JPS62122662A - Nerve stimulation apparatus for single tube type hearing correcting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a nerve stimulation device for a hearing corrector.

[Conventional technology]

The mechanical vibrations of the sound are transmitted to the lymph in the inner ear by the movement of the eardrum and ossicles, and then stimulate the ciliated sensory cells of the calf. Ciliated cells convert mechanical vibrations into electrophysiological signals and transmit them to the dendrites of auditory nerve fibers. These signals are then guided to the brain by the auditory nerve.

For severe alarm sounds with defective ciliary sensory cells, conventional hearing aids are ineffective as they only slightly increase the mechanical energy delivered to the ear. Therefore, conventional hearing aids must be replaced by devices that use electrical current to directly stimulate the auditory nerve.

Currently known neural stimulators for hearing aids are divided into "multi-tube" and "single-tube" devices.

The former is based on the following points. That is, a complex sound wave composed of many sinusoidal components with different frequencies generates vibrating peaks, and these vibrating peaks are distributed on the basement membrane containing ciliated cells in the white area. This basilar membrane vibrates with maximum amplitude, mechanically resonating with the sound frequency, causing the high-frequency Baka-oxu spiral to vibrate, and the low frequency to vibrate its top. Multi-tube stimulators take advantage of this property by providing n electrodes in the same area, each electrode being assigned to one of n consecutive fiber groups of the auditory nerve. These electrodes are selectively excited by separate tubes that are dedicated to certain frequency bands, so that together these separate tubes can cover a predetermined region of the audible spectrum.

These multitubular bovine nerve stimulators, an example of which can be found in Patent Specification FR-A-2383657, have excellent performance, but are very complex and therefore costly. or,
Placing n electrode bundles in the white area is a very difficult surgery and must be performed completely in - times.

This is because repeated surgeries can risk damaging certain very fragile internal fibers of the cow. Therefore, the installation of these expensive but high-performance multitubular devices is reserved for patients whose electrophysiological parameters indicate a good chance of realizing the full potential of the device.

Patients who cannot take advantage of the richness of spectral information provided by multi-tube devices are generally better off using single-tube devices, which are much cheaper but more difficult to install. In these devices, a single stimulation electrode is implanted near the base of the calf or outside the calf, ie, in the middle ear. Similar to multi-tube devices, single-tube devices include one microphone suitable for capturing sound signals, one electronic processor that converts the sound signals into electrical signals, and one that uses these electrical signals to stimulate the auditory nerve. Means for transmitting to the electrodes is incorporated.

The single-tube auditory nerve stimulation device is particularly well known in patent and patent application publication specification E.
It is described in PA-OU78069.

With such a device, people with congenital alarms or those who developed alarms as adults can perceive the rhythm and intensity of sounds, but they can also be used in conversations between multiple people without turning into lip reading. The alarm does not provide enough information to the nervous system to identify the interlocutor. Also, patent invention specification GB-A-213
The 3697 includes one transducer suitable for catching the sound signal, one low-pass filter, one logarithmic amplifier for compressing the filtered signal from the transducer, and extracting the fundamental frequency or voiced sound from the audio signal. Single-tube devices incorporating multiple peak detectors are known.

Extraction of voiced sounds allows patients equipped with this device to reproduce the "tone" of the sound signal emitted by the speaker.

However, this device has a serious drawback in this sense, since the stimulation signal consists of pulses with a time approximately equal to one-half of the fundamental period of the audio signal. In other words, the lower the speaker's voice, the stronger the sound perceived by the patient, and vice versa. This does not correspond to the reality of physical phenomena perceived by people with normal hearing.

In fact, if the speakers are located at different distances from the patient, the patient may experience an illusion. This is because the most strongly perceived sound does not necessarily come from the speaker closest to the patient.

It should be noted that this device incorporates relatively complex means used to distinguish between voiced and unvoiced signals. When an unvoiced sound is detected, a stimulus of predetermined characteristics is delivered to the patient.

