A new device for real-time peroperative monitoring of ossicular chain reconstruction during middle ear surgery.

To limit functional surgical failure and reduce the rate of revision surgery in case of surgical ossicular chain reconstruction, a piezoelectric device was developed for assessment of ossicular chain vibrations during the middle ear surgery. The device resembled a pen and consisted of a reusable main body and a disposable sensitive head including piezoelectric polymer sensor. Almost all of components of the device were made of polymer for light weight and for acoustic impedance matching to the middle ear system. Several frequencies can be analyzed simultaneously and several measures can be taken by time. The results showed that the device can record normal and reconstructed ossicular chain vibration in response to an acoustic stimulation, with similar results to those achieved by laser Doppler vibrometer. This light, handheld and low-cost device allows fast, easy and safe assessments of normal ossicular chain mobility and ossicular chain reconstruction efficiency. Primary pre-clinical trial showed very promising performance of the device that could be used to qualitatively control ossiculoplasty during real-time surgical procedure. Clinical assessments will be done to further evaluate the real-life performance of the device.

High frequency bone conduction auditory evoked potentials in the guinea pig: Assessing cochlear injury after ossicular chain manipulation.

Permanent high frequency (>4 kHz) sensorineural hearing loss following middle ear surgery occurs in up to 25% of patients. The aetiology of this loss is poorly understood and may involve transmission of supra-physiological forces down the ossicular chain to the cochlea. Investigating the mechanisms of this injury using animal models is challenging, as evaluating cochlear function with evoked potentials is confounded when ossicular manipulation disrupts the normal air conduction (AC) pathway. Bone conduction (BC) using clinical bone vibrators in small animals is limited by poor transducer output at high frequencies sensitive to trauma. The objectives of the present study were firstly to evaluate a novel high frequency bone conduction transducer with evoked auditory potentials in a guinea pig model, and secondly to use this model to investigate the impact of middle ear surgical manipulation on cochlear function. We modified a magnetostrictive device as a high frequency BC transducer and evaluated its performance by comparison with a calibrated AC transducer at frequencies up to 32 kHz using the auditory brainstem response (ABR), compound action potential (CAP) and summating potential (SP). To mimic a middle ear traumatising stimulus, a rotating bur was brought in to contact with the incudomalleal complex and the effect on evoked cochlear potentials was observed. BC-evoked potentials followed the same input-output function pattern as AC potentials for all ABR frequencies. Deterioration in CAP and SP thresholds was observed after ossicular manipulation. It is possible to use high frequency BC to evoke responses from the injury sensitive basal region of the cochlea and so not rely on AC with the potential confounder of conductive hearing loss. Ongoing research explores how these findings evolve over time, and ways in which injury may be reduced and the cochlea protected during middle ear surgery.

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.

Non-ossicular signal transmission in human middle ears: Experimental assessment of the "acoustic route" with perforated tympanic membranes.

Direct acoustic stimulation of the cochlea by the sound-pressure difference between the oval and round windows (called the "acoustic route") has been thought to contribute to hearing in some pathological conditions, along with the normally dominant "ossicular route." To determine the efficacy of this acoustic route and its constituent mechanisms in human ears, sound pressures were measured at three locations in cadaveric temporal bones [with intact and perforated tympanic membranes (TMs)]: (1) in the external ear canal lateral to the TM, P(TM); (2) in the tympanic cavity lateral to the oval window, P(OW); and (3) near the round window, P(RW). Sound transmission via the acoustic route is described by two concatenated processes: (1) coupling of sound pressure from ear canal to middle-ear cavity, H(P(CAV) ) identical withP(CAV)P(TM), where P(CAV) represents the middle-ear cavity pressure, and (2) sound-pressure difference between the windows, H(WPD) identical with(P(OW)-P(RW))P(CAV). Results show that: H(P(CAV) ) depends on perforation size but not perforation location; H(WPD) depends on neither perforation size nor location. The results (1) provide a description of the window pressures based on measurements, (2) refute the common otological view that TM perforation location affects the "relative phase of the pressures at the oval and round windows," and (3) show with an intact ossicular chain that acoustic-route transmission is substantially below ossicular-route transmission except for low frequencies with large perforations. Thus, hearing loss from TM perforations results primarily from reduction in sound coupling via the ossicular route. Some features of the frequency dependence of H(P(CAV) ) and H(WPD) can be interpreted in terms of a structure-based lumped-element acoustic model of the perforation and middle-ear cavities.

Intraoperative ossicular loading with the Otologics fully implantable hearing device.

