WO2010139376A1

WO2010139376A1 - Device and method for stimulating nerves by way of magnetic field pulses

Info

Publication number: WO2010139376A1
Application number: PCT/EP2010/001622
Authority: WO
Inventors: Stefan M. Götz; Thomas Weyh
Original assignee: Technische Universität München
Priority date: 2009-06-04
Filing date: 2010-03-15
Publication date: 2010-12-09
Also published as: DE102009023855A1; DE102009023855B4

Abstract

The invention relates to a device for generating brief, strong current pulses in a coil, wherein the coil generates magnetic field pulses with a duration of 20 to 3000 microseconds and a strength of 0.1 to 5 tesla, which cause electric stimulation currents in the body tissue according to the principle of electromagnetic induction for stimulating nerve and/or muscle cells, wherein the device comprises at least one capacitor for storing and dispensing the energy required for the field pulses and a suitable charge circuit for charging said capacitor, and the coil is designed such, and it can be positioned close enough to the body tissue to be stimulated such, that within the intended target region the magnetic field generated by the coil drops at maximum to one tenth of the strength at the coil surface, and wherein the electric stimulation currents generated by the magnetic field of the coil are at least one tenth and at maximum one fifth of the stimulation currents required for stimulating the cells. The device in the coil can generate a current pulse, the time curve of which is shaped such that the coil induces an electric field, wherein the mean edge steepness of rising edges differs from the mean edge steepness of falling edges.

Description

DEVICE AND METHOD FOR NERVE ENERGY WITH MAGNETIC FIELD PULSE

The present invention relates generally to a device for nerve and muscle stimulation according to the principle of inductive magnetic stimulation by pulsed magnetic fields. Furthermore, the invention relates to electrical power circuits for generating improved timing of pulse-shaped magnetic fields for nerve irritation.

In general, certain cells can be irritated by externally applied electric fields in the body tissue. This happens because the electrical fields in the tissue cause electrical currents, which in turn trigger action potentials in these cells, for example in nerve or muscle cells. In particular, the principle of magnetic induction can also be used for this type of irritation. In this case, a time-varying magnetic field generates an induced electric field. The time-varying magnetic field can be generated by a coil, which is traversed by a time-varying current. This coil, the treatment coil, for example, rests on the skin above the nerve tissue to be stimulated, so that the magnetic field generated can penetrate the tissue and generates the currents required for the stimulation in the tissue according to the induction principle. The stimulation by this so-called inductive magnetic stimulation can be done without contact, since the magnetic field can penetrate body tissue unhindered. The time-dependent magnetic fields are generated via short current pulses of a duration of usually 50-400 microseconds.

Figure 1 shows a typical arrangement of the use of inductive magnetic stimulation. The pulse source 110 generates a short strong current pulse and conducts it to the treatment coil 120. The treatment coil 120 is positioned close to the irritant nerve tissue of the body so that the generated magnetic field can penetrate this tissue structure. The magnetic field generated by the coil induces an electrical field in the body tissue, here on the upper arm 130, which excites nervous and muscular tissue via the resulting currents.

Figure 2 shows the basic circuit structure of an inductive stimulation device, as it was used in the first devices in particular for contactless irritation of cortical nerve structures through the intact skull bone. The circuit uses a powerful damped electrical resonant circuit (resonator) consisting of a capacitor 220, a damping resistor 230, a diode 240, a thyristor 250 and the treatment coil 260. The charging circuit 210 charges the capacitor 220 to a voltage of several thousand volts. The energy content of the capacitor is several hundred joules. The thyristor 250 serves as a switch that ignites the capacitor 220 with the magnetic! Behaπdlungsspuie 260 connects and so start the flow of current in the coil.

Figure 3 shows the time course of current and voltage in the treatment coil according to the circuit of Figure 2. After the ignition of the thyristor creates a first sinusoidally increasing current flow, which generates a correspondingly increasing with time magnetic field. This magnetic field in turn induces ring currents in the body tissue as a result of its temporal change. When the current peak value is reached, the phase-shifted coil voltage has exactly its first zero crossing. Since from this point on the coil voltage reverses its sign, now the damping circuit consisting of the resistor 230 and the diode 240 is active, which prevents further oscillation of the resonant circuit. Therefore, the coil current slowly returns to zero after reaching its peak value. The typical time between the thyristor ignition and the achievement of the current peak value is about 50 to 150 microseconds. By this damping circuit, however, the entire pulse energy of the capacitor is converted into heat in the resistor 230 and in the coil conductors of the treatment coil.

