A system of stimulating at least one nerve and/or muscle fibre.

The present invention relates to a system of stimu­lating at least one nerve and/or muscle fibre of an animate subject according to the preamble of claim 1.

An example of such a stimulating system for stimu­lating auditory nerves of a human being is known from IEEE Spectrum, volume 21, No. 1, January 1984. In this known sys­tem a receiving unit mounted in the neighbourhood of the ear of a sensory or cochlear deaf person comprises a microphone to "hear" or capture sounds existing around the deaf person and a speech processing unit spaced from the ear and connec­ted to the transmitting unit for processing the received sounds and for modulating waves to be transmitted to the implanted receiving section by the transmitting unit.

The present invention has for its object to provide a more accurate and versatile stimulating system.

Therefore the present invention is characterized according to claim 1.

The information supply means according to the present invention can comprise a receiver for radio frequency waves, but preferably comprise a detector for infrared radia­tion; the power supply means can comprise one or more batteries, but preferably comprise receiving means for radio frequency waves.

A search of prior art disclosed the following references: US-A-4.314.562, IEEE Spectrum, volume 21, No. 1, January 1984, US-A-4.142.532, DE-A-28 23 798, GB-A-2.134.335, US-E-26809.

Preferred embodiments of the present invention are claimed in the subclaims; embodiments of the present inven­tion will become clear on basis of the following description, including further advantages and details of the present invention, while referring to a drawing, in which are showing: <ul id="ul0001" list-style="none"><li>fig. 1 a perspective view of a deaf subject provi­ded with an implant according to the present invention;</li><li>fig. 2 a perspective and diagrammatic view of the transfer of electro-magnetic waves to the implant of fig. 1;</li><li>fig. 3 a view partly in section, partly in perspec­tive of another preferred embodiment of the stimulating sys­tem of the present invention;</li><li>fig. 4 a diagram illustrating the operation of the system of fig. 4;</li><li>fig. 5 an example of a signal arriving at the implant of fig. 3; and</li><li>fig. 6 an example of a stimulating signal.</li></ul>

An individual 2 (fig. 1, 2) is provided with an implant 3 for stimulating nerves (and/or muscle fibres) as is shown by curved broken lines 4. The implant 3 is supplied with energy and information by a transmitting member 6 provi­ded behind the ear flap or oracle 5, said transmitting member fed by a signal processor 7 which processes sound received by a (not shown) microphone.

The implant 3 (fig. 2) is provided with electronic components 8, 9, 10, 11 resp. and a coil or antenna 12. Electrical connections 13 of platinum or platinum iridium are used for supplying the required signals to an electrode. Arrows E show the radiated electro-magnetic energy, in which sound information is encoded.

A package 14 of the implant 3 consists of e.g. two casing parts 15 and 16 of biocompatible glass, e.g. Borosili­cate or lime glass of the Hermetronics Company from Slough in England. The parts 15 and 16 are sealed in a biocompatible way, e.g. by means of adhesive, laser welding, resist welding, ultrasonic welding or hot cap sealing. Conducts of the connections 13 through the package 14 are sintered.

In the package 14 helium gas can be inserted, such that by means of a helium sniffer the seal can be checked on hermeticity. It is also possible not to bring this package into an atmosphere consisting of helium or another gas during some time period and afterwards to check for hermeticity out­side this atmosphere (see e.g. Vakuum Technik, Rudolf A. Lang Verlag, 627 Idstein, 23 (1974) volume 3, pages 77-80). A hermeticity of 10⁻⁸ mbar.l/s can easily be achieved; this is sufficient for implantation in the human or other living body.

In another preferred embodiment of the present in­vention (fig. 3) an ear piece 20 which has the traditional shape to fit easily behind the ear 21 of a subject is provi­ded with a lead 22 for connection at 23 to a rod shaped ear piece or mold 24, e.g. of plastic material and formed such as to be inserted into the auditory duct of the subject. This ear mold 24 inludes a (not shown) coil or inductor to be coupled with an inductor 26 to be implanted around the audi­tory duct 25. Preferably this conductor or coil 26 - diameter and height e.g. 2 mm, diameter of the windings e.g. 0,7 mm - ­is conical, such as to fit around the inwardly tapering duct 25. The coil 26 is flexible by means of a layer of silicon around the windings, such as to prevent painful contact after implantation between ear piece 24 and coil 26.

By using the auditory duct 25 as site for transfer­ring energy into the body of the subject, by means of radio frequency waves, e.g. of a frequency of 100 - 500 kHz, accu­rate alignment between the two inductors will always be pro­vided. Conductor or coil 26 is connected by means of line 27 to implant 28 which consists of a housing 29 of titanium pro­vided with a window 38 of glass or transparant plastic or ceramic material.

