Sex-related disparities in vehicle crash injury and hemodynamics

Objective

Multiple studies evaluate relative risk of female vs. male crash injury; clinical data may offer a more direct injury-specific evaluation of sex disparity in vehicle safety. This study sought to evaluate trauma injury patterns in a large trauma database to identify sex-related differences in crash injury victims.

Methods

Data on lap and shoulder belt wearing patients age 16 and up with abdominal and pelvic injuries from 2018 to 2021 were extracted from the National Trauma Data Bank for descriptive analysis using injuries, vital signs, International Classification of Disease (ICD) coding, age, and injury severity using AIS (Abbreviated Injury Scale) and ISS (Injury Severity Score). Multiple linear regression was used to assess the relationship of shock index (SI) and ISS, sex, age, and sex*age interaction. Regression analysis was performed on multiple injury regions to assess patient characteristics related to increased shock index.

Results

Sex, age, and ISS are strongly related to shock index for most injury regions. Women had greater overall SI than men, even in less severe injuries; women had greater numbers of pelvis and liver injuries across severity categories; men had greater numbers of injury in other abdominal/pelvis injury regions.

Conclusions

Female crash injury victims' tendency for higher (AIS) severity of pelvis and liver injuries may relate to how their bodies interact with safety equipment. Females are entering shock states (SI > 1.0) with lesser injury severity (ISS) than male crash injury victims, which may suggest that female crash patients are somehow more susceptible to compromised hemodynamics than males. These findings indicate an urgent need to conduct vehicle crash injury research within a sex-equity framework; evaluating sex-related clinical data may hold the key to reducing disparities in vehicle crash injury.

Small Female Occupant Response in Reclined and Upright Seated Postures in Frontal Impacts

The objective of this study was to compare the kinematics of the head-neck, torso, pelvis, and lower extremities and document injuries and their patterns to small female occupants in frontal impacts with upright and reclined postures using an experimental model. Six postmortem human surrogates (PMHS) with a mean stature of 154 ± 9.0 cm and mass of 49 ± 12 kg were equally divided between upright and reclined groups (seatback: 25 deg and 45 deg), restrained by a three-point integrated belt, positioned on a semirigid seat, and exposed to low and moderate crash velocities (15 km/h and 32 km/h respectively). The response between the upright and reclined postures was similar in magnitude and curve morphology. While none of the differences were statistically significant, the thoracic spine demonstrated increased downward (+Z) displacement, and the head demonstrated an increased horizontal (+X) displacement for the reclined occupants. In contrast, the upright occupants showed a slightly increased downward (+Z) displacement at the head, but the torso displaced primarily along the +X direction. The posture angles between the two groups were similar at the pelvis and different at the thorax and head. At 32 km/h, both cohorts exhibited multiple rib failure, with upright specimens having a greater number of severe fractures. Although MAIS was the same in both groups, the upright specimens had more bi-cortical rib fractures, suggesting the potential for pneumothorax. This preliminary study may be useful in validating physical (ATDs) and computational (HBMs) surrogates.

THOR-05F biofidelity evaluation in reclined and upright seated postures subjected to frontal crash pulses

The THOR 5th percentile female dummy (THOR-05F) was evaluated for two seating postures/positions in frontal impacts using a generic automotive seat environment. The conditions included 2 crash pulses: a 15 km/h test that utilized 4.5 g acceleration and a 3-point restraint with 2 kN load limiter, and a 32 km/h test that utilized 9.5 g acceleration and a 3-point restraint with a 4.5 kN load limiter and pretensioner, and two seatback angles: 25°, a nominal upright posture, and 45°, a moderate reclined posture. The BRS scores were calculated using the NHTSA BioRank method. Overall biofidelity rating was consider excellent for both seating postures. This evaluation provides an understanding of the THOR-05F response and biofidelity evaluation of the ATD in two seating postures (nominal and reclined). This is essential in the assessment and development of safety measures in emerging ADS-equipped vehicles.