This damping circuit used in the first devices, which attenuates the oscillation from the first falling current edge (after one quarter of the period), characterizes the so-called monophasic stimulation, since the coil current only flows in one direction during the pulse, ie does not change its sign.

Advantages of inductive magnetic stimulation on the one hand, the contactlessness, since the magnetic field of the treatment coil body tissue also reaches a certain distance from the coil. Therefore, nerve cells can also be irritated sterile. On the other hand, in contrast to electrical stimulation via electrodes, the method is almost completely free of pain since, unlike electrostimulation, high current densities can not occur at feed locations of electrodes. For these reasons, this method is also particularly well suited to irritate deep tissue structures (eg the cerebral cortex through the skull bone) and for painless muscle stimulation eg in the field of rehabilitation. However, in inductive magnetic stimulation, this detour via the magnetic field of the treatment coil also has important technical problems:

The required magnetic flux densities are in the range of approximately 1 Tesla, so that high field energies must be conducted into the coil. Therefore, during the very short magnetic stimulation pulse, extremely high electrical power must be introduced into the coil; this power can reach values of several megawatts. Furthermore, since the pulse energy of the magnetic field is completely lost with the first devices at every pulse, these devices consume very high energy. Furthermore, the treatment coil overheats in this device technology very quickly, in which case it must also be noted that the coils may not reach too high temperatures as a treatment part, which can touch the body directly.

A further disadvantage is that the time course of the current induced in the tissue and used for the stimulation, in contrast to electrostimulation, can no longer be freely selected. In the body tissue, an electric field is induced according to the principle of magnetic induction only when the coil current and thus the magnetic field changes over time. In particular, it is not possible to generate efficient simple monophasic rectangular pulses with a short-term direct component, as used in electrostimulation. Instead, one is basically fixed on time-variable coil currents and thus also on temporally variable induced tissue currents.

Therefore, the high energy consumption and the associated rapid heating of the device and treatment coil in inductive magnetic stimulation proved to be the most important technical problems. In particular, these first devices are not suitable for the so-called repetitive stimulation, in which 10 to 50 pulses per second are required. This repetitive stimulation is used, for example, in neuro-rehabilitation for relearning movement patterns or for building muscle. Furthermore, the size of the devices and their high price make it difficult to open up further fields of application in neurodiagnosis and neurorehabilitation.

Therefore, the most important development goal of the devices for inductive magnetic stimulation in the reduction of energy consumption. By experimental investigations it could be shown that also an undamped sinusoidal Time course of the coil current and thus also the magnetic field at the same amplitude about an equivalent effect in terms of nerve irritation shows how the current waveform of Figure 3.

FIG. 4 shows the basic circuit structure of a stimulation device which generates sinusoidal current or field pulses. Again, the charging circuit 210 charges the

Capacitor 220 to a voltage of several thousand volts. The thyristor 410 serves again as a switch, the capacitor 220 with the magnetic when ignited

Treatment coil 260 connects. Unlike the monophasic

Stimulator circuit of Figure 2, however, no damping circuit is used in this circuit, so that even after the first zero crossing of the

Coil voltage of the resonant circuit continues to oscillate.

Figure 5 shows the time course of current and voltage in the treatment coil according to the circuit of Figure 4. After the ignition of the thyristor creates a sinusoidal rising current flow, which generates a correspondingly increasing with time magnetic field. After half a sine wave, at time T / 2, the current in the resonant circuit changes its polarity. At this time, the diode 420 takes over the conduction of the coil current until a full sinusoidal oscillation at time T is reached. A renewed reversal of the current direction and thus further oscillation is prevented because the thyristor 410 no longer conducts at this time T. Because of the reversal of the current direction during a pulse at time T / 2, this type of stimulation is commonly referred to as biphasic magnetic stimulation.

