Quantifying the Response of Relative Brain/Skull Motion to Rotational Input in the PMHS Head

Post-mortem human surrogate (PMHS) head specimens were subjected to two different angular speed pulses. Each pulse was approximately a half-sine with either a peak angular speed of either 40 or 20 rad/s and duration of either 30 or 60 milliseconds. Highspeed biplane x-ray was used to record the motion of the brain and skull via radio-opaque markers implanted at specified locations in the brain, and lead markers on the skull. Specimens were perfused to physiologic conditions throughout preparation and testing to maintain the integrity of the brain tissue and ensure coupling of the brain and skull. Intracranial pressure was measured anteriorly and posteriorly. The test event was controlled by a cam-follower-flywheel mechanism, which facilitated control of pulse parameters and provided a form of “extreme energy” so that the device and therefore the test input would not be influenced by the characteristics of the object under test. This approach kept the independent and dependent variables separated. The brain targets were also deployed in a prescribed manner with two methodologies that were scalable to different specimens. The repeatable input and target deployment schemes helped reduce experimental variation (between tests and subjects) to produce consistent response data. Displacement of the brain was calculated with respect to a body-fixed basis on the skull. The relative motion of the brain with respect to the skull was shown to be dependent on the location of the target in the brain. The major deformation axis of each target followed the contour of the skull or bony landmark to which it was closest. Intracranial pressure was relatively low because the changes were due to inertial effects in the absence of impact. Tests with lower speeds and longer durations produced less deformation, lower intracranial pressures, and longer pressure durations than the tests that were high-speed, short-duration. The response of the brain to rotation of the head was quantified at two test levels and on two PMHS specimens. Quantifying the Response of Relative Brain/Skull Motion to Rotational Input in the PMHS Head Allison Jean Guettler GENERAL AUDIENCE ABSTRACT Motor-vehicle collisions (MVCs) are the second leading cause of traumatic brain injury (TBI) in the United States and the leading cause of TBI-related death [1a]. Regulations are in place for vehicle design to reduce the occurrence and severity of head injuries during MVCs. The metric used is based on the resultant linear acceleration at the center of gravity of the occupant’s head. However, TBI are still occurring despite the current regulations. This suggests the importance of using additional injury metrics to predict TBI in MVCs. In automotive impact biomechanics, a combination of real world, experimental, and simulation data is used to determine how the human body responds during MVCs. While computer (finite element) simulations can provide extensive information about the kinematic and kinetic response of the human body, these models require experimental data to validate and evaluate their responses. This study focuses on determining the response of the human cadaver brain to angular speed loading without contact of the head. High-speed biplane x-ray and radiopaque markers were used to quantify the displacement of the brain with respect to the skull throughout rotational events. Two angular speed profiles with different peak angular speeds and durations were used. The methods were determined to reduce experimental variation to obtain data that is useful for finite element model validation. The average peak angular speed for the high-speed tests was 41.8 rad/s and the average peak angular speed for the low-speed tests was 22.0 rad/s. The peak angular speed only varied by 10% between similar tests. The motion of the brain lagged behind that of the skull, producing a relative displacement of the brain with respect to the skull. The magnitude and primary direction of the relative displacement was dependent on the location at which it was measured. The location of the radiopaque target with respect the anatomical coordinate system and bony landmarks of the skull are both important in determining the characteristics of the relative displacement profiles. The high-speed tests produced an average displacement of +/-5 mm, while the low-speed tests had an average displacement of +/-2.5 mm in the X-direction. Intracranial pressure (ICP) was also measured at two points in the cranial cavity, and showed the delayed response of the brain to the rotational loading of the head. [1a] M. Faul, L. Xu, M. M. Wald, and V. G. Coronado, “Traumatic brain injury in the United States: emergency department visits, hospitalizations, and deaths,” Atlanta (GA), 2010.