Mark W. Wood

Human middle ear transfer function measured by double laser interferometry system.

Hypothesis: Simultaneous measurements of vibrations on the stapes footplate, incudostapedial (IS) joint, and tympanic membrane (TM) can be made in both normal and drained cochleae, and the stapes displacement transfer function (S-DTF) and TM displacement transfer function (TM-DTF) are derived. Background: A single laser Doppler interferometer previously has been used for measuring movement of the stapes or TM in temporal bones. However, there may be a limitation to optimally describing acoustic–mechanical transmission when the interferometer and temporal bone are moved frequently during experimental recordings. Simultaneous measurements of vibrations of the TM and stapes footplate, or TM and IS joint may reveal different acoustic–mechanical characteristics of the middle ear. Methods: Dual laser interferometers simultaneously measured vibrations of the TM, IS joint, and stapes in 10 temporal bones with both intact and drained cochleae. From these measurements, the middle ear transfer function was expressed as the S-DTF, TM-DTF, and displacement transmission ratio (DTR). Results: Simultaneous displacements of the TM, IS joint, and stapes footplate induced by sound pressure in the ear canal were recorded in both amplitude and phase. The middle ear transfer functions in terms of displacement ratio confirmed published single interferometer data but provided new information from drained cochlea. Conclusion: Stapes and TM displacement transfer functions were determined using dual interferometry, provided accurate amplitude and phase relationships from stapes footplate, IS joint, and TM, with new data from drained and normal cochlea.

Finite element modeling of sound transmission with perforations of tympanic membrane

A three-dimensional finite element (FE) model of human ear with structures of the external ear canal, middle ear, and cochlea has been developed recently. In this paper, the FE model was used to predict the effect of tympanic membrane (TM) perforations on sound transmission through the middle ear. Two perforations were made in the posterior-inferior quadrant and inferior site of the TM in the model with areas of 1.33 and 0.82 mm(2), respectively. These perforations were also created in human temporal bones with the same size and location. The vibrations of the TM (umbo) and stapes footplate were calculated from the model and measured from the temporal bones using laser Doppler vibrometers. The sound pressure in the middle ear cavity was derived from the model and measured from the bones. The results demonstrate that the TM perforations can be simulated in the FE model with geometrical visualization. The FE model provides reasonable predictions on effects of perforation size and location on middle ear transfer function. The middle ear structure-function relationship can be revealed with multi-field coupled FE analysis.

Fixation and detachment of superior and anterior malleolar ligaments in human middle ear: Experiment and modeling

The aim of this study is to investigate the function of the superior malleolar ligament (SML) and the anterior malleolar ligament (AML) in human middle ear for sound transmission through simulations of fixation and detachment of these ligaments in human temporal bones and a finite element (FE) ear model. Two laser vibrometers were used to measure the vibrations of the tympanic membrane (TM) and stapes footplate. A 3-D FE ear model was used to predict the transfer function of the middle ear with ligament fixation and detachment. The results demonstrate that fixations and detachments of the SML and AML had different effects on TM and stapes footplate movements. Fixation of the SML resulted in a reduction of displacement of the TM (umbo) and the footplate at low frequencies (f<1000 Hz), but also caused a shift of displacement peak to higher frequencies. Fixation of both SML and AML caused a reduction of 15 dB at umbo or stapes at low frequencies. Detachment of the SML had almost no effect on TM and footplate mobility, but AML detachment had a minor effect on TM and footplate movement. The FE model was able to predict the effects of SML and AML fixation and detachment.

Laser interferometry measurements of middle ear fluid and pressure effects on sound transmission

An otitis media with effusion model in human temporal bones with two laser vibrometers was created in this study. By measuring the displacement of the stapes from the medial side of the footplate, the transfer function of the middle ear, which is defined as the displacement transmission ratio (DTR) of the tympanic membrane to footplate, was derived under different middle ear pressure and fluid in the cavity with a correction factor for cochlear load. The results suggest that the DTR increases with increasing frequency up to 4k Hz when the middle ear pressure was changing from 0 to 20 or -20 cm H20 (e.g., +/-196 daPa) and fluid level was increasing from 0 to a full middle ear cavity. The positive and negative pressures show different effects on the DTR. The effect of fluid on DTR varies between three frequency ranges: f < 1k, between 1k and 4k, and f > 4k Hz. These findings show how the efficiency of the middle ear system for sound transmission changes during the presence of fluid in the cavity and variations of middle ear pressure.