The advantage of this circuit principle according to FIG. 4 is that a large part of the field energy used for the treatment coil 260 can be returned to the capacitor 220, thus reducing the losses both in the pulse source and in the treatment coil 260. The losses of the circuit of Figure 4 are mainly due to the ohmic resistances of the circuit components involved and their connection cable.

However, since the current amplitude required for successful stimulation is approximately unchanged from monophasic pulse form devices, the necessary voltage and energy content of capacitor 220 also remain nearly the same, as in monophasic devices.

The preferred use of an electrical resonant circuit for generating the current pulses for the treatment coil instead of a direct control (eg over Longitudinal control) of the coil current from a power source is explained by the enormous power required during a magnetic pulse. This power is in the megawatt range. This means that coil voltages of up to three kilovolts and coil currents of up to eight kiloamps are required for the stimulation. The principle for generating powerful pulses for the treatment coil is thus based on a continuous charge of the resonant circuit capacitor via a charging device at relatively low power and the rapid release of the energy content of this capacitor to the treatment coil for generating the short strong magnetic field pulse.

Figure 6 illustrates a further development of the circuits of inductive magnetic stimulators. Again, the charging circuit 210 charges the capacitor 220 to a voltage of several thousand volts. The thyristor 610 again serves as a switch which connects the capacitor 220 to the magnetic treatment coil 260 during ignition.

Figure 7 shows the time course of current and voltage in the treatment coil according to the circuit of Figure 6. After the ignition of the thyristor 610 creates a sinusoidal rising current flow, which generates a correspondingly increasing with time magnetic field. After half a sinusoidal oscillation, at time T / 2, the current in the resonant circuit reaches its first zero point. If at this time the second thyristor, 620 is not ignited, a reversal of the current direction is not possible, so that further oscillation is prevented already after a half-wave. Ignition of the thyristor 620 at a later time generates in the treatment coil a further half-wave pulse with reverse current and magnetic field direction. Alternatively, however, the second thyristor 620 can also be ignited directly upon reaching the first current zero point, so that a full sinusoidal oscillation arises, similar to FIG. 5. In any case, however, the field energy of the coil is also returned to a large extent back into the capacitor in this circuit.

Depending on the choice of the end time of the pulse, a distinction is therefore made with respect to the pulse shapes of the inductive stimulation devices between a biphasic full-wave stimulation (duration of the current pulse a full sine period) and a biphasic half-wave stimulation. A disadvantage of the biphasic half-wave stimulation, however, is that after the pulse, the voltage direction in the capacitor is inverted compared to the state before the pulse output, whereby the corresponding charging circuit becomes more complex. Furthermore, in the case of biphasic half-wave stimulation, the direction of the magnetic field also changes, so that successive pulses easily produce different effects in the tissue.

The energy recovery according to the circuits of Figure 4 and Figure 6 allow a reduction in the power used and thus the construction of repetitive inductive stimulation devices, which can deliver up to 100 pulses per second. However, especially for this repetitive operation of the

Energy consumption and coil heating still significant. especially the

Coil heating is due to the very high required coil currents in the kiloampere range and the weight reasons, not arbitrarily reducible

Resistance of the treatment coil.

A further reduction of energy consumption and coil heating can therefore hardly be achieved by this energy recovery alone. In contrast to electrostimulation, in which the connections between pulse shape and irritation were already experimentally researched relatively early, sound investigations into more effective pulse shapes in the field of inductive magnetic stimulation hardly took place. This is mainly due to the fact that due to the high electrical power required for each change of a stimulus parameter, a complex modification of the pulse generation circuit is required. Therefore, only such parameters as the pulse duration or the current amplitude have been varied so far for such examinations and optimizations.

Therefore, these three modes, the attenuated monophasic pulses, the biphasic half-wave pulses and the biphasic full-wave pulses still represent the only pulse shapes used in the commercial inductive magnetic stimulation devices in therapy and research.

