DE102004056522A1 - Ear-drum acoustic irradiation measurement device for use during surgery, has microphone to receive acoustic signals irradiated by ear-drum for evaluating coupling quality of stimuli of transducer based on frequency responses of signals - Google Patents

Abstract

The device has an actuator to shift the stirrup to the cochlea side and the ear-drum to pars tensa side when a speech processor controls a hearing aid such that the ear-drum irradiates acoustic signals. A microphone provided external to the auditory canal receives the acoustic signals. Coupling quality of a stimuli generated by a transducer is evaluated based on the comparison of the frequency responses of the acoustic signals.

Description

Description (from DE patent application 199 14 922 A1)

since Recently, partially and fully implantable hearing aids for the rehabilitation of a pure inner ear hearing loss or a combined conduction and inner ear hearing loss with mechanical stimulation of the damaged ear in the market available (Journal HNO 46: 844-852, 10-1998, H. P. Zenner et al., "First Implantations of a complete implantable electronic hearing system in patients with inner ear hearing loss "; Journal HNO 46: 853-863, 10-1998, H. Leysieffer et al., "Ein Completely implantable hearing system for people with inner ear hearing loss: TICA LZ 3001 "; US-A5 277 694; US-A-5 788 711; US-A-5 814,095; US-A-5 554 096; US-A-5 624 376, DE patent application 198 59 171.3-31). Especially with fully implantable systems eliminates the Visibility of the system so that beside the advantages of the high sound quality of the open ear canal and the full practicality of a high future Patient acceptance can be assumed. Basically in these implantable hearing systems used as an output signal a mechanical, vibratory stimulus, which stimulates the middle ear or inner ear directly. The coupling of the mechanical stimuli generated by an electromechanical transducer, happens by direct mechanical connection of the oscillating Transducer element to the ossicular chain or an ossicle of the middle ear or to the inner ear (DE patent application 197 38 587 7-35) or by a power coupling over an air gap at e.g. electromechanical transducers.

The coupling quality The mechanical stimulus is affected by many parameters and contributes to the rehabilitation of hearing damage and the perceived listening quality with at. Intraoperatively, this quality of coupling is difficult or unpredictable, because the movement amplitudes of the vibrating parts, even at the highest stimulation levels in a range around or far below 1 micron and therefore by direct Visual inspection are not assessable. Even if this is done by others technical measuring methods succeeds, e.g. by intraoperative laser measurements / e.g. Laser Doppler vibrometer), the uncertainty of a long-term stable secure coupling remains, as these include, inter alia, necrosis, tissue regeneration, Air pressure changes and other external and internal influences can be negatively affected.

Especially remains at full implantable systems the need to increase the coupling quality of the transducer to be able to judge in a full implant is not possible, individual System components separated at their technical interfaces measure when e.g. the implant wearer laments a decayed transmission quality, by reprogramming individual audiological fitting parameters is not improvable and therefore an operative intervention for improvement the situation can not be excluded is. Even if such a case does not exist, there is basically that scientific interest, about one meaningful Monitor function of the long-term development of the quality of the converter coupling to feature.

Technical area

in the Framework of the study for Approval of the system for The US Federal Drug Administration (FDA) has 10 patients with an implantable hearing aid (Symphonix Soundbridge) provided. It was during the operation did not perform any functional checks of the system. This was not intended by the manufacturer. This is even more amazing because the surgeon uses the system, especially the floating mass transducer (FMT), must handle with pliers and hooks to install it. Here are technical defects can not be ruled out.

The Association of German-speaking audiologists and neuro-pathologists of the German Society of Otolaryngology, Head and Neck Surgery (ADANO) calls in the
Guideline Supply of Active Implantable Hearing Aids Design Version 2.0 dated 9/22/99
...
4.3 Special features in the ENT surgery
...
"Device for Intraoperative Functional Control of the Implant"
...
The system described below represents such a device.

