NL2008217C2

NL2008217C2 - Tissue- or neurostimulator.

Info

Publication number: NL2008217C2
Application number: NL2008217A
Authority: NL
Inventors: Marijn Dongen; Wouter Serdijn; Dirk Ridder
Original assignee: Univ Delft Tech
Priority date: 2012-02-01
Filing date: 2012-02-01
Publication date: 2013-08-06
Also published as: WO2013115643A2; WO2013115643A3

Abstract

Tissue- or neurostimulator, comprising a power supply (Vdd) and an implantable pulse generator (IPG) powered by said power supply (Vdd) to which an electrode or electrodes are connected or connectable for delivery of pulses from the pulse generator to a patient's region of interest or tissue so as to provide said region of interest or tissue with electrical stimulation, which pulse generator comprises a switching cir- cuit providing an intermittent connection with the electrode or electrodes, wherein the pulse generator comprises at least one inductor (L) for storing of energy from the power supply (Vdd) and subsequent release to the patient's region of inter- est or tissue through the electrode or electrodes.

Description

Tissue- or neurostimulator

The invention relates to a tissue- or neurostimulator, comprising a power supply, such as a battery, and an im-5 plantable pulse generator (IPG) powered by said power supply, to which pulse generator an electrode or electrodes are connected or connectable for delivery of pulses from the pulse generator to a patient's region of interest or tissue so as to provide said region of interest or tissue with electrical 10 stimulation, and which pulse generator comprises a switching circuit providing an intermittent connection with the electrode or electrodes.

Such a tissue- or neurostimulator is disclosed in Xiao Liu ; Demosthenous, A. ; Donaldson, N., "A Miniaturized, 15 Power-Efficent Stimulator Output Stage Based on the Bridge

Rectifier Circuit", IEEE Asia Pacific Conference on Circuits and Systems, 2006. APCCAS 2006. This document discloses the use of two high frequency, current based, signals to reconstruct a traditional stimulation signal. The goal is to reduce 20 the size of the blocking capacitors that are required for safety purposes. The switching circuit according to this document operates at a .low frequency that is derived from the two high frequency signals.

According to Wikipedia in medical technology a neu-25 rostimulator, also called an implanted pulse generator (IPG) is a battery powered device designed to deliver electrical stimulation to the brain. Within the scope of the invention the stimulator can also stimulate tissue that thus indirectly entices the brain. Neurostimulators are an integral component 30 of surgically implanted systems such as deep brain stimulation and vagus nervus stimulation or peripheral nerve stimulation, designed to treat neurological disorders. These devices are implanted within a person's body, usually beneath the clavicle .

35 The nervous system of the human body is an electro chemical system. Many pathologies find their origin in the nervous system (e.g. Parkinson's disease, Despression, Alzheimer Disease, Chronic Pain or Tinittus) or can be influenced using the nervous system (Rheumatoid arthritis, etc.). Tradi- 2 tionally medical technology has focused its treatment methods using drugs, thereby addressing the chemical aspect of the nervous system. This has however serious drawbacks: drugs do not work locally, but have impact on the whole body. In many 5 cases drugs can treat a particular disease, but they will also lead to unwanted side effects. Simply said, people are getting sick of drugs.

An alternative for drug treatment is neural stimulation. This treatment method uses the electrical component of 10 the nervous system for treatment purposes. Electrodes are implanted close to the pathological region in the nervous system and they are connected to an implantable pulse generator (IPG). In this way the pulses generated can interfere with the nervous system at'the desired location and reduce pathological 15 activity in an electrical way. The main advantage is that electrical stimulation acts locally on the nervous system. Therefore it suffers much less from side effects than traditional medical treatment by means of drugs.

The energy required for neurostimulation usually 20 comes from a battery integrated in the IPG and/or from energy harvested by other means (e.g. inductive coupling). Regardless of the way the energy is acquired, the components in the IPG that generate the energy (i.e. the battery or receiving coil) take up significant space and limit the implantability of the 25 system. Currently the size of the IPG is in general too big to be implanted close to the area of interest (e.g. inside the skull), setting the need for long electrode leads which severely decrease the reliability of the system (risk of breaking, infection and scar tissue).

30 It is therefore an object of the invention to improve the implantability of the IPG and to limit the required size of the energy storing element.

