Three-dimensional stapes footplate motion in human temporal bones

The literature provides conflicting information on whether the motion of the stapes footplate is piston-like or some other type of motion, such as rotational or rocking. Examination of the three-dimensional (3D) motion of the stapes footplate appears to be an excellent way to understand this complicated motion. Five microsphere reflective targets were placed on the stapes footplate in ten fresh human cadaver temporal bone preparations, and their vibration measured through an extended facial recess approach using a laser Doppler vibrometer. The five target sites on the stapes footplate were center, anterior, posterior, superior and inferior. The stimulus was a sound input of 80-120 dB SPL at the tympanic membrane over a frequency range of 0.1 to 10 kHz. The 3D motion of the stapes footplate was calculated using the velocity amplitude and phase obtained for each target. For frequencies up to 1.0 kHz the vibration of the stapes footplate was primarily piston-like; this motion became complex at higher frequencies, with rotary motion along both the long and short axis of the footplate. When the cochlea was drained, stapes footplate motion became essentially piston-like for all frequencies.     

Experimental study of vibration analysis in middle ear models by holographic interferometry. Effects of the cross-sectioned area of aditus on the vibration of tympanic membrane

To aid in the establishment of optimum conditions for postoperative function of the tympanic membrane, a model of the middle ear was experimentally prepared, the cross-sectioned area of aditus ad antrum was altered and the effects on the tympanic membrane vibrational characteristics were observed using the holographic interference method. The following results were obtained. 1) At the low frequencies below 2 kHz, the vibration mode of tympanic membrane was concentric on the whole, but the vibration pattern became fractionated at 4 kHz and above. The frequency of onset of the fractionated vibration pattern was changed only by the conditions of the membrane itself and was not affected much by the sound pressure, the volume of the middle ear cavity and the cross-sectioned area of aditus ad antrum. 2) There were resonance and anti-resonance points in the tympanic vibration pattern. These resonance and anti-resonance frequencies became higher as the diameter of aditus increased until eventually a constant value was reached. At diameters in excess of this constant value, the resonance frequency tended to fall and the anti-resonance frequency tended to rise. 3) The tympanic vibration in the middle ear cavity was not influenced very much by the diameter of aditus at 250Hz. Vibration decreased when aditus was blocked at 500Hz and the opening diameter had a major influence at 1kHz. Vibration was maximum at a diameter of about 2mm and a minimum when aditus was blocked. At 2 to 3kHz, the effects on vibration increased when aditus was blocked. 4) When aditus ad antrum was blocked, the vibration frequency characteristics of tympanic membrane deteriorated at under 1kHz and improved at 2 to 3kHz. When a comparison was made between the case with opened aditus, (which was considered to be equivalent to the closed method of tympano-plasty), and the case with closed aditus, (considered to be equivalent to the open method), the vibration frequency characteristics of the tympanic membrane improved in the low sound region up to 2kHz when the diameter was 4mm.     

Effects of an increase or decrease in the middle ear pressure on tympanic membrane vibrations (experimental study by holographic interferometry)

The effects of positive and negative pressure in the middle ear on tympanic membrane (TM) vibrations were studied in twenty canine temporal bones by holographic interferometry. The displacement of the TM was measured by moiré topography. 1) When pressure was applied to the tympanic cavity, the curvature of the TM became small under negative pressure and large under positive pressure, with the displacement being greater under positive pressure. 2) Without pressure load, the vibration pattern below 2 kHz was simple and there were peak displacement regions in the posterior and anterior parts of the membrane and the peaks occurred approximately halfway along the manubrium. The TM vibrations showed sectional patterns, above 3 kHz in the posterior and above 4 kHz in the anterior. The amplitude of the anterior peak was larger than that of the mallear tip, but smaller than that of the posterior. 3) At frequencies below 2 kHz, the vibration pattern was not affected by negative pressure load. At frequencies of 3 kHz or higher, the sectional patterns changed into the simpler patterns and the sectional vibrations diminished as the pressure increased. 4) Below 2 kHz, the TM amplitude decreased with increasing negative pressure. Above 3 kH, the amplitude showed an initial increase but decreased at higher negative pressure loading. With the amplitude of the mallear tip, the same tendency was observed. The resonance frequency shifted to a higher frequency range with pressure loading. 5) Under positive pressure, the vibration pattern remained unchanged below 2 kHz, and above 3 kH, sectional vibrations changed to the simple vibrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interferometric measurement of the amplitude and phase of tympanic membrane vibrations in cat