Temporary experiments with other pulse forms, as in Peterchev et al. 2008, with a rectangular shape (AV Peterchev, R. Jalinous, and SH Lisanby: A Transcranial Magnetic Stimulator Inducing Near-Rectangular Pulses With Controllable Pulse Width (cTMS), IEEE Transactions on Biomedical Engineering, vol. 55, no. 1, 2008) either energetically very ineffective, or they lead to extremely complex technical structures and are therefore too expensive for a commercial technical realization.

As a result of the described advantages - in particular the non-contact and the absence of pain - the inductive magnetic stimulation could be compared to the Electrical stimulation already enforce in some areas or even open up new application areas.

The procedure for neuronal diagnosis in both the central and the peripheral nervous system is very common.

Currently, it is the only non-invasive procedure that allows specific areas of the brain to be addressed in a targeted manner (ie triggering nerve action potentials or subliminally influencing nerve cells in these areas) without the pain of the patient, the reactions of the nerve cells to the body just as or at least very much as naturally occurring nerve impulses are processed.

For this reason, inductive magnetic stimulation is also used in basic research as a tool for joint examination together with functional magnetic resonance tomography. Pulse can be used to generate specific stimulation (and inhibition) of certain areas of the brain, the effects of which can in turn be investigated with this imaging method.

Furthermore, applications in neurorehabilitation in particular represent a large field of application of inductive magnetic stimulation. Primarily, peripheral motor nerves are activated and trained for muscle building and / or the re-learning of specific movement patterns. Especially the repetitive continuous stimulation with fast pulse sequences (about 10 to 50 pulses per second) is of great importance; However, in this type of nerve irritation, the described power and energy problems of previous devices become even clearer.

In addition, in sports medicine, the devices are already very often used to build muscle after injury or to use the usual training effect (especially in many top athletes). However, the force effect achievable on the muscle via the inductive magnetic stimulation has so far not been comparable with the willfully achievable force for purely technical-physical reasons.

In all these applications, the disadvantage of inductive magnetic stimulation in high energy consumption, the very fast overheating of the treatment coil and the high weight of the charging and pulse generating electronics. It is an object of the invention to provide a method for generating improved magnetic pulses for nerve irritation, by means of which the mentioned disadvantages are avoided.

This object is achieved by a method for generating magnetic field pulses with the features mentioned in claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

SUMMARY OF THE INVENTION

The invention is based on the finding that with an improved adaptation of the time-course of the currents induced in the tissue to the dynamic charge-transport phenomena of the nerve fibers, the required field strength and field energy for inductive irritation can be reduced. In particular, for this purpose of the associated power electronics, the time course of the short magnetic field pulse generates the treatment coil to change over previous systems in such a way that the mean edge steepness rising edges of the induced electric field differs from the mean edge steepness sloping edges.

In other words, the magnetic stimulation pulses produced by the power electronics according to the invention should no longer have a sinusoidal or attenuated sinusoidal profile, but be such that the electric field induced by the coil either increases significantly faster than it drops or increases significantly more slowly than it does drops. The course of the induced from the treatment coil electric field follows approximately the time course of the coil voltage. Accordingly, the mentioned time dependencies of the course of the induced electric field can be achieved via a corresponding course of the coil voltage.

The field pulses generated by the treatment coil can be designed so that only one rising and one falling edge of the induced electric field strength are generated or alternating within a pulse a plurality of rising and falling edges of the induced field strength, in each case in this case clearly distinguish the average edge steepnesses of the rising flanks from the mean edge steepnesses of the falling flanks. Furthermore, the associated power electronics can be designed so that in each case takes place at the zero crossing of the coil current, a brief interruption of the oscillation process. During these interruption times, no magnetic field is generated by the coil.

Preferably, the power electronics should be designed so that the power electronics together with the treatment coil represents a resonant system of one or more resonant circuits. In this way, the field energy of the coil can be returned to one or more capacitors. Through a corresponding coupling of several resonant circuits pulses can be generated which are composed of individual sections of sinusoids of different frequencies. In this way, the pulses can be shaped so that the mean edge steepness of the rising edge clearly differs from the mean edge steepness of the falling edge. At the same time, even with such pulses, which are no longer sinusoidal, the magnetic Feideπergie the treatment coil can be energy-efficiently fed back into one or more capacitors of the power electronics to a large extent.

An advantage of the present invention is the provision of an apparatus and method for inductive nerve stimulation which require relatively low field energy and field strength to irritate the nerves. With this reduction of energy and the one or more capacitors used for the intermediate storage of the pulse energy can be reduced in terms of their sizes.

Another advantage of the present invention is the provision of an inductive nerve stimulation device and method which requires a comparatively lower capacitor and coil voltage for the irritation of the nerves so that isolation distances can be reduced and necessary safety measures can be simplified.

Another advantage of the present invention is the provision of an inductive nerve stimulation apparatus and method which requires a relatively low coil current for stimulus initiation. In this way, on the one hand, the current heat losses in the treatment coil and in the supply cable can be reduced, on the other hand can be used in the power circuit used for pulse power electronic Leistυngsbauteile of comparatively lower current carrying capacity and correspondingly smaller size.

Another advantage of the present invention is to provide a device and a method for inductive nerve stimulation, which is due to their relatively low energy consumption, especially for repetitive stimulation with pulse repetition rates of 10 to 1000 pulses per second. At the same time, the devices for pulse generation according to the invention can be made comparatively small, lightweight and thus portable.

Another advantage of the present invention is the provision of an apparatus and method for efficiently generating non-sinusoidal time courses of the magnetic field pulses with simultaneously high power and low power Losses. In particular, the mean edge steepness of the rising edge of the coil voltage can be controlled independently of the mean edge steepness of the falling edge and thus also of these edges of the tissue induced voltages and currents in the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

1 shows a pulse source, the treatment coil coupled via a cable and the tissue structure to be stimulated (human upper arm);

Fig. 2 shows the basic structure of a monophasic power circuit;

Fig. 3 shows the voltage and current waveform in the coil of a monophasic stimulator during a pulse;

Fig. 4 shows the basic structure of a power circuit for generating full sine waves;

Fig. 5 shows the voltage and current waveform of a full-wave stimulator in the coil during a pulse;

Fig. 6 shows the basic structure of a power circuit for generating sinusoidal half-waves;

Fig. 7 shows the voltage and current waveform of a half-wave stimulator in the coil during a pulse;

Fig. 8 shows by way of example the time course of the coil current I _L and the coil voltage, which is composed of two juxtaposed sine half-waves of different frequency;

Fig. 9 shows the change of the triggering threshold for a nerve fiber as a function of the quotient of the frequencies of two juxtaposed half-waves of different frequency according to Fig. 8;

Fig. 10 shows by way of example a power circuit according to a first embodiment of the present invention; Fig. 11 shows by way of example the time course of the coil current I _L and the coil voltage U ₁ according to the first embodiment of the invention;

Fig. 12 shows by way of example a power circuit according to a second embodiment of the present invention;

Fig. 13 shows by way of example the time course of the coil current IL2 and the coil voltage U _L according to the second embodiment of the invention;

Fig. 14 shows by way of example a power circuit according to a third embodiment of the present invention;

Fig. 15 shows by way of example the timing of the coil current IL and the coil voltage UL according to the third embodiment of the invention;

Fig. 16 shows by way of example a power circuit according to a fourth embodiment of the present invention;

Fig. 17 shows by way of example the time characteristic of the coil current I _Ln and the coil voltage U _L according to the fourth embodiment of the invention;

Fig. 18 shows by way of example a power circuit according to a fifth embodiment of the present invention;

Fig. 19 exemplifies a power circuit according to a sixth embodiment of the present invention; and

Fig. 20 shows by way of example the time course of the coil current I _L and the coil voltage U _L according to the sixth embodiment of the invention.

In the drawings, like reference numerals shall designate like parts, components and arrangements.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention is based on the finding that the strength and energy of the magnetic field pulse required for nerve stimulation can be significantly reduced if the temporal current profile is adapted to the dynamic behavior of the ion transport processes in the nerve cell membrane. In particular, this can be achieved if the associated power electronics for pulse generation the time course of the short Magnetic field pulse, which generates the treatment coil, compared to previous systems changed in such a way that the mean edge steepness of the rising edge of the induced electric field differs significantly from the mean edge steepness of the falling edge. This in turn is achieved when the time course of the coil voltage generated by the power electronics is such that the mean edge steepness of rising edges clearly differs from the mean edge steepness of falling edges.

