Chronic Electrical Stimulation of the Otolith Organ: Preliminary Results in Humans with Bilateral Vestibulopathy and Sensorineural Hearing Loss

Stimulation Crosstalk Between Cochlear And Vestibular Spaces During Cochlear Electrical Stimulation

OBJECTIVES

Possible beneficial "crosstalk" during cochlear implant stimulation on otolith end organs has been hypothesized. The aim of this case-control study is to analyze the effect of electrical cochlear stimulation on the vestibule (otolith end-organ), when using a cochleo-vestibular implant, comparing vestibular stimulation (VI) and cochlear stimulation (CI).

METHODS

Four patients with bilateral vestibulopathy were included. A double electrode array research implant was implanted in all cases. Dynamic Gait Index (DGI), VOR gain measured by using vestibular head impulse test (vHIT), acoustic cervical myogenic responses (cVEMP) recordings, and electrical cVEMP were used in all cases. Trans-impedance Matrix (TIM) analysis was used to evaluate the current flow from the cochlea to the vestibule.

RESULTS

While patients did not have any clinical vestibular improvement with the CI stimulation alone, gait metrics of the patients revealed improvement when the vestibular electrode was stimulated. The average improvement in the DGI was 38% when the vestibular implant was activated, returning to the normal range in all cases. Our findings suggest that any current flow from the cochlear space to the otolith organs was insufficient for effective cross-stimulation. The functional results correlated with the data obtained in TIM analysis, confirming that there is no current flow from the cochlea to the vestibule.

CONCLUSION

The only way to produce effective electrical otolith end-organ stimulation, demonstrated with this research implant, is by direct electrical stimulation of the otolith end organs. No effective cross-stimulation was found from cochlear electrode stimulation.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:2349-2355, 2024.

[Rehabilitation in bilateral vestibulopathy: trends and perspectives]

A review of the literature on rehabilitation methods for bilateral vestibulopathy is presented using RSCI, Scopus and PubMed databases. The principles and effectiveness of physical vestibular rehabilitation, vestibular implants, galvanic vestibular stimulation, and biofeedback-based sensory substitution and augmentation systems are described. The advantages and disadvantages of each method and perspectives for their improvement are presented.

Triple Semicircular Canal Plugging versus Labyrinthectomy for Meniere Disease: A Retrospective Study

OBJECTIVES

The study goals were to compare the long-term efficacy of semicircular canal plugging (SCP) with labyrinthectomy in the treatment of advanced Meniere's disease (MD).

STUDY DESIGN

A retrospective study.

SETTING

Single tertiary medical center.

METHODS

A total of 116 MD patients (TSCP group of 90; labyrinthectomy group of 26) with complete medical documents in Shandong Provincial ENT Hospital, from March 2017 to March 2019 were retrospectively analyzed, including a battery of auditory and vestibular function tests, recovery time from imbalance and function level scores (FLS).

RESULTS

The total control rate of vertigo in the TSCP group was 96.7% (87/90). The rate of hearing loss was 23.3% (21/90). The control rate of vertigo in the labyrinthectomy group was 100% (26/26). All patients lost their auditory function after labyrinthectomy with a 100% hearing loss rate. There was no significant difference in the vertigo control rate between the two groups (P > 0.05). The hearing loss rate in the TSCP group was significantly lower than that in the labyrinthectomy group (P < 0.00). The median time recovered from imbalance was 15 days in TSCP group and 21 days in labyrinthectomy group, which is significantly different (P < 0.05). There was no significant difference in the FLS between the two groups (P > 0.05).

CONCLUSIONS

Compared to labyrinthectomy, TSCP can preserve hearing at a high probability; meanwhile, otolith organ function preservation benefits patients from faster vestibular compensation.

