With the increasing number of military personnel returning from conflicts with neurological manifestations of traumatic brain injury (TBI), there has been a great focus on the effects resulting from blast exposure (Okie 2005; Hicks et al. 2010). Recently, experimental studies have been reported which investigated the biomechanical response of the rat head exposed to a shock wave. The results indicated that the imparted shock wave may induce multiple response modes of the skull, including global flexure, which may have a significant contribution to the mechanism of injury (Bolander et al. 2011; Dal Cengio Leonardi et al. 2011). However, the question of whether head orientation could play a role in the level of energy imparted on the brain is still of concern. This study quantitatively measured the effect of head orientation on intracranial pressure (ICP) of rats exposed to a shock wave. Furthermore, the study examined how skull maturity affects ICP response at various orientations. It was hypothesized firstly that skull flexural modes dominate the ICP response, hence varying head orientation would be expected to alter this imparted stress waveform. The head orientation affects not only the shape and size of the “presented area” exposed to the incident wave, but the degree and nature of the response of the individual skull plate elements due to the variance of skull physiology. As such, this has a significant influence on the stress that the shock wave imparts on the brain due to changes in skull dynamics.

Studies on blast neurotrauma have focused on investigating the effects of exposure to free-field blast representing the simplest form of blast threat scenario without considering any reflecting surfaces. However, in reality personnel are often located within enclosures or nearby reflecting walls causing a complex blast environment, that is, involving shock reflections and/or compound waves from different directions. In fact, when a blast wave interacts with nearby structures, reflected shock waves are generated and complex three-dimensional shock waves are formed. Complex shock wave overpressure-time traces are significantly different from free-field profiles because reflections can cause super-positioning of shock waves resulting in increased pressure magnitudes and multiple pressure peaks. Very importantly, the shocks arrive from different directions which would invoke a different biomechanical response than a one-dimensional exposure. It has been reported that in complex wave environments, the extent of the injuries becomes a function of the location related to the surrounding structures rather than a function of the distance from the center of the explosion, as it is for free-field conditions (Yelverton et al. 1993; Mayorga 1997; Stuhmiller 1997). Furthermore, the resulting injuries when the individual is in confined spaces are noted to be more severe (Yelverton et al. 1993; Leibovici et al. 1996). The purpose of this study was to design a complex wave testing system and perform a preliminary investigation of the intracranial pressure (ICP) response of rats exposed to a complex blast wave environment. Furthermore, we explored the effects of head orientation in the same environment.

Blast-induced neurotrauma with no overt damage to the skull has been identified as a condition suffered by military personnel serving in Iraq and Afghanistan (Glasser 2007). Symptoms of mild blast neurotrauma include alterations in cognitive functions (memory, language, problem-solving-skills) and in emotional behavior (mood swings, depression, anxiety, emotional outbursts) (Okie 2005). Despite the improvements in helmets and body armors, many veterans returning from the war front are being diagnosed with mild blast-neurotrauma (Warden 2006). Little is known of the means by which brain injury results from exposure to blast where there is no evident physical damage to the head. This study looks at possible mechanisms of brain injury related to blast by examining how pressure transmission occurs within a skull/brain surrogate system. Investigations were carried out to resolve the variables affecting skull dynamics and their effect on pressure imparted to the brain. Testing assessed internal pressure profiles as a function of ambient overpressure, orientation of the sample to shock-front exposure, and the presence of apertures.

Blast associated injuries have been quantified into different classes based on the type of trauma that they create [1]. Of these types of trauma, the neuropathology invoked by shock wave exposure is the most ambiguous [1]. The properties associated with shock wave exposure have lead to multiple hypothesized mechanisms for brain trauma including: acceleration-based damage, a thoracic squeeze resulting in pressure pulses to the brain, or transference of energy from the shock wave into the brain via the skull [2, 3].

Traumatic brain injury due to blast exposure is quickly becoming the most frequently seen injury in today’s battlefields. Alterations in cognitive function, such as attention, memory, language and problem solving skills appear to occur as a result of blast-induced TBI. Furthermore, behavioral symptoms such as mood changes, depression, anxiety, impulsiveness and emotional outbursts are associated with blast-induced TBI (Okie et al , 2005). Observed overlaps between symptoms of post-traumatic stress disorder (PTSD) and TBI confound the differential diagnosis. Thus, soldiers with blast-induced TBI may be substantially under-diagnosed after exposure to blast waves. Animal models of blast-induced TBI are underdeveloped and there is a vital need for blast exposure biomarkers to help effectively diagnosis blast-induced TBI. In this study, we have investigated the mechanisms that underlie cognitive impairment of blast-induced neurotrauma. We have studied the cascade of neurochemical changes within the hippocampus of blast-exposed animals using 1 H-Magnetic Resonance Spectroscopy ( 1 HMRS). Furthermore, we examined changes in TBI protein markers using Western blotting and immunohistochemistry. Results suggest that exposure to blast waves has a significant effect on the hippocampus.