Acoustic stimulation of the human round window by laser-induced nonlinear optoacoustics.

The feasibility of low frequency pure tone generation in the inner ear by laser-induced nonlinear optoacoustic effect at the round window was demonstrated in three human cadaveric temporal bones (TB) using an integral pulse density modulation (IPDM). Nanosecond laser pulses with a wavelength in the near-infrared (NIR) region were delivered to the round window niche by an optical fiber with two spherical lenses glued to the end and a viscous gel at the site of the laser focus. Using IPDM, acoustic tones with frequencies between 20 Hz and 1 kHz were generated in the inner ear. The sound pressures in scala tympani and vestibuli were recorded and the intracochlear pressure difference (ICPD) was used to calculate the equivalent sound pressure level (eq. dB SPL) as an equivalent for perceived loudness. The results demonstrate that the optoacoustic effect produced sound pressure levels ranging from 140 eq. dB SPL at low frequencies ≤ 200 Hz to 90 eq. dB SPL at 1 kHz. Therefore, the produced sound pressure level is potentially sufficient for patients requiring acoustic low frequency stimulation. Hence, the presented method offers a potentially viable solution in the future to provide the acoustic stimulus component in combined electro-acoustic stimulation with a cochlear implant.

A Novel Method to Determine the Maximum Output of Individual Patients for an Active Transcutaneous Bone Conduction Implant Using Clinical Routine Data.

OBJECTIVES: The maximum output provided by a bone conduction (BC) device is one of the main factors that determines the success when treating patients with conductive or mixed hearing loss. Different approaches such as sound pressure measurements using a probe microphone in the external auditory canal or a surface microphone on the forehead have been previously introduced to determine the maximum output of active transcutaneous BC devices that are not directly accessible after implantation. Here, we introduce a method to determine the maximum output hearing level (MOHL) of a transcutaneous active BC device using patients' audiometric data. DESIGN: We determined the maximum output in terms of hearing level MOHL (dB HL) of the Bonebridge using the audiometric and direct BC threshold of the patient together with corresponding force levels at hearing threshold and the maximum force output of the device. Seventy-one patients implanted with the Bonebridge between 2011 and 2020 (average age 45 ± 19 years ranging from 5 to 84 years) were included in this study. The analyses of MOHLs were performed by (1) dividing patients into two groups with better or worse average audiometric BC threshold (0.5, 1, 2, 4 kHz), on the ipsilateral side or (2) by separating the MOHLs based on better or worse frequency-by-frequency specific audiometric BC thresholds on the ipsilateral (implanted) side. RESULTS: When using a frequency-by-frequency analysis obtained average ipsilateral MOHLs were in the range between 51 and 73 dB HL for frequencies from 0.5 to 6 kHz in the group with better audiometric BC threshold on the ipsilateral ears. The average contralateral MOHLs in the group with better contralateral hearing were in the range from 43 to 67 dB HL. The variability of the data was approximately 6 to 11 dB (SDs) across measured frequencies (0.5 to 6 kHz). The average MOHLs were 4 to 8 dB higher across frequencies in the group with better audiometric BC threshold on the ipsilateral ears than in the group with better audiometric BC threshold on the contralateral ears. The differences between groups were significant across measured frequencies ( t test; p < 0.05). CONCLUSIONS: Our proposed method demonstrates that the individual frequency-specific MOHL on the ipsilateral and contralateral side of individual patients with a transcutaneous BC device can be determined mainly using direct and audiometric BC threshold data of the patients from clinical routine. The average MOHL of the implant was found 4 to 8 dB higher on the ipsilateral (implanted) side than on the contralateral side.

Output performance of the novel active transcutaneous bone conduction implant Sentio at different stimulation sites.

OBJECTIVES: The output performance of a novel semi-implantable transcutaneous bone conduction device was compared to an established percutaneous bone-anchored hearing system device using cadaver heads. The influence of actuator position, tissue growth below the actuator and mounting it on the surface or in a flattened bone bed on the performance of the implanted actuator was investigated. MATERIALS AND METHODS: The percutaneous and the new transcutaneous device were sequentially implanted at two sites in five human cadaver heads: 55 mm superior-posterior to the ear canal opening (position A) and, closer to the cochlea, about 20 mm inferior-posterior to the ear canal opening behind the pinna on the mastoid (position B). The ipsi- and contralateral cochlear promontory (CP) velocity magnitude responses to percutaneous and transcutaneous stimulation were measured using laser Doppler vibrometry. In addition, the CP vibration of the transcutaneous device placed directly on the skull bone surface was compared with the placement in a flattened bone bed at a depth of about 3 mm. Finally, the influence of placing a thin silicone interposition layer under the implanted transducer was also explored. RESULTS: The percutaneous device provided about an 11 dB higher average CP vibration level than the transcutaneous device at frequencies between 0.5 and 10 kHz. The ipsilateral CP vibration responses with stimulations at position B were on average 13 dB higher compared to stimulation at position A. The placement of the transcutaneous transducer at position B provided similar or higher average vibration magnitudes than the percutaneous transducer at position A. The 3 mm deep flattened bone bed had no significant effects on the output performance. Placing a thin silicone layer under the transcutaneous transducer had no significant influence on the output of the transcutaneous device. CONCLUSIONS: Our results using the CP vibration responses show that at frequencies above 500 Hz the new transcutaneous device at position B provides similar output levels as the percutaneous device at position A. The results also indicated that neither a bone bed for the placement of the transcutaneous transducer nor a simulated tissue growth between the actuator and the bone affect the output performance of the device.