It is a further object of the invention to improve the power efficiency of the electrical stimulation; this effi-35 ciency should be as high as possible: from the energy used by the IPG as much as possible should be conveyed into the tissue. This is also beneficial for the purpose to limit the size of the power source.

Still a further object of the invention is to provide 40 a solution to the problem that stimulators of the prior art 3 usually only use part of the full range power supply voltage. When using current based stimulation, the voltage swing depends on the (highly unpredictable) tissue impedance and when using voltage stimulation the full range amplitude is almost 5 never used. This means that 'part of the available voltage1 is not used effectively thereby dramatically decreasing the power efficiency.

To address the above problems and to promote the realization of the objects of the invention, the tissue- or neu-10 rostimulator according to the invention has the features of one or more of the appended claims.

According to a first aspect of the invention the pulse generator comprises at least one reactive component, such as an inductor or capacitor for storage of energy from 15 the power supply and subsequent release to the patient's region of interest or tissue through the electrode or electrodes. With such a reactive component high-frequency pulses of differently selectable levels of energy can effectively be generated and provided to the tissue of interest utilizing a 20 regular battery. This thus limits the power requirements of said battery.

In order to effectively make use of the reactive component's properties, it is beneficial that the switching circuit is arranged for repeatedly interrupting and restoring the 25 reactive component's connection with the power source and during said interrupting of the connection with the power source, establish a connection of the reactive component with the electrode or electrodes so as to retrieve the energy from the reactive component and provide this energy via the electrodes 30 to the tissue being treated. Using an inductor interrupting the current through the inductor results in an upswung voltage over the inductor obviating the need to apply a power converter for transferring energy from the power supply to the stimulated tissue.

35 It is remarked that during operation the switching circuit preferably operates at a high frequency to arrange for an intermittent connection between the power supply and the reactive component on the one hand alternated by an intermittent connection between the reactive component and the elec-40 trode or electrodes on the other hand. Within the scope of the 4 invention a high frequency should be understood as being at least 100 kHz.

By alternatingly connecting and disconnecting the reactive component to the power supply and to the tissue at a 5 high frequency, which can be done either directly or via an electrical component or electronic circuit, the energy from the power supply can be transferred with a very high efficiency. Thus the fully available power range can be used to stimulate the tissue, and all of the available energy of the 10 power supply is used to generate an appropriate electrical field for stimulation.

By adjusting the duty cycle of the repeatedly connected and disconnected power supply to the reactive component and the repeatedly connected and disconnected reactive compo-15 nent with the tissue, the average energy delivery to the tissue can be controlled (i.e. the amplitude of the stimulation). In this way no voltage headroom is wasted and a theoretical efficiency of 100% can be reached.

When the tissue or neurostimulator of the invention 20 is arranged with plural channels for simultaneous stimulation of different tissue areas, it is preferable that the at least one reactive component is shared or multiplexed by said plural channels. In this way the use of these relatively bulky components do not stand in the way to the miniaturization of the 25 stimulator.

Preferably the high-frequency switching circuit is arranged to provide a first (voltage or current) pulse train and a second pulse train at a selectable repeat rate, wherein each first pulse train has a selectable first duration and is 30 followed by a second pulse train of opposite polarity that has a selectable second duration. The application of the opposite polarity is important to avoid that on average the stimulated tissue is subjected to electrochemical responses due to a remaining voltage over the tissue. For this purpose it may also 35 be beneficial that said first pulse train and second pulse train are followed by a phase for decharging the stimulated tissue. The selectable repeat rate is applied in order to be able to control the amount of stimulus that is applied to the tissue .

40 Preferably the first and/or second pulse train or 5 trains have a selectable frequency, preferably at least hundred kilohertz, more preferably in the megahertz range, and even more preferably about 10 MHz. The frequency is selected in order to match the requirements of the application based on 5 for instance electrode impedance, energy loss etc.

The consequence of this way of stimulation is that the stimulation current will be switched on and off at this high rate as well. However the electric field which is eventually responsible for the (de)-activation of the tissue is av-10 eraged out because of the low-pass filter nature of human tissue. This means that when the frequency of the stimulation signal is much higher than the time constant of the tissue, a similar electric field can be generated as is done with traditional stimulation.

