Intraoperative measurement of stapes mobility using a hand-guided electromagnetic probe

BACKGROUND: The hearing results of otosurgery are still unsatisfactory. Even after successful implantation of middle ear prostheses there often remains an air bone gap of 30 dB or more. As possible reasons dislocation of the prostheses due to scar growth, changes in prostheses' attachment or ventilation disorders are being discussed. Decreased stapes mobility, which has been judged only manually up to now, is supposed to be a further reason. METHOD: We are introducing a new electromagnetic probe. The output signal of this device is proportional to the impedance of the stapes-annular ligament cochlear fluid system at the sensor's resonance frequency (2.4 kHz). The advantage of this system is characterised by its hand-guidance. Injury of the sensitive stapes-annular ligament due to tremor movements of the surgeon can be excluded using a special construction of the sensor head. The maximum force of the sensor's tip onto the stapes during measurement is limited to below 5 mN. RESULTS: Preliminary measurement results of 20 patients are presented with normal and abnormal stapes mobility. These results are compared to the subjective impression of the surgeon, who usually tested the stapes mobility by hand. As a result of our investigations probe measurements can detect more exactly decreased mobility of the stapes than the surgeon. CONCLUSIONS: Our device may help to detect latent stapes fixation caused by chronic inflammation of the middle ear. The intraoperative measurement of stapes mobility may influence the strategy of the surgeon. Furthermore it would be helpful in patient consulting prior to a revision-tympanoplasty with predicting the potential hearing improvement.     

Human middle-ear sound transfer function and cochlear input impedance

The middle-ear pressure gain, defined as the ear canal sound pressure to cochlear vestibule pressure gain, GME, and the ear canal sound pressure to stapes footplate velocity transfer function, SVTF, simultaneously measured in 12 fresh human temporal bones for the 0.05 to 10 kHz frequency range are reported. The mean GME magnitude reached 23.5 dB at 1.2 kHz with a slope of approximately 6 dB/octave from 0.1 to 1.2 kHz and -6 dB/octave above 1.2 kHz. From 0.1 to 0.5 kHz, the mean GME phase angle was 51 degrees, rolling off at -78 degrees /octave above this frequency. The mean SVTF magnitude reached a maximum of 0.33 mm s(-1)/Pa at 1.0 kHz with nearly the same shape in magnitude and phase angle as the mean GME. The ratio of GME and SVTF provide the first direct measurements of Z(c) in human ears. The mean Z(c) was virtually flat with a value of 21.1 acoustic GOmega MKS between 0.1 and 5.0 kHz. Above 5 kHz, the mean Z(c) increased to a maximum value of 49.9 GOmega at 6.7 kHz. The mean Z(c) angle was near 0 degrees from 0.5 to 5.0 kHz, decreasing below 0.5 kHz and above 5 kHz with peaks and valleys.     

Malleus-to-footplate ossicular reconstruction prosthesis positioning: cochleovestibular pressure optimization.

AIMS: To determine 1) the best position for hydroxylapatite malleus-to-footplate (MFP), ossicular replacement prosthesis (ORP) in reconstructed ears, and 2) whether preserving the stapes superstructure (SS), when present, has acoustic advantages. BACKGROUND: Positioning of the MFP-ORP head beneath the neck of the malleus may produce maximal force, whereas positioning beneath the manubrium of the malleus may produce the greatest displacement. It is not clear which is the optimal placement position. In addition, we look at the effect of the SS on sound transmission to the inner ear in ossicular reconstruction. METHODS: The ear-canal air pressure and vestibular hydro-pressure were measured in human cadaver temporal bones with incus intact, removed, and replaced with the MFP-ORP; the ORP head was placed at three different positions on the malleus (head, mid-manubrium, and umbo) while keeping its base at the center of stapes footplate with intact or removed stapes SS. The vestibular pressure ratio between the ear with intact incus and MFP-ORP reconstructed ear is defined as Lmfp, the loss caused by the prosthesis in relation to the normal ossicular chain. RESULTS: The mean magnitude of Lmfp, averaged in the important speech frequency region of 0.5 to 3 kHz, is approximately 7.8 dB at the neck with stapes SS. In comparison, mean magnitude of Lmfp for mid-manubrium without stapes SS is 15 dB (p = 0.04), and with the stapes SS it is 16 dB (p = 0.05), whereas at the umbo without SS it is 15 dB (p = 0.03). In the 8 kHz region, the mean magnitude of Lmfp is approximately 1 dB with the stapes SS intact and approximately 8.5 dB when it was removed (p < 0.09). CONCLUSION: There are significant physiologic advantages to placing the hydroxylapatite MFP-ORP beneath the neck of the malleus and preserving the SS.     