CONCLUSIONS: Use of the recently introduced intraoperative loading instrumentation during surgery improves the coupling efficiency and consistency of a fully implantable hearing device to the ossicles and ultimately leads to better patient performance with the device. BACKGROUND: Patient performance with an implantable hearing device is dependent on effective coupling of the implant to the middle ear ossicles. New intraoperative instrumentation aids the surgeon in coupling the implantable hearing device and consistently optimizes patient performance. MATERIALS AND METHODS: The middle ear transfer function for the Otologics MET Ossicular Stimulator (METF(MET)) is a measure of transducer coupling efficiency, defined as acoustic threshold (in dB HL) minus implant threshold (in dB MET). This transfer function was measured in the Otologics US Phase I Semi-Implantable Clinical Trial without intraoperative loading instrumentation and in the Otologics US Phase I Fully Implantable Clinical Trial with intraoperative loading instrumentation. The same operative techniques and transducer design were used in both studies. The theory of operation and surgical technique for using this instrumentation are described. RESULTS: In the semi-implantable clinical trials, METF(MET) was -10 to -15 dB for frequencies above 1 kHz, and dropped to -15 to -20 dB for lower frequencies. Fully implantable clinical trial results were 10-20 dB better than the semi-implantable trial results, with less variability at all frequencies. These findings indicate more consistent and better coupling efficiency of the transducer to the ossicles.

[Auditory brainstem responses evoked by direct mechanical stimulation of the ossicular chain. Objective preoperative testing of candidates for implantable hearing aids]. / Frühe akustisch evozierte Potenziale bei direkter mechanischer Stimulation der Gehörknöchelchenkette. Objektive Eignungsdiagnostik vor Implantation von Hörsystemen.

BACKGROUND AND OBJECTIVE: The function of several implantable hearing systems is based on the vibratory excitation of the ossicular chain. For preoperative testing, malleus vibration audiometry has been described [7]. In special cases, it could be desirable to perform objective testing before implantation. We therefore studied the auditory brainstem responses (ABR) evoked by vibratory stimulation of the ear drum. METHOD: The ABR evoked by vibratory and acoustical click stimulation were recorded in 20 subjects with normal hearing at four different stimulus intensities. For the vibratory stimulation (v-ABR), the transducer rod was brought into mechanical contact with the eardrum under microscopic control. This setup was further used for the determination of the individual subjective threshold. The v-ABR were compared to conventional ABR recordings. RESULTS: In all subjects, the v-ABR could clearly be identified. At high stimulus levels, the complete wave pattern was observed in 15 of 20 cases. There is no essential difference between v-ABR and conventional ABR with respect to the incidence and parameters of the potentials. At high stimulus levels, a pronounced stimulus artefact impedes the identification of wave I in some cases. Moreover, the quality of v-ABR is limited by the uncomfortable situation and incomplete relaxation of the subject. CONCLUSIONS: The measurement of vibratory evoked ABR is practicable without hazards for the patient and it yields reliable results. The hearing threshold for click stimuli can be determined from the incidence and amplitude of the responses. The loudness associated with the click stimuli can be estimated from the response latency. Therefore, the investigation of v-ABR not only gives evidence of the individual suitability for implantable hearing aids but its outcome may also be useful as an orientation for the postoperative fitting.

The use of the startle reflex measurement in patients with various types of fixation of the ossicular chain.

The results of startle and acoustic stapedius reflex measurements can be used to subclassify various types of fixation of the ossicular chain. Reflex measurements were performed on a group of subjects with normal hearing and on a group of patients with surgically verified ossicular chain fixation. In 97% of the subjects with normal hearing (n = 30), reproducible impedance changes were observed as part of a startle reaction and four different reaction patterns could be distinguished. In a subgroup of subjects with normal hearing who had a relatively, statistically significant, high acoustic reflex threshold, a characteristic response was found which was most probably caused by contraction of the tensor tympani muscle only. The same response was detected in 77% of the patients (n = 22) with otosclerosis. In the remaining 23%, no middle ear impedance changes occurred as part of a startle reaction. In five out of six patients with fixation of the malleus, no response was observed. Although the startle reflex measurement is a valuable tool for distinguishing between stapes fixation and multiple ossicular chain fixations, the results are not conclusive.

Stapedius reflex growth function in cochlear implant patients.

The growth function of the contralateral stapedius reflex elicited by analog electrostimulation via cochlear implant was investigated in 9 patients and compared to reflex functions obtained for acoustic stimulation in 3 normal-hearing subjects. Sinusoidal signal bursts with the same time pattern were used for the two stimulation modes, the contraction of the middle ear muscle was monitored by sampling the compliance change in the contralateral ear. The reflex amplitudes were found to increase with increasing stimulus intensity in all individuals except in 1 with electrical stimulation. The slope of the intensity function for electrostimulation ranged between 5 and 85%/dB and in the acoustical mode between 2 and 4%/dB. In case of electrostimulation a frequency effect was observed.

