Biomechanical Responses of PMHS Subjected to Abdominal Seatbelt Loading.

Past studies have found that a pressure based injury risk function was the best predictor of liver injuries due to blunt impacts. In an effort to expand upon these findings, this study investigated the biomechanical responses of the abdomen of post mortem human surrogates (PMHS) to high-speed seatbelt loading and developed external response targets in conjunction with proposing an abdominal injury criterion. A total of seven unembalmed PMHS, with an average mass and stature of 71 kg and 174 cm respectively were subjected to belt loading using a seatbelt pull mechanism, with the PMHS seated upright in a freeback configuration. A pneumatic piston pulled a seatbelt into the abdomen at the level of the umbilicus with a nominal peak penetration speed of 4.0 m/s. Pressure transducers were placed in the re-pressurized abdominal vasculature, including the inferior vena cava (IVC) and abdominal aorta, to measure internal pressure variation during the event. Jejunum tear, colon hemorrhage, omentum tear, splenic fracture and transverse processes fracture were identified during post-test anatomical dissection. Peak abdominal forces ranged from 2.8 to 4.7 kN. Peak abdominal penetrations ranged from 110 to 177 mm. A force-penetration corridor was developed from the PMHS tests in an effort to benchmark ATD biofidelity. Peak aortic pressures ranged from 30 to 104 kPa and peak IVC pressures ranged from 36 to 65 kPa. Updated pressure based abdominal injury risk functions were developed for vascular Pmax and Pmax*Pmax.

Sequential biomechanics of the human upper thoracic spine and pectoral girdle.

Thoracic spine flexibility affects head motion, which is critical to control in motor vehicle crashes given the frequency and severity of head injuries. The objective of this study is to investigate the dynamic response of the human upper thoracic region. An original experimental/analytical approach, Isolated Segment Manipulation (ISM), is introduced to quantify the intact upper thoracic spine-pectoral girdle (UTS-PG) dynamic response of six adult post-mortem human subjects (PMHS). A continuous series of small displacement, frontal perturbations were applied to the human UTS-PG using fifteen combinations of speed and constraint per PMHS. The non-parametric response of the T1-T6 lumped mass segment was obtained using a system identification technique. A parametric mass-damper-spring model was used to fit the non-parametric system response. Mechanical parameters of the upper thoracic spine were determined from the experimental model and analyzed in each speed/constraint configuration. The natural frequencies of the UTS-PG were 22.9 ± 7.1 rad/sec (shear, n=58), 32.1 ± 7.4 rad/sec (axial, n=58), and 27.8 ± 7.7 rad/sec (rotation, n=65). The damping ratios were 0.25 ± 0.20 (shear), 0.42 ± 0.24 (axial), and 0.58± 0.32 (rotation). N-way analysis of variance (Type III constrained sum of squares, no interaction effects) revealed that the relative effects of test speed, pectoral girdle constraint, and PMHS anthropometry on the UTS-PG dynamic properties varied per property and direction. While more work is needed to verify accuracy in realistic crash scenarios, the UTS-PG model system dynamic properties could eventually aid in developing integrated anthropomorphic test device (ATD) thoracic spine and shoulder components to provide improved head kinematics and belt interaction.

Dynamic properties of the upper thoracic spine-pectoral girdle (UTS-PG) system and corresponding kinematics in PMHS sled tests.

Anthropomorphic test devices (ATDs) should accurately depict head kinematics in crash tests, and thoracic spine properties have been demonstrated to affect those kinematics. To investigate the relationships between thoracic spine system dynamics and upper thoracic kinematics in crash-level scenarios, three adult post-mortem human subjects (PMHS) were tested in both Isolated Segment Manipulation (ISM) and sled configurations. In frontal sled tests, the T6-T8 vertebrae of the PMHS were coupled through a novel fixation technique to a rigid seat to directly measure thoracic spine loading. Mid-thoracic spine and belt loads along with head, spine, and pectoral girdle (PG) displacements were measured in 12 sled tests conducted with the three PMHS (3-pt lap-shoulder belted/unbelted at velocities from 3.8 - 7.0 m/s applied directly through T6-T8). The sled pulse, ISM- derived characteristic properties of that PMHS, and externally applied forces due to head-neck inertia and shoulder belt constraint were used to predict kinematic time histories of the T1-T6 spine segment. The experimental impulse applied to the upper thorax was normalized to be consistent with a T6 force/sled acceleration sinusoidal profile, and the result was an improvement in the prediction of T3 X-axis displacements with ISM properties. Differences between experimental and model-predicted displacement-time history increases were quantified with respect to speed. These discrepancies were attributed to the lack of rotational inertia of the head-neck late in the event as well as restricted kyphosis and viscoelasticity of spine constitutive structures through costovertebral interactions and mid-spine fixation. The results indicate that system dynamic properties from sub-injurious ISM testing could be useful for characterizing forward trajectories of the upper thoracic spine in higher energy crash simulations, leading to improved biofidelity for both ATDs and finite element models.

Biomechanical responses of PMHS in moderate-speed rear impacts and development of response targets for evaluating the internal and external biofidelity of ATDS.

