A Laboratory Study on the Kinematic and Pressure Responses of an Internally Pressurized Novel Surrogate Headform Subjected to Blunt Impacts
Creators: Martin, Ashton Alexander
Publisher: name: University of Alberta Library
Year: 2024

<p>Instrumented surrogate head models – each of which exhibits varying degrees of complexity – are employed to study traumatic brain injury and mild traumatic brain injury. Despite advancements over the years, many existing surrogate head models lack a pressurized cerebrospinal fluid (CSF) or CSF-simulant layer. The significance of CSF has been underscored as a form of mechanical protection and a shock absorber during impacts between the brain and skull. However, the precise biomechanical role that CSF plays during head impacts remains largely unknown. The Brain Injury Protection Evaluation Device (BIPED) developed at Defence Research and Development Canada, was modified, and used to elucidate the role of CSF within an artificial surrogate headform.<br>
To better grasp the role of CSF, particularly its positive pressure, this thesis explored how changing the internal resting pressure in a novel surrogate headform (BIPED) affects its kinematic and pressure responses to blunt impacts. Furthermore, a limited biofidelity assessment of the pressurized BIPED was performed. This thesis aims to enhance our understanding of how resting pressure influences surrogate headforms and if it requires control when designing, constructing, and using these headforms to study head and neck injury.<br>
A set of Schrader valves were added to the second iteration of the BIPED (BIPED Mk. 2) which enabled and maintained headform pressurization. Further additions to the BIPED included four miniature pressure sensors embedded within the inner surface of the skull at the anterior, posterior, left, and right surfaces. The BIPED also possessed two intraparenchymal pressure (IPP) sensors embedded within the surrogate brain as well as a triaxial accelerometer and gyroscope sensor. <br>
The BIPED underwent blunt pendulum impacts to the forehead along the sagittal plane at four pressure levels: 0, 3, 6, and 9 inH2O-gauge. Each pressure level received five impacts at 18.8, 37.7, and 65.9 J of energy. Parameters such as peak linear head acceleration, maximum front CSF-layer intracranial pressure (ICP), maximum anterior (front) intraparenchymal pressure (IPP), maximum posterior (back) IPP, and minimum back IPP were recorded and analyzed. Comparisons between zero and non-zero gauge pressure cases revealed that, except for maximum back IPP away from the impact site, none of the listed response parameters differed by more than 10% from the zero-pressure configuration. Notably, the maximum back IPP increased by up to 35% when the resting ICP was raised. These results reflect the intricate nature of the cumulative pressure wave progression from the impact site throughout the intracranium. <br>
A limited biofidelity assessment was also undertaken to evaluate the efficacy of using the resting ICP to tune the surrogate head model’s response to improve consistency with a cadaver model. The BIPED’s responses to the pendulum impacts were compared to relevant sets of the cadaver experiments previously completed by Nahum and Smith. CORrelation and Analysis (CORA) was used to compare the time histories of the global head linear acceleration, and front and left CSF-layer ICP. Subsequently, the CSF ICP-acceleration responses of the BIPED were compared to cadaver data using linear regression methods. This involved incorporating additional parameters for head model type and the interaction effect between head model type and head acceleration to explore differences between the models. The CORA ratings for each BIPED Mk. 2 pressure configuration were 0.614, 0.616, 0.612, and 0.617 when compared to experiment 37 from Nahum and Smith. Overall, these ratings are below 0.7 – the generally accepted threshold for “good” biofidelity. The interaction effects for each BIPED resting ICP configuration were observed to be non-significant when compared to a diverse cadaver specimen set while the interaction effects compared to a single cadaver specimen were indeed significantly different. This suggests that the BIPED offers a reasonable representation of an aggregate response not significantly different from a diverse collection of specimens. Taken together, the BIPED Mk. 2 was considered to be moderately biofidelic. Additionally, these results indicate that altering the resting ICP does not improve or diminish the biofidelity of the BIPED.<br>
Overall, although changing the resting ICP may alter the intracranial and intraparenchymal pressure wave interactions, the absolute maximum pressures the surrogate brain experiences during a blunt impact are not expected to deviate significantly. The largest variations in the headform’s response due to changing resting ICPs were observed in the positive pressures opposite the impact site – away from where peak positive pressures typically occur in head impacts. Moreover, altering the resting ICP does not improve nor diminish the biofidelity of the BIPED</p>