LEVEL OF EVIDENCE

3 Laryngoscope, 133:3178-3184, 2023.

The Next Challenges of Vestibular Implantation in Humans

Patients with bilateral vestibulopathy suffer from a variety of complaints, leading to a high individual and social burden. Available treatments aim to alleviate the impact of this loss and improve compensatory strategies. Early experiments with electrical stimulation of the vestibular nerve in combination with knowledge gained by cochlear implant research, have inspired the development of a vestibular neuroprosthesis that can provide the missing vestibular input. The feasibility of this concept was first demonstrated in animals and later in humans. Currently, several research groups around the world are investigating prototype vestibular implants, in the form of vestibular implants as well as combined cochlear and vestibular implants. The aim of this review is to convey the presentations and discussions from the identically named symposium that was held during the 2021 MidWinter Meeting of the Association for Research in Otolaryngology, with researchers involved in the development of vestibular implants targeting the ampullary nerves. Substantial advancements in the development have been made. Yet, research and development processes face several challenges to improve this neuroprosthesis. These include, but are not limited to, optimization of the electrical stimulation profile, refining the surgical implantation procedure, preserving residual labyrinthine functions including hearing, as well as gaining regulatory approval and establishing a clinical care infrastructure similar to what exists for cochlear implants. It is believed by the authors that overcoming these challenges will accelerate the development and increase the impact of a clinically applicable vestibular implant.

Vestibular prosthesis: from basic research to clinics

Balance disorders are highly prevalent worldwide, causing substantial disability with high personal and socioeconomic impact. The prognosis in many of these patients is poor, and rehabilitation programs provide little help in many cases. This medical problem can be addressed using microelectronics by combining the highly successful cochlear implant experience to produce a vestibular prosthesis, using the technical advances in micro gyroscopes and micro accelerometers, which are the electronic equivalents of the semicircular canals (SCC) and the otolithic organs. Reaching this technological milestone fostered the possibility of using these electronic devices to substitute the vestibular function, mainly for visual stability and posture, in case of damage to the vestibular endorgans. The development of implantable and non-implantable devices showed diverse outcomes when considering the integrity of the vestibular pathways, the device parameters (current intensity, impedance, and waveform), and the targeted physiological function (balance and gaze). In this review, we will examine the development and testing of various prototypes of the vestibular implant (VI). The insight raised by examining the state-of-the-art vestibular prosthesis will facilitate the development of new device-development strategies and discuss the feasibility of complex combinations of implantable devices for disorders that directly affect balance and motor performance.

Dynamic Visual Acuity Results in Otolith Electrical Stimulation in Bilateral Vestibular Dysfunction

(1) Background. Patients with bilateral vestibular disease (BVD) experience oscillopsia with a detriment to visual acuity (VA). This VA is driven mainly by the VOR that has two components: rotational and translational. VA can be tested by using dynamic visual acuity (DVA) on a treadmill because both systems are activated. The aim of this study is to compare VA before and after chronic electrical stimulation of the otolith organ. (2) Materials and Method. Five patients suffering from bilateral vestibular dysfunction (BVD), previously implanted with a new vestibular implant prototype, were included in this study with the aim to check VA with and without vestibular implant use (W and W/O) in static, 2 km/h and 4 km/h walking situations. DVAtreadmill was measured on a treadmill with a dynamic illegible E (DIE) test in static and dynamic conditions (while walking on the treadmill at 2 and 4 km/h). The DVA score was registered in a logarithm of the minimum angle of resolution (LogMAR) for each speed. In addition, every patient completed the oscillopsia severity questionnaire (OSQ) and video head impulse test (vHIT) before and after activation of the vestibular implant. (3) Results. The analysis shows a significant difference in OSQ scores and DVA with an improvement in dynamic conditions. Organized corrective saccades during the use of a vestibular implant with no changes in gain were also detected in the video head impulse tests (vHIT). (4) Conclusion. The vestibular implant with otolithic stimulation offers changes in the response of DVA, which makes this paper one of the first to address the possible restoration of it. It is not possible to rule out other contributing factors (presence of covert saccades, somatosensory system, …). More work seems necessary to understand the neurophysiological basis of these findings, but this implant is added as a therapeutic alternative for the improvement of oscillopsia.