The objectives of this study were to obtain biomechanical responses of post mortem human subjects (PMHS) by subjecting them to two moderate-speed rear impact sled test conditions (8.5g, 17 km/h; 10.5g, 24 km/h) while positioned in an experimental seat system, and to create biomechanical targets for internal and external biofidelity evaluation of rear impact ATDs. The experimental seat was designed to measure external loads on the head restraint (4 load cells), seat back (6 load cells), and seat pan (4 load cells) such that subject dynamic interaction with the seat could be evaluated. This seat system was capable of simulating the dynamic characteristics of modern vehicle seat backs by considering the moment-rotation properties of a typical passenger vehicle, thus providing a more realistic test environment than using a rigid seat with a non-rotating seat back as done in previous studies. Instrumentation used to measure biomechanical responses of the PMHS included both accelerometers and angular rate sensors (ARS). A total of fourteen sled tests using eight PMHS (males 175.8 ± 6.2 cm of stature and 78.4 ± 7.2 kg of weight) provided data sets of seven PMHS for both test conditions. The biomechanical responses are described at both speeds, and cervical spine injuries are documented. Biomechanical targets are also created for internal and external biofidelity evaluation of rear impact anthropomorphic test devices (ATDs).

Evaluation of the internal and external biofidelity of current rear impact ATDs to response targets developed from moderate-speed rear impacts of PMHS.

The goal of this study is to evaluate both the internal and external biofidelity of existing rear impact anthropomorphic test devices (BioRID II, RID3D, Hybrid III 50th) in two moderate-speed rear impact sled test conditions (8.5g, 17 km/h; 10.5g, 24 km/h) by quantitatively comparing the ATD responses to biomechanical response targets developed from PMHS testing in a corresponding study. The ATDs and PMHS were tested in an experimental seat system that is capable of simulating the dynamic seat back rotation response of production seats. The experimental seat contains a total of fourteen load cells installed such that external loads from the ATDs and PMHS can be measured to evaluate external biofidelity. The PMHS were instrumented to correspond to the instrumentation contained in the ATDs so that direct comparison between ATDs and PMHS could be made to evaluate internal biofidelity. The NHTSA Biofidelity Ranking system was used to quantitatively evaluate the biofidelity of the ATDs and an additional tool was introduced and utilized which allows for the biofidelity score to be partitioned into components of amplitude, phase, and shape. For internal biofidelity, the BioRID II and RID3D were more biofidelic than the Hybrid III in the 17 km/h test, and the BioRID II was most biofidelic in the 24 km/h test. For external biofidelity, the BioRID II was most biofidelic in the 17 km/h test, while both the BioRID II and the RID3D were more biofidelic than the Hybrid III in the 24 km/h test. Overall, the BioRID II demonstrated the best biofidelity in both the 17 km/h and 24 km/h tests.

Response of PMHS to high- and low-speed oblique and lateral pneumatic ram impacts.

In ISO Technical Report 9790 (1999) normalized lateral and oblique thoracic force-time responses of PMHS subjected to blunt pendulum impacts at 4.3 m/s were deemed sufficiently similar to be grouped together in a single biomechanical response corridor. Shaw et al. (2006) presented results of paired oblique and lateral thoracic pneumatic ram impact tests to opposite sides of seven PMHS at sub-injurious speed (2.5 m/s). Normalized responses showed that oblique impacts resulted in more deflection and less force, whereas lateral impacts resulted in less deflection and more force. This study presents results of oblique and lateral thoracic impacts to PMHS at higher speeds (4.5 and 5.5 m/s) to assess whether lateral relative to oblique responses are different as observed by Shaw et al. or similar as observed by ISO. Twelve PMHS were impacted by a 23 kg pneumatic ram with a 152.4 mmx304.8 mm rectangular face plate at the level of the xyphoid process in either the pure lateral or 30° anterior-to-lateral oblique direction. Because these tests were potentially injurious, only one test per subject was conducted. Normalized responses demonstrate similar characteristics for both lateral and oblique impacts, indicating that it may be reasonable to combine lateral and oblique responses together at these higher speeds to define characteristic PMHS response as was done by ISO. The small number of tests conducted indicates that less chest compression may be required to obtain serious thoracic injury in oblique impacts as compared to lateral impacts at speeds of 4.5 or 5.5 m/s.

Pressure-based abdominal injury criteria using isolated liver and full-body post-mortem human subject impact tests.

Liver trauma research suggests that rapidly increasing internal pressure plays a role in liver injury. Previous work has shown a correlation between pressure and liver injury in pressurized ex vivo human livers when subjected to blunt impacts. The purpose of this study was to extend the investigation of this relationship between pressure and liver injury by testing full-body post-mortem human surrogates (PMHS). Pressure-related variables were compared with one another and also to previously proposed biomechanical predictors of abdominal injury. Ten PMHS were tested. The abdominal vessels were pressurized to physiological levels using saline, and a pneumatic ram impacted the right side of the specimen ribcage at a nominal velocity of 7.0 m/s. Specimens were subjected to either lateral (n = 5) or oblique (n = 5) impacts, and the impact- induced pressures were measured by transducers inserted into the hepatic veins and inferior vena cava. The liver injuries observed were similar to those documented in the Crash Injury Research Engineering Network (CIREN) trauma database. Using binary logistic regression to develop injury risk functions, it was determined the peak rate of pressure change (Pmax) was a statistically significant predictor of AIS ≥ 3 liver injury for both the PMHS and ex vivo testing. This suggests that Pmax is a good predictor of liver injury regardless of the impact boundary conditions.

