Fully implantable hearing device with transducer on the round window as a treatment of mixed hearing loss

doi:10.1016/j.anl.2008.09.003

Auris Nasus Larynx

Volume 36, Issue 3, June 2009, Pages 353-358

https://doi.org/10.1016/j.anl.2008.09.003 Get rights and content

Abstract

Objective

To demonstrate the safety and efficacy of the Otologics Carina Middle Ear Transducer for treatment of mixed hearing loss through a case report.

Methods

A Carina fully implantable device with the MET transducer for conductive applications was implanted in a 48-year-old woman suffering from right mixed hearing loss (mean PTA loss: 80 dB). A facial recess approach was used to access the middle ear. Sclerotic tissue obliterated the stapes footplate so the approach selected was to place the transducer directly on the round window. The mounting bracket was placed on the mastoid and the prosthesis was advanced toward the round window until the Otologics surgical software indicated contact. Effective stimulation of the cochlea was confirmed intraoperatively by ABR monitoring.

Results

Postoperative unaided PTA thresholds were unchanged after surgery. When the implant was activated, the mean PTA functional gain was 39 dB.

Discussion-conclusion

The capability of the Carina MET Ossicular stimulator to provide appropriate gain relative to the degree of hearing loss indicates that the device offers a viable treatment option for mixed hearing loss. However, these promising initial results establish the need for future work on two fronts: (1) further studies are needed including a greater number of patients to confirm these preliminary results; (2) a long term follow-up must be carried out to detect any possible cochlear adverse effects on the cochlea, in particular on the basilar membrane.

Introduction

Conventional hearing aids are subject to many limitations, including occlusion of the ear canal, chronic irritation, acoustic feedback, sound distortion and other limitations [1]. Recently, implantable hearing devices have been developed to overcome some of these problems [1], [2], [3]. The Symphonix Vibrant Soundbridge was the first device to be used routinely, starting in February 1998 in Europe and August 2000 in United Stated [3]. It possesses an external auditory processor which transfers the information to the implant where the vibration is transmitted to the long process of the incus by a vibrating floating mass. The Middle Ear Transducer (MET) from Otologics LLC is also available on the market in EU as a semi implantable device. It is similarly composed of an external part containing the microphone, the battery and the sound processor, and of an internal part implanted in the middle ear whose vibrator is connected to the body of the incus [1], [2]. A new fully implantable hearing device has recently been made available by Otologics [1], [4]: the Otologics Middle Ear Transducer™ (also known commercially as the Carina™ fully implantable system) which is an available treatment for moderate to severe sensorineural hearing loss in adults. This system is registered and approved for sale in EU, and is in FDA clinical trials in the US.

Until recently, the transducers of the various devices have been attached to the various part of the ossicular chain. It has therefore been mandatory to implant a rather normal middle ear with a normally functioning ossicular chain. Recently, Colletti et al. have reported successful sound direct transfer to the inner ear through the round window membrane using the floating mass of the Vibrant Soundbridge [5].

The Otologics device is also indicated for mixed losses, and has been reported in a series of atresia patients [4], [6]. The end of the prosthesis is placed directly on the stapes footplate or directly on the round window if the oval window is completely obliterated by tissue and stapes footplate could not be identified [5]. As described, both the Soundbridge and the Otologics device have the potential to bypass the conductive hearing loss component to deliver vibratory stimulus to the cochlea. The development of these mixed loss applications can therefore offer a therapeutic option to patients whose other options may be limited.

We report the case of a patient with a mixed hearing loss who underwent a novel middle ear implantation surgery in which a vibratory transducer was placed in the round window niche, thus bypassing the damaged ossicular chain.

Section snippets

Case report

A 48-year-old woman suffered from a bilateral hearing loss: the right ear presented a mean PTA (pure tone average of 0.5, 1, 2 and 4 kHz thresholds) loss of 80 dB (Fig. 1) secondary to a cholesteatoma following three surgical procedures; the left ear presented a neurosensory hearing loss with mean PTA loss of 46.6 dB. The left tympanic membrane was normal and on the right tympanic membrane, no recurrence was demonstrated. She had a chronic bilateral irritation of the external ear canal. On the CT

Discussion

In a previous study of 282 patients, the Otologics MET ossicular stimulator was established to be safe and effective in treating moderate to severe sensorineural hearing loss in adults [1]. As demonstrated in the study, implantation of the electromechanical transducer should not result in a change of cochlear status and even if the transducer was attached to the ossicular chain, no change in bone conduction threshold was found [1], [2].