Working principle of the middle ear

The Sound signal reaches through the external auditory canal the eardrum. Here the signal is transmitted to the chain, from different ossicles (Hammer, anvil, Stirrup) consists. At the other end of the chain, the signal is through an auditory bone (Stirrup) transferred to the inner ear with the snail (cochlea). Here is the mechanical Signal converted into an electrical signal and relayed in the auditory nerve (N.cochlearis), see picture 1.

Now hits a sound wave on the drum This is deflected by the sound pressure. This movement is on the order of about 1 to 3 angstroms = 10 ^-10 m. At the Pars tensa the hammer is fused with the eardrum. The anvil (incus) is connected to the hammer by a joint. The other side of the anvil is connected to the stapes again via a joint. The base plate of the stirrup is fused with the oval window of the snail and transfers the movements to the inner ear, see picture 2.

Between Anvil and stirrup there is a flat ball joint and between the hammer and anvil a saddle joint. The ossicles have only a very small joint mobility to each other. This is by it justified that the Joints between the individual ossicles of various ligaments and Slime pylons are held in place and supplied. There is a mechanical connection between the eardrum and the snail over the chain.

The Rotary axes of hammer and anvil are marked by the dots. These are formed by the bands. The movement on the eardrum inwards is indicated by the arrows in the Picture 3 marked. The new position due to the deflection is spotted located. By the lever laws finds a reduction of the Deflection of the eardrum instead. A big deflection of the eardrum requires a small deflection on the stapes and vice versa, see picture 3.

Functional principle of implantable hearing Aids:

The Functional principle is the same for all implantable hearing aids. The chain will by an actor, in addition to the natural Movement through the eardrum, set in mechanical motion.

Fully implantable system "TICA"

The first fully implantable hearing aid is of three components connected by wires. The microphone is located in the external auditory canal the skin and absorbs the sound. In the following picture 4 the lower one Component. The signal is passed to the speech processor, in the Picture 4 shows the component on the left side. The speech processor contains also the battery. The charging and control is done inductively by the skin from the outside. The Processed sound signal is forwarded to an actuator. This works on the piezo principle. The signal is transmitted by a pushrod transferred to a blind hole in the anvil. A typical feature of the piezo actuator is a relatively low transmission power in the low-frequency range, see Figure 4.

Semi-implantable system "Symphonix-Soundbridge"

The Sound signal is picked up by the microphone and in the speech processor modulated. This high-frequency modulated with the speech signal Signal is transmitted wirelessly through the patient's skin to the internal recipient (implant). Here, the low-frequency electrical signal is demodulated regained and through a line on the actor, here floating Mass Transducer (FMT), transmitted. This is attached to an auditory bone (anvil), clamped. The FMT transmits the sound signal due to vibrations on the chain. Through these additional movements of the chain becomes the natural Sound signal of the eardrum reinforced, see Figure 5.

Operating principle of floating Mass Transducer (FMT):

Of the FMT is a spring-mass system that is electrodynamic with the voice signal is controlled. The mass represents a small permanent magnet, which over the Power of an electrical coil is deflected. Two small rubber balls The springs form at both ends of the magnet, see picture 6.

c

= Federkonstante der Gummikugeln,

m

= Masse des Magneten

Functional principle of the FMT is an oscillatory spring-mass system. According to the motion differential equation, there is a natural resonance frequency:

c

= Spring constant of the rubber balls,

m

= Mass of the magnet

At this frequency (f ₀ ), the deflection is greatest when the system is always driven with the same excitation, here the same electrical signal. The natural resonance frequency of the FMT is approx. 2kHz, see picture 7.

Theory of the measuring arrangement

When the implant is electrically actuated by the speech processor, the actuator causes the chain to move mechanically. This movement is transmitted on one side of the chain through the stirrup to the worm. On the other side of the chain, the eardrum on the pars tensa is also put into mechanical vibration by the hammer. This causes a radiation of sound over the eardrum instead. This can be recorded with a microphone in the external auditory canal. Especially if you ver the auditory canal behind the microphone to the outside ver closes.