15 The invention will hereinafter be further elucidated with reference to the drawing.

In the drawing: -figure 1 shows schematically the tissue- or neurostimulator in a first embodiment of the invention connected 20 to tissue; -figure 2 shows schematically the tissue- or neurostimulator in a second embodiment of the invention connected to tissue; -figure 3 shows an example of exciting said tissue 25 with a constant duty cycle; and -figure 4 shows in detail the excitation during a first pulse train A as shown in figure 3.

With reference first to figure 1 showing a first embodiment, and figure 2 showing a second embodiment, the tis-30 sue- or neurostimulator of the invention is generally denoted with reference 1. The neurostimulator 1 of the invention comprises a power supply Vdd and an implantable pulse generator (IPG) SI, S2, S3, S4, S5, L powered by said power supply Vdd to which an electrode or electrodes 2, 3 are connected or con-35 nectable for delivery of pulses from the pulse generator to a patient's region of interest or tissue 4 so as to provide said tissue 4 with electrical stimulation.

The pulse generator comprises a high frequency switching circuit SI, S2, S3, S4, S5 providing an intermittent 40 connection between the power supply Vdd and the reactive com- 6 ponent L on the one hand, alternated by an intermittent connection between the reactive component L and the electrode or electrodes 2, 3 on the other hand. The reactive component L is this way used for storing of energy from the power supply Vdd 5 and subsequent release of energy to the patient's region of interest 4 through the electrode or electrodes 2, 3. To make this arrangement satisfactorily work the switching circuit Si, S2, S3, S4, S5 is arranged for repeatedly interrupting and restoring the reactive component's connection with the power 10 source Vdd and during said interrupting of the connection with the power source Vdcn to establish an intermittent connection of the reactive component L with the electrode or electrodes 2, 3 so as to provide the desired power pulses to the con nected tissue 4.

15 The switches of the circuit of figure 1 operate for instance according to the following steps A-E.

A. SI is closed, all other switches are open; the inductor L charges up to a particular current.

B. S2 & S5 are closed, all other switches are' open; 20 the inductor L discharges its energy through the tissue 4. It is remarked that switches S2 and S5 need to open when the current crosses 'zero' to prevent oscillations.

Step A and B are repeated with a predetermined and desired switching frequency for as long as the pulse of the 25 desired polarity needs to be. After completion of the pulse, the following steps C and D are executed.

C. SI is closed, all other switches are open; the inductor L charges up to a particular current.

D. S3 & S4 are closed, all other switches are open; 30 the inductor L discharges its energy in opposite direction through the tissue 4 in comparison with step B.

Steps C and D are repeated with a predetermined and desired switching frequency for as long as the second pulse having its polarity opposite to the pulse according to the 35 steps A and B needs to be.

E. Following the steps A, B, C and D, the tissue is shorted, for example by closing S4 and S5.

In a similar fashion as in the embodiment according to figure 1, the switches of the circuit of figure 2 operate 40 for instance according to the following steps A-E.

7 A. S2 and S5 are closed, all other switches are open; the inductor L charges up to a particular current.

B. S5 & Si are closed or S2 & SI are closed, all other switches are open; the inductor L discharges its energy

5 through the tissue 4. It is again a remark that switch SI

needs to open when the current crosses 'zero' to prevent oscillations .

Step A and B are repeated with a predetermined and desired switching frequency for as long as the pulse of the 10 desired polarity needs to be. After completion of the pulse, the following steps C and D are executed.

C. S3 & S4 are closed, all other switches are open; the inductor L charges up to a particular current in opposite direction.

15 D. S3 & Si are closed or S4 & Si are closed, all oth er switches are open; the inductor L is discharging its energy in opposite direction through the tissue.

Steps C and D are repeated with a predetermined and desired switching frequency for as long as the second pulse 20 having its polarity opposite to the pulse according to the steps A and B needs to be.

E. After completion of the steps A, B, C and D, the tissue 4 is shorted, for example by just closing Si. Furthermore one of the switches S2-S5 need to be closed as well to 25 keep the tissue at a well-defined voltage.