The same applies when a voiced sound is not detected or a voiced sound is determined to be a non-voiced sound for some reason. Therefore, the information conveyed to the patient in these two cases is arbitrary.

[Problem that the invention seeks to solve]

It is an object of the present invention to improve the conversational ability of severe alarm patients using a simple single-tube device that provides more detailed information to the patient's nervous system than that provided by conventional single-tube devices. It is in.

[Means and effects for solving the problem] Therefore, the invention provides a microphone suitable for capturing sound signals, converting this sound signal into an electrical signal, and expressing voiced sound from the speaker's audio signal. A single-tube type that includes one electronic processor with a built-in circuit that can extract the component and generate an electrical signal with the same frequency as the component, and a means for transmitting the electrical signal to the excitation circuit of the auditory nerve stimulation electrode. Targeting nerve stimulation devices for hearing correction devices. The feature of this device is that the stimulation signal representing the total energy and possible voiced sounds of the sound signal is applied to the stimulation electrode by an excitation circuit, so that the above-mentioned modulation of the electrical signal is performed depending on the total energy of the sound signal caught. The circuit that performs the encoding is built into the electronic processor.

The excitation circuit also includes a power source that emits constant current stimulation pulses with a predetermined charge that is a function of the total energy of the sound signal, and after each stimulation pulse of a given polarity, a power supply of the opposite polarity and a preceding one. Preferably, means are incorporated for generating an electrochemical reaction neutralizing pulse having the same charge as the stimulation pulse.

This desirable form of construction allows for reversibility and harmlessness of the complex electrochemical reactions produced in biological tissue by electrical stimulation, which in conventional devices may alter the electrical properties of the stimulation.

The invention is particularly applicable to the treatment of severe alarm sounds and tinnitus.

〔Example〕

Other features and advantages of the invention can be understood more clearly by reference to the accompanying drawings and from reading the description given below, by way of non-limiting example.

FIG. 1 shows the circuitry that makes up the transmitter subassembly 1 and the receiver subassembly 2 of the device.

The transmitter subassembly 1 includes a microphone 3 for catching sound signals, and depending on its output, for example, 3m-10
An amplifier 4 with a gain adjustable between 0.00 and 0.00 is driven.

The output of the variable gain amplifier 4 is applied to the input of a compressor 5, which serves to adapt the dynamics of the sound information signal to the dynamics of the ear.

Thus, for example, from 40 dBA (perceptual limit) to 100 dBA
Sounds up to BA (pain threshold) can be compressed in circuit 5 so that a deviation of 6 dB is obtained with respect to the energy of the stimulation electrical signal. This compression is, of course, always proportional to the instantaneous energy of the sound collected, so as not to distort the perceptual scale in the brain (in people with normal sensation, such compression is achieved by the eardrum and middle ear). ). The compressor 5 can be composed of an electronic circuit having a logarithmic transfer function, for example. The output of compressor 5 is the rectification of the compressed signal.
applied to the input of the filter stage 6 and pulse generator 7
To control this, a voltage representing the compressed energy of the original sound signal is generated. The output of the compressor 5 is also applied to the input of a low-pass filter 8, such as a third-order filter, with a cutoff frequency of several hundred hertz, for example about 400 Hz. The output signal of the filter 8 is coupled to the input of a detector 9, which has an adjustable limit value so as to only take in signals representing sound signals with a lowest level, for example 40 dBA. However, it should be noted that the detector 9 can also be installed upstream of the filter 8 or the compressor 5.

The electrical signal passed through the filter 8 and the detector 9 corresponds to the fundamental frequency of the sound signal applied to the microphone 3. That is, in the case of an audio signal, it represents the voiced sound of the speaker's voice.

