Normative data of incus and stapes displacement during middle ear surgery using laser Doppler vibrometry

Design of Piezoelectric Dual-Bandwidth Accelerometers for Completely Implantable Auditory Prostheses

For the last 20 years, researchers have developed accelerometers to function as ossicular vibration sensors in order to eliminate the external components of hearing aid and cochlear implant systems. To date, no accelerometer has met all of the stringent performance requirements necessary to function in this capacity. In this work, we present an accelerometer design with an equivalent noise floor less than 20 phon equal-loudness-level over a 0.1-8 kHz bandwidth in a package small enough to be implanted in the middle ear. Our approach uses a dual-bandwidth (two sensing elements) microelectromechanical systems piezoelectric accelerometer, sized using an area-minimization process based on an experimentally-validated analytical model of the sensor. The resulting bandwidth of the low-frequency sensing element is 0.1-1.25 kHz and that of the high-frequency sensing element is 1.25-8 kHz. These sensing elements fit within a silicon frame that is 795 μm × 778 μm, which can reasonably be housed along with a required integrated circuit in a 2.2 mm × 2.7 mm × 1 mm package. The estimated total mass of the packaged system is approximately 14 mg. This dual-bandwidth MEMS sensor fills a technological gap in current completely implantable auditory prosthesis research and development by enabling a device capable of meeting physical and performance specifications needed for use in the middle ear.

Long-Term Hearing Results of Endoskeletal Ossicular Reconstruction in Chronic Ears Using Titanium Prostheses Having a Helical Coil: Part 1-Kraus K-Helix Crown, Incus to Stapes

OBJECTIVES

1) To assess long-term hearing results after endoskeletal ossicular chain reconstruction (eOCR) using the titanium Kraus K-Helix Crown prosthesis, implanted incus to stapes, with glass-ionomer cement (GIC) in chronic ears and 2) to determine safety of the prosthesis and cement.

STUDY DESIGN

Prospective, nonrandomized, sequential, single center, single surgeon.

SETTING

Private practice, ambulatory surgical center.

PATIENTS

N = 15 males (42%) and 21 females (58%). Mean age was 40.4 years (range, 6-81 years); 38 ears (22 right ears [58%] and 16 left ears [42%]).

INTERVENTIONS

eOCR in chronic ears. Comprehensive preoperative and postoperative hearing measurements were performed for up to 9 years.

MAIN OUTCOME MEASURES

Postoperative hearing results at 1 year showed statistically significant improvement as compared with preoperative hearing. Long-term hearing results remained stable and showed no statistically significant change over 9 years.

RESULTS

Estimated mean pure-tone air conduction average improved by 14.5 dB (95% confidence interval = 10.3-18.7). Estimated mean speech reception thresholds improved by 15.5 dB (10.8-20.2). Word recognition scores improved by -2.2% (-5.3 to 1.0). The estimated mean postoperative air-bone gap was 10.5 dB (7.2-13.8). The estimated mean calculated air-bone gap was 11.3 dB (8.0-14.5). The estimated mean change in high-tone bone conduction (HTBC) average was +3.5 dB (0.9-6.0). Two prostheses extruded (5%). No patients experienced any unanticipated serious adverse effects or events.

CONCLUSION

eOCR using the K-Helix Crown prosthesis, incus to stapes, and GIC can significantly improve hearing at 1 year and maintain stable hearing over 9 years. Both prosthesis and cement are safe.

Handheld laser-fiber vibrometry probe for assessing auditory ossicles displacement

SIGNIFICANCE

Measurements of auditory ossicles displacement are commonly carried out by means of laser-Doppler vibrometry (LDV), which is considered to be a gold standard. The limitation of the LDV method, especially for in vivo measurements, is the necessity to expose an object in a straight line to a laser beam operating from a distance. An alternative to this approach is the use of a handheld laser-fiber vibrometry probe (HLFVP) with a curved tip.