Recently, this application has been extended to patients

Conclusion

The mixed hearing loss described in this case was successfully treated by implantation of the Otologics fully implantable system, with vibratory stimulation direct to the round window. This is a promising new result, given the severity of the mixed loss treated and the fact that the stapes was obliterated by sclerotic tissue. For this patient, the fully implantable system was a suitable choice particularly because of the chronic ear canal irritation. It should be noted, however, that these are

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The abnormal growth of stapes and stapedial annular ligament (SAL) caused by otosclerosis will seal the OW; its effect on reverse stimulation needs to be investigated. Many scholars were devoted to the reverse driving actuators in the past decade [8–14]. A series of experiments was carried out by Arnold et al. [9] to research the factors of improving vibration transmission.
The cochlear windows consist of the round window (RW) and the oval window (OW). These two openings connect the cochlea and the middle ear; its activity plays a vital role in sound transmission into the cochlea. However, it is difficult to capture a brief description of how cochlear windows activity affects reverse stimulation with physiological third windows. In the present study, a hybrid circuit model considering the vestibular and cochlear aqueducts was used to investigate the relationship between cochlear windows activity and reverse stimulation. Meanwhile, a finite element (FE) model of the RW was established to perform stiffness calibration on the RW thickening. Then, middle ear disorders involving the activity of the RW and the OW were simulated: otosclerosis and otitis media. Finally, the intracochlear differential pressure transfer function were calculated to predict the influence of cochlear windows activity on sound perception under reverse stimulation. The results show that the resonant response of the auditory system complicates the effects of cochlear windows activity on reverse sound transmission. Moreover, the physiological third windows produce volume velocity shunt flow, which mitigates the deterioration caused by the reduced cochlear windows activity during reverse stimulation.
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Subsequently, the amplified sounds are transmitted into cochlea by the normal conductive path. Meanwhile, the MEI with a transducer on the RW have got much attention in recent years due to its advantages on treating patients with mixed hearing loss [3]. In most mixed-loss situations, patients often suffer from middle ear diseases such as chronic otitis media, cholesteatoma and otosclerosis.
Acoustic energy can be transmitted into the cochlea by two modes: one mode is the forward stimulation where acoustic waves are normally transmitted from the tympanic membrane (TM) to the cochlea via the ossicular chain, another mode is the reverse stimulation where a transducer is coupled to the round window (RW) and it provides a direct mechanical stimulation to the cochlea via the RW membrane. Due to the difference of the energy transmission pathway, the acoustic waves encounter different impedances and the basilar membrane (BM) vibrates with different forms during the acoustic transmission processes. To understand the dynamic characteristics of human cochlea during forward and reverse stimulations, a finite element model of human ear is developed in this study. And the cochlear input impedance, the cochlear reverse impedance, and the BM displacement responses are derived. The results show that the cochlea input impedance keeps stable in a certain frequency range, while the RW impedance and middle ear impedance vary obviously with frequency. And the middle ear impedance is higher than the cochlear input impedance at lower frequencies. Furthermore, the BM motions in response to two stimulations not only have the phase difference, but also have the efficiency difference. The vibration efficiency of the BM in response to forward stimulation is about 13 dB higher than that to reverse stimulation. But under the impulsive stimulus, the maximum displacement of the BM occurs in the middle cochlea for both of stimulations.
Limits on normal cochlear ‘third’ windows provided by previous investigations of additional sound paths into and out of the cat inner ear
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Though the data suggest window volume displacements can differ by as much as 40% (up to 3 dB), this near equality is used as evidence against the importance of additional cochlear sound pathways. Our interest in investigating the contribution of additional normal sound pathways in the inner ear (besides the OW and RW) comes from recent clinical data by Coletti and others, who use direct mechanical stimulation of the RW as a treatment for conductive hearing loss (Colletti et al., 2006; Beltrame et al., 2009; Tringali et al., 2009). This work suggests that direct RW stimulation can help patients with multiple conductive disorders, including those with immobilized stapes footplates.
While most models of cochlear function assume the presence of only two windows into the mammalian cochlea (the oval and round windows), a position that is generally supported by several lines of data, there is evidence for additional sound paths into and out of the inner ear in normal mammals. In this report we review the existing evidence for and against the ‘two-window’ hypothesis. We then determine how existing data and inner-ear anatomy restrict transmission of sound through these additional sound pathways in cat by utilizing a well-tested model of the cat inner ear, together with anatomical descriptions of the cat cochlear and vestibular aqueducts (potential additional windows to the cochlea). We conclude: (1) The existing data place limits on the size of the cochlear and vestibular aqueducts in cat and are consistent with small volume-velocities through these ducts during ossicular stimulation of the cochlea, (2) the predicted volume velocities produced by aqueducts with diameters half the size of the bony diameters match the functional data within ±10 dB, and (3) these additional volume velocity paths contribute to the inner ear's response to non-acoustic stimulation and conductive pathology.
