Shinji Hamanishi

Piezoelectric materials mimic the function of the cochlear sensory epithelium

Cochlear hair cells convert sound vibration into electrical potential, and loss of these cells diminishes auditory function. In response to mechanical stimuli, piezoelectric materials generate electricity, suggesting that they could be used in place of hair cells to create an artificial cochlear epithelium. Here, we report that a piezoelectric membrane generated electrical potentials in response to sound stimuli that were able to induce auditory brainstem responses in deafened guinea pigs, indicating its capacity to mimic basilar membrane function. In addition, sound stimuli were transmitted through the external auditory canal to a piezoelectric membrane implanted in the cochlea, inducing it to vibrate. The application of sound to the middle ear ossicle induced voltage output from the implanted piezoelectric membrane. These findings establish the fundamental principles for the development of hearing devices using piezoelectric materials, although there are many problems to be overcome before practical application.

A new electromagnetic hearing aid using lightweight coils to vibrate the ossicles

As the first stage in the development of a noninvasive electromagnetic hearing aid, we made a new transducer that generates a high-excitation force to vibrate ossicles via the tympanic membrane. This transducer consists of a core, driving and induction coils, a rare-earth magnet, and a vibrator coil. We designed the core, the driving and induction coils, and the magnet so as to generate the greatest excitation force possible when installed in the external ear canal of humans. With regard to the vibrator coil, which was attached to the center of the tympanic membrane to vibrate the ossicles, we determined its optimal mass, position, and shape both by finite-element method (FEM) analysis and by experiments using an artificial middle ear. A prototype of the optimally designed transducer can generate an excitation force of more than 95 dB sound pressure level (SPL) in terms of sound pressure at frequencies between 0.1 and 10 kHz. This result indicates that the transducer developed in this study can be used to treat patients with a hearing loss up to 70 dB hearing level (HL).

Autophony in Patients with Patulous Eustachian Tube: Experimental Investigation Using an Artificial Middle Ear

Objective: To investigate the contribution of anatomical factors, such as the caliber of the patent eustachian tube (ET) and the volume of the middle ear cavity, on vocalized sound transmission to the inner ear. Methods: Model experiment using artificial middle ear. Results: In the present model experiment, sound transmission from the pharynx to the inner ear under patulous conditions was affected by the caliber of the ET and by the mastoid volume, especially in the low-frequency region, that is, a larger caliber of the ET and smaller mastoid volume resulted in greater sound transmission from the pharyngeal space to the inner ear. Conclusion: Patulous symptoms may be more distressful in patients with poorly developed mastoid cavity than in those with well-aerated mastoid under similar conditions of patulous ET.

Dynamic characteristics of the middle ear in neonates.

OBJECTIVE Early diagnosis and treatment of hearing disorders in neonates is highly effective for realization of linguistic competence and intellectual development. To objectively and quickly evaluate the dynamic characteristics of the middle ear, a sweep frequency impedance (SFI) meter was developed, which allowed the diagnosis of middle-ear dysfunctions in adults and children. However, this SFI meter was not applicable to neonates since the size of the measurement probe was too large. In the present study, therefore, the SFI meter was improved, i.e., the diameter of the probe was reduced to that of the neonatal external ear canal. By using this newly designed SFI meter, SFI tests were performed in healthy neonates. METHODS A sound of the sweeping sinusoidal frequency between 0.1 kHz and 2.0 kHz in 0.02-kHz step intervals is presented to the ear canal by an SFI probe while the static pressure of the ear canal is kept constant. During this procedure, the sound pressure level (SPL) is measured. The measurements are performed at 50-daPa intervals of static pressure from 200 daPa to -200 daPa. RESULTS Measurements were conducted in 10 ears of 9 neonates. The SPL showed two variations at 0.26 ± 0.03 kHz and 1.13 ± 0.12 kHz. Since the SPL is known to show a variation at frequencies from 1.0 kHz to 1.6 kHz due to the resonance of the middle ear in adults and children with normal hearing, the second variation is probably related to such resonance in neonates. The measurement of gel models, which mimics the neonatal external ear canal, showed a variation in SPL at around 0.5 kHz. This implies that the source of the first variation may possibly be related to the resonance of the external ear canal wall. CONCLUSIONS SFI tests revealed that there were two variations in the SPL curve in neonates, one at 0.26 ± 0.03 kHz and the other at 1.13 ± 0.12 kHz, the former and the latter being possibly related to the resonance of the external ear canal wall and that of the middle ear, respectively. This result suggests that the dynamic characteristics of the middle ear in neonates are different from those in adults.

An electromagnetic hearing aid using coils to vibrate the ossicles-evaluation of excitation force and distortion

In this study, as the first stage in the development of a non-implantable hearing aid, a new electromagnetic transducer composed of three coils and a magnet was made which generates high-excitation force to vibrate ossicles via the tympanic membrane. To evaluate the excitation force of the electromagnetic transducer, cochlear microphonic (CM) was measured in anesthetized guinea pigs. The non-implantable electromagnetic hearing aid consists of two parts, i.e., an electromagnetic transducer and an amplifier. Results show that over the entire frequency, CM amplitude caused by the electromagnetic transducer is larger than that caused by acoustical stimulus. Because of the linear relationship between the acoustical stimulus level and the CM amplitude, the value of the excitation force caused by the electromagnetic transducer can be converted to the equivalent value in dB SPL. The excitation force generated by the prototype of electromagnetic transducer is 93-106 dB SPL in the frequency range of 0.5 to 10 kHz. This study showed that the electromagnetic transducer is able to generate sufficient excitation force to treat patients with high-frequency hearing loss.