ACUTE INTRACRANIAL HYPERTENSION AND AUDITORY BRAIN-STEM RESPONSES .1. CHANGES IN THE AUDITORY BRAIN-STEM AND SOMATOSENSORY EVOKED-RESPONSES IN INTRACRANIAL HYPERTENSION IN CATS

Changes in auditory brain-stem responses (BER's) and somatosensory evoked responses (SER's) were investigated to correlate mass volume, intracranial pressure, and neurological dysfunction in mass-induced intracranial hypertension in cats. As the intracranial pressure was raised by expansion of a supratentorial balloon, the late components of the SER's were suppressed first, followed by the early components of the SER's, then Wave V and Wave IV of the BER's, in that order. This suggests that the nonspecific reticular projections are most vulnerable to compression ischemia, and the specific somatosensory pathways are the next most vulnerable. Neural activity of the auditory pathways in the upper brain stem was also gradually suppressed, but less so than that of the somatosensory pathways. After complete transtentorial herniation, in spite of immediate mass evacuation, the function of the somatosensory pathways was greatly impaired, often irreversibly. The neural activity of the auditory pathways in the upper brain stem revealed progressive recovery during a 3-hour period. The measurements of BER Wave V is thought to be useful in predicting transtentorial herniation.