Stimulation efficiency of an actuator driven piston at the biological interface to the inner ear.

Direct acoustic cochlear stimulation uses piston motion to substitute for stapes footplate (SFP) motion. The ratio of piston to stapes footplate motion amplitude, to generate the same loudness percept, is an indicator of stimulation efficiency. We determined the relationship between piston displacement to perceived loudness, the achieved maximum power output and investigated stapes fixation and obliteration as confounding factors. The electro-mechanical transfer function of the actuator was determined preoperatively on the bench and intraoperatively by laser Doppler vibrometry. Clinically, perceived loudness as a function of actuator input voltage was calculated from bone conduction thresholds and direct thresholds via the implant. The displacement of a 0.4 mm diameter piston required for a perception equivalent to 94 dB SPL at the tympanic membrane compared to normal SFP piston displacement was 27.6-35.9 dB larger, consistent with the hypothesis that the ratio between areas is responsible for stimulation efficiency. Actuator output was 110 ± 10 eq dB SPLFF @1Vrms ≤ 3 kHz and decreased to 100 eq dB SPLFF at 10 kHz. Output was significantly higher for mobile SFPs but independent from obliteration. Our findings from clinical data strongly support the assumption of a geometrical dependency on piston diameter at the biological interface to the cochlea.

A Precision Driver Device for Intraoperative Stimulation of a Bone Conduction Implant.

Semi-implantable bone conduction implants (BCI) and active middle ear implants (AMEI) for patients with sensorineural, conductive or mixed hearing loss commonly use an amplitude modulation technology to transmit power and sound signals from an external audio processor to the implant. In patients, the distance dependence of the signal amplitude is of minor importance as the skin thickness is constant and only varies between 3-7 mm. In this range, critical coupling transmission technique sufficiently reduces the variability in amplitude, but fails to provide well-defined amplitudes in many research and clinical applications such as intraoperative integrity tests where the distance range is exceeded by using sterile covers. Here we used the BCI Bonebridge (BB, Med-El, Austria) as an example to develop and demonstrate a system that synthesizes the transmission signal, determines the distance between the transmitter and the receiver implant coil and compensates transmission losses. When compared to an external audio processor (AP304) on an artificial mastoid, our system mainly decreased amplitude variability from over 11 dB to less than 3 dB for audio frequencies (0.1-10 kHz) at distances up to 15 mm, making it adequate for intraoperative and audiometric tests.

Outer ear canal sound pressure and bone vibration measurement in SSD and CHL patients using a transcutaneous bone conduction instrument.

The intraoperative and postoperative objective functional assessment of transcutaneous bone conduction implants is still a challenge. Here we compared intraoperative Laser-Doppler-vibrometry (LDV, Polytec Inc.) to measure vibration of the bone close to the implant to Outer Ear Canal Sound Pressure Level (OEC-SPL) measurements. Twelve single sided deafness (SSD) patients with contralateral intact ossicular chains and eight bilateral conductive hearing loss (CHL) patients were included in the study. SSD patients had a minor average air-bone-gap (ABG) of 0.4 ± 0.4 dB (0.5, 1, 2, 4 kHz mean value (MV) ± standard deviation (SD)) on the contralateral side where a normal transmission between cochlea and the tympanic membrane can be assumed. CHL patients had an impaired middle ear transmission with a mean ABG of 46.0 ± 7.9 dB (MV±SD). Vibration and OEC-SPL responses could reliably be recorded with a minimal signal-to-noise ratio of at least 12 dB. Average OEC-SPL on the contralateral side and intraoperative vibration measurements were strongly correlated in SSD (r2 = 0.75) and CHL (r2 = 0.86) patients. The correlation in individual results between OEC-SPL and vibration measurements was weak, indicating some underlying inter-individual variability. The high correlation of average responses showed that OEC-SPL are closely linked to bone vibration, although both cannot be equivalently used for intraoperative testing due to the high variability in individual results. On the other hand, OEC-SPL provides an easy and affordable measurement tool to monitor stability and functionality postoperatively using individual reference measurements. We observed no significant differences (t-test, p < 0.05) by comparing results from contralateral OEC-SPL in twelve SSD and eight CHL patients at frequencies between 0.5 and 8 kHz. This implies that the part of the measured sound pressure in the ear canal originating from the cochlea and emitted by the tympanic is not dominant and OEC-SPL is mainly due to vibration of the external ear-canal walls as the only other pathway of BC sound to reach the ear canal. In addition, the transcranial attenuation (contralateral outer ear canal sound pressure divided by ipsilateral) was compared to previous studies measuring vibration by LDV and accelerometer. The trend in the average transcranial attenuation in patients was similar to previous studies measuring the OEC-SPL with less than 5 dB difference.