The ear piece 20 is provided with a microphone 30. Electrical signals supplied by this microphone are fed through line 31 to a not shown speech processor (see e.g. fig. 2). This speech processor encodes information as required by the implant. This information is fed from the ear piece 20 opposite to the window 38 by means of a not shown infrared radiation emitting element 39 to the implant. This infrared radiation emitting element 39 is contacted directly to the skin. Although it appears almost form experiments that e.g. 30% or even 10% of this infrared radia­tion is lost in the tissue 32 before the window, the remai­ning part is sufficient to be detected behind the window 38 by means of an infrared radiation, without causing any damage to the tissue. The required power for the IR-detector is only a few µWatt so that the emitting element 39 wil emit e.g. a few mWatt of power, but more emitting power will be possible without damaging the animate tissue. The IR-transmitter and IR-detector are aligned in a natural way by means of the ear and traditionally shaped ear piece and mold; there is no significant anatomical spread in different ear locations. Also the implant can easily be secured to the skull 33 of the subject. Pulses can be transmitted at the high rate, pulses having a width of less than 400 nsec are achievable.

From the implant 28 there is provided a lead 34 to an electrode 35 which is to be implanted in the cochlea of the deaf subject. The electrode 35 has branches (not shown) for stimulating different locations within the cochlea. the electrode is flexible and provided with a hook shaped end part (not shown) such as to be easily implantable into the cochlea by a surgeon. Stimulation is achieved through physio­logical fluid and nerve fibres 36. Also there is connected to the implant 28 an antenna 37, the function of which will be described hereinafter.

Power from the lead 27 (fig. 4) is rectified in rectifier 40 and fed to a voltage supply 41, which supplies voltage to all the different functional blocks within broken line 42, as is indicated by arrows A. The functions within broken line 42 are included in a custom integrated circuit especially designed for the system of the present invention. The infrared radiation is detected by detector 43 and fed to input monitor 44; in case the puls shape is not correct - ­e.g. if a spike occurs -, a signal is fed to reset 45 which resets the integrated circuit and prevents a stimulating current within the cochlea. A pulse accepted by the input monitor will be fed to a pulse sequence detection unit 46 which detects time intervals between pulses, as hereinafter will be more fully described. The first pulse determines at 46 the mode in which the system will operate, the second pulse determines at 48 which of eight channels 51-58 of the electrode 35 will be activated, while at 49 the magnitude or quantity of the chosen channel is determined. At 60 the shape of the stimulating pulse is chosen by mode unit 47. Mode measuring is also chosen by mode unit 47 at 61. In the measu­ring mode a signal is provided by output 62 to the antenna 37. Clock 32 provides clock signals for the circuit; the clock rate can be set before implantation between 250nsec- 2 µsec. The clock is synchronized at receiving each next accep­ted pulse.

Fig. 5 shows an example of a pulse sequence to be transmitted by the ear piece and to be received by the IR-­detector 43 (fig. 4). T₀ is the period of one cycle of the clock 63 while P_s designates the synchronizing pulse having a width of 4 × T₀; T₁ selects the mode (in this case biphasic see fig. 6), which means that T₁ is between 2 × T₀ and 4 × T₀); P_m stands for mode selection pulse and a duration of 2 × T₀; T₂ defines the channel to be activated, in this case channel 2, which means that T₂ is in between 4 × T₀ and 6 × T₀; P_ch stands for channel selection pulse and has a duration of 2 × T₀; T₃ defines the strenght of the stimulating pulse at channel 2, in this case e.g. 1,5 mA; P_cs has a width of 2 × T₀.

Fig. 6 shows a biphasic pulse with a duration τ. and extending between V_max and ⁻V_max in which τ can be set before implantation and V_max is determined by T₃. The biphasic pulse is symmetric around the zero-axis, such that no charge will build up in the cochlea of the subject. The inverse of fig. 6 is called biphasic negative, in which the first edge of the pulse is going negative and the last edge is going downwardly. Other modes in which the system of the present invention can operate are so called normal modes (positive and negative) in which a constant current is supplied to two electrode branches, in which negative or positive decides which way the current will have to flow.

In the measuring mode there is supplied a measuring signal to the antenna, giving an indication of the supply voltage at 41 or the measured voltage at a selected elec­trode. The signals have e.g. a frequency of 1 MHz and can be detected outside the subject, such that the surveillance of correct operation of the implant can be established. When T₁, T₂ and T₃ have a relatively large value, the relative spread in those values is approximately held constant, such that the allowed absolute spread in values to be detected is increased.

The clock is only activated when the input monitor detects a synchronization pulse.

Reset unit 45 provides in resetting the circuit of fig. 4 at missing one pulse, at erroneous detection of the synchronizing pulse, detection of decreasing power supply, and spikes occurring in the information supply. Therefore the described coding provides a very safe stimulating system, without inducing damaging current in an anminate body.

The shown preferred embodiment for stimulating auditory nerves of a subject has external parts outside the animate body to be easily removed at e.g. swimming. It is expected that with this system a person having a good function of the auditory nerves will be able to comprehend speech.

As the system of the present invention uses coding in time sequence and the signal processing within the implant has a pipeline structure - not an operation according to the Von Neumann principle - a high rate of information transfer is achieved. IR-pulses can be made smaller than 400 nsec. At each sequence the implant is again synchronized and reset. The shown embodiments show systems for stimulating nerves, but the present invention can also be used for stimulating muscles, e.g. hard muscles. The scope of protection is defined by the following claims: