Fatal brainstem damage caused by linear acceleration impact--relationship between pathophysiological findings and far field acoustic response (author's transl)

Abstract

The present experiment was undertaken to clarify the correlation between pathological findings of primary brainstem damage and alteration of the far field acoustic response of the rhesus monkey by linear acceleration head impact using a HYGE sled and slider impactor system. Brainstem damage was produced by the impact upon the frontal or occipital part of the head, at an linear acceleration in parallel to orbito-meatal line, 1, 000 1, 500 G and duration 3 ?? 5 msec. In 4 out of 12 monkeys, the electron microscopic cellular changes and disturbance of microcirculation at the lower brainstem were observed and they died within one hour after the impact. The far field acoustic response disappears just after the impact without any relation to cortical EEG. In the 6 monkeys that survived following the impact, the far field acoustic response did not disappear even just after the impact. Normal microcirculation and slight electron microscopic cellular changes were observed at the brainstem. Monkeys that died of cervical cord injury or intrathoracic bleeding by the impact, had slight electron microscopic changes with normal microcirculation at the brainstem as in survival group. The far field acoustic responses did not disappear just after the impact but disappeared when EEG became flat by death. According to these results, it is concluded that: 1) The primary brainstem damage consists of electron microscopic changes and disturbances of microcirculation is induced by pure linear acceleration head impact without any cranial fracture, intracranial hematoma or cerebral contusion; and 2) This primary brainstem damage is fatal in monkeys whenever all waves of the far field acoustic responses disappear.