Force Corridors of Post Mortem Human Surrogates in Oblique Side Impacts from Sled Tests

To develop region-specific force corridors in side impacts under oblique loadings using post mortem human surrogates (PMHS). Unembalmed PMHS were positioned on a sled. Surrogates contacted a segmented, modular/ scalable load-wall to isolate region-specific forces (shoulder, thorax, abdomen, pelvis). Heights and widths of segmented load-wall plates were adjustable in sagittal and coronal planes to accommodate anthropometry variations. Load cells were used to gather region-specific forces. Tests were conducted at 6.7 m/s. Peak forces and times of attainments, and standard corridors (mean ± 1 SD) are given for the four torso regions and summated forces. The mean age, stature, and total body mass of the five male PMHS were: 56.6 ± 4.4 years, 183 ± 3.5 cm and 70.6 ± 9.0 kg. Peak pelvis forces were the greatest, followed by thorax, abdomen and shoulder. Sequence of times of attainments of peak forces initiating from pelvis increased rostrally to abdomen to thorax and shoulder regions. Corridors were tight in all regions, except shoulder. As previous force corridors were based solely on pure-lateral impacts and region-specific forces were not extracted, the present oblique responses using anthropometry-specific load-wall design can be used to develop injury criteria and evaluate the biofidelity of dummies.     

Biomechanical Impact Response of the Human Chin and Manubrium

Chin-to-chest impact commonly occurs in frontal crash simulations with restrained anthropomorphic test devices (ATDs) in non-airbag situations. This study investigated the biofidelity of this contact by evaluating the impact response of both the chin and manubrium of adult post-mortem human subjects (PMHSs). The adult PMHS data were scaled to a 10-year-old (YO) human size and then compared with the Hybrid III 10YO child (HIII-10C) ATD response with the same test configurations. For both the chin and manubrium, the responses of the scaled PMHS had different characteristics than the HIII-10C ATD responses. Elevated energy impact tests to the PMHS mandible provided a mean injury tolerance value for chin impact force. Chin contact forces in the HIII-10C ATD were calculated in previously conducted HYGE sled crash simulation tests, and these contact forces were strongly correlated with the Head Injury Criterion (HIC_36 ms). The mean injurious force from the PMHS tests corresponded to a HIC_36 ms value that would predict an elevated injury risk if it is assumed that fractures of the chin and skull are similarly correlated with HIC_36 ms. Given the rarity of same occupant-induced chin injury in booster-seated occupants in real crash data and the disparity in chin and manubrium stiffnesses between scaled PMHS and HIII-10C ATD, the data from this study can be made use of to improve biofidelity of chin-to-manubrium contact in ATDs.     

Head-trunk coordination in elderly subjects during linear anterior-posterior translations

This study examined whether the head of elderly subjects was less stable in space when the trunk was free to move than when the trunk was fixed to a linearly moving platform. Fourteen healthy elderly subjects were seated on a linear sled with their trunk either fixed to the seat or free to move. Subjects received 10 cm, 445 cm/s² anterior-posterior ramps and 0.35–4.05 Hz sum-of-sines translations while performing a mental distraction task in the dark. Kinematics of the head and trunk were derived from an Optotrak motion analysis system and a linear accelerometer placed on the head. Electromyographic (EMG) signals were collected for neck and paraspinal muscles. Data were tested for significance with paired t-tests corrected for multiple testing and compared (Mann-Whitney U-test) with previously published data from 12 healthy young adults (Keshner 2003). Linear acceleration trajectories of the head corresponded to the direction of sled linear acceleration when the trunk was fixed and countered the direction of the sled when the trunk was free. Angular head accelerations countered the sled or the trunk when the trunk was fixed or free, respectively. Peak amplitudes of head angular acceleration in space were greater with a fixed trunk. With the trunk free, amplitudes of head linear peak acceleration, angular accelerations, and response gains exceeded those of the young adults. Muscle EMG response latencies did not vary with the timing of head acceleration onset but the neck muscles were activated more frequently in a direction consistent with a vestibulocollic or cervicocollic reflex. Differences in angular motion of the head could be explained by the biomechanical constraints of the two tasks having one freely moving mass (head) with the trunk fixed and two freely moving masses (head and trunk) with the trunk free. These data suggest that elderly subjects rely upon active trunk mechanics in order to coordinate their head and trunk motion; however, a contribution by vestibular and ascending segmental inputs cannot be completely ruled out. A less flexible trunk in the elderly could explain why they were not as successful as young adults in stabilizing their heads in space when the trunk was free to move.     