Influence of bending pre-load on the tensile response of the lumbar spine

Previous full body cadaver testing has shown that both obliquely oriented seats in survivable aircraft crashes and far-side oblique crashes in vehicles present distinctive occupant kinematics that are not yet well understood. Knowledge surrounding how these loading scenarios affect the lumbar spine is particularly lacking as there exists minimal research concerning oblique loading. The current study was created to evaluate a novel experimental method through comparison with existing literature, and to examine the impact of a static bending pre-load (posture) on the load-displacement response for the whole lumbar spine loaded in non-destructive axial distraction. T12-S1 lumbar spines were tested in tension to 4 mm of displacement while positioned in one of three pre-load postures. These postures were: the spine's natural, unloaded curvature (neutral), flexed forward (flexed), and combined flexion and lateral bending (oblique). Deviations from a neutral spine position were shown to significantly increase peak loads and tensile stiffness. The presence of a flexion pre-load caused statistically significant increases in tensile stiffness, tensile force, and bending moments. The addition of a lateral bending pre-load to an already flexed spine did not significantly alter the tensile response. However, the flexion moment response was significantly affected by the additional postural pre-load. This work indicates that the initial conditions of distraction loading significantly affect lumbar spine load response. Therefore, future testing that seeks to emulate crash dynamics of obliquely seated occupants must account for multi-axis loading.

Obese Occupant Response in Reclined and Upright Seated Postures in Frontal Impacts

The American population is getting heavier and automated vehicles will accommodate unconventional postures. While studies replicating mid-size and upright fore-aft seated occupants are numerous, experiments with post-mortem human subjects (PMHS) with obese and reclined occupants are sparse. The objective of this study was to compare the kinematics of the head-neck, torso and pelvis, and document injuries and injury patterns in frontal impacts. Six PMHS with a mean body mass index of 38.2 ± 5.3 kg/m2 were equally divided between upright and reclined groups (seatback: 23°, 45°), restrained by a three-point integrated belt, positioned on a semi-rigid seat, and exposed to low and moderate velocities (15, 32 km/h). Data included belt loads, spinal accelerations, kinematics, and injuries from x-rays, computed tomography, and necropsy. At 15 km/h speed, no significant difference in the occupant kinematics and evidence of orthopedic failure was observed. At 32 km/h speed, the primary difference between the cohorts was significantly larger Z displacements in the reclined occupant at the head (190 ± 32 mm, vs. 105 ± 33 mm p < 0.05) and femur (52 ± 18 mm vs. 30 ± 10 mm, p < 0.05). All the moderate-speed tests produced at least one thorax injury. Rib fractures were scattered around the circumference of the rib-cage in the upright, while they were primarily concentrated on the anterior aspect of the rib-cage in two reclined specimens. Although MAIS was the same in both groups, the reclined specimens had more bi-cortical rib fractures, suggesting the potential for pneumothorax. While not statistical, these results suggest enhanced injuries with reclined obese occupants. These results could serve as a data set for validating the response of restrained obese anthropometric test device (ATDs) and computational human body models.

A novel posture control device to induce high-rate complex loads for spine biomechanical studies

Modern environmental scenarios such as autonomous vehicles, aircrafts, and military vehicles position the human body in a nonstandard posture and induce multiplanar loads; however, current spine alignment methods and loading are based on sagittal and planar loads. The objective of this study is to develop a posture control device and demonstrate its ability to induce multiplanar loads to the human cadaver spinal columns. The inferior end of the device was designed to allow a full six degree-of-freedom control for positioning the specimen via a coupled x-y cross table, vertical lift platform, and triaxial rotation mechanism. The superior end of the device was designed such that the cranial fixation of the specimen could be attached to the piston of the electrohydraulic testing apparatus directly or via a rotary disc through a slider-crank mechanism. The former attachment induces complex forces and moments, while the latter induces controlled moments with minimal forces. The usability of the posture control device was demonstrated by conducting experiments with a thoracolumbar spinal column for combined forces and moments, and with a head-neck column for complex moments, and in both cases, the uniaxial travel of the piston was at a dynamic rate. The posture control device can be used to study the biomechanics of the spine under complex loads and with different postures and develop injury criteria for different field environments.