Practice of the measuring arrangement:

Out the above considerations results in the following measuring arrangement while Implantation: The implant is packed through a sterile belonging to the implant system Voice processor activated. The packaging may e.g. me an OP camera cover respectively. This is a proven technique in cochlear implantation.

The The signal emitted by the eardrum is picked up by a microphone in the auditory canal. The auditory canal is otherwise outward sealed by a commercial Ear protection, see Figure 8. Stimulation is stimulated acoustically by a commercially available active box with appropriate frequency range from safe distance with approx. 1 m distance. The whole system is controlled by a notebook, see picture 9.

The following parameters have proven to be practical:
Stimulus: sweep from 100 Hz to 10 kHz, about 60 dB, duration 1 minute.
Recording: Max. Sample rate, 48 kHz, Max. Sensitivity.

Meßdurchführung:

step 1: First, with the sweep from 100 Hz to 10 kHz at about 60 dB a zero curve of the level in the closed auditory canal without the speech processor recorded. This curve serves as a calibration curve and represents the base for the further considerations; in the curves in Figure 10, 11, 12 in each case the lower curve.

step 2: In a further measuring run the speech processor is placed in sterile packaging on the patient. Then the patient is measured as in step 1. The measured values are each recorded in the PC. In the curves in Figure 10, 11, 12 each the upper curve.

measurement evaluation:

The sampled values are essentially Fourier transformed, so that he in each case the frequency range of the measurement of step 1 and step 2 receives. The difference of the curves is for the rating is crucial.

Examples of measured patients:

Patient 1:

Of the Patient is very satisfied with the system. The FMT is fully oscillatory. The Self-resonant frequency at about 2000 Hz is easy to recognize. The peak at about 5000 Hz is the noise the fan of the notebook and caused by the inadequate damping against the external noise, see Picture 10.

Patient 2:

identical Measuring system. The natural resonance frequency of the FMT at 2 kHz can be clearly seen. Of the Patient uses the system, see Figure 11.

Patient 3:

To recognize is just a kink in the frequency response at about 2 kHz. The system is therefore technically functional. But there is hardly any radiation of sound through the eardrum instead. The patient is non-user, because he claims to have no advantage through the system. Presumably, the free vibration of the system is hindered, that it on the wall in the middle ear, see picture 12.

Summary:

at all measured patients using the system (Figs. 10 and Picture 11), let himself clearly detect a difference in amplitude or a resonance peak. A measured patient (3) with scarcely detectable resonance peak later than Non-users out (Figure 12).

Transferability to other implantable Hearing Aids:

The measuring arrangement is also transferable to other implantable hearing aids as long as the chain remains functional and through the eardrum a sound radiation can take place.

Outlook:

The measuring arrangement is easy and cheap. The time required is 2 minutes pure measuring time plus Operation of the system as well as setup (fitting of the microphone) and Degradation justifiable. The measuring system Fulfills the criterion of simple functional control of the implant during the OP.

• – Laserdopplervibrometrie DE 198 01 959 A1
• – Mark Winter: Erstes Messsystem für die Implantation von Hörsystemen entwickelt, Hörakustik 4/2002 S.5

Other options of intraoperative function control are:

• - Laser Doppler Vibrometry DE 198 01 959 A1
• - Mark Winter: First measuring system developed for the implantation of hearing systems, Hörakustik 4/2002 p.5

Claims (5)

Device for measuring the Schallabstrah development of the eardrum through a microphone in the external auditory canal; in fully or partially implantable hearing aids intraoperatively or postoperatively. External acoustic stimulation by a sound signal with corresponding for the implant suitable frequency range for generating the vibrations of the Chain. In this case, the implant belonging to the speech processor for signal conversion used acoustically-electrically. Alternatively: Stimulation by an internal implant generated signal for generating the vibrations of the chain. Assessment of the coupling quality by comparing the frequency responses of the radiated sound signal from 1. with / without active speech processor from 2. or 3. according to the frequency response of the entire system of Speech processor and mechanical converter. Assessment of the coupling quality by the frequency response of the Difference signal in the time domain.