Effect of the mono- and tetra-sialogangliosides, GM1 and GQ1b, on long-term potentiation in the CA1 hippocampal neurons of the guinea pig

 Effects of the mono- and tetra-sialogangliosides, GM1 and GQ1b, on long-term potentiation (LTP) were investigated in the CA1 neurons of guinea-pig hippocampal slices. The magnitude of LTP induced by a strong tetanus (100 Hz, 100 pulses) was not significantly affected by application of either ganglioside. In contrast, when LTP was induced by a weak tetanus (100 Hz, 4 pulses), a significantly greater LTP was induced in the presence of either ganglioside. Similarly, when slices were incubated in low-Ca²⁺ (1.0–1.1 mM) medium for more than 2 h, the LTP was usually small or absent, but showed a significant increase in amplitude of population spike (A-PS) when the slices were incubated with either GM1 or GQ1b (4–5 μg/ml). In addition, the application of GQ1b (4 μg/ml) reversed the blocking effect of an NMDA-receptor antagonist, APP-5 (10 μM), on the induction of LTP and resulted in forming LTP. Based on these findings, we conclude that GM1 and GQ1b exert positive modulatory effects on the induction of LTP in hippocampal CA1 neurons and suggest that GM1 and GQ1b may participate in the induction of LTP as donors of Ca²⁺ ions. Received: 21 April 1998 / Accepted: 5 May 1998     

Development and validation of a modified Hybrid-III six-year-old dummy model for simulating submarining in motor-vehicle crashes

In motor-vehicle crashes, young school-aged children restrained by vehicle seat belt systems often suffer from abdominal injuries due to submarining. However, the current anthropomorphic test device, so-called "crash dummy", is not adequate for proper simulation of submarining. In this study, a modified Hybrid-III six-year-old dummy model capable of simulating and predicting submarining was developed using MADYMO (TNO Automotive Safety Solutions). The model incorporated improved pelvis and abdomen geometry and properties previously tested in a modified physical dummy. The model was calibrated and validated against four sled tests under two test conditions with and without submarining using a multi-objective optimization method. A sensitivity analysis using this validated child dummy model showed that dummy knee excursion, torso rotation angle, and the difference between head and knee excursions were good predictors for submarining status. It was also shown that restraint system design variables, such as lap belt angle, D-ring height, and seat coefficient of friction (COF), may have opposite effects on head and abdomen injury risks; therefore child dummies and dummy models capable of simulating submarining are crucial for future restraint system design optimization for young school-aged children.     

Linear Homeomorphic Models for Muscles in the Head–Neck Region

The linear homeomorphic muscle model proposed by Enderle and coworkers for the rectus eye muscle is fitted to reflect the dynamics of muscles in the head–neck complex, specifically in muscles involved in gaze shifts. This parameterization of the model for different muscles in the neck region will serve to drive a 3D dynamic computer model for the movement of the head–neck complex, including bony structures and soft tissues, and aimed to study the neural control of the complex during fast eye and head movements such as saccades and gaze shifts. Parameter values for the different muscles in the neck region were obtained by optimization using simulated annealing. These linear homeomorphic muscle models provide non-linear force–velocity profiles and linear length tension profiles, which are in agreement with results from the more complex Virtual Muscle model, which is based on Zajac’s non-linear muscle model.     

Principles of linear and angular vestibuloocular reflex organization in the frog.

We compared the spatial organization patterns of linear and angular vestibuloocular reflexes in frogs by recording the multiunit spike activity from cranial nerve branches innervating the lateral rectus, the inferior rectus, or the inferior obliquus eye muscles. Responses were evoked by linear horizontal and/or vertical accelerations on a sled or by angular accelerations about an earth-vertical axis on a turntable. Before each sinusoidal oscillation test in darkness, the static head position was systematically altered to determine those directions of horizontal linear acceleration and those planes of angular head oscillation that were associated with minimal response amplitudes. Inhibitory response components during angular accelerations were clearly present, whereas inhibitory response components during linear accelerations were absent. Likewise was no contribution from the vertical otolith organs (i.e., lagena and saccule) observed during vertical linear acceleration. Horizontal linear acceleration evoked responses that originated from eye muscle-specific sectors on the contralateral utricular macula. The sectors of the inferior obliquus and lateral rectus muscles on the utricle had an opening angle of 45 and 60 degrees, respectively and overlapped to a large extent in the laterorostral part of the utricle. Both sectors were coplanar with the horizontal semicircular canals. The sector of the inferior rectus muscle was narrow (opening 5 degrees), laterocaudally oriented, and slightly pitched up by 6 degrees. Angular acceleration evoked maximal responses in the inferior obliquus muscle nerve that originated from the ipsilateral horizontal and the contralateral anterior vertical canals in a ratio of 50:50. Lateral rectus excitation originated from the contralateral horizontal and anterior vertical semicircular canals in a ratio of 80:20. The excitatory responses of the inferior rectus muscle nerve originated exclusively from the contralateral posterior vertical canal. Measured data and known semicircular canal plane vectors were used to calculate the spatial orientation of maximum sensitivity vectors for the investigated eye muscle nerves in semicircular canal coordinates. Comparison of the directions of maximal sensitivity vectors of responses evoked by linear or angular accelerations in a given eye muscle nerve showed that the two vector directions were oriented about orthogonally with respect to each other. With this arrangement the linear and the angular vestibuloocular reflex can support each other dynamically whenever they are co-activated without a change in the spatial response characteristics. The mutual adaptation of angular and linear vestibuloocular reflexes as well as the differences in their organization described here for frogs may represent a basic feature common for vertebrates in general.     