This voiced signal drives a trigger input of a pulse generator 7 which generates square pulses with a pulse width that is a function of the volume signal emerging from the rectification and filtering stage 6, synchronously with the voiced signal. This pulse generator contains two potentiometers 10.11. The potentiometer 10 allows the doctor to adjust the maximum duration of the pulses emitted by the generator 7 when installing the device on the patient, and the potentiometer 11 allows the patient to adjust the "volume" during use. It is something. The patient can therefore reduce the maximum pulse duration himself, for example by one third of the maximum duration set by the doctor.

The output signal Sc of the pulse generator turf is shown in FIG. Here, T is the time of the pulse and P is the period of the voicing signal. The adjustment by the potentiometer 10 is such that T is always within the range of about 5 to 500 μs, and about 4
It is desirable to adjust the sound level between 0 dBA and 80 dBA so as to vary between the two extremes according to a logarithmic law. A high frequency signal of 3 MHz, for example, generated from the oscillator 12 is modulated within the modulator 13 by a pulse train output from the generator 7. The signal resulting therefrom drives the transmitting antenna 14 via a power stage 15 .

The signal emitted by antenna 14 is received by a receiver subassembly using receive antenna 16 tuned to the frequency of the carrier wave emitted by oscillator 12. Following the receiving antenna 16 is a demodulation stage 17 which rectifies and filters the received signal and reproduces a pulse signal adapted to the pulse signal of FIG. One of the output terminals of the stage 17 is connected to the stimulation electrode 18 via a constant power supply 19 and a capacitor 20. Also, the other terminal is the stimulation electrode 18.
The ground electrode 21 is connected to the ground electrode 21 combined with the ground electrode 21 . Step 1
An electronic switch 22 operated by the output signal of 7 is connected between a point common to the power supply 19 and the capacitor 20 on one side and a ground electrode 21 on the other side. This electronic switch 22, which may consist of a conventional circuit of two transistors, for example, is turned off when the output signal of stage 17 (see FIG. 2) is at a high level and when power supply 19 excites the stimulating electrodes.
become. Further, when the signal switches to a low level, it becomes ON, and as a result, the capacitor 20 is discharged through the circuit including the electronic switch 22 and the interelectrode gap. A Zener diode 23 is also connected between the output terminals of stage 17 in order to limit any overvoltage that may occur between these terminals to a permissible value, for example 20V.

Generally, the receiver subassembly forming the excitation circuit is implanted between the patient's skin and the skull near the ear. The stimulating electrode can be grounded outside the carcass or the cow if it is within the electric field induced by the active electrode and the ground electrode. The external transmitter subassembly 1 is held by the patient such that the transmitting antenna is positioned opposite the receiving antenna. Microphone 3 is
It is preferable that the transmitting antenna 14 be fixed on the pinna or around the ear.

These two devices are connected by electrical cords to a patient-held pocket case that contains the other circuitry of the transmitter subassembly.

As for the principle of operation, the audio signal caught by the microphone 3 is processed by stages 4 to 9, and the signal Sc shown in FIG. 2 is output from the pulse generator 7. After modulation, amplification, transmission and demodulation, this signal Sc controls the constant power supply 19. When the signal SC switches to high level I, the power supply 19 becomes conductive and the electronic switch 22 is turned off. The equivalent electrical diagram of the excitation circuit at that time is as shown in FIG.

There, a power supply 19 delivers a constant current through a capacitor 20 in an impedance Z (a symbol representing the impedance of the biological tissue located between electrodes 28 and 21). As shown in the graph of FIG. 2, in which the movement of the current in the stimulating electrode is represented by the second curve I, the stimulating electrode is at a predetermined strength for a period T during which the control signal is at a high level. Power is supplied by a constant current Is. When the control signal switches to low level B, the power supply 19 is blocked by this control signal, and the switch 22 is turned on. The equivalent electrical diagram of the excitation circuit at that time is as shown in FIG. Where,
Capacitor 20 is connected in series with impedance Z via electrodes 18 and 21. When the switch 22 is turned on, the capacitor 20 is discharged in the impedance Z, so that the current direction is reversed, as shown in FIG. 2, until a new pulse of the control signal Sc appears. Note that when a new pulse of the control signal Sc appears, the conduction cycle of the power source 19, the charging cycle of the capacitor 20, and the discharging cycle of the capacitor 20 by turning on the switch 22 start anew.

