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Such transient events of an impact cannot be monitored in a clinical setting the development and use of animal models are needed for further detailed studies into the effect of pressure waves and their relation to subsequent injury. Since the brain is 75% water, it may be hypothesized secondary injuries may be related to induced cavity formation from impact and pressure wave propagation through the brain tissue ( 5). These events may lead to a subsequent increase in intracranial pressure and a negative spiral of further secondary injuries ( 4). Sometimes bleeding, inflammation, hypoxia, and edema follow primary brain injuries. Often the brain response results in temporary and limited brain malfunction known as concussion, although a primary injury with permanent brain tissue damage at the cellular level is commonly sustained. Once injured the brain response varies vastly from case to case due to the size, age, genetics, and gender of the victim, as well as the characteristics of any external force.
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Traumatic brain injury (TBI) is defined as the result of external forces applied to the head and transmitted to the brain, which in turn induce brain tissue responses including a combination of short lasting strain and shear stress and pressure changes ( 1– 3). The new data can serve as validation data for finite element models of the trauma model and the animal and to correlate physical measurements with secondary injuries. We concluded cavity expansion rate rather than cavity size correlated with pressure changes in the gel or brain secondary to probe impact. Pressure changes in the gel were similar to those recorded in the animals, although amplitudes were lower in the gel samples.
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High-speed videos of the gel samples revealed the formation of spherically shaped cavities when flat and spherical probes were applied. The pressure changes in the periphery of the probe, in the Cisterna Magna, and the spinal canal, were significantly less than those recorded in the CLV or the vicinity of the skull base. The pTBI generated short lasting pressure changes in the brain tissue the pressure in the contralateral ventricle (CLV) increased to 8 bar followed by a drop to 0.4 bar when applying flat probes. In addition, pressure recordings from the gel experiments were compared to values recorded in the animal experiments. Experiments on ballistic gel samples were carried out to study the formation of any temporary cavities. Pressure changes were measured in rat brains while subjected to pTBI for a variety of different probe velocities and shapes pointy, blunt, and flat. This data may be used to validate mathematical models of the animal model and to facilitate correlation studies between pressure changes and pathology. The aim of this study is to characterize the pressure distribution in an animal model of penetrating traumatic brain injuries (pTBI). Monitoring pressure changes in a clinical setting is difficult detailed studies into the effect of pressure changes in the brain call for the development and use of animal models. Such impacts may also give rise to temporary pressure changes that produce secondary injuries in brain volumes distal to the impact site. Severe impacts to the head commonly lead to localized brain damage. 2Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.1Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden.