The Impact of a Cochlear Implant Electrode Array on the Middle Ear Transfer Function.

OBJECTIVES: As a treatment for partial deafness with residual hearing in the lower frequency range, the combined acoustic and electric stimulation of the cochlea has become widespread. Acoustic stimulation is provided by a hearing aid's airborne sound and the electric stimulation by a cochlear implant electrode array, which may be inserted through the round window or a cochleostomy. To take advantage of that concept, it is essential to preserve residual hearing after surgery. Therefore, the intracochlear electrode array should not compromise the middle ear vibration transmission. This study investigates the influence of different electrode types and insertion paths on the middle ear transfer function and the inner ear fluid dynamics. DESIGN: Sound-induced oval and round window net volume velocities were calculated from vibration measurements with laser vibrometers on six nonfixated human temporal bones. After baseline measurements in the "natural" condition, a cochleostomy was drilled and closed with connective tissue. Then, four different electrode arrays were inserted through the cochleostomy. Afterwards, they were inserted through the round window while the cochleostomy was patched again with connective tissue. RESULTS: After having drilled a cochleostomy and electrode insertion, no systematic trends in the changes of oval and round window volume velocities were observed. Nearly all changes of middle ear transfer functions, as well as oval and round window volume velocity ratios, were statistically insignificant. CONCLUSIONS: Intracochlear electrode arrays do not significantly increase cochlear input impedance immediately after insertion. Any changes that may occur seem to be independent of electrode array type and insertion path.

Performance of the round window soft coupler for the backward stimulation of the cochlea in a temporal bone model.

The round window vibroplasty is a feasible option for the treatment of conductive, sensorineural and mixed hearing loss. Although clinical data suggest a satisfying clinical outcome with various coupling methods, the most efficient coupling technique of the floating mass transducer to the round window is still a matter of debate. For this, a soft silicone-made coupler has been developed recently that aims to ease and optimize the stimulation of the round window membrane of this middle ear implant. We performed a temporal bone study evaluating the performance of the soft coupler compared to the coupling with individually shaped cartilage, perichondrium and the titanium round window coupler with loads up to 20 mN at the unaltered and fully exposed round window niche. The stimulation of the cochlea was measured by the volume velocities of the stapes footplate detected by a laser Doppler vibrometer. The coupling method was computed as significant factor with cartilage and perichondrium allowing for the highest volume velocities followed by the soft and titanium coupler. Exposure of the round window niche allowed for higher volume velocities while the applied load did not significantly affect the results. The soft coupler allows for a good contact to the round window membrane and an effective backward stimulation of the cochlea. Clinical data are mandatory to evaluate performance of this novel coupling method in vivo.

Evaluation of a New Material From an Allogenic Collagen Scaffold as a Suitable Coupling Option for Round Window Vibroplasty.

INTRODUCTION: In round window vibroplasty the most efficient coupling technique for contact of the floating mass transducer (FMT) to the round window membrane (RWM) is yet to be determined. Various materials placed between the FMT and the RWM have been proposed to enable better stimulation of the cochlea. Collagenous scaffolds derived from decellularized extracellular cartilage matrices as a commercially available biomaterial are already used for other applications in ear surgery. We aimed to examine the coupling properties of collagen scaffolds compared with commonly used other materials (round window soft coupler, porcine perichondrium, and cartilage) as interponate between the FMT and the RWM in vibroplasty. METHODS: A well-established in vitro temporal bone model was used. Volume velocities were measured with collagen scaffold compared with different interponates (round window soft coupler, porcine perichondrium, and cartilage) at 800, 1000, 1250, 1600, 2000, 2500, 3150, and 4000 Hz levels. RESULTS: Statistical analysis revealed no superiority of commonly used materials compared with collagen scaffolds at all tested volume velocities (p > 0.05). DISCUSSION: We could demonstrate that collagenous scaffolds of decellularized extracellular cartilage matrices have similar vibrational properties as conventional coupling materials of the FMT to the RWM in vibroplasty. Therefore, as a commercially available new material they display a suitable coupling option for round window vibroplasty.

Nitinol in Passive Ossicular Reconstruction-First Results From Temporal Bone Experiments.

HYPOTHESIS: Nitinol is a suitable material for passive middle ear prosthesis. BACKGROUND: In modern ear microsurgery, the restitution of hearing is tremendously important. In passive ossicular reconstruction, rigid alloplastic materials are widespread in use. However, rigid prostheses fail to adapt to atmospheric pressure changes. We describe the use of the super-elastic material nitinol in passive ossicular reconstruction to overcome this limitation. METHODS: Together with an industrial partner, we developed a nitinol clip prosthesis equipped with a flexible prosthesis headplate. The new prosthesis was evaluated for flexibility and its sound transmission properties were compared with standard clip prostheses. For this purpose, the sound-induced acceleration of the stapes footplate was measured by laser-doppler vibrometry in temporal bones. Furthermore, the flexibility of the prosthesis plate was tested in a load-cell experiment. RESULTS: On average, the pure tone transmission characteristics of the nitinol prosthesis is statistically not distinguishable from standard titanium clip prostheses. The tests in the load cell confirmed the flexibility of the prosthesis. Any measured prosthesis returns to its original state after deformation. CONCLUSION: The newly developed nitinol clip prosthesis shows similar sound transmission properties in comparison to established prostheses with high flexibility indicating a step forward to a physiological ossicular chain reconstruction.

