[Active hearing implants in chronic otitis media]

In patients with inadequate hearing improvement after tympanoplasty and failure of conventional hearing aid fitting, active hearing implants provide an alternative treatment option. Active middle ear implants function as a vibromechanical bypass of the stiffness and damping effect of a poorly oscillating tympanic membrane and the (reconstructed) ossicular chain. The selection of the hearing system depends on the maximum output levels of the hearing system and the anatomical conditions in mostly multiply operated ears. The development of variable coupling elements for active middle ear implants led to an extension of the indications to include not only purely sensorineural hearing loss but also mixed and conductive hearing loss in patients, as the transducer can now be coupled to the (mobile) stapes or the round window membrane. The article provides an overview of current clinical study results and recommendations on the indications for active hearing implants in patients with chronic otitis media.

Sensor-actuator component for a Floating Mass Transducer-based fully implantable hearing aid

We propose a novel system based on the Floating Mass Transducer (FMT) to be used as the active component of a fully implantable, Vibrant Soundbridge-like middle ear implant. The new system replaces the external microphone used in the currently available design with an implantable piezoelectric sensor that is inserted into the incudostapedial joint and picks up the vibrations transmitted to the long process of the incus. The FMT is coupled to the round window of the cochlea. We characterize the system by measuring the gain in intracochlear sound pressure using laser Doppler vibrometry at a surgically installed "third window" into the cochlea of six temporal bones. Closed-loop feedback oscillations limit the system's available output. We show that using an adaptive control algorithm, a mean functional gain of up to 40 dB is achieved, which is similar to Soundbridge functional gain. The concept matches the FMT's one-point fixation philosophy and offers several advantages over other designs, namely an easy and time-efficient surgery, reversibility of implantation, and natural hearing for the prospective patient.

Middle ear reconstruction with a flexible prosthesis

The middle ear plays a crucial role in the quality of hearing. This complex construct performs different tasks like the protection against large air pressure input, the transmission of sound and its adaption to the inner ear impedance. Traumas, erosion by chronic otitis media or cholesteatoma, as well as other degenerative or damaging diseases, are reasons for a necessary reconstruction of specific middle ear structures. The reconstruction of the ossicular chain is very often performed by using rigid ossicular replacement prostheses made out of titanium, ceramics or bone. Tilting and dislocation of these passive implants are some of the known complications after middle ear surgery. They are related to loads at the implant coupling points in response to a tension change in the middle ear. The healing process, scar tension and ventilation problems are possible causes.

To increase the sound transmission quality of total reconstructions and safety in case of pressure dependent movement of the tympanic membrane, a novel flexible total ossicular replacement prosthesis (TORP) with a silicone coated ball joint prototype was developed and investigated. Besides measurements of first middle ear transfer functions of temporal bones, the mechanical properties of the flexible TORP were examined with stress relaxation investigations.

The novel silicone coated ball and socket joint TORP provides a sound transfer equivalent to the intact human middle ear at normal pressure and negative pressure in the middle ear. Together with the low stiffness values at an anatomically typical deflection of about 500 μm the prevention of a stiffening of the stapes annular ligament could be approved. Thus, improved acoustic transmission quality and reconstruction stability in comparison to common rigid titanium TORP could be determined. Nevertheless, further design improvements should be accomplished. The demonstrated flexible TORP can solve some common problems in middle ear reconstruction.

Health-related quality of life measurement after cholesteatoma surgery: comparison of three different surgical techniques

The objective of this study was to compare health-related quality of life (HRQOL) after sequential cholesteatoma surgery including exclusively transcanal technique (ETC), combined transcanal transmastoidal technique (TCM) and canal wall down surgery with obliteration (CWD). It was a clinical case study conducted in a tertiary referral center. 97 patients at least 12 months after cholesteatoma surgery were included. Interventions included sequential cholesteatoma surgery with ETC, TCM or CWD; ossiculoplasty with partial and total ossicular replacement prostheses. HRQOL assessed by Chronic Otitis Media Outcome Test 15 including an overall score and three subscores ('ear symptoms', 'hearing function' and 'mental health') as well as a general evaluation of HRQOL and the frequency of physician consultations, audiometric outcome related to HRQOL were the main outcome measures. Patients, who had undergone sequential cholesteatoma surgery, showed moderate restrictions in HRQOL postoperatively. Stratified for the three surgical techniques, patients receiving ETC tended to report lower restrictions in HRQOL. The ETC group offered a significantly lower value in the subscore 'ear symptoms'. The 'hearing function' was attributed to be the most restriction criteria for all techniques. The overall score and all subscores correlated moderately with the postoperative air conduction threshold. The strongest correlation coefficient was achieved for the subscore 'hearing function' (r(s) = 0.49, p < 0.001). Sequential cholesteatoma surgery offers acceptable moderate restrictions in HRQOL postoperatively. Patients receiving canal wall down surgery with obliteration showed equivalent limitations in HRQOL compared to closed techniques (ETC, TCM). The postoperative air conduction threshold was shown not to be a sufficient indicator for HRQOL. Therefore, disease-specific validated and reliable measuring instruments for HRQOL should be transferred from clinical research to clinical practice to provide an individualized postoperative assessment after cholesteatoma surgery.