AIM

We evaluate the feasibility of an HLFVP with a curved tip for measuring sound-induced displacement of the auditory ossicles.

APPROACH

A handheld vibrometer probe guiding the laser beam with a fiber-optic cable was used for displacement measurements of the incus body and the posterior crus of the stapes. Tonal stimuli at frequencies of 0.5, 1, 2, and 4 kHz were presented by means of an insert earphone positioned in the outer ear canal. The probe was fixed at the measurement site using a tripod or hand-held by one of the two surgeons.

RESULTS

The measurements were carried out on six fresh temporal bones. Multivariate analysis of variance showed statistically significant differences for stimulus frequency (F3,143  =  29.37, p  <  0.001, and η2  =  0.35), bone (F5,143  =  4.61, p  =  0.001, and η2  =  0.01), and measurement site (F1,143  =  4.74, p  =  0.03, and η2  =  0.02) in the absence of statistically significant differences for the probe fixation method (F2,143  =  0.15, p  =  0.862, and η2  =  0.001). Standard deviations of the means were 6.9, 2.6, 1.9, and 0.6  nm  /  Pa for frequency, bone, site, and fixation, respectively. Ear transfer functions were found to be consistent with literature data.

CONCLUSIONS

The feasibility of applying HLFVP to measure the displacement of auditory ossicles has been confirmed. HLFVP offers the possibility of carrying out measurements at various angles; however, this needs to be standardized taking into account anatomical limitations and surgical convenience.

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.

Measurement of Vibrating Tympanic Membrane in an In Vivo Mouse Model Using Doppler Optical Coherence Tomography

Optical coherence tomography (OCT) has a micro-resolution with a penetration depth of about 2 mm and field of view of about 10 mm. This makes OCT well suited for analyzing the anatomical and internal structural assessment of the middle ear. To study the vibratory motion of the tympanic membrane (TM) and its internal structure, we developed a phase-resolved Doppler OCT system using Kasai’s autocorrelation algorithm. Doppler optical coherence tomography is a powerful imaging tool which can offer the micro-vibratory measurement of the tympanic membrane and obtain the micrometer-resolved cross-sectional images of the sample in real-time. To observe the relative vibratory motion of individual sections (malleus, thick regions, and the thin regions of the tympanic membrane) of the tympanic membrane in respect to auditory signals, we designed an experimental study for measuring the difference in Doppler phase shift for frequencies varying from 1 to 8 kHz which were given as external stimuli to the middle ear of a small animal model. Malleus is the very first interconnecting region between the TM and cochlea. In our proposed study, we observed that the maximum change in Doppler phase shift was seen for the 4 kHz acoustic stimulus in the malleus, the thick regions, and in the thin regions of the tympanic membrane. In particular, the vibration signals were higher in the malleus in comparison to the tympanic membrane.

Totally Implantable Active Middle Ear Implants

The Envoy Esteem and the Carina system are the 2 totally implantable hearing devices. The Esteem is designed for patients with bilateral moderate to severe sensorineural hearing loss who have an unaided speech discrimination score of greater than and equal to 40%. The Carina system is designed for patients with moderate to severe sensorineural hearing loss or those with mixed hearing loss. The Esteem offers a technologically advanced method to provide improvements in hearing and is available in the United States, whereas the Carina system is currently not available in the United States.

Ten years of active middle ear implantation for sensorineural hearing loss

OBJECTIVES

To evaluate long-term benefits of a totally implantable active middle ear implant (AMEI) that has been used in a single implanting center for over 10 years.

METHODS

Forty-one subjects who underwent implantation with an Esteem^® AMEI during a 10-years period were evaluated on the auditory benefits, as derived from pure tone and speech audiometry tests. The analysis included a comparison with a conventional hearing aid, the problematics related to the battery duration and surgical replacement and, finally, the complication rate.

