Abstract
Severe impacts to the head commonly lead to localized brain damage. Such impacts may also give rise to temporary pressure changes that produce secondary injuries in brain volumes distal to the impact site. 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. The aim of this study is to characterize the pressure distribution in an animal model of penetrating traumatic brain injuries (pTBI). This data may be used to validate mathematical models of the animal model and to facilitate correlation studies between pressure changes and pathology. Pressure changes were measured in rat brains while subjected to pTBI for a variety of different probe velocities and shapes; pointy, blunt, and flat. Experiments on ballistic gel samples were carried out to study the formation of any temporary cavities. In addition, pressure recordings from the gel experiments were compared to values recorded in the animal experiments. 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. 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. High-speed videos of the gel samples revealed the formation of spherically shaped cavities when flat and spherical probes were applied. Pressure changes in the gel were similar to those recorded in the animals, although amplitudes were lower in the gel samples. We concluded cavity expansion rate rather than cavity size correlated with pressure changes in the gel or brain secondary to probe impact. 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.
Highlights
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 [1,2,3]
The results demonstrate that the pressure changes were slighter in the Cisterna Magna (CM) and changed even less in the upper most spinal canal
The results obtained with the resistive transducer and the measurement system applied indicate that the Fiber optic pressure transducers (FOPTs) transducers and control unit used throughout this study provided useful data; the two systems measured similar pressure change during penetration trauma (Figure 11)
Summary
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 [1,2,3]. 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] 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. Experimental models can be analyzed with mathematical models, with finite element (FE) models, and compared to carefully categorized clinical TBI cases [7, 8] For such an analysis to be useful, the animal FE-models should be thoroughly validated using physical measurement data from relevant animal experiments
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