Evaluation of Coupling Efficiency in Round Window Vibroplasty With a New Handheld Probe.

HYPOTHESIS: A handheld measuring probe was developed that analyzes the vibration characteristics of the stapes footplate after backward stimulation of the cochlea in round window vibroplasty. In temporal bone experiments, the measuring accuracy of the probe was tested. BACKGROUND: In round window vibroplasty, the effectiveness of the transmitted vibrations into the inner ear is provided with limited visual and tactile information. Currently, there is no objective measuring tool available. METHODS: In five unfixed temporal bones, a floating mass transducer was coupled to the round window membrane. During the excitation with different voltage levels (0, 5, 25, 100, 300 mV root mean square) corresponding to 0, 80, 94, 106, and 116 dB equivalent ear canal sound pressure respectively, the deflections of the footplate were recorded in parallel by laser Doppler vibrometry and the measuring probe. RESULTS: The probe allowed for differentiation of the coupling efficiency. The measured footplate vibrations from the excitation levels of 106 dB (and 116 dB) were statistically significant compared with the testing without excitation. The footplate deflections determined in parallel by laser Doppler vibrometry showed comparable results. CONCLUSION: In principal, the newly developed measuring probe allows for measuring the quality of retrograde cochlear excitation in a round window vibroplasty by detecting footplate vibrations. Further developments are directed for its application in clinical, intraoperative procedures.

Acoustic effects of the reconstructed lateral epitympanic wall in a temporal bone and clinical study.

OBJECTIVE: Acoustic evaluation of reconstruction of the lateral epitympanic wall with bone or cartilage in a temporal bone study, and evaluation of audiometric data of patients who underwent cholesteatoma surgery with reconstruction of the lateral epitympanic wall with horseshoe-shaped cartilage. STUDY DESIGN: Temporal bone study and retrospective chart review. METHODS: Preparation of temporal bones included reconstruction of the epitympanic wall with fixated and loose cartilage and bone. The volume velocities of the stapes footplate were measured from the inner-ear side of the footplate by laser scanning doppler vibrometry following sound stimulation in the outer ear canal. Additionally, the audiometric data of 13 consecutive patients who underwent epitympanic cholesteatoma surgery, with an intact ossicular chain and reconstruction of the scutum with a horseshoe-shaped cartilage in contact with the malleus' neck, were evaluated retrospectively. RESULTS: The experimental results showed similar volume velocities at the stapes footplate for the fixated and unfixated cartilage as well as for the unfixated bone. However, the fixated bone yielded significantly reduced volume velocities. Clinical data confirmed that the cartilaginous horseshoe- technique allowed for a stable reconstruction of the scutum with satisfying audiometric outcome. CONCLUSION: In case of cholesteatoma surgery and the need for the reconstruction of the scutum, no adverse effects on hearing outcome are to be expected by using the malleus' neck as an anchoring point for cartilaginous scutum reconstruction. LEVEL OF EVIDENCE: NA. Laryngoscope, 127:1427-1434, 2017.

Loads and Coupling Modalities Influence the Performance of the Floating Mass Transducer as a Round Window Driver.

HYPOTHESIS: High loads forcing the floating mass transducer (FMT) of a single active middle ear implant toward the round window membrane (RWM) affect the backward stimulation of the cochlea. BACKGROUND: Various factors influence the backward stimulation of the cochlea. We investigated the effects of various loads applied to the FMT together with different coupling techniques at the fully exposed RWM on the vibration transmission. METHODS: Experimental study on temporal bones with the FMT linked to a load cell mounted on a translation stage moving it against the fully exposed RWM with increasing loads up to 200 mN by itself, with interposed perichondrium, cartilage or connected to the round window coupler. Cochlear stimulation is measured by the volume velocities of the stapes footplate using LASER-Doppler-vibrometry. RESULTS: Loads ranging from 5 to 20 mN induce the highest volume velocities of the stapes footplate. Increasing loads decrease the transmission of vibration in the low-frequency range but enhance the transmission of high frequencies. The interposition of perichondrium and cartilage proved to be advantageous. CONCLUSION: The load applied to the FMT distinctly affects the backward stimulation of the cochlea. Although increasing loads have inverse effects on the transmission of low and high frequencies, high loads lead to an overall decrease of cochlear stimulation. Out of the applied coupling techniques interposed perichondrium and cartilage allow for the most efficient stimulation.