Effects of neck muscles vibration on the perception of the head and trunk midline position

The present study focused on the influence of neck vibration on the perception of the head and trunk midline position (orientation and localization). The orientation of the head and trunk was investigated by the rolling adjustment of a rod on their midline while their localization was investigated by the adjustment of the position of a visual dot as being straight-ahead the eyes or the sternum. The first experiment investigated whether a head–trunk dissociation was induced by the unilateral vibration of neck muscles in upright and restrained subjects. Results showed that the subjective orientation and localization of whole-body midline were shifted toward the vibrated side. The second experiment determined the effect of the neck muscles vibration when the subjects were lying on their side. The effect of vibration disappeared when the side of vibration was opposed to the side of postural inclination and it was stronger than in the upright position when the side of vibration and the side of postural inclination were congruent. Whereas, results suggested that the input from neck muscle proprioceptors participates directly to the elaboration of the egocentric space, the question may be raised as to how the sensory cues interacted in their contribution to the neural generation of an egocentric, body centred coordinate system.     

Wheelchair integrated occupant restraints: feasibility in frontal impact

Individuals often use their wheelchair as a motor vehicle seat when traveling in motor vehicles. The current use of fixed vehicle-mounted wheelchair occupant restraint systems (FWORSs) often results in poor belt fit and discomfort. Additionally, satisfaction, usability and usage rate of FWORSs during transit use are often low. The automotive industry has shown improved occupant restraint usage, belt fit and injury protection when integrating the upper torso and pelvic restraint in a motor vehicle seat. This study compared occupant injury measures of a FWORS to a concept wheelchair integrated restraint system (WIRS) using a 20g frontal sled impact test with a 30 mph change in velocity. Neck loads, neck moments, head, pelvis and chest acceleration, sternum compression and knee and head excursion data were recorded from the wheelchair seated 50th percentile male hybrid III anthropomorphic test dummy (ATD). The WIRS resulted in a lower head injury criteria (HIC) value, lower sternum compression and a lower upper-torso restraint load than the FWORS.

Compared with the FWORS, increased head, knee and wheelchair excursions and higher neck loads and moments were measured in the WIRS test. Both restraint scenario injury parameters were complied with occupant injury criteria based on General Motors Injury Assessment Reference Values (GM-IARVs) and occupant kinematic requirements defined by the Society of Automotive Engineers (SAE) voluntary standard, J2249. A higher motion criteria index was calculated for the WIRS scenario and a comparable combined injury criteria index was calculated for both restraint scenarios.

The sled impact test showed WIRS concept feasibility, facilitating further development by industrial manufacturers who might further want to pursue this restraint principle to increase wheelchair occupant safety and comfort during transport in motor vehicles.     

Three-dimensional organization of vestibular-related eye movements to off-vertical axis rotation and linear translation in pigeons

During linear accelerations, compensatory reflexes should continually occur in order to maintain objects of visual interest as stable images on the retina. In the present study, the three-dimensional organization of the vestibulo-ocular reflex in pigeons was quantitatively examined during linear accelerations produced by constant velocity off-vertical axis yaw rotations and translational motion in darkness. With off-vertical axis rotations, sinusoidally modulated eye-position and velocity responses were observed in all three components, with the vertical and torsional eye movements predominating the response. Peak torsional and vertical eye positions occurred when the head was oriented with the lateral visual axis of the right eye directed orthogonal to or aligned with the gravity vector, respectively. No steady-state horizontal nystagmus was obtained with any of the rotational velocities (8–58°/s) tested. During translational motion, delivered along or perpendicular to the lateral visual axis, vertical and torsional eye movements were elicited. No significant horizontal eye movements were observed during lateral translation at frequencies up to 3 Hz. These responses suggest that, in pigeons, all linear accelerations generate eye movements that are compensatory to the direction of actual or perceived tilt of the head relative to gravity. In contrast, no translational horizontal eye movements, which are known to be compensatory to lateral translational motion in primates, were observed under the present experimental conditions. Received: 29 January 1999 / Accepted: 14 June 1999