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

Abstract: A system is described for stimulating a nerve or a muscle fibre of a living body, e.g. a hearing nerve in the cochlea. The system comprises an implant (28) and an electrode (35) for stimulating the nerve or the fibre, which electrode is connected with the implant. To supply electrical power to the implant, a small sized transformer is used, of which one coil (26) is implanted into the body and the other is outside the body but in the vicinity of the implanted coil. In case of the ear, the implanted coil is around the auditory duct and the outer coil is inserted into the duct, so that both coils are substantially coaxial. For supplying information to the implant, infrared transmission through the skin is used, wherein the transmitter (39) is provided adjacent to the skin on the outside and the receiver, possibly forming a part of the implant is located on the inside of the skin and adjacent thereto.

Description: The present invention relates to a system for stimulating at least one nerve and/or muscle fibre of an animate subject, comprising a receiving unit to be implanted into said subject and a transmitting unit to be mounted outside said subject, in which information is transmitted by means of electromagnetic waves from the transmitting unit to the receiving unit for inducing stimulating electrical signals in said fibre, in which the receiving unit comprises supply means to supply power received by means of electromagnetic waves transmitted by means of primary and secondary cooperable inductors to a circuit for providing said stimulating electrical signal. Such a system is known from EP-A-0179536 in which a cochlear implant is described, restoring hearing sensations for profoundly deaf people by direct electrical stimulation of the nerve fibres in the inner ear or cochlea. This known system is concerned with improving the Q factor of the tuned transmitter circuit. It is an object of the present invention to provide a more accurate and versatile stimulating system, and to provide for an accurate alignment of the primary and secondary cooperable inductors. The system according to the present invention is characterized in that said primary inductor is to be inserted into the auditory duct of said subject and is part of said transmitting unit and said secondary inductor or coil is to be implanted around the auditory duct of said subject and is part of said receiving unit. An inductor to be inserted into the auditory is known from US-A-4,495953, which does however not disclose an implanted receiving unit. 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: fig. 1 a perspective view of a deaf subject provided with an implant according to the present invention; fig. 2 a perspective and diagrammatic view of the transfer of electro-magnetic waves to the implant of fig. 1; fig. 3 a view partly in section, partly in perspective of another preferred embodiment of the stimulating system of the present invention; fig. 4 a diagram illustrating the operation of the system of fig. 4; fig. 5 an example of a signal arriving at the implant of fig. 3; and fig. 6 an example of a stimulating signal. 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 10⁻⁶ Pa.l/s (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 will emit e.g. a few µWatt 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 x T₀; T₁ selects the mode (in this case biphasic see fig. 6), which means that T₁ is between 2 x T₀ and 4 x T₀); P m stands for mode selection pulse and a duration of 2 x T₀; T₂ defines the channel to be activated, in this case channel 2, which means that T₂ is in between 4 x T₀ and 6 x T₀; P ch stands for channel selection pulse and has a duration of 2 x 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 x 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.

Claims: A system for stimulating at least one nerve and/or muscle fibre of an animate subject, comprising a receiving unit to be implanted into said subject and a transmitting unit to be mounted outside said subject, in which information is transmitted by means of electromagnetic waves from the transmitting unit to the receiving unit for inducing stimulating electrical signals in said fibre, in which the receiving unit comprises supply means (41) to supply power received by means of electromagnetic waves transmitted by means of primary (24) and secondary (26) cooperable inductors to a circuit for providing said stimulating electrical signal, characterized in that said primary inductor (24) is to be inserted into the auditory duct of said subject and is part of said transmitting unit and said secondary inductor (26) or coil is to be implanted around the auditory duct of said subject and is part of said receiving unit. A stimulating system according to claim 1, provided at the receiving side with a detector (38) for detecting infrared radiation to be transmitted by the transmitting unit which is to be provided in contact with or closely spaced to the skin of the subject. A stimulating system according to claim 1 or 2, wherein the information to be transmitted is encoded in time sequence. A stimulating system according to claim 1, 2 or 3, wherein the information to be transmitted is processed in a pipelined way. A stimulating system according to anyone of the preceding claims, wherein the implant is provided with an antenna (37) for transmitting back information outside the subject. A stimulating system according to any one of the preceding claims, wherein the receiving unit is provided in a housing (14, 29) at least partly of biocompatible material. A stimulating system according to any claim 6, wherein said material is glass. A stimulating system according to claim 6 or 7, wherein the housing (29) consists of at least two preformed titanium parts, one of which is provided with a transparent window (38) of glass. A stimulating system according to claim 7, wherein said housing (14) is completely made out of biocompatible glass. A stimulating system according to any one of the claims 6-9, wherein said housing is sealed hermetically. A stimulating system according to any one of the claims 1-5, provided with a housing at least partly of ceramic material. A stimulating system according to any one of the preceding claims, wherein the receiving unit is provided with at least one integrated unit. A stimulating system according to any one of the preceding claims, provided with an electrode (35) to be inserted into the cochlea of a subject and including a hook shaped end portion. A stimulating system according to any one of the preceding claims, wherein the coil (26) to be implanted around an auditory duct, is provided with windings having a flexible lining, e.g. of silicon.

Inventors: BOSIERS WILLIAM A S, KINSBERGEN JACQUES, PEETERS STEFAAN, BOSIERS, WILLIAM A.S., KINSBERGEN, JACQUES, PEETERS, STEFAAN
Applicants: ANTWERP BIONIC SYSTEMS NV, ANTWERP BIONIC SYSTEMS N.V.
Application year: 1987
Main classification: A61F2
IPC codes: H04R25, A61F11, A61N1