A new tool for testing ossicular mobility during middle ear surgery: preliminary report of four cases.

OBJECTIVE: We developed an ossicular vibration tester for the objective and quantitative assessment of ossicular mobility, which is one of the most critical factors affecting postoperative hearing after tympanoplasty. METHODS: Our device consists of three components: a probe shaft with a curved tip to be attached to the target ossicle, a vibration exciter to activate the probe, and a piezoelectric sensor to detect vibrations of the probe. These components are encased in a stainless steel holder, allowing easy hand manipulation during ear surgery. The probe is activated with an electric signal at around 1,600 Hz. The system is controlled with a laptop computer, and the results are presented as the ratio of the ossicular resistance (ROR) to a reference value as a percentage. One measurement takes 10 ms. The device was applied in four selected patients during ear surgery. RESULTS: Several measurements in two of the cochlear implantees showed a greater difference in the RORs of the stapes (15-20% in Case 1 and 35-45% in Case 2), whereas the RORs of the malleus and incus were within the same range. This was thought to correspond to the partial cochlear calcification noted in Case 2. In Case 3, who underwent surgery because of otosclerosis, the ROR of the stapes was high, ranging from 70 to 80%. When measured for the malleus-incus fixation anomaly (Case 4), the ROR of the malleus and incus was in the range of 60 to 70%. Owing to the limited surgical view, the ROR of the stapes could not be measured. No problems related to the measurements with this device were noted. CONCLUSION: The design, principles, measuring procedures, and preliminary results of our new tool for testing ossicular mobility are reported. Measuring the ossicular mobility during surgery may provide important information for deciding the surgical procedures.     

A novel implantable hearing system with direct acoustic cochlear stimulation

A new implantable hearing system, the direct acoustic cochlear stimulator (DACS) is presented. This system is based on the principle of a power-driven stapes prosthesis and intended for the treatment of severe mixed hearing loss due to advanced otosclerosis. It consists of an implantable electromagnetic transducer, which transfers acoustic energy directly to the inner ear, and an audio processor worn externally behind the implanted ear. The device is implanted using a specially developed retromeatal microsurgical approach. After removal of the stapes, a conventional stapes prosthesis is attached to the transducer and placed in the oval window to allow direct acoustical coupling to the perilymph of the inner ear. In order to restore the natural sound transmission of the ossicular chain, a second stapes prosthesis is placed in parallel to the first one into the oval window and attached to the patient's own incus, as in a conventional stapedectomy. Four patients were implanted with an investigational DACS device. The hearing threshold of the implanted ears before implantation ranged from 78 to 101 dB (air conduction, pure tone average, 0.5-4 kHz) with air-bone gaps of 33-44 dB in the same frequency range. Postoperatively, substantial improvements in sound field thresholds, speech intelligibility as well as in the subjective assessment of everyday situations were found in all patients. Two years after the implantations, monosyllabic word recognition scores in quiet at 75 dB improved by 45-100 percent points when using the DACS. Furthermore, hearing thresholds were already improved by the second stapes prosthesis alone by 14-28 dB (pure tone average 0.5-4 kHz, DACS switched off). No device-related serious medical complications occurred and all patients have continued to use their device on a daily basis for over 2 years.     

Stapes Vibration in the Chinchilla Middle Ear: Relation to Behavioral and Auditory-Nerve Thresholds

The vibratory responses to tones of the stapes and incus were measured in the middle ears of deeply anesthetized chinchillas using a wide-band acoustic-stimulus system and a laser velocimeter coupled to a microscope. With the laser beam at an angle of about 40 ° relative to the axis of stapes piston-like motion, the sensitivity-vs.-frequency curves of vibrations at the head of the stapes and the incus lenticular process were very similar to each other but larger, in the range 15–30 kHz, than the vibrations of the incus just peripheral to the pedicle. With the laser beam aligned with the axis of piston-like stapes motion, vibrations of the incus just peripheral to its pedicle were very similar to the vibrations of the lenticular process or the stapes head measured at the 40 ° angle. Thus, the pedicle prevents transmission to the stapes of components of incus vibration not aligned with the axis of stapes piston-like motion. The mean magnitude curve of stapes velocities is fairly flat over a wide frequency range, with a mean value of about 0.19 mm^.(s Pa⁻¹), has a high-frequency cutoff of 25 kHz (measured at −3 dB re the mean value), and decreases with a slope of about −60 dB/octave at higher frequencies. According to our measurements, the chinchilla middle ear transmits acoustic signals into the cochlea at frequencies exceeding both the bandwidth of responses of auditory-nerve fibers and the upper cutoff of hearing. The phase lags of stapes velocity relative to ear-canal pressure increase approximately linearly, with slopes equivalent to pure delays of about 57–76 μs.     

