Charles K. Kroell

Impact tolerance and response of the human thorax II

Previous studies of human thoracic injury tolerance and mechanical response to blunt, midsternal, anteroposterior impact loading were reported by the authors at the 1970 SAE International Automobile Safety Conference and at the Fifteenth Stapp Car Crash Conference. The present paper documents additional studies from this continuing research program and provides an expansion and refinement of the data base established by the earlier work. Twenty-three additional unembalmed cadavers were tested using basically the same equipment and procedures reported previously, but for which new combinations of impactor mass and velocity were used in addition to supplementing other data already presented. Specifically, the 43 lb/11 mph (19.5 kg/4.9m/s) and 51 lb/16 mph (23.1 kg/7.2 m/s) conditions were intercrossed and data obtain at 43 lb/14 mph (19.5 kg/7.2 m/s) and 51 lb/11 mph (23.1 kg/4.9 m/s). Several additional tests were run at 22 mph (9.8 m/s) and confirm a strong velocity sensitivity of the force response throughout the velocity range investigated. Also included are several tests in which the cadaver subjects were rigidly supported midsagittally along the spine to preclude whole body motion. Finally, the kinematics of thoracic compression under blunt, A-P impact have been demonstrated by high-speed cinematography of a thorax unilaterally denuded of skin and superficial tissues to enable visualization of the rib surfaces and intercostal musculature during loading. Response in terms of force-time histories and force versus deflection crossplots, and tolerance in terms of associated necropsy findings and AIS ratings, are presented for all tests. Correlations of the AIS rating with both maximum force and normalized chest deflection, several composite summary plots, and a general data tabulation are also included. /Author/

Impact Response of the Human Thorax

Part I — Biomechanics Response Data — Thoracic impact response data for unembalmed human cadavers previously published by three of the authors are reviewed. These data are then “averaged,” adjusted to reflect an estimate for muscle tensing, and used as the basis for recommended force-deflection corridors to serve as dummy design guidelines. A volunteer study of muscle tensing, as related to thoracic stiffness at low force and deflection levels, is discussed, and comments are made concerning additional response data recently acquired by other investigators. Finally, consideration is given to possible “second order” refinements for future generations of a high fidelity dummy thorax.

Prediction of thoracic injury from dummy responses

Currently used criteria based on functions of spinal acceleration obtained from crash test dummies are shown to be invalid indicators of chest injury in blunt frontal impacts. Cadaver impact data are analyzed; and injury is found to be a statistically significant function of chest deflection, chest depth, and cadaver age at death. Based on the resulting regression equations, injury-limiting chest deflections are recommended for various size test dummies. The recommendations apply only to test dummies that have significant thoracic biofidelity for blunt frontal impact. They are valid for environments which include significant blunt frontal impact. Their extension to other environments has not been validated.

Interrelationship of velocity and chest compression in blunt thoracic impact to swine

As part of a continuing study of thoracic injury resulting from blunt frontal loading, the interrelationship of velocity and chest compression was investigated in a series of animal experiments. Anesthetized male swine were suspended in their natural posture and subjected to midsternal, ventrodorsad impact. Twelve animals were struck at a velocity of 14.5 plus or minus 0.9 m/s and experienced a controlled thoracic compression of either 15,19,or 24%. Six others were impacted at 9.7 plus or minus 1.3 m/s with a greater mean compression of 27%. For the 14.5 m/s exposures the severity of trauma increased with increasing compression, ranging from minor to fatal. Injuries included skeletal fractures, pulmonary contusions, and cardiovascular ruptures leading to tamponade and hemothorax. Serious cardiac arrhythmias also occurred, including one case of lethal ventricular fibrillation. The 9.7 m/s exposures produced mainly pulmonary contusion, ranging in severity from moderate to critical. Cardiac arrhythmias occurred but were typically minor. In contrast to the lower compression impacts at 14.5 m/s, there were no rib fractures or cardiovascular ruptures. In general, peak sternal acceleration and applied force correlated with impact velocity but not with normalized compression; and spinal acceleration did not correlate with any parameter. Overall, the high velocity exposures, produced higher mechanical responses, more severe gross trauma and more serious cardiac arrhythmias despite lower compression levels. The results of this study while reconfirming normalized compression as one correlate of injury, emphasize the importance of loading velocity in determining the overall severity of blunt thoracic impact.

Response of belt restrained subjects in simulated lateral impact

Far-side lateral impacts were simulated using a Part 572 dummy and human cadavers to compare responses for several belt restraint configurations. Sled tests were conducted having a velocity change of 35 km/hr at a 10 g deceleration level. Subjects restrained by a three-point belt system with an outboard anchored diagonal shoulder belt rotated out of the shoulder belt and onto the seat. The subject received some lateral restraint due to interaction with the shoulder belt and seatback. The subjects restrained by a three-point belt system with an inboard anchored diagonal shoulder belt remained essentially upright due to shoulder belt interaction with the neck and/or head. Kinematic responses of the Part 572 dummy were generally similar to those of the cadaver subjects. Injuries were found in cadavers restrained by both shoulder belt configurations, but were more extensive to the cervical region for those subjects receiving direct neck and/or head loading from the belt.

Assessment of lap-shoulder belt restraint performance in laboratory testing

Hyge sled tests were conducted using a rear-seat sled fixture to evaluate submarining responses (the lap belt of a lap-shoulder belt restraing loads the abdominal region instead of the pelvis). Objectives of these test included: an evaluation of methods to determine the occurrence of submarining; an investigation into the influence of restraint system parameters, test severity, and type of anthropomorphic test device on submarining response; and an exploration of the mechanics of submarining. The results of of the laboratory tests are presented in this paper.

Postural influences on thoracic impact

The influence of body posture, and inherently support, on thoracic impact response was investigated in an animal model. Twelve anesthetized and postmortem domestic swine were exposed to blunt, midsternal loading while supported in their natural quadrupedal posture, and the results were compared with previously reported data from similar tests involving an upright body orientation. Measured mechanical responses included applied load, sternal and spinal accelerations, thoracic compression and aortic overpressure. Injury response was assessed from a thoracico-abdominal necropsy as well as pre- and post-impact electrocardiogram traces. Language: en