[Observation on the change of electrode impedance and THR/MCL values in 20 cases with Med-EL Combi 40+ cochlear...

To investigate the changes of electrode impedance, THR/MCL values, and dynamic range (DR) in Combi 40+ cochlear implant after implantation.

A respective study was carried out collecting 20 consecutively implanted children's electrode impedances, THR/MCL values, and DR at seven time point during the first three years after implantation. Their variation and correlations were analyzed.

Overall, electrode impedances were lowest during the operation, and significantly rise to the highest at the first stimulation, then followed by a gradual decrease. After three months, electrode impedance of apical and medial cochlear segment were basically stable, while that of the basal segment was gradually increased. Dynamic range (DR) of apical and medial group electrode increased early after the operation and showed a stabilization from the second year, whereas that of basal group have a downward trend since the first year. However, the electric charge of each group increased significantly after three months, and then become stable after first year. Otherwise, a stronger negative rectilinear correlation was found between impedance changes with DR than with THR/MCL level.

The electrode impedances vary clue to different electrode position. Measuring the electrode impedance can effectively evaluate the working status of Combi C40+ cochlear implant. The dynamic range of the electrode was negatively correlated with the impedances, which made it possible to predict the width of the dynamic range by measuring the impedance 3 or 6 months after operation.