Miller Scott T, Cooper Candice F, Elsbernd Paul, Kerwin Joseph, Mejia-Alvarez Ricardo, Willis Adam M
Computational Solid Mechanics & Structural Dynamics, Sandia National Laboratories, Albuquerque, NM, United States.
Terminal Ballistics Technology, Sandia National Laboratories, Albuquerque, NM, United States.
Front Neurol. 2021 May 20;12:547655. doi: 10.3389/fneur.2021.547655. eCollection 2021.
Blast traumatic brain injury is ubiquitous in modern military conflict with significant morbidity and mortality. Yet the mechanism by which blast overpressure waves cause specific intracranial injury in humans remains unclear. Reviewing of both the clinical experience of neurointensivists and neurosurgeons who treated service members exposed to blast have revealed a pattern of injury to cerebral blood vessels, manifested as subarachnoid hemorrhage, pseudoaneurysm, and early diffuse cerebral edema. Additionally, a seminal neuropathologic case series of victims of blast traumatic brain injury (TBI) showed unique astroglial scarring patterns at the following tissue interfaces: subpial glial plate, perivascular, periventricular, and cerebral gray-white interface. The uniting feature of both the clinical and neuropathologic findings in blast TBI is the co-location of injury to material interfaces, be it solid-fluid or solid-solid interface. This motivates the hypothesis that blast TBI is an injury at the intracranial mechanical interfaces. In order to investigate the intracranial interface dynamics, we performed a novel set of computational simulations using a model human head simplified but containing models of gyri, sulci, cerebrospinal fluid (CSF), ventricles, and vasculature with high spatial resolution of the mechanical interfaces. Simulations were performed within a hybrid Eulerian-Lagrangian simulation suite (CTH coupled Zapotec to Sierra Mechanics). Because of the large computational meshes, simulations required high performance computing resources. Twenty simulations were performed across multiple exposure scenarios-overpressures of 150, 250, and 500 kPa with 1 ms overpressure durations-for multiple blast exposures (front blast, side blast, and wall blast) across large variations in material model parameters (brain shear properties, skull elastic moduli). All simulations predict fluid cavitation within CSF (where intracerebral vasculature reside) with cavitation occurring deep and diffusely into cerebral sulci. These cavitation events are adjacent to high interface strain rates at the subpial glial plate. Larger overpressure simulations (250 and 500kPa) demonstrated intraventricular cavitation-also associated with adjacent high periventricular strain rates. Additionally, models of embedded intraparenchymal vascular structures-with diameters as small as 0.6 mm-predicted intravascular cavitation with adjacent high perivascular strain rates. The co-location of local maxima of strain rates near several of the regions that appear to be preferentially damaged in blast TBI (vascular structures, subpial glial plate, perivascular regions, and periventricular regions) suggest that intracranial interface dynamics may be important in understanding how blast overpressures leads to intracranial injury.
爆炸所致创伤性脑损伤在现代军事冲突中很常见，具有较高的发病率和死亡率。然而，爆炸超压波导致人类特定颅内损伤的机制仍不清楚。回顾治疗过爆炸伤军人的神经重症监护医生和神经外科医生的临床经验，发现了脑血管损伤的一种模式，表现为蛛网膜下腔出血、假性动脉瘤和早期弥漫性脑水肿。此外，一项关于爆炸所致创伤性脑损伤（TBI）受害者的开创性神经病理学病例系列研究显示，在以下组织界面出现了独特的星形胶质细胞瘢痕形成模式：软脑膜下胶质板、血管周围、脑室周围和脑灰白质界面。爆炸所致TBI临床和神经病理学发现的共同特征是损伤位于物质界面，无论是固液界面还是固固界面。这促使人们提出这样的假设，即爆炸所致TBI是颅内机械界面处的损伤。为了研究颅内界面动力学，我们使用简化的人体头部模型进行了一组新颖的计算模拟，该模型包含脑回、脑沟、脑脊液（CSF）、脑室和血管模型，对机械界面具有高空间分辨率模拟在混合欧拉-拉格朗日模拟套件（CTH与Zapotec耦合到Sierra Mechanics）中进行。由于计算网格较大，模拟需要高性能计算资源。在多种暴露场景下进行了20次模拟——超压分别为150、250和500 kPa，超压持续时间为l ms——针对多种爆炸暴露情况（正面爆炸、侧面爆炸和墙壁爆炸），涉及材料模型参数（脑剪切特性、颅骨弹性模量）的大幅变化。所有模拟均预测脑脊液（脑内血管所在处）内会出现液体空化，空化发生在脑沟深部且广泛分布。这些空化事件与软脑膜下胶质板处高界面应变率相邻。更大超压模拟（250和500 kPa）显示脑室内出现空化——也与相邻的高脑室周围应变率有关。此外，直径小至0.6 mm的脑实质内血管结构模型预测血管内会出现空化，且与相邻的高血管周围应变率有关。在爆炸所致TBI中似乎优先受损的几个区域（血管结构、软脑膜下胶质板、血管周围区域和脑室周围区域）附近，应变率局部最大值的共存表明，颅内界面动力学可能对理解爆炸超压如何导致颅内损伤很重要。