Simultaneous bilateral stapes surgery--a pilot study

CONCLUSIONS: The short-term postoperative results of bilateral stapes surgery were satisfactory. Hearing results between the two ears were comparable and there was no increased complication risk for the second ear. The results are encouraging, although a larger series and longer follow-up time are needed to confirm them. OBJECTIVE: The purpose of our study was to evaluate the preliminary outcome of simultaneous bilateral stapes operation. PATIENTS AND METHODS: Eight patients suffering from bilateral otosclerosis and one from osteogenesis imperfecta were prospectively included in the pilot study. Both ears were operated under general anesthesia by the same surgeon. Inclusion criteria were mean conductive hearing loss of 15 dB or more at frequencies 0.5-4.0 kHz and negative Rinne fork test (256 Hz) on both sides. Patients with mean thresholds for sensorineural hearing over 40 dB or other otoneurological diseases or medications were excluded. Pure tone audiogram was performed 3 months after the operation. RESULTS: The air-bone gap diminished from 28 (range 19-41) to 10 (range 4-23) dB in the first ear and from 24 (range 16-40) to 8 (range 3-19) dB in the second. Four patients experienced mild, temporary dizziness during rapid head movements, but that resolved fully. No patient suffered significant sensorineural hearing loss.     

Simultaneous Measurements of Ossicular Velocity and Intracochlear Pressure Leading to the Cochlear Input Impedance in Gerbil

Recent measurements of three-dimensional stapes motion in gerbil indicated that the piston component of stapes motion was the primary contributor to intracochlear pressure. In order to make a detailed correlation between stapes piston motion and intracochlear pressure behind the stapes, simultaneous pressure and motion measurements were undertaken. We found that the scala vestibuli pressure followed the piston component of the stapes velocity with high fidelity, reinforcing our previous finding that the piston motion of the stapes was the main stimulus to the cochlea. The present data allowed us to calculate cochlear input impedance and power flow into the cochlea. Both the amplitude and phase of the impedance were quite flat with frequency from 3 kHz to at least 30 kHz, with a phase that was primarily resistive. With constant stimulus pressure in the ear canal the intracochlear pressure at the stapes has been previously shown to be approximately flat with frequency through a wide range, and coupling that result with the present findings indicates that the power that flows into the cochlea is quite flat from about 3 to 30 kHz. The observed wide-band intracochlear pressure and power flow are consistent with the wide-band audiogram of the gerbil.     

Perioperative glucocorticoid treatment does not influence early post-laser stapedotomy hearing thresholds

OBJECTIVE: The aim of this study was to evaluate the efficiency of prophylactic perioperative glucocorticoid treatment during stapes surgery in preventing damage to the inner ear and reducing the frequency of early postoperative complications. STUDY DESIGN: A prospective, randomized, unblinded study design was selected. SETTING: The study was conducted at an academic tertiary referral center. PATIENTS: Ninety-five consecutive patients undergoing erbium:YAG laser-assisted stapedotomy for otosclerosis between 1996 and 1999 were included. MAIN OUTCOME MEASURES: The preoperative minus postoperative (1-4 days and at least 6 weeks) average pure-tone bone conduction thresholds at 1, 2, and 4 kHz were compared in the prednisolone and control groups by the Mann-Whitney U Test. In addition, the occurrences of sensorineural hearing loss of >10 dB, nystagmus, vertigo, and tinnitus were counted and evaluated by use of the Freeman-Halton or Fisher's exact test, respectively. RESULTS: Prophylactic perioperative prednisolone treatment was not able to improve the early postoperative average bone conduction thresholds or reduce the frequency of early sensorineural hearing loss (p > 0.5). The patients who received perioperative prednisolone treatment experienced postoperative vertigo more frequently than did the control patients (p < 0.05). CONCLUSION: Perioperative cortisone prophylaxis for prevention of inner ear damage during stapes surgery is ineffective and is associated with increased postoperative patient discomfort.     