The amplitude and phase of the tympanic membrane and malleus vibrations were measured over a wide frequency range with a homodyne interferometer. When sound pressure was maintained constant near the tympanic membrane, the malleus frequency response followed the typical pattern up to 10 kHz as measured by previous investigators. At higher frequencies the response changes dramatically. Instead of decreasing with frequency, between 10 and 20 kHz the vibration amplitude oscillates around a value which is only about 20 dB lower than the low frequency plateau level. Measurements of malleus vibration at several points along its length indicate that its mode of vibration changes at high frequencies, and no longer consists of a simple rotational component. All points on the tympanic membrane vibrate in phase with the malleus up to a frequency of 1 kHz. Above 5 kHz discrete resonances are observed, and the response varies strongly with position on the tympanic membrane.     

Effects of the perforation of the tympanic membrane on its vibration--with special reference to an experimental study by holographic interferometry

Using canine temporal bone, perforations were surgically prepared at the anterior, inferior and posterior parts of the tympanic membrane, and the influences of these perforations on the tympanic vibration were observed and analyzed by holographic interferometry. Normal canine tympanic membrane had its respective single maximum amplitude points at its anterior and posterior parts at a frequency from the low compass to 2 kHz or so and showed a concentric circular vibration pattern centering mainly there around. At 3 and 4 kHz or so, the posterior and anterior parts began to show their respective sectional vibrations and with an increase in frequency, showed their further complicated multi-sectional vibrations. Resonance frequency was 1 or 2 kHz or so. The tympanic vibration following the preparation of perforations was as follows: 1) For the posterior perforation, the frequency at which the anterior sectional vibration began passed to a higher frequency, while for the other perforations, no change was noted in vibration pattern of the remaining tympanic membrane. 2) Comparative examination of the vibration amplitude at the mallear tip revealed that for a small perforation, no change in resonance frequency was noted regardless of the location of perforation and an increase in vibration amplitude was noted near the resonance frequency. 3) For the anterior perforation, no change in resonance frequency was noted even with an expansion of perforation and an increase in vibration amplitude was noted near the resonance frequency. 4) For the posterior and inferior perforations, the resonance frequency passed to a higher frequency with an expansion of perforation and an increase in vibration amplitude was noted near the resonance frequency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ossicular vibration in human temporal bones

Vibration mode of the ossicles was investigated in twelve fresh human temporal bones using a video measuring system (VMS, Technical Instrument). This system allows one to observe the ossicular vibration and to measure its vibration amplitude (up to 0.2 micron) and phase angle. In this study the inner and middle ear was kept intact except for two small holes in the tympanic tegmen. These holes were for the observation of ossicular movement and were covered with a thin cover glass during the experiment. The vibration amplitude and phase angle of the umbo, malleus head, lenticular process and stapes head were measured at 19 frequencies between 0.1 kHz and 4.5 kHz. The umbo moved piston-like at 0.1-0.8 kHz and 2.6-4.5 kHz but in an ellipse at 1.0-2.4 kHz. The malleus head showed elliptical movement with its long axis anteriorly tilted around 45 degrees from the direction of the umbo vibration at 0.1 kHz. Both the lenticular process and stapes head showed similar movement; piston-like in lower frequencies and elliptical in higher frequencies. The umbo, lenticular process and stapes head vibrated parallel at lower frequencies. The position, displacement and phase angle of the rotation axis of the ossicles was calculated based on the displacement and phase angle of the umbo, malleus head and lenticular process. The axis was around the level of the neck of the malleus in frequencies lower than the resonant frequency, beneath the level of the short process near the resonant frequency and at the top of the malleus head in higher frequencies. The average axis displacement was 0.9 microns at 1 kHz but much smaller at frequencies lower than 0.8 kHz or higher than 2 kHz. This suggests that such axis movement may reduce the efficiency of the middle ear sound transmission.     