IGST Combined with Conventional Drug Therapy and TCM Therapy for Treatment of Bilateral Vestibular Hypofunction

Objective

To investigate the effects of intensive gaze stability training (IGST) combined with conventional drug therapy and traditional Chinese medicine (TCM) therapy on hearing recovery and quality of life (QOL) in patients with bilateral vestibular dysfunction.

Materials and Methods

A total of 120 patients with bilateral vestibular dysfunction admitted to our hospital from January 2019 to January 2020 were recruited and assigned to group A (n = 60) and group B (n = 60) based on the order of admission. Group B received conventional medication and TCM therapy, and group A received IGST plus conventional medication and TCM therapy. The serum biochemical indexes, blood rheology indexes, symptoms disappearance time, hearing recovery time, pure-tone hearing threshold, vestibular symptom index (VSI), and QOL of the two groups were compared.

Results

The serum biochemical indexes and blood rheology indexes in group A were lower than those in group B after treatment (P < 0.001). Patients in group A had a shorter time lapse before symptoms disappearance and hearing recovery than those in group B (P < 0.001). Group A had lower results of the pure-tone hearing threshold (P < 0.001) and of VSI (P < 0.05) than group B. Patients in group A had higher QOL scores than those in group B after treatment (P < 0.001).

Conclusion

IGST plus conventional drug therapy effectively improves the serum biochemical indexes and blood rheological indexes of patients with bilateral vestibular hypofunction, accelerates their hearing recovery process, and alleviates their clinical symptoms, thereby improving their QOL, which shows good potential in clinical application.

Why Should Constant Stimulation of Saccular Afferents Modify the Posture and Gait of Patients with Bilateral Vestibular Dysfunction? The Saccular Substitution Hypothesis

An ongoing EU Horizon 2020 Project called BionicVEST is investigating the effect of constant electrical stimulation (ES) of the inferior vestibular nerve in patients with bilateral vestibular dysfunction (BVD). The evidence is that constant ES results in improved postural stability and gait performance, and so the question of central importance concerns how constant ES of mainly saccular afferents in these BVD patients could cause this improved performance. We suggest that the constant ES substitutes for the absent saccular neural input to the vestibular nuclei and the cerebellum in these BVD patients and indirectly via these structures to other structures, which have been of great recent interest in motor control. One target area, the anterior midline cerebellum (the uvula), has recently been targeted as a location for deep-brain stimulation in human patients to improve postural stability and gait. There are projections from midline cerebellum to basal ganglia, including the striatum, which are structures involved in the initiation of gait. It may be that the effect of this activation of peripheral saccular afferent neurons is analogous to the effect of deep-brain stimulation (DBS) by electrodes in basal ganglia acting to help alleviate the symptoms of patients with Parkinson’s disease.

Nonlinearity in bone-conducted amplitude-modulated cervical vestibular evoked myogenic potentials: Harmonic distortion products

Otolith organs of the balance system, the saccule and utricle, encode linear acceleration. Integrity of the saccule is commonly assessed using cervical vestibular evoked myogenic potentials (cVEMPs) arising from an inhibitory reflex along the vestibulospinal pathway. Conventional approaches to eliciting these responses use brief, transient sounds to elicit onset responses. Here we used long-duration amplitude-modulated (AM) tones to elicit cVEMPs (AMcVEMPs) and analyzed their spectral content for evidence of nonlinear processing consistent with known characteristics of vestibular hair cells. Twelve young adults (ages 21-25) with no hearing or vestibular pathologies participated in this study. AMcVEMPs were elicited by bone-conducted AM tones with a 500 Hz carrier frequency. Eighteen modulation frequencies were used between 7 and 403 Hz. All participants had robust distortion products at harmonics of the modulation frequency. Total harmonic distortion ranged from approximately 10 to 80%. AMcVEMPs contain harmonic distortion products consistent with vestibular hair cell nonlinearities, and this new approach to studying the otolith organs may provide a non-invasive, in vivo method to study nonlinearity of vestibular hair cells in humans.

Effect of hearing aids on body balance function in non-reverberant condition: A posturographic study

Objective

The purpose of this study was to evaluate the effect of hearing aids on body balance function in a strictly controlled auditory environment.