Using pressure to predict liver injury risk from blunt impact.

Liver trauma research suggests that rapidly increasing internal pressure plays a role in causing blunt liver injury. Knowledge of the relationship between pressure and the likelihood of liver injury could be used to enhance the design of crash test dummies. The objectives of this study were (1) to characterize the relationship between impact-induced pressures and blunt liver injury in an experimental model to impacts of ex vivo organs; and (2) to compare human liver vascular pressure and tissue pressure in the parenchyma with other biomechanical variables as predictors of liver injury risk. Test specimens were 14 ex vivo human livers. Specimens were perfused with normal saline solution at physiological pressures, and a drop tower applied blunt impact at varying energies. Impact-induced pressures were measured by transducers inserted into the hepatic veins and the parenchyma (caudate lobe) of ex vivo specimens. Experimentally induced liver injuries were consistent with those documented in the Crash Injury Research and Engineering Network (CIREN) database. Binary logistic regression analysis demonstrated that injury predictors associated with tissue pressure measured in the parenchyma were the best indicators of serious liver injury risk. The best injury predictor overall was the product of the peak rate of tissue pressure increase and the peak tissue pressure, P T max * P T max (pseudo-R2 = .82, p = .001). A burst injury mechanism directly related to hydrostatic pressure is postulated for the ex vivo liver loaded dynamically in a drop test experiment.

Oblique and lateral impact response of the PMHS thorax.

This study characterizes the PMHS thoracic response to blunt impact in oblique and lateral directions. A significant amount of data has been collected from lateral impacts conducted on human cadavers. Substantially less data has been collected from impacts that are anterior of lateral in an oblique direction. In the past, data collected from the handful of oblique impact studies were considered to be similar enough to the data from purely lateral impacts such that the oblique data were combined with data from lateral impacts. Defining the biomechanical response of the PMHS thorax to oblique impact is of great importance in side impact vehicle crashes where the loading is often anterior-oblique in direction. Data in this study was obtained from a chestband placed on the thorax at the level of impact to measure thoracic deflection. Two low energy impacts were conducted on each of seven subjects at 2.5 m/s, with one lateral impact and one oblique impact to opposite sides of each PMHS. Data was normalized using the Mertz-Viano method for a two mass system to allow for inter-subject comparisons. Force versus deflection response corridors were generated for the two impact types using an objective mathematical approach and compared to one another. Results were also compared to existing data for oblique and lateral thoracic impacts. The oblique thoracic response in low speed pendulum impacts was found to be different than the lateral thoracic response, in terms of force and deflection. Specifically, the lateral force was greater than the oblique force, and oblique deflection greater than lateral deflection for equal energy impacts.

Shoulder impact response and injury due to lateral and oblique loading.

Little is known about the response of the shoulder complex due to lateral and oblique loading. Increasing this knowledge of shoulder response due to these types of loading could aid in improving the biofidelity of the shoulder mechanisms of anthropomorphic test devices (ATDs). The first objective of this study was to define force versus deflection corridors for the shoulder corresponding to both lateral and oblique loading. A second focus of the shoulder research was to study the differences in potential injury between oblique and lateral loading. These objectives were carried out by combining previously published lateral impact data from 24 tests along with 14 additional recently completed lateral and oblique tests. The newly completed tests utilized a pneumatic ram to impact the shoulder of approximately fiftieth percentile sized cadavers at the level of the glenohumeral joint with a constant speed of approximately 4.4 m/sec. Of the 14 tests, four of them were conducted lateral to the shoulder along the subject's y-axis, four of them were conducted 15 anterior to this axis, and six were conducted 30 anterior to the subject's y-axis. As in the previous testing, the first thoracic vertebrae and both shoulders of the subject were instrumented with tri-axial linear accelerometers on the sternum, clavicle, acromion process, and inferior angle of the scapula. The impacting mass was instrumented with an accelerometer and displacement transducer. In addition to this instrumentation, the tests were documented by high-speed digital imagery. Radiographs (x-rays), magnetic resonance images (MRIs), and autopsies were used to document injury to the subjects. The results from the tests revealed differences between the stiffness of the shoulder when loaded laterally to that when it is loaded obliquely. The shoulder was found to deflect twice as much medially when loaded obliquely then when it is loaded laterally. This can be attributed to the ability of the scapula to slide posteriorly around the thoracic cage. The ability of the shoulder to displace medially while simultaneously deflecting posteriorly in oblique impact is important to replicate in the ATDs because it results in the load being transmitted to the upper thoracic cage.