Effects of an expanding supratentorial mass on the auditory brain-stem responses in baboons.

This study was carried out to investigate the effects of an expanding supratentorial mass on auditory brain-stem responses (ABRs). A balloon was inserted into the supratentorial epidural space of seven baboons (in two cases, in the right occipital area; in five cases, in the right temporal area). The balloons were inflated at a rate of 0.2 ml/minute to increase intracranial pressure (ICP). ICP (right frontal epidural pressure) and blood pressure (BP) were continuously recorded. Recordings of ABRs (vertex to mastoid on both sides) were made serially. Pupillary changes were also recorded. At 30 mmHg ICP, the amplitude of wave V on the right side was observed to be significantly attenuated (p less than 0.02). At 50 mm Hg ICP, the latency of wave V on the right side was significantly prolonged compared with that at 30 mm Hg ICP (p less than 0.02). At 70 mmHg ICP, significantly decreased amplitude of wave V on the left side was also observed (p less than 0.02, from the control), associated with significant increased latency of wave IV on the right side (p less than 0.01, from the control; p less than 0.05, from 50 mm Hg ICP). Finally, waves IV and V on both sides substantially disappeared at 100 mm Hg ICP. Anisocoria appeared in four animals at 30-50 mm Hg (mean +/- SD; 45 +/- 8.7) ICP. The amplitude of wave V was significantly decreased in these circumstances (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)