Head injury in the chimpanzee

Part 1: Biodynamics of traumatic unconsciousness

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✓ Requirements for extrapolating head injury tolerance levels from subhuman primates to man necessitated data from a primate species with a brain weight between that of the rhesus monkey (100 gm) and man (1200 gm). Cerebral concussion (traumatic unconsciousness) in the chimpanzee (brain weight, 400 gm) is found to occur when the head experiences angular velocities exceeding 70 to 120 radians/ sec irrespective of how such head rotations are produced, i.e., whether indirectly by a whiplash mechanism or directly by impact to the occiput. The threshold for the production of skull fracture and visible brain lesions appears to be quite close to that found for traumatic unconsciousness. Associated neurological, cardiovascular, and pathological effects of head injury in this species are also described, and a new hypothesis for traumatic unconsciousness (cerebral concussion) is presented.

Article Information

Present address for Dr. Corrao: Department of Pathology, Georgetown University School of Medicine, Washington, D.C.Present address for Dr. Letcher: Division of Neurosurgery, Washington University School of Medicine, St. Louis, Missouri 63110Address reprint requests to: Ayub K. Ommaya, M.D., F.R.C.S., National Institute of Neurological Diseases and Stroke, Department of Health, Education, and Welfare, National Institutes of Health, Bethesda, Maryland.

© AANS, except where prohibited by US copyright law.

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Figures

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    Drawing showing restraint system for chimpanzee. Plaster casts immobilize the ankle and elbow joints only. Electrode cable shown in left carries the output from the extradural, ground, and eye-movement electrodes.

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    Tolerance curve for the onset of traumatic unconsciousness after direct and indirect impacts in the chimpanzee. The derivation of this type of curve and its relationship to scaling such data for extrapolation to man are described in Ref. 6. All rotations refer to displacements in the sagittal plane of the head.

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    Animal H245 (C14). Blood pressure (systolic and diastolic), pulse, and respiratory changes after subconcussive (Shot 1) and concussive (Shot 2) impacts. Note the apnea and bradycardia following the concussive impact. The unit on the ordinate (Beats) refers to mm Hg for the blood pressure, and rate per minute for pulse and respiration. The abscissa marks off the minutes after impact.

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    Animal H247. Alterations in blood pressure, pulse, and respiratory rates after a succession of three subconcussive impacts (Shots 1, 2, and 3) and one impact causing traumatic unconsciousness with skull fracture leading to death (Shot 4). Note the identical nature of the subconcussive response and the lack of cumulative effects on these responses. Also note the apnea, bradycardia, and early hypertension preceding hypotension and death in Shot 4. The ordinates and abscissae and the data values recorded are the same as in Fig. 3.

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    Animal F140. Electrocardiographic changes after impact causing traumatic unconsciousness and skull fracture. Associated responses in respiratory rate and pattern and arterial blood pressure are also shown. Note EKG changes (see Table 3) that persisted beyond the recovery of consciousness for 187 seconds after impact. Severe pathological lesions caused by this impact (see Table 4) correlated well with the persisting EKG abnormalities (note change of time scale at segment 20 minutes after impact).

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    Sagittal sections through the human and chimpanzee head to show the relative proportions of brain to its coverings (chimpanzee section enlarged to comparative size).

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    Superior surface views of typical locations of cortical contusions after removal of subdural hematomas. Left: Animal G637. Right: Animal F140.

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    Animal E114. Coronal sections showing massive intracerebral hematoma produced after one blow without associated traumatic unconsciousness or skull fracture.

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    Recovery scale for cerebral concussion. The clinicopathological observations summarized in this diagram have to be explained by any acceptable hypothesis for cerebral concussion (traumatic unconsciousness) in man. Note that such “unconsciousness” is conceived as ranging from simple confusion and disorientation without motor and sensory paralysis through the states of complete coma with akinesis. R.G.A. = retrograde amnesia. P.T.A. = posttraumatic amnesia.

References

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