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Technical Brief

Untangling the Effect of Head Acceleration on Brain Responses to Blast Waves

[+] Author and Article Information
Haojie Mao, Ginu Unnikrishnan, Vineet Rakesh

Department of Defense,
Biotechnology High Performance Computing
Software Applications Institute,
Telemedicine and Advanced Technology Research Center,
U.S. Army Medical Research and Materiel Command,
Fort Detrick, MD 21702

Jaques Reifman

Department of Defense,
Biotechnology High Performance Computing
Software Applications Institute,
Telemedicine and Advanced Technology Research Center,
U.S. Army Medical Research and Materiel Command,
504 Scott Street,
Fort Detrick, MD 21702
e-mail: jaques.reifman.civ@mail.mil

1Corresponding author.

Manuscript received May 8, 2015; final manuscript received September 21, 2015; published online October 30, 2015. Assoc. Editor: Barclay Morrison.This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. government's contributions.

J Biomech Eng 137(12), 124502 (Oct 30, 2015) (7 pages) Paper No: BIO-15-1229; doi: 10.1115/1.4031765 History: Received May 08, 2015; Revised September 21, 2015

Multiple injury-causing mechanisms, such as wave propagation, skull flexure, cavitation, and head acceleration, have been proposed to explain blast-induced traumatic brain injury (bTBI). An accurate, quantitative description of the individual contribution of each of these mechanisms may be necessary to develop preventive strategies against bTBI. However, to date, despite numerous experimental and computational studies of bTBI, this question remains elusive. In this study, using a two-dimensional (2D) rat head model, we quantified the contribution of head acceleration to the biomechanical response of brain tissues when exposed to blast waves in a shock tube. We compared brain pressure at the coup, middle, and contre-coup regions between a 2D rat head model capable of simulating all mechanisms (i.e., the all-effects model) and an acceleration-only model. From our simulations, we determined that head acceleration contributed 36–45% of the maximum brain pressure at the coup region, had a negligible effect on the pressure at the middle region, and was responsible for the low pressure at the contre-coup region. Our findings also demonstrate that the current practice of measuring rat brain pressures close to the center of the brain would record only two-thirds of the maximum pressure observed at the coup region. Therefore, to accurately capture the effects of acceleration in experiments, we recommend placing a pressure sensor near the coup region, especially when investigating the acceleration mechanism using different experimental setups.

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Figures

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Fig. 1

Description of the computational blast simulation. We developed the 2D rat head model based on MRI data from the Duke University (anatomical features of the skull and brain at 100 μm resolution) [23] and the University of Utah (anatomical features of the scalp/fleshand facial bones at 150 μm resolution) [24]. We used ls-dyna (Livermore Software Technology Corporation, Livermore, CA) to perform the shock tube blast simulations.

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Fig. 2

Study design. We investigated the effects of head orientation by simulating lateral, frontal, and 45-deg angled impacts for both the all-effects and acceleration-only rat head models.

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Fig. 3

Temporal and spatial distributions of brain pressure in the all-effects model. (a) Time histories of brain pressure at the coup, middle, and contre-coup regions for lateral impacts. The three time histories were different in the first 0.20 ms after the initial pressure increase, but rapidly converged. (b) Blast-wave-induced spatial distributions of brain pressure at three time points.

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Fig. 4

Effect of blast-wave-induced head acceleration on brain pressure. (a) Typical brain pressure distribution predicted by the acceleration-only model. Head acceleration caused a positive pressure at the coup region and a negative pressure at the contre-coup region. (b) The pressure predicted by the acceleration-only model was 36.6% of that predicted by the all-effects model, indicating a moderate additive effect (with respect to other injury mechanisms) on brain pressure. Head acceleration did not affect brain pressure in the middle region. The brain pressure predicted by the acceleration-only model was −83.7% of that predicted by the all-effects model, indicating a subtractive effect on brain pressure due to head acceleration.

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Fig. 5

Effect of head orientation on brain pressures. (a) Despite the difference in wave dynamics, (b) head orientations only modestly affected the contributions of head acceleration to brain pressure. For the frontal impact, the coup pressure predicted by the acceleration-only model was 38.2% of that predicted by the all-effects model. For theangled impact, this percentage was 44.8%. The contre-coup pressure predicted by the acceleration-only model was −80.9% of that predicted by the all-effects model for the frontal impact and −89.3% for the angled impact. For both the all-effects and acceleration-only models, the brain pressures in the frontal impact were the lowest, because of the energy absorption and wave divergence by facial components. The brain pressures in the 45-deg angled impact were between those of the lateral impact and the frontal impact.

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