Methods

We recorded the findings of 10 experienced hearing aid users and 10 normal-hearing participants. All the participants were assessed using posturography under eight conditions in an acoustically shielded non-reverberant room: (1) eyes open with sound stimuli, with and without foam rubber, (2) eyes closed with sound stimuli, with and without foam rubber, (3) eyes open without sound stimuli, with and without foam rubber, and (4) eyes closed without sound stimuli, with and without foam rubber.

Results

The auditory cue improved the total path area and sway velocity in both the hearing aid users and normal-hearing participants. The analysis of variance showed that the interaction among eye condition, sound condition, and between-group factor was significant in the maximum displacement of the center-of-pressure in the mediolateral axis (F [1, 18] = 6.19, p = 0.02). The maximum displacement of the center-of-pressure in the mediolateral axis improved with the auditory cues in the normal-hearing participants in the eyes closed condition (5.4 cm and 4.7 cm, p < 0.01). In the hearing aid users, this difference was not significant (5.9 cm and 5.7 cm, p = 0.45). The maximum displacement of the center-of-pressure in the anteroposterior axis improved in both the hearing aid users and the normal-hearing participants.

New Frontiers in Managing the Dizzy Patient

Despite progress in vestibular research in the last 20 years, much remains poorly understood about vestibular pathophysiology and its management. A shared language is a critical first step in understanding vestibular disorders and is under development. Telehealth will continue for patients with dizziness, and ambulatory monitoring of nystagmus will become a diagnostic tool. In the next 2 decades, it is anticipated that vestibular perceptual threshold testing will become common in tertiary centers, imaging with improved spatial resolution will yield better understanding of vestibular pathophysiology, and that vestibular implants will become a part of clinical practice.

3D-reconstructions of Bast's Valve and Membranous Labyrinth: Insights for Vestibular Implantation and Meniere's Disease

HYPOTHESIS/BACKGROUND

Bast's valve is a poorly understood inner ear structure located at the junction between pars superior and inferior in the membranous labyrinth. Anatomically precise three-dimensional reconstructions (3D-reconstructions) of Bast's valve can help illuminate the morphology of the valve, and point toward its role in normal physiology and pathological states such as endolymphatic hydrops. This is of particular relevance to the development of a vestibular implant, a device intended to rehabilitate deficits in the vestibular system.

METHODS

Six postmortem human temporal bones from healthy donors were scanned using a micro-computed tomography (microCT) scanner. The microCT data allowed 3D-reconstructions of the membranous labyrinth, with a particular focus on Bast's valve, vestibule, and cochlear duct.

RESULTS

The microCT images of Bast's valve showed a rigid lip containing a core of soft tissue, opposing the thin membranous wall of the utricle. The maximum recorded length and width of the rigid lip were 440.4 μm and 88 μm, respectively. The 3D-reconstructions illustrated the slit-like opening of Bast's valve into the utricle, the twisting course of the basal turn of the cochlear duct, and the spatial orientation of utricle and saccule with respect to the stapes footplate.

CONCLUSIONS

The present study provided a novel anatomical perspective on the microscopic structure of Bast's valve. The interplay between endolymphatic hydrops and Bast's valve is an ongoing area of research, but defining this anatomy in 3D will play a key role in furthering our understanding of the disease process. Implications for vestibular implantation are explored through the various 3D-reconstructions.

Differences in Vestibular-Evoked Myogenic Potential Responses by Using Cochlear Implant and Otolith Organ Direct Stimulation

