Current distribution of distributed all-polar cochlear implant stimulation mode measured in-situ

Abstract

Oticon Medical cochlear implants use a stimulation mode called Distributed All-Polar (DAP) that connects all non-stimulating available intracochlear electrodes and an extracochlear reference electrode. It results in a complex distribution of current that is yet undescribed. The present study aims at providing a first characterization of this current distribution. A Neuro Zti was modified to allow the measurement of current returning to each electrode during a DAP stimulation and was implanted in an ex-vivo human head. Maps of distributed current were then created for different stimulation conditions with different charge levels. Results show that, on average, about 20% of current returns to the extracochlear reference electrode, while the remaining 80% is distributed between intracochlear electrodes. The position of the stimulating electrode changed this ratio, and about 10% more current to the extracochlear return in case of the first 3 basal electrodes than for apical and mid position electrodes was observed. Increasing the charge level led to small but significant change in the ratio, and about 4% more current to the extracochlear return was measured when increasing the charge level from 11.7 to 70 nC. Further research is needed to show if DAP yields better speech understanding than other stimulation modes.

Electrical Field Interactions during Adjacent Electrode Stimulations: eABR Evaluation in Cochlear Implant Users

“…The derived eABR IS was based on recordings from stimulation on single electrodes, therefore neural channel interaction was not present in the corresponding results. In line with earlier studies, e.g., [ 32 , 33 , 34 ], eABR wave V amplitudes to increasing stimulation intensity on the middle electrode increased, hence the wave V amplitude in IS also increased. Regarding the latency of wave V, previous studies have reported both an increase [ 35 ] and decrease [ 36 ] with increasing the stimulus pulse duration.…”

Cochlear Implant Stimulation Parameters Play a Key Role in Reducing Facial Nerve Stimulation

“…Note: We improved the software between S1 and S2 to allow current coding. 2 Distributed-all-polar (DAP) [7] indicates that current returns via the case electrode, like MP (monopolar) grounding, and simultaneously to all non-stimulating intra-cochlear electrodes, sometimes called 'common ground' (CG) (Figure 1).…”

“…Subject S2 used d coding for stimuli B−/B+ (current = 0.4 mA) and current coding for stimuli A+/A− (duration Note: We improved the software between S1 and S2 to allow current coding. 2 Distributed-(DAP) [7] indicates that current returns via the case electrode, like MP (monopolar) ground simultaneously to all non-stimulating intra-cochlear electrodes, sometimes called 'common (CG) (Figure 1). In each trial, we gradually increased the stimulation charge (i.e., pulse duration or amplitude) until either (1) the sound was too loud or (2) non-auditory sensations became too intense for the subject.…”

“…6 Observed nystagmus (involuntary eyes moving), a vestibular effect. 7 The subject reported deterioration of sound quality. 8 Unpleasant non-auditory sensations.…”

“…While surgical adjustments such as varying array geometries and positioning may play a role, there are also distinct implant-related attributes to consider. These include the unique stimulation parameters used by OM devices, such as anodic leading pulses, passive capacitive charge return, and their unconventional distributed all-polar (DAP) grounding scheme [7]. Both elements are distinct from other CI systems.…”