Acoustic responses of the human middle ear

Measurements on human cadaver ears are reported that describe sound transmission through the middle ear. Four response variables were measured with acoustic stimulation at the tympanic membrane: stapes velocity, middle-ear cavity sound pressure, acoustic impedance at the tympanic membrane and acoustic impedance of the middle-ear cavity. Measurements of stapes velocity at different locations on the stapes suggest that stapes motion is predominantly ‘piston-like’, for frequencies up to at least 2000 Hz. The measurements are generally consistent with constraints of existing models. The measurements are used (1) to show how the cavity pressure and the impedance at the tympanic membrane are related, (2) to develop a measurement-based middle-ear cavity model, which shows that the middle-ear cavity has only small effects on the motion of the tympanic membrane and stapes in the normal ear, although it may play a more prominent role in pathological ears, and (3) to show that inter-ear variations in the impedance at the tympanic membrane and the stapes velocity are not well correlated.     

Effects of middle ear pressure changes on umbo vibration

Effects of middle ear pressure changes on umbo vibration were studied in 5 fresh human temporal bones taken from cadavers. Umbo vibration to a constant sound pressure of 120 dB SPL at the tympanic membrane was measured with an MTI 1000 Fotonic Sensor. The results showed that there was a loss of umbo vibration at lower frequencies below 2 kHz; 5.0 +/- 1.0 dB loss at -100 mmH2O, 9.2 +/- 1.3 dB loss at -200 mmH2O, and 13.1 +/- 1.8 dB loss at -300 mmH2O. In contrast, there was a slight increase in umbo vibration at around 2-3 kHz. The effect was considered to be mainly due to increased stiffness of the tympanic membrane and decreased air volume in the middle ear cavity.     

Stapes vibration produced by the output transducer of an implantable hearing aid. Experimental study

The function of the output transducer of an implantable hearing aid was assessed by applying it to the stapes head in seven fresh human cadaver temporal bones while observing vibration of the stapes under a microscope with the use of a stroboscope and a video measuring system. The transducer was a 5 X 1.2 X 0.6-mm piezoelectric ceramic bimorph with attached metal holder. Transmission changed with the amount of force holding the transducer tip on the head of the stapes. An optimal connection between the vibrator and stapes produced better transmission than a tight or loose connection. Gluing the connection with cyanoacrylate cement decreased transmission in the optimal connection, produced no change in the tight connection, and improved transmission in the loose connection. Comparison of stapes displacement produced by the vibrator at 1 kHz with that produced by normal middle-ear sound transmission revealed that the vibrator-induced stapes displacement for a 1 V peak-to-peak input was equivalent to that produced by a sound stimulus of 90-dB sound pressure level at the tympanic membrane.     

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.     

Towards quantitative diagnosis of ossicular fixation: Measurement of stapes fixations using magnetically driven ossicles in human temporal bones

Conclusion: Information on the degree of stapes fixation can be found by measuring the ratio of stapes to umbo and stapes to incus velocity. Objectives: To evaluate a method of quantifying ossicular fixation in an ear with elevated tympanic membrane. Method: Measurements were made on four fresh-frozen human temporal bones. After elevating the tympanic membrane, a small magnet was attached to the manubrium and an electromagnetic excitation coil was used to vibrate the ossicles. The vibration response of the umbo, the tip of the incus long process, and the posterior crus of the stapes were measured before and after partially fixing the footplate with luting cement. Results: The velocities at the different measurement points were unequally affected by the fixation. The difference in the velocity ratio between different points provides an indication of the degree of footplate fixation.     

镫骨环韧带固定对中耳传声的影响——有限元模型研究

目的　有限元模型分析镫骨环韧带固定对中耳传声的影响。方法　依据1例成年男性颞骨标本Micro-CT扫描数据,建立正常成人中耳有限元模型。通过调整镫骨环韧带的杨氏模量,建立镫骨环韧带固定的有限元模型。计算一定声压刺激下鼓膜与镫骨底板振幅,进而反映建立镫骨环韧带固定时对中耳传声的影响。结果　有限元模型计算结果显示：镫骨环韧带固定时,镫骨底板振动显著减小达47 dB,而对鼓膜振动影响不明显。结论  有限元模型理论分析,镫骨环韧带固定对中耳传声的影响接近于临床观察结果,但需进一步与颞骨实验研究结果对照。深入认识中耳传声机制,为临床耳硬化症提供基础数据。     