A tri-coil bellows-type round window transducer with improved frequency characteristics for middle-ear implants
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Thus, frequencies starting from about 100 Hz are important for perceived naturalness of speech (Moore and Tan, 2003). A well-known example of the fixed type driving method is the Carina system developed by Cochlear, Ltd. (Tringali et al., 2009, 2010). This fixed-type system has better output characteristics at low frequencies than the FMT.
A number of methods to drive the round window (RW) using a floating mass transducer (FMT) have been reported. This method has attracted attention because the FMT is relatively easy to implant in the RW niche. However, the use of an FMT to drive the RW has been proven to produce low outputs at frequencies below approximately 1 kHz. In this study, a new tri-coil bellows-type transducer (TCBT), which has excellent low frequency output and is easy to implant, is proposed. To design the frequency characteristics of the TCBT, mechanical and electrical simulations were performed, and then a comparative analysis was conducted between a floating mass type transducer (like the FMT) and a fixed type transducer (like the TCBT). The features of the proposed TCBT are as follows. First, the TCBT's housing is fixed to the RW niche so that it does not vibrate. Second, the internal end of a tiny bellows is connected to a vibrating three-pole permanent magnet located within three field coils. Finally, the rim of the bellows bottom is attached to the end of the housing that hermetically encloses the three field coils. In this design, the only vibrating element is the bellows itself, which efficiently drives the RW membrane. To evaluate the characteristics of this newly developed TCBT, the transducer was installed in the RW niche of temporal bones and the velocity of the stapes was measured using a laser Doppler vibrometer. The experimental results indicate that the TCBT can produce 100, 111, and 129 dB SPL equivalent pressure outputs at below 1 kHz, 1–3 kHz, and above 3 kHz, respectively. Thus, the TCBT with one side coupled to the RW via a bellows will be easy to implant and offer better performance than an FMT.
The measurement of transmission loss and absorption coefficient of the rat and porcine skin: Synthesizing artificial material for an implantable microphone test
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The implantable hearing aids are composed of four parts (microphone, amplifier, transducer, and battery); the microphone is most challenging part to be become fully implantable because of various noises from the human body. This is due to the microphone being inserted into the skin above the ear, which means the effects of ear canal resonance and pinna cannot be used [8,9]. Therefore, performance reduction of the microphone becomes another major issue when developing fully implantable hearing aids.
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Dynamic properties of human round window membrane in auditory frequencies running head: Dynamic properties of round window membrane
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Middle ear diseases such as otitis media usually induce the changes of RWM in thickness and permeability and induce possible sensorineural hearing loss [6–8]. Recently, it has been reported that the vibration transducer of middle ear implantable hearing device has been attached on the RWM to stimulate cochlear fluid for restoring hearing level [9–11]. Beltrame et al. [12] coupled the floating mass transducer (Soundbridge, MED-EL, Austria) onto the RWM and assessed its function for patients with mixed hearing loss associated with otitis media or otosclerosis.
Round window is one of the two openings into cochlea from the middle ear. Mechanical properties of round window membrane (RWM) affect cochlear fluid motion and play an important role in the transmission of sound into cochlea. However, no measurement of mechanical properties of RWM has been reported because of the complication of its location and small size. This paper reports the first investigation on dynamic properties of human RWM using acoustic stimulation and laser Doppler vibrometry measurement. The experiments on RWM specimens were subsequently simulated in finite element (FE) model and an inverse-problem solving method was used to determine the complex modulus in frequency-domain and the relaxation modulus in time-domain. The results show that the average storage modulus of human RWM changes from 2.32 to 3.83 MPa and the average loss modulus from 0.085 to 0.925 MPa over frequencies of 200–8000 Hz. The effects of specimen geometry and experimental condition on complex modulus measurements were discussed through FE modeling analysis. Dynamic properties of RWM reported in this paper provide important data for the study of middle ear and cochlear mechanics.

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Fully implantable hearing device with transducer on the round window as a treatment of mixed hearing loss

Abstract

Objective

Methods

Results

Discussion-conclusion

Introduction

Section snippets

Case report

Discussion

Conclusion

Otolaryngol Clin North Am

Int J Pediatr Otorhinolaryngol

Otolaryngol Clin North Am

Otolaryngol Clin North Am

Otolaryngol Head Neck Surg