Furthermore, it is advantageous if the power electronics can generate pulses which have a plurality of voltage zero crossings and thus also a plurality of rising and falling edges of the time profile of the induced electric field strength during a single pulse and thereby also the respective mean edge steepnesses of rising edges from the mean edge steepnesses clearly distinguish between sloping flanks.

Furthermore, the associated power electronics can be designed so that during a pulse at least one zero crossing of the coil current takes place a short interruption of the oscillation process. During these interruption times, no magnetic field is generated by the coil.

The knowledge of the necessary temporal course of the field is based on a mathematical modeling of the nerve cells, as first established by Hodgkin and Huxley (AL Hodgkin, AF Huxley: Quantitative Description of Membrane Current and its Application to Conduction and Excitation in Nerve Journal of Physiology 117, 1952, pp. 500-544). The model is based on a set of nonlinear differential equations and simulates the behavior of nerve cells, especially the behavior of axons. For example, this model models the response of an axon to external electrical currents. Therefore, the required stimulus currents can be computationally determined with different pulse shapes, which are necessary in order to trigger an action potential in the nerve cell.

The model incorporates the dynamic, nonlinear behavior of, for example, the sodium and potassium ion channels of the cell membrane into the simulation. Such models describe the temporal behavior of neurons with nonlinear terms of high order. Direct inversion of the equations is therefore generally not possible. Optimizations must therefore be made via skillful estimates with subsequent quantitative confirmation in the forward model. Especially in relation On the sodium ion channels, it can be deduced from the model that there exists both an underlying mechanism that favors the induction of an action potential and an inhibitory mechanism that tends to suppress triggering. These two mechanisms have a very different time behavior, which can be exploited for the optimization of particularly energetic stimuli. In particular, it can be inferred from the mathematical consideration of these mechanisms that the amplitude of the current required for an irritation current pulse can be reduced if the mean slope of the rising edge of the time course of the stimulus current is significantly higher than the mean edge steepness of the falling edge, or more generally when the mean edge steepness of the rising edge significantly different from the mean edge steepness of the falling edge. The stimulation current in the tissue follows approximately the course of the induced by a stimulation coil in the tissue electric field strength. The course of this induced electric field strength in turn directly follows the course of the voltage in the treatment coil. Therefore, for an optimization of the stimulus pulse, the average slope of the rising edge of the coil voltage should be significantly different from the mean slope of the falling edge. Furthermore, it can be inferred from the model that stimulus pulses are also particularly efficient if several rising and falling edges of the time course of the coil voltage alternate in rapid succession, whereby in turn the respective mean edge steepnesses of the rising edges of the coil voltage are dependent on the mean edge steepnesses of the coil voltage clearly distinguish between sloping flanks.

An electronic circuit according to the invention, which generates pulses with the properties described above, requires a lower magnetic field strength for the treatment coil and thus also a lower field energy for stimulus triggering in comparison to previous systems for inductive magnetic stimulation. Accordingly, it also allows the required coil current and thus the losses of the coil, and their heating can be reduced. By reducing the field energy, the coil voltage required for the stimulation can furthermore be reduced.

In particular, it is advantageous if the circuit for generating the optimized coil pulses according to the invention generates current pulses in the treatment coil, which are composed of two sine half-waves of different frequency, wherein the first half wave sinusoidally rising current (and thus with maximum Coil voltage) begins and the transition from the first half-wave to the second takes place in the current zero crossing.

A sine wave is defined as a time course of the respective variable in the form of a sine function. The course may also be slightly damped, i. the amplitude of the wave decreases slightly with increasing time. Furthermore, a full sine wave is defined as a time characteristic of the respective quantity in the form of a sine function over a full period, ie sin (x) for 0 ≦ x ≦ 2π. Correspondingly, a sine half-wave is defined as a time characteristic of the respective quantity in the form of a sine function over half a period, ie sin (x) for 0 <x ≦ π.