As a result of the above, a constant current Is of a predetermined strength is sent into the stimulated biological tissue for a time T proportional to the amount of wa suppressed.

This is the electric charge inside the capacitor 20 and inside the tissue Q-■sXT
corresponds to This method of stabilizing constant current stimulation eliminates impedance differences in biological tissue that can be observed between individuals, as well as time-dependent impedance deviations in electrical circuits - for example, changes in electrode position and electrical characteristics, and changes in implantable devices. It is possible to avoid deviations caused by deterioration of electronic components, changes in the position of the transmitting antenna with respect to the receiving antenna, etc. Furthermore, since the capacitor discharges as a result of each charging assumption or each charging alternation, it can be seen that the average value of the current in the stimulating electrode is zero over all cycles. In other words, it can be seen that the balance of charges sent to the auditory nerve is perfectly balanced over the entire cycle. This is very important from a physiological point of view.

Another advantage of the device described above lies in the way the sound signal is processed. That is, from the audio signal, the patient's auditory nerve can be stimulated with an electrophysiological signal representing the amplitude of the audio as well as the voiced sound. In other words, this electrophysiological signal retains the highly characteristic voiced sounds of each person, but has been stripped of information tied to the speech itself. Therefore, with some training, it is possible with the above-mentioned device to determine the voice of an interlocutor who is having a severe alarm conversation directly from the sound of the person's voice, rather than from the movements of the person's lips. We can think that it must be. Of course, this does not mean that the patient does not have to rely on lip reading to provide intelligible content to the speaker's voice, but it does mean that the patient may only be able to perceive dissonances modulated to barely discernible amplitudes. This is a significant advance compared to the single tube devices of previous technology.

The only difference between the construction alternative of the excitation circuit of FIG. 5 and that of FIG. 1 is that the discharge current regulator 25 is connected in series between the electronic switch 22 and the ground electrode 21. This regulator makes it possible to limit the maximum value of the current in the ground electrode 21 to the value 1d during the discharge process of the capacitor 20, as shown in the negative part of the curve I in FIG. Furthermore, the excitation circuit of FIG. 5 is the same as the excitation circuit of FIG. 1 in all respects.

Zener diode 23, which protects the tissue from overvoltages that may occur between terminals 26 and 27, is optional.

Next, reference will be made to FIG. Here, the same reference numerals are used to represent the positions of the same components as in FIG. 1, but each number has been increased by 100.

The difference between this second manufacturing form and the first manufacturing form shown in Fig. 1 is as follows.
It concerns only the volume encoding method of the caught signal. Therefore, the rectification and filtering stage 106 drives the modulator 113 via the current amplitude encoding stage 130 rather than the pulse generator 107.

The pulse signal resulting from this encoding is shown in demodulated form in FIG. This pulse signal includes a current encoded first pulse T1 and a second pulse T'l. The time t1 of the first pulse is variable, for example from 1 to 5/I11, and is proportional to the strength of the current that must be generated from the power supply 119. Also, the time To of the second pulse is constant in this application, during which a current is sent to the electrode 118, the intensity of which is determined by the pulse T1. Encoding stage 13
0 operates similarly to the pulse generator 7 and emits a pulse T1 of time t1 proportional to the sound volume under the control of a voiced signal applied to its trigger input. pulse·
The generator 107 outputs a pulse T'2 for a fixed time To with a predetermined delay relative to the rising edge of the pulse T1. Therefore, three consecutive pulses T'1,
T'2. The time P separating the rising edge of T'3 represents the fundamental period of the audio signal, as in the first production configuration. After modulation, this signal is transmitted to receive antenna 116.

The decoding stage 131 connected to the receiving antenna 116 is
Corresponding pulses T1, T2 . A current 1s1, 1112. whose intensity is proportional to the time of T3. This current generator 119 is controlled so that IS3 is generated by the current generator.

This constant current, which is proportional to the volume of the sound signal caught, causes pulses T'1. T' 2. In this application, T' 3 is sent to electrode 118 for a time TO which is constant. In other respects, the operation of the second manufacturing configuration is exactly the same as the operation of FIG. 1. It is clear that this second construction also allows a completely controlled amount of electricity to be delivered into the auditory nerve.

Further, FIG. 9 shows a signal illustrating an alternative of the second manufacturing form for reference. In this alternative, the pulse generator 107 emits a pulse of time TO whose reproduction period T is the reproduction period of the fundamental wave of the captured sound signal. The encoding stage 130 determines the amplitude of the carrier wave modulated by the output signal of the generator 107 depending on the strength of the current generated.

In the receiver subassembly 102, a decoding stage 131
controls the current generator so that a current is generated that is proportional to the amplitude of the carrier wave applied to it.

Of course, in order to generate a current proportional to the volume of the sound signal sent to the stimulation electrode for a predetermined period of time,
It is also possible to use other techniques such as frequency modulation or phase modulation. The common feature of these various schemes is that they allow a completely defined amount of electricity to be delivered to the auditory nerve.

However, it is understood that the invention is in no way limited to the use of this advantageous property, and that the electrophysiological signals representing voiced sounds or captured audio signals may be variable, e.g. in voltage, rather than in intensity or pulse width. It must be understood that it can also have a sinusoidal waveform or other waveforms.

〔Effect of the invention〕

As mentioned above, the single-tube neural stimulation device for auditory correction according to the present invention can provide more detailed information to the patient's nervous system than that obtained with conventional single-tube devices, thereby reducing the severity of severe alarm sounds. Conversation skills can be improved.

[Brief explanation of drawings]

Figure 1 is a block diagram of the first manufacturing form of the nerve stimulation device, Figure 2 is a diagram showing the waveform of the control signal and the waveform of the current sent to the stimulation electrode of the device in Figure 1, and Figure 3 is the stimulation Figure 4 is an equivalent electrical diagram of part of the excitation circuit of the apparatus during the neutralization process; Figure 5 is an alternative electrical diagram of the excitation circuit of the apparatus of Figure 1; 6 is a diagram similar to the diagram in FIG. 2, showing the waveform of the current obtained in the excitation circuit of FIG. 5, and FIG. A block diagram, FIG. 8 is a diagram showing the waveform of the control signal and the waveform of the pulsed current generated by the excitation circuit of the device of FIG. 7, and FIG. 9 is a waveform of the signal illustrating an alternative fabrication of the device of FIG. 7. This is a chart showing the following. DESCRIPTION OF SYMBOLS 1... Transmitter subassembly, 2... Receiver subassembly, 3... Microphone, 4... Variable gain amplifier, 5... Compressor, 6,106...
Rectification/filtering stage, 7,107...Pulse generator, 8...Low pass filter, 9...Detector,
10゜11... Potentiometer, 12... Oscillator, 13.113... Modulator, 14... Transmitting antenna, 15... Power stage, 16.116...
Receiving antenna, 17... Demodulation stage, 18, 118...
... Stimulation electrode, 19.119 ... Power supply, 20...
... Capacitor, 21 ... Ground electrode, 22 ...
Electronic switch, 23... Zener diode, 13
0...Encoding means, 131...Decoding stage.

Claims (14)

[Claims] (1) Microphone suitable for capturing sound signals (3) 1
, one electronic processor (4-9; 104-109) that converts this sound signal into an electrical control signal (Sc), one auditory nerve stimulation electrode (18; 118), and one control signal (Sc).
an excitation circuit (18-23; 118-123, 131) for applying a stimulation signal to the aforementioned electrodes that is a function of Sc);
and means (12-17; 112-117) for transmitting the above-mentioned electrical control signal (Sc) to the excitation circuit,
The electronic processor is capable of extracting a component representing a voiced sound from the speaker's audio signal and generates an electrical signal having the same frequency as the component (7-9; 107-109);
a control signal and a circuit for modulating and encoding said electrical signal in response to the total energy of the captured sound signal to generate a stimulus signal representative of the total energy and possible voiced tones of the sound signal;
6, 7; 106, 113, 130). (2) a power source (19; 11) that emits constant current stimulation pulses with a predetermined charge that is a function of the total energy of the sound signal;
9), as well as means for generating, after each stimulation pulse of a given polarity, an electrochemical reaction neutralizing pulse of opposite polarity and the same charge as the previous stimulation pulse (
20, 22; 120, 122) are included in the excitation circuit. (3) The power supply (19; 119) is connected to the capacitor (20; 12
0) to the stimulating electrode (18; 118) and a capacitor (20; ; 120) is provided with an electronic switch (22; 122) which is operated by the transmission means (12-17; 112-117). The device described. (4) A discharge current regulator (25) of the capacitor (20) connected in series between the electronic switch (22) and the other electrode (21) is included ( 3). (5) Power supply (19; 119) and capacitor (20; 1
20) are connected in series with the stimulation electrodes (18; 118) and that an electronic switch (22; 122) is connected to the common point for the power supply and capacitor on the one hand and the ground electrode (2
1; 121). (6) The electrical control signal (Sc) is a square signal, and when the signal is at the first level, the power supply (19; 119) becomes conductive, the switch (22; 122) is turned OFF, and the signal becomes the second level. The device according to claim 3, characterized in that the power supply is blocked and the switch is turned on when the level is on. (7) The device according to claim (1), characterized in that the extraction circuit for the above-mentioned components representing voiced sounds (8; 100) is a low-pass filter. (8) a compressor (with its output connected to each of the rectifying and filtering stage (6; 106) and the low-pass filter (8; 108), from which an output signal representative of the compressed energy of the captured sound signal is generated; 5; 105) and a variable gain amplifier (
4; 104) is included in an electronic processor. (9) the outputs of the low-pass filter (8) and the rectification and filtering stage (6) are modulated for a time (T) proportional to the above-mentioned energy with a recurrence period (P) equal to the reproduction period of the above-mentioned components; Device according to claim 8, characterized in that it is connected to a generator (7) emitting pulses of. (10) An excitation circuit (1
8-23). The device according to claim (9). (11) In response to the output signal of the rectification and filtering stage (106), a coding stage (130) of the current strength of the stimulus signal (this coding stage provides the above-mentioned control signal Sc) has the same frequency as the above-mentioned component. Claim (8) characterized in that the output of the low-pass filter (108) is connected to a generator (107) that applies pulses (T'1, T'2, T'3) of
). (12) During the time (T0) of the above-mentioned pulses (T'1, T'2, T'3), the stimulation electrode (118) is connected to the power source (119).
) is included in the excitation circuit (118-123, 131) a coding stage (131) and a power supply (119) for a control signal (Sc) that determines the strength of the current (Is1, Is2, Is3) supplied to the The device according to claim (11), characterized in that: (13) Claims characterized in that the above-mentioned pulses (T'1, T'2, T'3) have a fixed time (T0) (
The device according to any one of 11) and (12). (14) Excitation circuit (18-23; 118-123, 13
2) and stimulation electrodes (18; 118) forming a first subassembly (2) implantable under the patient's skin, a microphone (3) and an electronic processor (4-
9; 104-109) constituting a second subassembly (1) adapted to be held externally by the patient, as well as the transmission means (12-17; 112-1);
Device according to claim 1, characterized in that 17) comprises a receiving antenna (16) and a transmitting antenna (14) adapted and associated with the first and second subassemblies, respectively.