Multiple frequency, multiple component tympanometry: new approaches to an old diagnostic problem.

Tympanometry with low-frequency probe tones provides useful clinical information for patients with disorders of the tympanum, the tympanic membrane, and the Eustachian tube. Low-frequency, single component tympanometry, however, is relatively insensitive to many lesions that affect the ossicular chain. This review focuses upon a collection of four, interrelated acoustic measurement techniques that have been developed for identification and differential diagnosis of those middle ear disorders that do not always yield pathognomonic patterns with conventional tympanometry. Specifically, the initial hypotheses, the methods, normative data and representative clinical findings are summarized for: (1) a multiple frequency magnitude array; (2) a multiple frequency phase-angle array; (3) a three-dimensional array; and (4) a differential sound pressure level and phase plot.

Sweep-frequency tympanometry: its development and diagnostic value.

This reports a newly developed tympanometric system using a sweep-frequency probe tone. For a sweep-frequency tone ranging from 220 to 2 000 Hz, measurements of sound pressure (P) and phase were performed at ear canal pressures of 0 and -200 mm H2O. The results were expressed as a sound pressure curve (P0-P-200 in decibels), a phase curve (formula: see text) and a polar curve (formula: see text) against probe tone frequency. Both the frequency at which the sound pressure curve crossed the 0-dB difference line and the peak frequency of the phase curve shifted lower than normal for ossicular disruption and higher than normal for ossicular fixation. Changes in the sound pressure curve and in the phase curve were exaggerated for ossicular disruption and limited for fixation. As the result of these, the polar curve showed an expanded type for disruption and a compressed type for fixation. A review of 220-Hz tympanograms and of the polar curves for 10 patients demonstrated that the latter permitted a better discrimination among ossicular disorders.

Extratympanic manometry in man. Clinical and experimental investigations of the acoustic stapedius and tensor tympani contractions in normal subjects and in patients.

New ideas and inspirations for future human investigations have emerged from the experience obtained in this study. These investigations ought to be performed for both scientific and clinical reasons. It is the author's opinion that the ETM method is extremely useful and valuable. The author intends to continue the human investigations if proper conditions are available. The ETM equipment can also be further improved for scientific and special clinical investigations. For normal clinical practice a more "simplified" ETM equipment should be developed. Clinical investigations concerning the diagnosis of brain stem disorders and the selection of noise susceptible persons will be two of the primary clinical tasks.

[The use of the stapedius reflex in the fitting of hearing aids (author transl)]. / Utilisation du réflexe stapédien pour l'adaptation des prothèses auditives

The authors made experiments concerning the stapedius reflex without and with an hearing aid; there is a relation between this reflex and the discomfort threshold for the selection. The stimulus is given on a loudspeaker and the stapedius reflex permits in some cases to know the gain of the hearing aid and also the limit of discomfort. This method very useful particulary for children is objective.

Acoustic reflex relaxation in sensorineural hearing loss.

This study examined stapedial reflex recordings of pulsed pure tones (500, 1,000, 2,000, and 4,000 Hz) in 26 subjects with normal hearing and 18 with sensorineural impairment. The stapedial reflex tracings clearly differentiated the two groups of subjects. Like many of our special audiometric procedures, this test was least effective in those with mild hearing loss. The test also appeared to be useful in identifying high-frequency hearing losses. Although this reflex measurement appears to have potential as a clinical tool, additional field study appears necessary.

Stapedius reflex abnormalities in multiple sclerosis.

Thirteen patients suffering from multiple sclerosis were analyzed by a Madsen ZO 70 electroacoustic bridge connected to an electronystagmograph through an impedance adaptor. Threshold, amplitude, decay and difference limen of intensity (DLI) of the stapedius reflex were examined for the frequencies 500, 1 000, 2 000 and 4 000 Hz. The difference between standard audiometric results and stapedius reflex data stresses the value of reflex measurements in assessing brain stem pathology.

The role of the stapedius reflex in poststimulatory auditory fatigue.

The human ear is very resistant against noise-induced damage in the low frequency range. The aim of the present study was to investigate whether or not the stapedium reflex is of any importance for this resistance. Subjects with peripheral facial palsy (Bell's palsy) including unilateral stapedius muscle paralysis were exposed to several different levels of narrow band noise centered at 0.5 and 2.0 kHz. Temporary threshold shift (TTS) at 0.75 kHz was significantly higher in the affected than in the nonaffected ear after 0.5 kHz noise at and above 110 dB SPL. After the exposure with 2.0 kHz narrow band noise there was no difference in TTS at 3.0 kHz between the affected and nonaffected ear. It is concluded that the attenuation provided by the stapedius reflex reduces TTS after low frequency noise exposure. An implication is that the stapedius reflex also may have the function of protecting the ear from hearing damage caused by low frequency noise exposure.