RESULTS

Over 80% of the implanted subjects maintained over time a satisfactory auditory gain, ranging from 10 to over 30 dB in respect to the unaided situation, as mean at 0.5, 1, 2 and 4 kHz. In more than 60% of them, an improvement has also been found at 4 and 8 kHz. Battery duration varied according to the severity of the hearing loss and to the daily use of the device. No major post-operative complications were recorded, whilst explantation was necessary in five subjects, although none for device failure.

CONCLUSIONS

The Esteem^® can be considered a reliable device for rehabilitation of sensorineural hearing loss in alternative to conventional hearing aids.

In Vivo Vibration Measurement of Middle Ear Structure Using Doppler Optical Coherence Tomography: Preliminary Study

Objectives

Doppler optical coherence tomography (DOCT) is useful for both, the spatially resolved measurement of the tympanic membrane (TM) oscillation and high-resolution imaging. We demonstrated a new technique capable of providing real-time two-dimensional Doppler OCT image of rapidly oscillatory latex mini-drum and in vivo rat TM and ossicles.

Methods

Using DOCT system, the oscillation of sample was measured at frequency range of 1–4 kHz at an output of 15 W. After the sensitivity of the DOCT system was verified using a latex mini-drum consisting of a 100 μm-thick latex membrane, changes in displacement of the umbo and contacted area between TM and malleus in normal and pathologic conditions.

Results

The oscillation cycles of the mini-drum for stimulus frequencies were 1.006 kHz for 1 kHz, 2.012 kHz for 2kHz, and 3.912 kHz for 4 kHz, which means that the oscillation cycle of the mini-drum become short in proportional to the frequency of stimuli. The oscillation cycles of umbo area and the junction area in normal TM for frequencies of the stimuli showed similar integer ratio with the data of latex mini-drum for stimuli less than 4 kHz. In the case of middle ear effusion condition, the Doppler signal showed a tendency of attenuation in all frequencies, which was prominent at 1 kHz and 2 kHz.

Conclusion

The TM vibration under sound stimulation with frequencies from 1 kHz to 4 kHz in normal and pathologic conditions was demonstrated using signal demodulation method in in vivo condition. The OCT technology could be helpful for functional and structural assessment as an optional modality.

Objective Measurements of Ossicular Chain Mobility Using a Palpating Instrument Intraoperatively

BACKGROUND

The judgment of a normal or impaired mobility of middle ear ossicles is based on palpation and depends highly on the surgeon's subjective experience. The aim of this study was to develop and test a palpating instrument recording force and vector and allowing to support the surgeon's subjective impression with objective measurement results.

STUDY DESIGN

Prospective recordings at surgery.

SETTING

Tertiary referral center.

PATIENTS AND METHODS

A fiberoptic force-sensing element allowing force measures in three orthogonal directions was integrated into a handheld 45 degree hook and tested in temporal bones. Clinical data series from patients with a functionally normal chain (e.g., cochlear implants (CI)) and impaired ossicles (otosclerosis) were collected. The ossicles were palpated until their first movements out of the resting stage were visualized, the applied force, and vector were recorded by an independent observer.

RESULTS

Four CI and 19 otosclerosis patients were further evaluated. The minimum detectable force change of the sensor was 0.2 gF (2 mN). In the otosclerosis patients the average force applied to move the malleus was 9.5 gF, on the incus 8.7 gF. These values were slightly lower after separation of the incudostapedial joint, reaching 8.5 gF and 6.9 gF, respectively. The fixed stapes showed a rigidity of 14.7 gF or higher. The values were lower in the CI group measuring 4.4 gF, 4.1 gF, and 3.3 gF on the three ossicles, respectively.

CONCLUSIONS

We were able to produce a disposable, easy-to-handle palpating probe that enables the otologist to record continuously tip contact forces in three dimensions during his standard palpation of each ossicle. Normative values were reproduced for each ossicle, as well as increased rates for stapes fixation in otosclerosis.