The effects of mass loading the ossicles with a floating mass transducer on middle ear transfer function.

HYPOTHESIS: The aim of this study was to measure the mass loading effect of an active middle-ear implant (the Vibrant Soundbridge) in cadaver temporal bones. BACKGROUND: Implantable middle ear hearing devices such as Vibrant Soundbridge have been used as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Other than the obvious disadvantage of requiring implantation middle ear surgery, it also applies a direct weight on the ossicular chain which, in turn, may have an impact on residual hearing. Previous studies have shown that applying a mass directly on the ossicular chain has a damping effect on its response to sound. However, little has been done to investigate the magnitude and the frequency characteristics of the mass loading effect in devices such as the Vibrant Soundbridge. METHODS: Five fresh cadaver temporal bones were used. The stapes displacement was measured using laser Doppler vibrometry before and after the placement of a Vibrant Soundbridge floating mass transducer. The effects of mass and attachment site were compared with the unloaded response. Measurements were obtained at frequencies between 0.1 and 10 kHz and at acoustic input levels of 100 dB sound pressure level. Each temporal bone acted as its own control. RESULTS: Placement of the floating mass transducer caused a reduction of the stapes displacement. There were variations between the bones. The change of the stapes displacement varied from 0 dB to 28 dB. The effect was more prominent at frequencies above 1,000 Hz. Placing the floating mass transducer close to the incudostapedial joint reduced the mass loading effect. CONCLUSION: The floating mass transducer produces a measurable reduction of the stapes displacement in the temporal bone model. The effect is more prominent at high frequencies.     

Effect of freezing and thawing on stapes-cochlear input impedance in human temporal bones

The use of thawed frozen temporal bones offers advantages over fresh bones in the study of middle-ear and inner-ear mechanical function. We show, however, that freezing and thawing can cause a reduction in the magnitude of the input impedance of the stapes and cochlea Z_SC in unfixed temporal bones from human cadavers of as much as a factor of 3–10 over the frequency range 25 Hz–7 kHz. Z_SC is considered to be the sum of the impedances of the annular ligament Z_S and the cochlea Z_C and has been shown to be controlled by Z_S below 1 kHz and by Z_C at higher frequencies [Merchant et al., 1996. Hear. Res. 97, 30–45]. Experiments in which the inner ear was opened, drained, and refilled identified two mechanisms by which freezing and thawing can cause a reduction in the magnitude of Z_SC (|Z_SC|). Freezing can allow air to enter the inner ear, with the result that |Z_C| is reduced above about 1 kHz; and freezing can reduce |Z_S|, which causes a reduction in |Z_SC| below 1 kHz. Changes in the phase angle of Z_SC induced by freezing were small and were consistent with changes in |Z_SC|. Removing air from the inner ear returned Z_C to near its value in fresh bones, but |Z_SC| remained lower in some thawed bones by a factor of 2–3. Investigations of middle-ear function for which Z_SC is critical should use fresh temporal bones only or should allow for the possible reduction in |Z_SC| in thawed frozen bones.     

耳硬化症和中耳畸形患者的宽频声导抗研究

目的探讨宽频声导抗测试对耳硬化症和中耳畸形辅助诊断中的应用价值。方法收集耳硬化症组45耳,先天性中耳畸形组13耳,另有正常组76耳作为对照,所有受试者均行宽频声导抗测试,对各组峰压下的声能吸收率进行分析比较。结果峰压下,耳硬化症组的声能吸收率在917/972~1029/1091~1297/1456/1731/2059~3462/4000~5339Hz比正常组的显著减小(P<0.05)。耳硬化症患者在1kHz以下较正常组无异常切迹。峰压下,先天性中耳畸形组的声能吸收率在408~749/7336~7772Hz比正常组的显著增大(P<0.05),在1059~1224/1297/1414~1456/4000~4490Hz比正常组的显著减小(P<0.05)。69%(9/13)的先天性中耳畸形患者在1kHz以下有一切迹。结论声能吸收率鼓室图在1kHz以下出现切迹提示患者存在镫骨畸形合并锤骨和/或砧骨畸形。仅镫骨固定患者1kHz以下无切迹。宽频声导抗对于术前评估耳硬化症和中耳畸形患者中耳听骨链情况具有现实意义,可作为辅助耳硬化症和中耳畸形诊断的听力学检查之一。     