In both the embodiments of figures 1 and 2 the ratio A/B and C/D determine the duty cycle, and therefore the stimulation amplitude. This can vary during the pulse and also between the first pulse I and second pulse II as shown in figure 30 3 discussed hereafter. Figure 3 shows as an example an image of a signal with a constant duty cycle of approximately 50% to which the tissue 4 is subjected. The figure shows that the high-frequency switching circuit SI, S2, S3, S4, S5 is arranged to provide a first pulse train I and a second pulse 35 train B. Each first voltage pulse train I has a selectable first duration (this duration can be for instance 100 ps) which is followed by a second voltage pulse train II of opposite polarity that has a selectable second duration (also approximately 100 ps). The duration of the pulses can in prac-40 tice vary between 0,05 msec and 0,5 msec. Both the first pulse 8 train I and the second pulse train II are for instance operated with the same frequency of 1 MHz.

Figure 4 shows the effect of the repeated interrupting and restoring of the reactive component's connection with 5 the power source Vdd whilst during said interrupting of the connection with the power source Vdcn the connection of the reactive component L with the electrode or electrodes 2, 3 is established or maintained so as to provide the tissue high energy and high-frequency (approximately 1 MHz) pulses.

10 Figure 3 and 4 both show the power trains resulting from the application of a tissue or neurostimulator which is arranged with plural channels (Channel 1 and Channel 2) for simultaneous stimulation of different tissue areas, in which situation it is preferable that the at least one reactive com-15 ponent L is shared or multiplexed by said plural channels 1 and 2 .

As a caveat the inventors remark that the above description of possible embodiments of the invention are not limiting to the appended claims. The protective scope of such 20 claims must therefore be understood in the broadest possible sense without being considered limited to the offered example, which merely serves to elucidate these claims.

Claims

A tissue or neurostimulator (1) comprising a power supply (Vdd) and an implantable pulse generator (IPG) (S1, S2, S3, S4, S5, L) fed by said power supply (Vdd) with which an electrode or electrodes ( 2, 3) are connected or connectable for delivering pulses from the pulse generator (S1, S2, S3, S4, S5, L) to an area of interest of a patient or tissue (4) so as to be mentioned of interest provide region or tissue (4) with electrical stimulation, which pulse generator (S1, S2, S3, S4, S5,

L) comprises a circuit (S1, S2, S3, S4, S5, L) which provides a repeatedly interrupted connection to the electrode or electrodes (2, 3), characterized in that the pulse generator (S1, S2, S3, S4, S5, L) comprises at least one reactive component (L) for storing energy from the power supply (Vdd) and subsequent release to the area of interest of the patient or tissue (4) via the electrode or electrodes (2, 3).

2. Tissue or neurostimulator (1) according to claim 1, characterized in that the circuit (Si, S2, S3, S4, S5) is adapted to repeatedly interrupt and restore the connection of the reactive component to the power supply. (Vdd) and during said interruption of the connection to the power supply (Vdd), providing a connection between the reactive component (L) and the electrode or electrodes (2, 3) in order to provide them with voltage or current pulses.

A tissue or neurostimulator (1) according to claim 1 or 2, characterized in that during operation of the circuit (S1, S2, S3, S4, S5) it operates at a high frequency in order to establish an alternating connection between the power supply (Vdd) and the reactive component (L) on the one hand, alternating with a repeated connection between the reactive component (L) and the electrode or electrodes (2, 3) on the other hand.

Tissue or neurostimulator according to one of the preceding claims, characterized in that the high frequency circuit (S1, S2, S3, S4, S5) is arranged around a first pulse train (I) and a second pulse train (II ) on a selectable repeat frequency, wherein each first pulse train (I) has a selectable first duration and is followed by a second pulse train (II) with opposite polarity which has an adjustable second duration.

Tissue or neurostimulator (1) according to claim 5, characterized in that said first pulse train (I) and two the pulse train (II) are followed by a phase for discharging the stimulated region of interest or tissue (4) ).

Tissue or neurostimulator according to one of the preceding claims 4-5, characterized in that the first 10 and / or second pulse train or trains (I, II) have a selectable frequency, preferably at least one hundred kilohertz, more at preferably in the megahertz region, and more preferably about 10 MHz.

A tissue or neurostimulator according to any one of the preceding claims, characterized in that the reactive component is selected from the group comprising an induction, a capacitance.

A tissue or neurostimulator according to any one of the preceding claims, characterized in that it is arranged with a multitude of channels for simultaneously stimulating different tissue regions, and in that the at least one reactive component (L) is shared or multiplexed is through said multiple channels.