部分人工听骨植入位置对中耳传声影响——有限元模型研究

目的　研究部分人工听骨（partial ossicular replacement prosthesis,PORP）植入位置对中耳传声的影响。方法　在去除砧骨的中耳有限元模型上,建立钛金属柱状结构连接锤骨与镫骨的有限元模型,模拟PORP功能。计算锤骨柄不同位置放置PORP,以及软骨片置入PORP和移植筋膜之间对中耳传声的影响。结果　PORP分别置于锤骨颈部、锤骨柄中部和锤骨头去除后的3种情况下,鼓膜脐部振幅于200～8000 Hz均减低,于200～3200 Hz减低大于3200～8000 Hz减低幅度。同样上述3种情况下,镫骨振幅于200～8000 Hz增加,PORP放置于锤骨柄和锤骨颈部基本一致;锤骨头去除后,1000～8000 Hz镫骨振幅较前二者有轻度增高,约2～3 dB。当PORP与鼓膜间置入软骨片时,镫骨底板振动均轻度增强,但不同材料的软骨片差别不大。结论　PORP材料属性和放置位置对实现中耳传声至关重要。     

Effects of ossicular prosthesis mass and section of the stapes tendon on middle ear transmission

BACKGROUND: The effects of changing prosthesis mass on middle ear transmission have not been previously systematically studied. Neither has the effect of stapes tendon sectioning. These are important parameters that can be surgically varied. HYPOTHESIS: Because the middle ear is compliance dominated at low frequencies, prosthesis mass will affect transmission of higher frequencies in the middle ear. METHODS: Eight fresh cadaveric temporal bones, with the incus removed, were loaded with a replacement prosthesis from the tympanic membrane to the stapes head. Laser Doppler vibrometry was used to measure stapes footplate vibrations. Vibrations were measured in response to chirps from 250 to 8 kHz at 90 dB SPL in the ear canal. The unloaded prosthesis mass was approximately 16 mg. Loadings with masses of approximately 2, 12, and 30 mg were placed on the stem. Recordings were repeated after cutting the stapes tendon. RESULTS: Mass loading affected the higher frequencies only, with significant effects only above 4 kHz. There was little low-frequency effect. Stapes tendon section showed an improvement in the lower frequencies but did not reach statistical significance. CONCLUSIONS: Mass of prostheses affects mainly higher frequencies. There is no drop in lower frequencies from using lower masses, so lighter-mass prostheses may be preferred. Stapes tendon section does not have a detrimental effect on middle ear transmission after ossiculoplasty.     

Tympanic membrane collagen fibers: a key to high-frequency sound conduction

OBJECTIVE: To investigate the significance of tympanic membrane collagen fiber layers in high frequency sound transmission. STUDY DESIGN: Human cadaver temporal bone study. METHODS: Laser Doppler vibrometry was used to measure stapes footplate movement in response to acoustic stimulation. The tympanic membrane was altered by creating a series of slits and applying paper patches to isolate the effects of specifically oriented collagen fibers. Three groups of membrane alterations were evaluated: 1) circumferentially oriented slits involving each quadrant to primarily disrupt radial fibers, made sequentially within superior-anterior, inferior-anterior, inferior-posterior, and superior-posterior quadrants; 2) the same slits made in the reverse order; and 3) radially oriented slits from the umbo to the annulus to primarily disrupt circumferential fibers. For each group, measurements of the middle-ear cavity pressure, ear canal pressure, and stapes velocity were made each time the tympanic membrane was altered. RESULTS: Regardless of the order in which the circumferentially oriented slits were made, there was a consistent decrease in stapes velocity above 4 kHz for the third and fourth cuts compared to the control. The mean decrease in the range of 4 to 12.5 kHz was 11 dB for the third patched slit and 14 dB for the fourth patched slit (P < .01). Radially oriented slits appear to produce smaller effects. CONCLUSIONS: Radial collagen fibers in the tympanic membrane play an important role in the conduction of sound above 4 kHz.     

Three-dimensional finite-element analysis of the cochlear hypoplasia

Abstract

Objectives: Based on CT scan images of healthy human ear, the effects of cochlear hypoplasia on auditory functions was studied.

Methods: Three-dimensional nonlinear finite-element numerical model was developed and used to predict frequency responses of hypoplastic cochleae. The numerical model was validated by comparing the modeling results to reported experimental data.

