Predictions of neonatal porcine bridging vein rupture and extra-axial hemorrhage during rapid head rotations.

When the head is rotated rapidly, the movement of the brain lags that of the skull. Intracranial contents between the brain and skull include meninges, cerebrospinal fluid (CSF), and cerebral vasculature. Among the cerebral vasculature in this space are the parasagittal bridging veins (BVs), which drain blood from the brain into the superior sagittal sinus (SSS), which is housed within the falx cerebri, adhered to the inner surface of the skull. Differential motion between the brain and skull that may occur during a traumatic event is thought to stretch BVs, causing damage and producing extra-axial hemorrhage (EAH). Finite element (FE) modeling is a technique often used to aid in the understanding and prediction of traumatic brain injury (TBI), and estimation of tissue deformation during traumatic events provides insight into kinematic injury thresholds. Using a FE model of the newborn porcine head with neonatal porcine brain and BV properties, single and cyclic rapid head rotations without impact were simulated. Measured BV failure properties were used to predict BV rupture. By comparing simulation outputs to observations of EAH in a development group of in vivo studies of rapid non-impact head rotations in the piglet, it was determined that failure of 16.7% of BV elements was associated with a 50% risk of EAH, and showed in a separate validation group that this threshold predicted the occurrence of EAH with 100% sensitivity and 100% specificity for single rapid non-impact rotations. This threshold for failed BV elements performed with 90% overall correct prediction in simulations of cyclic rotational head injuries. A 50% risk of EAH was associated with head angular velocities of 94.74 rad/s and angular accelerations of 29.60 krad/s2 in the newborn piglet. Future studies may build on these findings for BV failure in the piglet to develop predictive models for BV failure in human infants.

Measurement and Finite Element Model Validation of Immature Porcine Brain-Skull Displacement during Rapid Sagittal Head Rotations.

Computational models are valuable tools for studying tissue-level mechanisms of traumatic brain injury, but to produce more accurate estimates of tissue deformation, these models must be validated against experimental data. In this study, we present in situ measurements of brain-skull displacement in the neonatal piglet head (n = 3) at the sagittal midline during six rapid non-impact rotations (two rotations per specimen) with peak angular velocities averaging 51.7 ± 1.4 rad/s. Marks on the sagittally cut brain and skull/rigid potting surfaces were tracked, and peak values of relative brain-skull displacement were extracted and found to be significantly less than values extracted from a previous axial plane model. In a finite element model of the sagittally transected neonatal porcine head, the brain-skull boundary condition was matched to the measured physical experiment data. Despite smaller sagittal plane displacements at the brain-skull boundary, the corresponding finite element boundary condition optimized for sagittal plane rotations is far less stiff than its axial counterpart, likely due to the prominent role of the boundary geometry in restricting interface movement. Finally, bridging veins were included in the finite element model. Varying the bridging vein mechanical behavior over a previously reported range had no influence on the brain-skull boundary displacements. This direction-specific sagittal plane boundary condition can be employed in finite element models of rapid sagittal head rotations.

Risk of concussion due to head acceleration in rear impact sled tests of passenger automobile seats.

OBJECTIVE: Acceleration-based injury metrics can be useful for quantitatively evaluating risk of concussion (a form of mild traumatic brain injury, or mTBI) after automobile collisions, especially when objective medical findings may be negative, as in many cases of concussion. In the present study, head acceleration data were used to evaluate the risk of concussion or more serious head injury to the driver of an automobile that experiences a rear impact resulting in a forward change in velocity (delta-V) of 15.5 km/h (9.6 mph). METHODS: Data were collected from 34 Insurance Institute for Highway Safety (IIHS) rear impact sled tests conducted from 2009 through 2017 for driver seats from 10 passenger car models leading in U.S. sales in 2017. Resultant translational head acceleration data were used to compute the head injury criterion (HIC; HIC15, HIC36) and A-3ms (the 3-ms resultant acceleration criterion utilized by the European New Car Assessment Protocol and others), and maximum resultant translational acceleration (aT). Maximum resultant rotational acceleration (aR) was estimated based on Biofidelic Rear Impact Dummy (BioRID) data from Welch et al. ( 2010 ). RESULTS: No sled test included in the study resulted in a HIC15 value exceeding 55, a HIC36 value exceeding 85, A-3ms exceeding 28 g, aT exceeding 28 g, or estimated aR exceeding 1,400 rad/s2. These values are far below published automotive injury risk values (IARV) used to evaluate crashworthiness. Further, contemporary concussion risk curves place the HIC15, aT, aR, and paired combination of aT and aR sustained by the BioRID anthropomorphic test dummy (ATD) in the IIHS tests at a negligible risk of concussion (mTBI). CONCLUSIONS: The 15.5 km/h delta-V IIHS rear impact sled tests conducted between 2009 and 2017 for common passenger automobile driver seats resulted in injury metrics associated with minimal risk of concussion or more severe head injuries.

Failure and Fatigue Properties of Immature Human and Porcine Parasagittal Bridging Veins.

Tearing of the parasagittal bridging veins (BVs) is thought to be a source of extra-axial hemorrhage (EAH) associated with abusive traumatic brain injuries (TBIs) in children. However, the pediatric BV mechanical properties are unknown. We subjected porcine adult, porcine newborn, and human infant BVs to either a low rate pull to failure, a high rate pull to failure, or 30 s of cyclic loading followed by a pull to failure. An additional subset of human infant BVs was examined for viscoelastic recovery between two cycling episodes. We found that human infant BVs are stronger than porcine BVs, and BV mechanical properties are rate dependent, but not age dependent. Successive cyclic loading to a uniform level of stretch softened BVs with decaying peak stresses, and shifted their stress-stretch relationship. These data are critical in understanding BV tissue behavior in accidental and abusive trauma scenarios, which in turn may clarify circumstances that may be injurious to young children.

Repeated Loading Behavior of Pediatric Porcine Common Carotid Arteries.

Rapid flexion and extension of the neck may occur during scenarios associated with traumatic brain injury (TBI), and understanding the mechanical response of the common carotid artery (CCA) to longitudinal stretch may enhance understanding of contributing factors that may influence CCA vasospasm and exacerbate ischemic injury associated with TBI. Immature (4-week-old) porcine CCAs were tested under subcatastrophic (1.5 peak stretch ratio) cyclic loading at 3 Hz for 30 s. Under subcatastrophic cyclic longitudinal extension, the immature porcine CCA displays softening behavior. This softening can be represented by decreasing peak stress and increasing corner stretch values with an increasing number of loading cycles. This investigation is an important first step in the exploration of fatiguelike behavior in arterial tissue that may be subjected to repeated longitudinal loads.