AN INTEGRITY TEST BATTERY FOR THE NUCLEUS MINI-22 COCHLEAR IMPLANT SYSTEM

The probability of system failures increases as the number of cochlear implants increases throughout the world. Whether a malfunction is a t echnical or physiological problem remains to be defined, particularly in very young children, while a psychogenic hearing disorder after imp lantation must not be excluded in adults. The battery of objective mea surements used clinically at the Medizinische Hochschule, Hannover has provided useful diagnostic information for distinguishing possible ca uses of failure. In a normally functioning device, an electrical signa l equivalent to the biphasic rectangular stimulation pulse can be reco rded by measuring skin potentials from surface electrodes placed on th e mastoid of the implant side and the forehead. The signal from the st imulated implanted electrodes is derived by applying a constant pulse rate. Signal averaging is not necessary. If no signals are observed, a non-functioning device should be suspected. If the device works norma lly, function of the auditory pathways can be examined by recording th e electrically elicited stapedius reflex or electrically evoked brain- stem responses. In our experience with more than 450 cochlear implant patients, eight internal device failures occurred, while an additional three patients had either reduced or no hearing sensations due to a d isorder of the auditory pathways.