Objective: Several studies have demonstrated the possibility to obtain vestibular potentials elicited with electrical stimulation from cochlear and vestibular implants. The objective of this study is to analyze the vestibular-evoked myogenic potentials (VEMPs) obtained from patients implanted with cochlear and vestibulo-cochlear implant. Material and Methods: We compared two groups: in the first group, four cochlear implant (CI) recipients with present acoustic cVEMPs before CI surgery were included. In the second group, three patients with bilaterally absent cVEMPs and bilateral vestibular dysfunction were selected. The latter group received a unilateral cochleo-vestibular implant. We analyze the electrically elicited cVEMPs in all patients after stimulation with cochlear and vestibular electrode array stimulation. Results: We present the results obtained post-operatively in both groups. All patients (100%) with direct electrical vestibular stimulation via the vestibular electrode array had present cVEMPs. The P1 and N1 latencies were 11.33-13.6 ms and 18.3-21 ms, respectively. In CI patients, electrical cVEMPs were present only in one of the four subjects (25%) with cochlear implant ("cross") stimulation, and P1 and N1 latencies were 9.67 and 16.33, respectively. In these patients, the responses present shorter latencies than those observed acoustically. Conclusions: Electrically evoked cVEMPs can be present after cochlear and vestibular stimulation and suggest stimulation of vestibular elements, although clinical effect must be further studied.

Vestibular drop attacks in Ménière's disease

The aim of the present study was to evaluate the severity of vestibular drop attack (VDA) in Ménière's disease (MD) and to examine the association between VDA severity and other MD-related complaints. The study used a cross-sectional survey design using an electronic questionnaire. The mean age of participants was 56.7 years, and the mean duration of MD was 12.4 years. Four categories of VDA were identified based on level of severity. VDA occurred in 305 (50.7%) of the 602 patients. Of these, 133 patients (22%) experienced mild VDA (i.e., associated with tripping); 80 (13%) experienced moderate VDA (i.e., associated with fall threat unless they had been able to grab support); and 92 (15%) experienced severe VDA (i.e., patients fell to the ground, as in a classical Tumarkin attack). In 70%of participants, VDA occurred less than once a week. VDA lasted for only a few seconds in 90%of participants. 87%reported single attacks, whereas 13%experienced VDA in clusters. VDA was associated with visual auras, reduced quality of life, poor postural control, and fatigue. Approximately half of MD patients experience VDA with varying degrees of severity. If VDA causes falls or near-falls, the attacks should be appropriately treated.

Minimally important differences for subjective improvement in postural stability in patients with bilateral vestibulopathy

OBJECTIVE

To determine minimally important differences (MIDs) for subjective improvement in postural stability after a therapeutic intervention in patients with bilateral vestibulopathy (BVP).

METHODS

Thirteen BVP patients received noisy galvanic vestibular stimulation (nGVS) for 30 min and their static posture with eyes closed was monitored after the stimuli. The velocity of the center of pressure (COP) movement, the area enclosed by the COP movement, and the root mean square (RMS) of the displacement of the COP were measured for 30 s. Subjective evaluation of postural stability after nGVS was graded as worsened, slightly worsened, unchanged, slightly improved and improved in comparison with postural stability measured without nGVS. Anchor-based methods were used to estimate MIDs for subjective improvement. Velocity, area and RMS for each anchor-response group were averaged (2 sessions, each with 5 measurement periods during 3 h after the stimuli). The mean changes between the slightly improved group and unchanged group were used as estimates for MID for improvement.

RESULTS

A total of 129 anchors were analyzed. Subjective evaluations numbered 83 (64%) for unchanged and 33 (26%) for slightly improved. Anchor-based methods yielded estimates for MIDs of -0.43 cm/s in velocity improvement (p < 0.01), -0.77 cm² for area improvement (p < 0.01) and -0.23 cm for RMS improvement (p < 0.001).

CONCLUSION

The present study provides the estimation of MIDs for improving postural stability in BVP patients and may be useful for interpreting whether the results from clinical trials are meaningful in future studies.

Simultaneous activation of multiple vestibular pathways upon electrical stimulation of semicircular canal afferents

Background and purpose

Vestibular implants seem to be a promising treatment for patients suffering from severe bilateral vestibulopathy. To optimize outcomes, we need to investigate how, and to which extent, the different vestibular pathways are activated. Here we characterized the simultaneous responses to electrical stimuli of three different vestibular pathways.

