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A freshly dead Stumptail (Macaca speciosa) monkey brain hemisection model has been subjected to translation, pure rotation and a combination motion. Linear and angular head accelerations were measured as well as brain displacement relative to the skull and shear strain at several locations. Much higher than previously predicted shear strain was measured at acceleration levels which have been recorded during impacts which produced concussion in live monkeys. Pure rotation produced the highest, most diffuse and long lasting shear strain and brain displacement, while translation produced very low shear strain. Highest shear strain during rotation was recorded in the brainstem rather than on the periphery as many have predicted. Results suggest that the mechanism of brainstem injury, regardless of head motion, is due to shear caused by stretching of the cervical cord.

The purpose of this study was to increase our understanding of the head impact level that will produce concussion in humans. The technique employed was that of accident restaging. The investigation reported here was composed of three parts: 1. The Cornell accident records were reexamined to establish the frequency of brain concussion as a function of windshield damage. 2. Tests were conducted with instrumented cadavers to determine the head accelerations achieved when the appropriate windshield damage levels were obtained. 3. Head injury indexes were calculated from the measured accelerations, and their predictions were compared to the Cornell field data. The present reexamination of the Cornell accident data found that the percentage of victims who received a concussion involving known unconsciousness reduces to, at most, 11% for the case of radial crack with bulge. The percentage obtained for radial crack-no bulge was, at most, 2.8%.

Impacts have been analyzed in terms of degree of injury, head injury criterion (HIC), and average acceleration as a function of time for frontal impacts against the following surfaces: 1. Rigid flat surface-fractured cadaver skull. 2. Astroturf-head drop of football-helmeted cadaver. 3. Windshield penetrating impact of a dummy. 4. Airbag-dynamic test by human volunteers. It is concluded that the linear acceleration/time concussion tolerance curve may not exist and that only impacts against relatively stiff surfaces producing impulses with short rise times can be critical. The authors hypothesize that if a head impact does not contain a critical HIC interval of less than 0.015 s, it should be considered safe as far as cerebral concussion is concerned.

A human head model has been developed primarily for use in evaluation of impact attenuation properties of football helmets, but is also applicable in automobile impact safety tests. Using firm silicon rubber molds made from impressions of cadaver bones, a skull and mandible were each cast in one piece using a self-skinning urethane foam that hardens into cross section geometry similar to the human bone. A rubber gel material is used to simulate the brain. The skull and attached mandible are overlayed with repairable silicon rubber skin having puncture and sliding-over-bone characteristics similar to human skin. At present, the model has a rudimentary solid silicon rubber neck, through the center of which runs a flexible steel cable attached at the foramen magnum. The cable is used to attach the head to a carriage or anthropometric dummy and can be adjusted in tension to give various degrees of flexibility.

The head acceleration pulses obtained from monkey concussion, cadaver skull fracture (t = 0.002 sec), and football helmet experiments (0.006< t< 0.011 sec) have been subjected to injury hazard assessment by the Severity Index method. Although not directly applicable, the method correlates well with degree of monkey concussion. The range of Severity Indices for acceleration pulses obtained during impact to nine cadavers, all of which produced a linear fracture, was 540-1760 (1000 is danger to life) with a median value of 910. The helmet experiments showed good correlation between the Severity Index and the Wayne State University tolerance curve. These helmet tests also showed that a kinematics chart with curves of velocity change, stopping distance, average head acceleration, and time, with a superimposed Wayne State tolerance curve, can be useful in injury assessment.

This paper is an in-depth study of the mechanism of concussion. Prior to 1967, concussion experiments were conducted exclusively on dogs, but after results of trials on dogs, cats, and stumptail monkeys, the authors concentrated on the latter. Varying numbers of blows, from different angles, were delivered to 12 monkeys. Results, both organic and behavioral, are discussed.

Three human male cadaver heads were statically loaded along anteroposterior, posterioanterior, side to side, and vertex to base lines of action, while simultaneously measuring skull deflections at four or five locations and intracranial volume changes. Volume changes due to loading along the long (A-P) axis were small and either increased or decreased, while loads transverse to the A-P axis decreased the volume. Transverse loads produced volume changes on the order of 10 times larger than those due to A-P forces. Two skulls loaded to fracture in the A-P direction, failed at 1150 and 2200 lb, respectively, into the right orbit. These magnitudes and linear fracture direction correspond to four fractures produced by impact to the frontal bone of intact cadavers in previous work.

It is shown that the response of the occiput of a cadaver to sinusoidal vibration input to the frontal bone corresponds closely to that of a simple damped spring-mass system having a natural frequency equal to the first mode frequency of the skull, 0.17 damping factor. The first and third bending mode of the skull occurred near 300 and 900 Hz for both the cadaver preparation with silicon gel filled cranial cavity and the live human head. A second mode was found near 600 Hz in the live human. Head acceleration levels at which opposite pole pressure reached near —1 atm were 170 g and 500–600 g in the human cadaver and live monkey head, respectively, which values are roughly inversely proportional to major intracranial diameters. A method is derived for comparing the impact response of a simple system to a general shaped pulse to that of the cadaver head.

Certain physical characteristics such as apparent mass and stiffness influence the dynamic response of the head and thereby the degree of trauma suffered from impact with another body. These characteristics are a function of frequency and can be determined by mechanical impedance measurement techniques. A force generator was attached directly to the skull and the force input and resulting motion at the point of attachment were measured respectively by a force and acceleration transducer. The magnitude as well as phase angle between these two vectors were measured over the frequency range from 5 to 5,000 Hz. A plot of the ratio of force and acceleration vs. frequency and phase angle vs. frequency on a nomograph reveal that both the apparent mass and stiffness of the head vary markedly from static values, and with location.

Experiments have revealed that the brain of the experimental animal behaves elastically in response to dynamic forces in situ. The response of the skull of the human cadaver has been investigated by means of static load-deflection tests and impact and mechanical impedance tests. This information has been used to construct a two-dimensional head model consisting of a polyester resin shell reinforced with fiberglas with plexiglass sides; a clear silicone gel brain; and spinal cord simulated by a plexiglass tube containing silicone gel supported by a piston-spring assembly. Several frames taken from motion pictures recorded at 7,000 frames/sec. show how pressure gradients in the model are displayed by observing the growth and location of bubbles during impact.

It has been found that a blow to the sagittal crest of the fixed head of the intact dog generally will produce an experimental concussion twice as severe as an equivalent blow to the free head. In preliminary experiments the dog has been found to be much more susceptible to concussion from a blow to the external occipital protuberance than any other location, and the effect appears to be equally severe in either fixed or free head condition. The physiological response of the macaca speciosa (stump tail) monkey in the 15 to 20 lb range has been found to be different and much less sensitive than that of the dog or cat. The authors believe that to relate experimental concussion results to man more investigation is necessary on the anesthetized and relatively conscious primate.

Experiments were conducted primarily on human cadavers to determine the response characteristics and tolerance of several of the prominent facial bones to blunt impact. Most of the data compiled for the experiments on the zygoma showed that bone strain and head acceleration are almost directly proportional to input force and that tolerance to fracture is dependent upon both magnitude and time duration of the force pulse. The magnitude of force in turn is almost directly proportional to the velocity of impact while the pulse duration is virtually independent of velocity. Preliminary results on the effects of cadaver soft tissue covering the bone indicates that with soft tissue protection the zygoma can absorb blows of 40% to 80% higher energy than without the soft tissue, before fracture occurs. Also, preliminary results on the monkey show only a slight difference in response to blows to the zygomatic arch between the live and a 15 day embalmed animal.