A totally implantable hearing system – Design and function characterization in 3D computational model and temporal bones ☆

Implantable middle ear hearing devices are emerging as an effective technology for patients with mild to moderately severe sensorineural hearing loss. Several devices with electromagnetic or piezoelectric transducers have been investigated or developed in the US and Europe since 1990. This paper reports a totally implantable hearing system (TIHS) currently under investigation in Oklahoma. The TIHS consists of implant transducer (magnet), implantable coil and microphone, DSP-audio signal processor, rechargeable battery, and remote control unit. The design of TIHS is based on a 3D finite element model of the human ear and the analysis of electromagnetic coupling of the transducer. Function of the TIHS is characterized over the auditory frequency range in three aspects: (1) mass loading effect on residual hearing with a passive implant, (2) efficiency of electromagnetic coupling between the implanted coil and magnet, and (3) functional gain of whole unit in response to acoustic input across the human skin. This paper focuses on mass loading effect and the efficiency of electromagnetic coupling of TIHS determined from the FE model of the human ear and the cadaver ears or temporal bones. Some preliminary data of whole unit function are also presented in the paper.

Combined effect of fluid and pressure on middle ear function.

In our previous studies, the effects of effusion and pressure on sound transmission were investigated separately. The aim of this study is to investigate the combined effect of fluid and pressure on middle ear function. An otitis media with effusion model was created by injecting saline solution and air pressure simultaneously into the middle ear of human temporal bones. Tympanic membrane displacement in response to 90 dB SPL sound input was measured by a laser vibrometer and the compliance of the middle ear was measured by a tympanometer. The movement of the tympanic membrane at the umbo was reduced up to 17 dB by the combination of fluid and pressure in the middle ear over the auditory frequency range. The fluid and pressure effects on the umbo movement in the fluid-pressure combination are not additive. The combined effect of fluid and pressure on the umbo movement is different compared with that of only fluid or pressure change in the middle ear. Negative pressure in fluid-pressure combination had more effect on middle ear function than positive pressure. Tympanometry can detect the middle ear pressure of the fluid-pressure combination. This study provides quantitative information for analysis of the combined effect of fluid and pressure on tympanic membrane movement.

Tympanometry and laser Doppler interferometry measurements on otitis media with effusion model in human temporal bones.

Hypothesis: The aim of this study is to investigate the effect of middle ear fluid and pressure on tympanic membrane mobility by using laser Doppler interferometry and to compare these results with tympanometry. Background: Tympanometry has been commonly used for evaluation of otitis media with effusion, a middle ear disease with fluid in the cavity. However, this test lacks specific interpretations of middle ear disorders based on tympanometric data. Laser interferometry, as an advanced research tool to measure middle ear function, may provide knowledge of how tympanic membrane mobility is affected by middle ear fluid and pressure. Methods: An otitis media with effusion model was created in seven human temporal bones for conducting experiments with tympanometry and laser interferometry. Middle ear pressure varied from −20 to +20 cm water, and the amount of fluid in the middle ear was gradually increased to fill the cavity. Results: The displacement of the tympanic membrane measured by laser interferometry at selected frequencies decreased significantly corresponding to the middle ear air pressure changes. Tympanometry detected middle ear pressure by the change of tympanometric peak location, but the tympanogram shape was not affected by the middle ear pressure. The middle ear fluid was detected by tympanometry with as little as 0.3 mL, and laser interferometry was able to measure the displacement change of the tympanic membrane with 0.2 or 0.3 mL fluid at different frequencies. Conclusion: Laser interferometry can detect the effect of middle ear pressure and fluid on tympanic membrane movement as well as tympanometry does.

EFFECTS OF MIDDLE EAR SUSPENSORY LIGAMENTS ON ACOUSTIC-MECHANICAL TRANSMISSION IN HUMAN EAR

Two laser vibrometers were used to measure simultaneously the movement of the tympanic membrane and stapes footplate in human temporal bones. After control study of the normal ear, the stapedial tendon, posterior incudal ligament, tensor tympani tendon, and superior malleus/incus ligament were sectioned sequentially. The displacements of the umbo and footplate were measured repeatedly for each section. A 3-D finite element model of human ear which has accurate anatomic structure was used to mimic the middle ear structure changes and to derive the umbo and footplate vibrations in response to those alterations. The results show that the effects of ligaments on transfer function of the middle ear are frequency sensitive and vary with individual ligament.

A Totally Implantable Hearing Device for Restoration of Hearing

Middle ear implantable hearing devices as an emerging and ffective technology can offer advantages to the individuals with ild to moderately severe sensorineural hearing loss. Several deices with piezoelectric or electromagnetic transducers have been eveloped. A totally implantable hearing system TIHS consistng of a subcutaneous microphone, sound processor, and electroagnetic transducer has been investigated. The design of the IHS has incorporated the bioengineering approaches based on a D finite element FE computational model of the human ear and