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.