Animal Orientation Affects Brain Biomechanical Responses to Blast-Wave Exposure

Abstract

In this study, we investigated how animal orientation within a shock tube influences the biomechanical responses of the brain and cerebral vasculature of a rat when exposed to a blast wave. Using three-dimensional finite-element models, we computed the biomechanical responses when the rat was exposed to the same blast-wave overpressure (100 kPa) in a prone (P), vertical (V), or head-only (HO) orientation. We validated our model by comparing the model-predicted and the experimentally measured brain pressures at the lateral ventricle. For all three orientations, the maximum difference between the predicted and measured pressures was 11%. Animal orientation markedly influenced the predicted peak pressure at the anterior position along the mid-sagittal plane of the brain (P = 187 kPa; V = 119 kPa; and HO = 142 kPa). However, the relative differences in the predicted peak pressure between the orientations decreased at the medial (21%) and posterior (7%) positions. In contrast to the pressure, the peak strain in the prone orientation relative to the other orientations at the anterior, medial, and posterior positions was 40-88% lower. Similarly, at these positions, the cerebral vasculature strain in the prone orientation was lower than the strain in the other orientations. These results show that animal orientation in a shock tube influences the biomechanical responses of the brain and the cerebral vasculature of the rat, strongly suggesting that a direct comparison of changes in brain tissue observed from animals exposed at different orientations can lead to incorrect conclusions.

Cerebral Vasculature Influences Blast-Induced Biomechanical Responses of Human Brain Tissue

“…First, we evaluated the influence of the vasculature for frontal blast loading only, necessarily excluding occipital and lateral blast-loading scenarios. While the head orientation influences brain VMS and MPS values (Wang et al, 2014;Unnikrishnan et al, 2021), we believe that the redistribution of MPS observed in our study will remain valid for occipital and lateral blast-wave exposure. Second, we did not model cerebral veins and arteries with diameters less than 0.52 and 0.24 mm, respectively.…”

“…Briefly, for the material properties of the brain, the cerebral vasculature, and the skin tissue, we used values from previous studies that estimated the material parameters from mechanical tests performed on post-mortem human brain-tissue samples ( Estes and McElhaney, 1970 ), freshly excised human cortical veins and arteries ( Monson et al, 2003 ), and post-mortem human skin-tissue samples ( Ottenio et al, 2015 ). We represented the brain tissue as a nearly incompressible, hyper-viscoelastic material using a Mooney-Rivlin model with a two-term Prony series ( Mendis et al, 1995 ), whereas we modeled the cerebral vessels and the skin tissue as a nearly incompressible, hyperelastic material using a one-term Ogden model ( Unnikrishnan et al, 2021 ). For the material properties of the eyes, we used values from previous studies that estimated the material parameters from mechanical tests performed on fresh human corneas ( Elsheikh et al, 2007 ; Kok et al, 2014 ).…”

“…To simulate blast loading, we applied the measured incident pressure at the inlet surface of the partial shock tube ( Figure 2 ) ( Ganpule et al, 2013 ; Unnikrishnan et al, 2021 ). Next, to model a non-reflecting boundary, we defined an Eulerian outflow condition at the exit of the partial shock tube ( Tan et al, 2014 ).…”

Investigation of the direct and indirect mechanisms of primary blast insult to the brain

“…To enhance the blast-wave interaction with the body of the animal, we performed all experiments with the animal positioned in a vertical orientation facing the incident blast wave. We previously used these configurations to investigate the influence of animal orientation on the biomechanical responses of the brain when exposed to a blast wave 16 .…”

“…1 A, right). To implant the sensors, we followed the protocol described in our previous work 16 . We connected all pressure sensors to a data recorder (model TMX-18; Astro-Nova, Inc., West Warwick, RI) and sampled all measurements at a frequency of 0.8 MHz.…”