Holographic observation of the tympanic membrane vibration after stapes fixation

Sclerosis of auditory ossicle was experimentally induced by fixation of the stapes, and its effect on the tympanic membrane vibration was examined using fresh 10 canine temporal bones by means of holographic interferometry. By changing the sound pressure (from 90 to 110dB) and the frequency (from 250Hz to 8kHz) in steps, vibration of the membrane was induced in a free field. At each frequency, the vibration of the membrane was photographed by the time averaged method using He-Ne laser. A small hole was created in the tympanic bulla and the stapes was fixed with an adhesive (Alon Alpha), followed by closure of the hole. Before stapes fixation, the posterior part of the membrane showed a simple vibration pattern, forming cocentric interference circles at frequencies from 250Hz to 2kHz. At 3kHz, segmental vibration began to be noted, and complex segmental vibration was seen at frequencies 4.5 and 6kHz. The vibration after stapes fixation became simpler at frequencies over 3kHz, accompanied by decrease in the number of segmental vibrations. Vibration amplitude in the posterior part of the membrane decreased from 250Hz to 3kHz, while it increased at frequencies over 4kHz. In the anterior part of the membrane, the amplitude decreased at frequencies under 2kHz, remained unchanged at 3kHz and increased at frequencies over 4kHz after stapes fixation. In the tip of the manubrium mallei, the amplitude decreased at frequencies under 3kHz and increased at frequencies over 4kHz. Thus, a shift of peak vibration to high sound region was observed after stapes fixation at every part of tympanic membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of a direct acoustic cochlear stimulator

This study aimed to assess the functional results of a new, active, acoustic-mechanical hearing implant, the Direct Acoustic Cochlear Stimulation Partial Implant (DACS PI), in a preclinical study. The DACS PI is an electromagnetic device fixed to the mastoid by screws and coupled to a standard stapes prosthesis by an artificial incus (AI). The function of the DACS PI-aided reconstruction was assessed by determining: (1) the maximum equivalent sound pressure level (SPL) of the implant, which was obtained from measurements of the volume displacement at the round window in normal and implanted ears, and (2) the quality at the coupling interface between the AI of the DACS and the stapes prosthesis, which was quantified from measurements of relative motions between the AI and the prosthesis. Both measurements were performed with fresh temporal bones using a scanning laser Doppler interferometry system. The expected maximum equivalent SPL with a typical driving voltage of 0.3 V was about 115-125 dB SPL up to 1.5 kHz in reconstruction with the DACS PI, and decreased with a roll-off slope of about 65 dB/decade, reaching 90 dB SPL at 8 kHz. The large roll-off relative to a normal ear was presumed to be a relatively high inductive impedance of the coil of the DACS PI actuator at higher frequencies. Good coupling quality between the AI and the prosthesis was achieved below the resonance (～1.5 kHz) of the DACS PI for all tested stapes prostheses. Above the resonance, the SMart Piston, which is composed of a shape-memory alloy, had the best coupling quality.     

Inner ear depression after middle ear interventions

BACKGROUND: Any type of otosurgical procedure involves the risk of inner ear damage. As middle ear surgery is also performed for functional reasons this risk should be taken into consideration. The aim of this study was to analyse the frequency and the nature of sensorineural hearing loss following chronic ear surgery. PATIENTS: A total of 3989 middle ear cases operated on between 1991 and February 1999 at the Department of Otorhinolaryngology, Head and Neck Surgery, University of Würzburg, Germany were studied retrospectively: 781 type I tympanoplasties, 2408 type III tympanoplasties and 800 cases of stapes surgery. The pre- and the postoperative audiograms in the frequency range between 500 and 8000 Hz were analysed and correlated to the different intraoperative findings. RESULTS: Sensorineural hearing loss occurred in a total of 1.3% of 2224 patients with normal preoperative bone conduction thresholds: 0.2% became deaf, 0.8% acquired a high tone loss at 4 kHz and in 0.3% patients also 2 kHz was affected. None of the documented intraoperative complications such as bleeding, unexpected opening of a semicircular canal, extensive manipulation at the ossicular chain or a gusher phenoma showed a relevant effect on postoperative bone conduction thresholds. The incidence of high tone loss was not increased in cases of extensive drilling of the temporal bone. An unexpected opening of the vestibulum led to a small, but statistically significant change in postoperative bone conduction thresholds. CONCLUSIONS: Our results demonstrated that the risk for sensorineural hearing loss caused by middle ear surgery is low. None of the analysed factors seems to be a relevant prognostic risk factor for postoperative inner ear depression.     