Acoustic Properties of Collagenous Matrices of Xenogenic Origin for Tympanic Membrane Reconstruction.

HYPOTHESIS: The acoustic properties of scaffolds made from decellularized extracellular cartilage matrices of porcine origin are comparable to those of the human tympanic membrane. BACKGROUND: Currently, the reconstruction of tympanic membrane in the context of chronic tympanic membrane defects is mostly performed using autologous fascia or cartilage. Autologous tissue may be associated with lack of graft material in revision patients and requires more invasive and longer operative time. Therefore, other materials are investigated for reconstruction. An increasingly important role could be played by scaffolds from different materials, which are known to induce constructive tissue remodeling. METHODS: To analyze the acoustic properties, the vibrations of the scaffolds, cartilage, perichondrium and tympanic membrane were measured by laser scanning doppler vibrometry under different static pressures. RESULTS: The analysis of volume velocities serves as an indicator for sound transmission. The results of the average volume velocities at atmospheric pressure show a similar frequency response of the tympanic membrane and the scaffolds with a peak at about 800 Hz. After changing the artificial ear-canal pressure from atmospheric pressure to negative pressure (-100, -200, and -300 daPa) the vibration characteristics of the different membranes remain fairly constant, whereas the results of the perichondrium show a decrease after changing the pressure into the negative range in the frequencies 1 to 3 kHz. CONCLUSION: The present study showed that the vibration characteristics of the scaffolds under atmospheric and negative pressure can be interpreted as similar to those of thin cartilage (<0.5 mm) and human tympanic membranes. However, in relation to the behavior of these scaffolds made from decellularized extracellular cartilage matrices in vivo, further investigations should be carried out.

Impact of coupling techniques of an active middle ear device to the round window membrane for the backward stimulation of the cochlea.

HYPOTHESIS: Interposed cartilage and the round window coupler (RWC) increase the efficiency of cochlea stimulation with the floating mass transducer (FMT) of a single active middle ear implant (AMEI) placed against the round window membrane. BACKGROUND: Treatment of mixed and conductive hearing loss with an AMEI attached to the round window is effective, yet the best placement technique of its FMT for the most efficient stimulation of the cochlea remains to be determined. METHODS: Experimental study on human temporal bones with the FMT placed against firstly the unaltered round window niche and then subsequently against the fully exposed round window membrane with and without interposed cartilage and the RWC. Cochlea stimulation is measured by the volume velocities of the stapes footplate using LASER vibrometry. RESULTS: At the undrilled round window niche, placement of the FMT by itself and with the RWC resulted in similar volume velocities. The response was significantly raised by interposing cartilage into the undrilled round window niche. Complete exposure of the round window membrane allowed for significantly increased volume velocities. Among these, coupling of the FMT with interposed cartilage yielded responses of similar magnitude compared with the RWC but significantly higher compared with the FMT by itself. CONCLUSION: Good contact to the round window membrane is essential for efficient stimulation of the cochlea. Therefore, interposing cartilage into the undrilled round window niche is a viable option. At the drilled round window membrane, the FMT with interposed cartilage and attached to the RWC are similarly effective.

Laser Eustachian tuboplasty: efficiency evaluation in the pressure chamber.

OBJECTIVE: Laser Eustachian tuboplasty (LETP) with ablation of the epipharyngeal orifice of the Eustachian tube (ET) shows good results in clinical observation. However, to this day, there are no reports evaluating the surgical procedure with valid test methods. The purpose of this study was to test the effect of minimally invasive LETP by means of a pressure chamber ET function test. STUDY DESIGN: Prospective surgical trial. SETTING: Tertiary and university hospital. PATIENTS: Thirty patients with a history of ET dysfunction during pressure changes were examined. INTERVENTION: Minimally invasive LETP was performed with an 812-nm diode laser under local anesthesia as an outpatient procedure. MAIN OUTCOME MEASURE: The ET function was tested preoperatively and postoperatively by pressure chamber ET function test. Eustachian tube closing pressure (ETCP) was evaluated as a measure of the tissue pressure of the ET. In cases of a severely impaired ET function, a "blocked" pattern was evident, and no measurement of ETCP was possible. RESULTS: Before minimally invasive LETP, 17 patients showed a completely blocked pattern. Postoperatively, 13 patients of this group showed an improved ET function with a restored normal opening pattern (p < 0.001). The ETCP was reduced from 6.24 ± 3.46 mbar preoperatively to 4.06 ± 2.36 mbar postoperatively (p < 0.013). CONCLUSION: The results strongly indicate that the effect of minimally invasive LETP can be proven by measuring the ET function in a pressure chamber. Results must be interpreted in combination with clinical methods like Valsalva maneuver and tympanometry. Patients with ET dysfunction during pressure changes seem to benefit from the minimally invasive LETP.