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Triphasic Pulses Reduce Facial Nerve Stimulation in CI Users: Intra- and Postoperative Electromyographic Data
18 April 2018 (online)
Facial nerve stimulation (FNS) can be observed in cochlear implant (CI) users as an undesirable side effect. Triphasic pulses were shown to reduce FNS, but no objective measure quantified their clinical benefit. This study presents electromyographic (EMG) data collected intra- and postoperatively in CI users.
Postoperative EMG recordings were conducted in awake CI users (n = 4). Adhesive electrodes were attached at orbicularis oris and oculi muscles. Stimuli were 1-ms pulse trains at 100 pps with pulse duration of 100µs. They had either symmetric cathodic-leading biphasic or triphasic pulse shape. Intraoperative EMG recordings were conducted in subjects under general anesthesia after receiving a CI (n = 5). Subdermal electrodes were attached to the aforementioned muscles. Stimuli were 1-ms pulse trains at 100 pps with pulse duration of 150µs. They had symmetric biphasic or triphasic pulse shape with different polarities.
Postoperative EMG data showed high variability between subjects, but individual input-output (IO) functions showed relatively smaller current levels for triphasic pulses to elicit FNS equivalent to biphasic pulses as reflected by EMG amplitudes, i.e. the IO function of biphasic pulses was steeper than that of triphasic pulses. Intraoperative EMG data confirmed this finding. Furthermore, a polarity-dependent effect was found where observed differences were diminished for anodic- compared with cathodic-leading stimulation.
Triphasic pulses can effectively reduce FNS in CI users due to smaller gradient of EMG IO function compared with biphasic pulse stimulation. This could possibly be explained by differences in spatiotemporal spread of the electrical field, which needs to be investigated in future studies.