Intraoperative measures of electrically evoked auditory nerve compound action potential

A method for recording the electrically evoked whole-nerve action potential (EAP) at the time of cochlear implant surgery is described. Measures of EAP growth with stimulus level and functions describing the rate of recovery of the auditory nerve from the refractory state are reported for patients tested intraoperatively and for a group of patients using the ineraid implant, from whom recordings were made following implantation. Subjects tested intraoperatively were separated into three categories: congenitally deaf children (n = 14), prelingual meningitic children (n = 5), and postingual adults (n = 13). A fourth group consisted of postlingual adults (n = 14) tested postoperatively. Results from all groups showed a similar range of EAP growth and recovery rates across patients. Data from congenitally deaf children formed the exception showing steeper EAP growth functions than other subject groups. Electrically evoked whole-nerve action potential growth and recovery functions of the postoperative group of subjects showed modest correlations to speech perception scores measured after at least 18 months of implant use. The possible use of these measures in fitting an implant to an individual is discussed.