Results: The cochlear hypoplasia compromises sound conduction of middle ear and results in significant decrease of vibration displacement amplitude of stapes foot-plate at frequencies 100?～?1200?Hz with a maximal decrease of 9.1?dB at ～1000?Hz. Consequently, the displacement ratio of basement membrane vibration at the longitudinal location ～12?mm from the apex to the stapes vibration decreases at 100?～?4000?Hz with the biggest decrease of 15.2?dB at ～?4000?Hz.

Conclusions: Numerical modeling was used to demonstrate the effect of cochlear hypoplasia on sound conduction and cochlear sensitivity. Cochlear hypoplysia causes changes in biomechanics of middle ear and inner ear, which lead to hearing loss. The current modeling results suggest that the frequency-dependent decrease of the stapes vibration can be used in clinics for diagnosing cochlear hypoplasia. This is particularly important because the middle ear function measurement can be used to diagnose unmeasurable inner ear disorders.     

Experimental study of an adjustable-length prosthesis in a temporal bone model

CONCLUSIONS: This prosthesis has the advantage of rapid adjustment at the time of insertion in order to achieve optimal tension and, as a result, optimal sound transmission. OBJECTIVE: To test the acoustic performance of a new, adjustable incus replacement prosthesis in a human temporal bone model. MATERIAL AND METHODS: Experiments were performed in seven human temporal bones, before and after removal of the incus and insertion of the prosthesis. The input comprised 406 pure tones ranging in frequency between 0.1 and 10 kHz at an intensity of 80 dB SPL at the tympanic membrane. The output measurement was stapes footplate displacement, determined by means of a laser Doppler vibrometer. Three lengths of the prosthesis were investigated: optimal, optimal +0.2 mm and optimal +0.4 mm. RESULTS: The optimal-length prosthesis produced similar results to those of an intact middle ear. The slightly longer prostheses decreased middle ear sound transmission at all test frequencies, except those near 1.5 kHz.     

A new L-shaped titanium prosthesis for total reconstruction of the ossicular chain.

OBJECTIVE: To describe the technique used for total ossiculoplasty with the Fisch titanium total prosthesis and evaluate the 1-year postoperative functional results in patients presenting with the stapes (or footplate) without the malleus handle. STUDY DESIGN: Prospective trial with preoperative and postoperative comparison. SETTING: Academic and private practice tertiary care center for otologic surgery. PATIENTS: Forty-nine consecutive patients operated on from September 1996 to December 2000. SURGERY:: Staged ossicular reconstruction with a Fisch titanium total prosthesis placed between the footplate and the tympanic membrane without regard to the presence or absence of the stapes arch. Coupling of the prosthesis to the footplate was achieved by various techniques, including perforation, foot and spike on the footplate without perforation, and shaft alone (without foot) with tragal cartilage fixation (disc or small wedges). There was no interposition of cartilage between the prosthesis head and the tympanic membrane. MAIN OUTCOME MEASURES: Pre- and postoperative air and bone-conduction thresholds and air-bone gaps for pure-tone averages of three and four frequencies and for single frequencies. RESULTS: Postoperative air-bone gap closures within 20 dB distributed equally (50%) between 0.5, 1, and 4 kHz and reached the highest rate (89%) at 2 kHz (p < 0.05). The postoperative air-bone gaps for pure-tone averages reached 0 to 20 dB in 57% and 0 to 30 dB in 87% of the cases. There were no dead ears and no partial or total extrusions of prostheses. The best functional results were achieved through perforation coupling of the spiked foot to the footplate in large oval windows and after fixation of the shaft (without foot) with tragal cartilage disc in narrow oval windows. CONCLUSION: The functional results of the L-shaped Fisch titanium total prosthesis implanted in ears with the stapes but no malleus handle are best at 2 kHz and better than those of comparable columellar titanium prostheses over the remaining tested frequencies.     

Studies on the mechanics of the normal human middle ear

The middle ear was studied in temporal bone preparations using a laser-Doppler interferometer. For measurements at a sound level of 80 dB SPL this method proved to be very reliable, as was shown by good reproducibility of results in experiments over more than 6 hours. The vibrations of the tympanic membrane and stapes footplate were studied from 200 Hz to 10 KHz and the results demonstrate a piston-like movement of the stapes footplate up to 120 dB SPL. The damping effect of the normal ear is located mainly at the footplate/cochlea level and the middle ear cavity per se does not contribute significantly to the stiffness of the middle ear system.