Influence of the middle ear anatomy on the performance of a membrane sensor in the incudostapedial joint gap

There is a great demand for implantable microphones for future generations of implantable hearing aids, especially Cochlea Implants. An implantable middle ear microphone based on a piezoelectric membrane sensor for insertion into the incudostapedial gap is investigated. The sensor is designed to measure the sound-induced forces acting on the center of the membrane. The sensor mechanically couples to the adjacent ossicles via two contact areas, the sensor membrane and the sensor housing. The sensing element is a piezoelectric single crystal bonded on a titanium membrane. The sensor allows a minimally invasive and reversible implantation without removal of ossicles and without additional sensor fixation in the tympanic cavity. This study investigates the implantable microphone sensor and its implantation concept. It intends to quantify the influence of the sensor's insertion position on the achievable microphone sensitivity. The investigation considers anatomical and pathological variations of the middle ear geometry and its space limitations. Temporal bone experiments on a laboratory model show that anatomical and pathological variations of the middle ear geometry can prevent the sensor from being placed optimally within the incudostapedial joint. Beyond scattering of transfer functions due to anatomic variations of individual middle ears there is the impact of variations in the sensor position within the ossicular chain that has a considerable effect on the transfer characteristics of the middle ear microphone. The centering of the sensor between incus and stapes, the direction of insertion (membrane to stapes or to incus) and the effect of additional contact points with surrounding anatomic structures affect the signal yield of the implanted sensor. The presence of additional contact points has a considerably impact on the sensitivity, yet the microphone sensitivity is quite robust against small changes in the positioning of the incus on the sensor. Signal losses can be avoided by adjusting the position of the sensor within the joint. The findings allow the development of an improved surgical insertion technique to ensure maximally achievable signal yield of the membrane sensor in the ISJ and provides valuable knowledge for a future design considerations including sensor miniaturization and geometry. Measurements of the implanted sensor in temporal bone specimens showed a microphone sensitivity in the order of 1 mV/Pa. This article is part of a special issue entitled "MEMRO 2012".

[Evaluation of the Dresden Tympanoplasty Model (DTM)]

The training of microsurgical motor skills is essentiell for surgical education if the interests of the patient are to be safeguarded. In otosurgery the complex anatomy of the temporal bone and variations necessitate a special training before performing surgery on a patient. We therefore developed and evaluated a simplified middle ear model for acquiring first microsurgical skills in tympanoplasty.The simplified tympanoplasty model consists of the outer ear canal and a tympanic cavity. A stapes model is placed in projection of the upper posterior tympanic membrane quadrant at the medial wall of the simulated tympanic cavity. To imitate the annular ligament flexibility the stapes is fixed on a soft plastic pad. 41 subjects evaluated the model´s anatomical analogy, the comparability to the real surgical situation and the general model properties the using a special questionnaire.The tympanoplasty model was very well evaluated by all participants. It is a reasonably priced model and a useful tool in microsurgical skills training. Thereby, it closes the gap between theoretical training and real operation conditions.

Laser Doppler vibrometry of the middle ear in humans: derivation dependence, variability, and bilateral differences

OBJECTIVE

Derivation dependence, inter- and intrasubject/intertest variability, bilateral differences of the eardrum vibration characteristics have been investigated using laser Doppler vibrometry (LDV).

MATERIAL AND METHODS

A total of 31 normally hearing adults were examined. In each subject, both ears were consecutively stimulated by the chirp acoustic stimulus that covered 500-3700-Hz frequencies. The laser beam was directed to and the reflection was consecutively picked up from the tympanic membrane surface.

RESULTS

LDV curves derived from different eardrum loci possessed dissimilar characteristics. The derivation area dependence was particularly apparent for the stimulus frequency constituents above 1500 Hz. The intersubject variability of LDV parameters exceeded the intrasubject/intertest one. The intersubject divergences looked selectively distinct for the frequencies over 2000 Hz. Under repeated recordings, LDV parameters remained stable. The intertest differences, if appeared, concerned predominantly the magnitudes of separate frequency bands. LDV waveforms registered by experienced and beginner investigators were alike. Bilaterally derived LDV curves regularly differed from each other. In individual cases, the bilateral divergences approximated the intersubject deviation.

CONCLUSIONS

The derivation area on the eardrum should be taken into account when estimating the actual LDV recording. Over repeated recordings in separate individuals, LDV waveforms are stable while the experience of investigator has slight if any influence on the principal LDV characteristics. Due to bilateral differences in the middle ear transfer function, in LDV testing of the ear suspected to the pathology, LDV recording from the opposite healthy ear could hardly be taken as an appropriate reference sample.

[A new model for training in tympanoplasty]

BACKGROUND

Functional simulation of middle ear reconstruction is a valuable tools for training in otosurgery. We introduce a new experimental model which provides a direct acoustic feedback of the functional quality of ossicular chain reconstruction.

METHOD

In this model the tympanic membrane and the ossicular chain have to be reconstructed for proper sound transmission to an artificial inner ear receptor. The received signal is converted into acoustic information and consecutively provided via headphone.

RESULTS

Any changes in the reconstruction (e. g. tilting the prosthesis) can be experienced online and immediately optimized by the surgeon or a trainee.

CONCLUSION

The experimental model can be used for demonstration and training in otosurgery. This model is also suitable for comparing measurements of transfer functions in a calibrated version and can be applied to development and critical evaluation of middle ear prostheses.