Investigating the Spread of Excitation in MED-EL Cochlear Implant Subjects after Stimulation with Triphasic Pulses

Background:

Facial nerve stimulation (FNS) is an undesirable side effect of the electrical stimulation in 6.5 % of cochlea implant (CI) patients. Its symptoms range from awareness to facial spasm and conventional preventive measures can limit the patient’s hearing performance. The results of recent studies show that a strong FNS reducing effect is achieved when stimulating with triphasic pulses (TP) instead of biphasic pulses (BP). It has been hypothesized that this effect results from short-term temporal effects of TP that may focus the current spread in the cochlea or adjacent structures.

Objective:

The overlap of neuron populations elicited by single stimulation electrodes can be estimated using the spread of excitation (SOE) method, which consists of evoked compound action potentials (ECAP) measurements in a masker/probe paradigm. To gain more information about the spatial effects of TP, SOE profiles after stimulation with BP and TP need to be compared.

Methods:

A test setup based on the research interface box (MED-EL, Innsbruck) was developed, which features the application of TP in SOE tasks. The corresponding graphical user interface written in MATLAB (The MathWorks, Natick) allows the user to control all parameters of stimulation and data acquisition.

Conclusion:

The practicability of the developed setup was proven in pilot tests with a CI subject and the RIB Detector Box (MED-EL, Innsbruck). SOE profiles stimulated by BP and TP were recorded at three intracochlear electrode positions. Future work will include ten CI subjects and the development of analysis algorithms to evaluate excitation spreads in the cochlea.