Acceleration induced head injury in the monkey.I. The model, its mechanical and physiological correlates.

A system has been developed which is capable of inducing brain injuries of graded severity from mild concussion to instantaneous death. A pneumatic shock tester subjects a monkey to a non-impact controlled single sagittal rotation which displaces the head 60 degrees in 10-20 msec. Results derived from 53 experiments show that a good correlation exists between acceleration delivered to the head, the resultant neurological status and the brain pathology. A simple experimental trauma severity (ETS) scale is offered based on changes in the heart rate, respiratory rate, corneal reflex and survivability. ETS grades 1 and 2 show heart rate or respiratory changes but no behavioral or pathological abnormality. ETS grades 3 and 4 have temporary corneal reflex abolition, behavioral unconsciousness, and post-traumatic behavioral abnormalities. Occasional subdural haematomas are seen. Larger forces cause death (ETS 5) from primary apnea or from large subdural haematomas. At the extreme range, instantaneous death (ETS 6) occurs because of pontomedullary lacerations. This model and the ETS scale offer the ability to study a broad spectrum of types of experimental head injury and underscore the importance of angular acceleration as a mechanism of head injury.