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.     

On the influence of the middle ear muscles upon changes in sound transmission

Summary The influence of artificially induced impedance changes on the frequency response of the middle ear has been investigated in three experienced listeners. The tensor-reflex has been simulated by application of positive and negative air-pressure to the outer ear canal. In this test-situation, the thresholdshift (L) obtained is greatest in the surrounding of the first resonance of the middle ear (L = 8 dB at 500 Hz). For bone-conduction, the effect is weaker by about 2 dB than for air-conduction. The change in sound transmission is constant for all SPL's and is mainly due to the impedance change of the middle ear.In contrast the influence of the stapedial reflex is strongly dependent on SPL. In the range between hearing-threshold and 70 dB (HL) the attenuation is only 2 dB below 1 kHz. At higher levels the attenuation may amount to 30 dB. Thus, excitation of the cochlea remains nearly constant. We suppose that the intensitydependent influence of the stapedius reflex on sound transmission is due to a change of the stapes motion. The regulating device works without considerable distortion but with an attack-time of about 100 ms. The phenomenon of conductive recruitment in otosclerosis is probably due to the lack of this regulating effect by the fixed stapes. One function of the stapedial reflex could be the protection of the ear from high amplitudes during phonation and shouting. Furthermore, because frequencies above 1 kHz are also attenuated, a protective function of the stapedial reflex in industrial noise exposure can be assumed.     

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.     

Multi-frequency tympanometry in experimentally-induced cochlear lesions in chinchillas and guinea pigs

OBJECTIVES: To establish that susceptance-conductance tympanograms at a probe-tone frequency of 2 kHz reflects the status of the annular ligament (AL) and through it of the cochlea. METHODS: Experimental study in 5 chinchillas and 22 guinea pigs. Six validating experiments were used: blockages of the stapes and of the round window membrane (RWM), fistula of the RWM, fluid removal from the cochlea, injection of saline in the scala tympani (ST) and acoustic trauma (AT). Quantitative data (mean values of Y226, FR, Y2000, G2000 and B2000) and shape of the curves were analyzed before and immediately after lesions were done. RESULTS: Guinea pig was the most convenient provided bulla was vented and the same tip was used along the experiments. Only the shape of the curves are discriminant: 1/a supplementary sharp peak, centered around negative pressures, is observed in Y/G tympanograms in every case of RWM fistulas and in some case of AT. 2/injection of saline into ST induces immediate and reproducible Y2000, G2000, et B2000 curves modifications. 3/RWM and stapes blockages provoke foreseeable stiffening and sharpening of the tympanograms at 2 kHz. 4/on the contrary, fluid removal from the cochlea induces multiple peaks curves. CONCLUSIONS: Experimentally-induced modifications at the AL either direct (stapes blockage) or indirect by AT or decrease/increase of pressure load at the cochlear interface at the footplate result in noticeable, constant, reproducible changes of curves registered at 2 kHz. The stapes behaves both as the plotter of the curves and the interpreter of the inner ear pressure.     

Effect of middle ear fluid on sound transmission and auditory brainstem response in guinea pigs

Combined measurements of middle ear transfer function and auditory brainstem response (ABR) in live guinea pigs with middle ear effusion (MEE) are reported in this paper. The MEE model was created by injecting saline into the middle ear cavity. Vibrations of the tympanic membrane (TM), the tip of the incus, and the round window membrane (RWM) were measured with a laser vibrometer at frequencies of 0.2-40?kHz when the middle ear fluid increased from 0 to 0.2?ml (i.e., full fill of the cavity). The click and pure tone ABRs were recorded as the middle ear fluid increased. Fluid introduction reduced mobility of the TM, incus and RWM mainly at high frequencies (f?>?1?kHz). The magnitude of this reduction was related to the volume of fluid. The displacement transmission ratio of the TM to incus varied with frequency and fluid level. The volume displacement ratio of the oval window to round window was approximately 1.0 over most frequencies. Elevation of ABR thresholds and prolongation of ABR latencies were observed as fluid level increased. Reduction of TM displacement correlated well with elevation of ABR threshold at 0.5-8?kHz. Alterations in the ratio of ossicular displacements before and after fluid induction are consistent with fluid-induced changes in complex ossicular motions.