Effectiveness of center-mounted airbag in far-side impacts based on THOR sled tests

Objective: The study aimed to evaluate the protection offered by a center-mounted airbag in far-side impacts using the Test device for Human Occupant Restraint (THOR) anthropometric test device (ATD). Methods: A rigid buck was designed based on a production vehicle. The buck consisted of a rigid seat, center console, dash, and far-side door structure. The center console and dash were covered with paper honeycomb (152 kPa), and the far-side door structure was covered with Ethafoam 220 padding material. The airbag was mounted on the seat, to the right of the occupant. The THOR-M50 ATD was positioned according to the standard seating procedure and restrained using a standard 3-point seat belt with a pretensioner and retractor. The buck was mounted on an acceleration sled in 2 orientations. Four tests at 45° (oblique) and 2 tests at 90° (lateral) orientations were conducted. Tests were performed with and without an airbag at 30 km/h delta-V and 14 g acceleration. The head accelerations, neck forces and moments, thoracic accelerations and forces, pelvis accelerations, anterior superior iliac spine (ASIS) forces and moments, and belt webbing loads were obtained from sensors, and the external kinematics was obtained using an optical motion capture system and high-speed digital cameras. Results: With the center-mounted airbag, in 90° and 45° tests, reductions were observed for the following parameters: head lateral excursions by 6% and 11%, head vertical excursions by 19% and 26%, and peak head resultant accelerations by 36% and 11%. Other regional accelerations, forces, and moments were also reduced for both impact angles. A reduction in seat belt forces with the airbag was observed in 90° tests. Conclusion: The center-mounted airbag reduced the ATD excursions and accelerations in the 45° and 90° tests, thus reducing the risk of injury due to contact with the intruding structure. The results of this study may assist in designing countermeasures for vehicles in far-side impact.

Biomechanics of Lumbar Motion-Segments in Dynamic Compression

Recent epidemiology studies have reported increase in lumbar spine injuries in frontal crashes. Whole human body finite element models (FEHBM) are frequently used to delineate mechanisms of such injuries. However, the accuracy of these models in mimicking the response of human spine relies on the characterization data of the spine model. The current study set out to generate characterization data that can be input to FEHBM lumbar spine, to obtain biofidelic responses from the models. Twenty-five lumbar functional spinal units were tested under compressive loading. A hydraulic testing machine was used to load the superior ends of the specimens. A 75N load was placed on the superior PMMA to remove the laxity in the joint and mimic the physiological load. There were three loading sequences, namely, preconditioning, 0.5 m/s (non-injurious) and 1.0 m/s (failure). Forces and displacements were collected using six-axis load cell and VICON targets. In addition, acoustic signals were collected to identify the times of failures. Finally, response corridors were generated for the two speeds. To demonstrate the corridors, GHBMC FE model was simulated in frontal impact condition with the default and updated lumbar stiffness. Bi-linear trend was observed in the force versus displacement plots. In the 0.5 m/s tests, mean toe- and linear-region stiffnesses were 0.96±0.37 and 2.44±0.92 kN/mm. In 1.0 m/s tests, the toe and linear-region stiffnesses were 1.13±0.56 and 4.6±2.5 kN/mm. Lumbar joints demonstrated 2.5 times higher stiffness in the linear-region when the loading rate was increased by 0.5 m/s.

Deep brain stimulation in rats: different targets induce similar antidepressant-like effects but influence different circuits

Recent studies in patients with treatment-resistant depression have shown similar results with the use of deep brain stimulation (DBS) in the subcallosal cingulate gyrus (SCG), ventral capsule/ventral striatum (VC/VS) and nucleus accumbens (Acb). As these brain regions are interconnected, one hypothesis is that by stimulating these targets one would just be influencing different relays in the same circuitry. We investigate behavioral, immediate early gene expression, and functional connectivity changes in rats given DBS in homologous regions, namely the ventromedial prefrontal cortex (vmPFC), white matter fibers of the frontal region (WMF) and nucleus accumbens. We found that DBS delivered to the vmPFC, Acb but not WMF induced significant antidepressant-like effects in the FST (31%, 44%, and 17% reduction in immobility compared to controls). Despite these findings, stimulation applied to these three targets induced distinct patterns of regional activity and functional connectivity. While animals given vmPFC DBS had increased cortical zif268 expression, changes after Acb stimulation were primarily observed in subcortical structures. In animals receiving WMF DBS, both cortical and subcortical structures at a distance from the target were influenced by stimulation. In regard to functional connectivity, DBS in all targets decreased intercorrelations among cortical areas. This is in contrast to the clear differences observed in subcortical connectivity, which was reduced after vmPFC DBS but increased in rats receiving Acb or WMF stimulation. In conclusion, results from our study suggest that, despite similar antidepressant-like effects, stimulation of the vmPFC, WMF and Acb induces distinct changes in regional brain activity and functional connectivity.