Computational biology - modeling of primary blast effects on the central nervous system.

Defense and Veterans Brain Injury Center, Walter Reed Army Medical Center, Building 1, Room B207, 6900 Georgia Avenue NW, Washington DC 20309-5001, USA.
NeuroImage (Impact Factor: 6.13). 03/2009; 47 Suppl 2:T10-20. DOI: 10.1016/j.neuroimage.2009.02.019
Source: PubMed

ABSTRACT Recent military conflicts in Iraq and Afghanistan have highlighted the wartime effect of traumatic brain injury (TBI). The reason for the prominence of TBI in these particular conflicts as opposed to others is unclear but may result from the increased survivability of blast due to improvements in body armor. In the military context blunt, ballistic and blast effects may all contribute to CNS injury, however blast in particular, has been suggested as a primary cause of military TBI. While blast effects on some biological tissues, such as the lung, are documented in terms of injury thresholds, this is not the case for the CNS. We hypothesized that using bio-fidelic models, allowing for fluid-solid interaction and basic material properties available in the literature, a blast wave would interact with CNS tissue and cause a possible concussive effect.
The modeling approach employed for this investigation consisted of a computational framework suitable for simulating coupled fluid-solid dynamic interactions. The model included a complex finite element mesh of the head and intra-cranial contents. The effects of threshold and 50% lethal blast lung injury were compared with concussive impact injury using the full head model allowing upper and lower bounds of tissue injury to be applied using pulmonary injury as the reference tissue.
The effects of a 50% lethal dose blast lung injury (LD(50)) were comparable with concussive impact injury using the DVBIC-MIT full head model.
CNS blast concussive effects were found to be similar between impact mild TBI and the blast field associated with LD(50) lung blast injury sustained without personal protective equipment. With the ubiquitous use of personal protective equipment this suggests that blast concussive effects may more readily ascertained in personnel due to enhanced survivability in the current conflicts.

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    ABSTRACT: There is growing concern that blast-exposed individuals are at risk of developing neurological disorders later in life. Therefore, it is important to understand the dynamic properties of blast forces on brain cells, including the endothelial cells that maintain the blood-brain barrier (BBB), which regulates the passage of nutrients into the brain and protects it from toxins in the blood. To better understand the effect of shock waves on the BBB we have investigated an {\em in vitro} model in which BBB endothelial cells are grown in transwell vessels and exposed in a shock tube, confirming that BBB integrity is directly related to shock wave intensity. It is difficult to directly measure the forces acting on these cells in the transwell container during the experiments, and so a computational tool has been developed and presented in this paper. Two-dimensional axisymmetric Euler equations with the Tammann equation of state were used to model the transwell materials, and a high-resolution finite volume method based on Riemann solvers and the Clawpack software was used to solve these equations in a mixed Eulerian/Lagrangian frame. Results indicated that the geometry of the transwell plays a significant role in the observed pressure time series in these experiments. We also found that pressures can fall below vapor pressure due to the interaction of reflecting and diffracting shock waves, suggesting that cavitation bubbles could be a damage mechanism. Computations that include a simulated hydrophone inserted in the transwell suggest that the instrument itself could significantly alter blast wave properties. These findings illustrate the need for further computational modeling studies aimed at understanding possible blast-induced BBB damage.
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    ABSTRACT: Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts.
    PLoS ONE 11/2014; 9(11):e113264. DOI:10.1371/journal.pone.0113264 · 3.53 Impact Factor
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    ABSTRACT: Primary blast wave induced traumatic brain injury and posttraumatic stress disorders have been observed in great number among military personnel in the recent Iraq and Afghanistan wars. Although combat helmets provide good protection against blunt/ballistic type threats, the current issue with military helmets is protection concerning the threats from primary blast wave. This study focused on investigating how combat helmets influence the blast-induced biomechanical loads in the human brain. Multi-Material Arbitrary Lagrangian Eulerian method was applied to simulate the wave propagation in the shock tube, the interaction of the shock wave with the human head, and the subsequent blast overpressure transformation through the head. The finite element model (FE) of Wayne State University shock wave generator (WSUSG) was developed and validated against experimentally measured side-on pressure time histories within the tube. Validated 3-D FE models of the human head and Advanced Combat Helmet (ACH) reported previously were used to predict the internal brain responses and assess the performance of the helmet in mitigating shock wave of various severities generated by WSUSG. Effectiveness of helmet with respect to various head orientations to oncoming shock waves was also evaluated. Biomechanical response parameters including the peak brain pressures and strains at various regions of the brain were calculated and compared between the heads with and without helmet. Wearing ACH was found to mitigate the intracranial pressures up to 33% at given blast loading conditions. The peak brain strain was reduced by 13-40% due to the use of helmet. In generally, ACH exhibited increased protective performance as the shock intensity increased. The current ACH helmet design offered superior protection to the brain in sideways blast than that in forward blast loading condition of same severity.

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