Comparison of the auditory-evoked brainstem response wave I to distortion-product otoacoustic emissions resulting from changes to inner ear blood flow

Objective/Hypothesis: Examine and compare in detail the time courses of the auditory brainstem response (ABR) wave I amplitude and latency to the dist ortion-product otoacoustic emission (DPOAE) amplitude and phase measured in the rabbit model following deliberate obstruction of cochlear blood flow ( CBF). Methods: Using a posterior fossa craniotomy in five rabbits, the inte rnal auditory artery (IAA) was compressed with a probe. ABR and otoacoustic emission were continuously monitored before, during, and after the compres sions. Results: ABR wave I amplitudes demonstrated measurable decreases at a mean of 28.3 a after IAA compression, whereas DPOAE amplitudes decreased after a mean of 14.8 s, Wave I latencies began to increase at a mean of 18. 3 s after occlusion, while DPOAE phase measures changed after a mean of onl y 4.8 a following IAA compression. The time-course patterns were similar fo r the amplitudes of both ABR wave I and DPOAE, Conclusions: ABR wave I ampl itude follows a similar, though delayed (by approximately 10 s) time-course pattern to that of the DPOAE following IAA compression. The implication of these findings for intraoperative auditory monitoring is that changes in m any currently employed measures will lag actual surgically induced alterati ons in CBF by at least 20 to 30 s.