively. By combining the interspecies scaling developed and existing tests data, injury risk models were derived for short overpressure duration blast exposures.

The contributions and conclusions of this dissertation serve to inform the injury biomechanics field and to improve future research efforts. The consideration by researchers of the recommendations presented in this dissertation for in vivo animal model testing will serve to maximize the value gained from experimentation and improve our understanding of blast injury mechanisms and thresholds. The injury risk models presented in this work help to improve our ability to prevent, diagnose, and treat blast neurotrauma.