Methods

Three vestibular implant recipients were included. First, activation thresholds and amplitude growth functions of electrically evoked vestibulo-ocular reflexes (eVOR), cervical myogenic potentials (ecVEMPs) and vestibular percepts (vestibulo-thalamo-cortical, VTC) were recorded upon stimulation with single, biphasic current pulses (200 µs/phase) delivered through five different vestibular electrodes. Latencies of eVOR and ecVEMPs were also characterized. Then we compared the amplitude growth functions of the three pathways using different stimulation profiles (1-pulse, 200 µs/phase; 1-pulse, 50 µs/phase; 4-pulses, 50 µs/phase, 1600 pulses-per-second) in one patient (two electrodes).

Results

The median latencies of the eVOR and ecVEMPs were 8 ms (8–9 ms) and 10.2 ms (9.6–11.8 ms), respectively. While the amplitude of eVOR and ecVEMP responses increased with increasing stimulation current, the VTC pathway showed a different, step-like behavior. In this study, the 200 µs/phase paradigm appeared to give the best balance to enhance responses at lower stimulation currents.

Conclusions

This study is a first attempt to evaluate the simultaneous activation of different vestibular pathways. However, this issue deserves further and more detailed investigation to determine the actual possibility of selective stimulation of a given pathway, as well as the functional impact of the contribution of each pathway to the overall rehabilitation process.

Functional Loss After Meningitis-Evaluation of Vestibular Function in Patients With Postmeningitic Hearing Loss

Introduction: The inner ear vestibular system is essential to balance function. Although hearing loss is well-described and quite common following meningitis, the literature evaluating vestibular function following meningitis is very limited. In particular, information on results of contemporary vestibular function tests, e.g., the video head impulse test (VHIT), is scarce. Using contemporary vestibular function tests, this study examines the vestibular function of patients with profound hearing loss (HL) after meningitis. Methods: Review of the literature and retrospective controlled study. Patients: Twenty-one consecutive patients with profound HL after meningitis (cochlear implant candidates) matched with 20 patients with profound HL of unknown etiology and examined during the period 2013-2018. Outcome Measure: Vestibular function loss, as evaluated with VHIT vestibulo-ocular reflex (VOR) gain, eye movement saccades, and cervical vestibular-evoked myogenic potentials (cVEMPs). The results of these tests were correlated to inner ear imaging findings (MRI/CT) and the level of hearing loss. Results: Mean VHIT gain was 0.48 in the meningitis group compared to 0.86 in the control group (p < 0.01). Saccades were present in 21 ears (62%) in the meningitis group compared to six ears (15%) among the controls (p < 0.01). cVEMP responses were present on five ears (18%) in the meningitis group and 25 ears (66%) in the control group (p < 0.01). Discussion: Postmeningitic hearing loss is associated with poor vestibular function, as evaluated by VHIT, saccades, and cVEMP. Loss of vestibular function correlates with the degree of hearing loss and inner ear imaging findings, although not in all cases. Vestibular function should be examined in patients surviving meningitis with hearing loss in order to individualize rehabilitation and improve balance outcome.

Influence of systematic variations of the stimulation profile on responses evoked with a vestibular implant prototype in humans

OBJECTIVE

To explore the impact of different electrical stimulation profiles in human recipients of the Geneva-Maastricht vestibular implant prototypes.

APPROACH

Four implanted patients were recruited for this study. We investigated the relative efficacy of systematic variations of the electrical stimulus profile (phase duration, pulse rate, baseline level, modulation depth) in evoking vestibulo-ocular (eVOR) and perceptual responses.

MAIN RESULTS

Shorter phase durations and, to a lesser extent, slower pulse rates allowed maximizing the electrical dynamic range available for eliciting a wider range of intensities of vestibular percepts. When either the phase duration or the pulse rate was held constant, current modulation depth was the factor that had the most significant impact on peak velocity of the eVOR.

SIGNIFICANCE

Our results identified important parametric variations that influence the measured responses. Furthermore, we observed that not all vestibular pathways seem equally sensitive to the electrical stimulus when the electrodes are placed in the semicircular canals and monopolar stimulation is used. This opens the door to evaluating new stimulation strategies for a vestibular implant, and suggests the possibility of selectively activating one vestibular pathway or the other in order to optimize rehabilitation outcomes.