Alternatively, it is also advantageous if the circuit generates current pulses in the treatment coil, which are composed of several sections of sine waves, each having a different frequency, so that the respective mean edge slopes of rising edges of the coil voltage clearly differ from the mean edge slopes sloping edges.

Furthermore, it is also advantageous if the circuit generates current pulses in the treatment coil, which are composed of two or more juxtaposed sinusoidal half waves with the same polarity, since here too mean edge slopes of the rising edges of the coil voltage resulting from the mean edge slopes of the clearly distinguish between sloping flanks.

FIG. 8 shows, by way of example, a time profile of the spin current I _L and of the coil voltage U _L , which are composed of two sinusoidal half-waves of different frequencies. The induced in the tissue electric field strength and the resulting current follow approximately the course of the coil voltage U _L.

FIG. 9 shows the result of a computational simulation in which the current amplitude required for an irritation was investigated for different pulse shapes. For this simulation, the pulse duration, ie the total time for the two sinusoidal half-waves juxtaposed, as shown in FIG. 8, was kept constant. In the calculations, the quotient, consisting of the duration of the first half-wave through the duration of the second half-wave, was varied. Depending on this ratio, the relative threshold current that is currently required for a depolarization, ie for the triggering of an action potential in the nerve fiber (axon), was determined. This current amplitude is also called the triggering threshold. Since in these pulses the maximum induced tissue flow is directly proportional to the maximum coil current and to the maximum capacitor voltage, a change in this triggering threshold is a crucial value for the effectiveness of the inductive stimulus devices. The scaling of the triggering threshold is normalized in Figure 9 so that they are for a pure sine wave - as it is currently used in commercial devices - reaches the value one. It can be seen from FIG. 9 that, compared to a pure sine wave, the required tissue current (and thus also the coil current and the capacitor voltage) decreases with increasing quotient. For example, if the duration of the first half-wave is four times greater than the second half-wave (quotient = 4), the coil current required for an excitation decreases to less than 50% of the value needed for sinusoidal excitation. Due to the quadratic relationship between coil current and field energy, the required pulse energy can even be reduced to less than 25% due to this improved pulse shape. Since the ohmic current heat losses of the resonant circuit also depend on the square of the current, the losses and the coil heating in this example can be reduced to less than 25%. Conversely, if this quotient is reduced, the stimulus threshold is increased in comparison with an irritation with full-wave sine waves.

By using pulses, which are composed of more than two juxtaposed half-waves with the current curves shown in Figure 8, a further increase in efficiency over the single wave shown here is possible.

This application of pulses with the described courses of events can be used as a method of irritating nerve and muscle cells. In particular, a method according to the present invention may also be used for non-therapeutic purposes. For example, such a method can be used for targeted muscle building or the representation of functional relationships of the neuromotor system in humans and animals.

The duration of the magnetic field pulses are approximately in the range of 20 to 3000 microseconds; preferably, the duration should be in the range of 100 to 500 microseconds.

The strength of the magnetic field pulses should be at the coil surface in the range of a flux density of 0.1 to 5 Tesla. Preferably, the magnetic flux density should be in the range of 0.3 to 1 Tesla. About the distance of the coil to be stimulated body tissue, the current in the coil and the mean edge steepness of the coil current, the induced electric field strength and thus the electrical stimulation current in the tissue can be controlled. This electrical stimulation current in the tissue should be at least one-tenth and a maximum of five times the stimulus currents required for irritation of the cells. Preferably, the stimulation current should be at least half and at most twice the stimulation currents needed to stimulate the cells.

In order to be able to additionally use the energy-efficient principle of resonant oscillating circuits with the treatment coil as inductance, it is advantageous for implementing such pulse shapes to directly couple a plurality of electrical resonant circuits in such a way that they alternately determine the time characteristic of the current and the voltage in the treatment coil. Thus, time courses of the coil current pulse can be generated, which are composed of parts of sine waves of different frequency. At the same time, by using these resonant circuits or resonant circuit elements, it can also be achieved that a large part of the magnetic field energy stored in the coil can be recovered back into the capacitor. In the exemplary embodiments, these time courses of the coil current are realized by means of switchable capacitors and / or switchable coils, the inductance of the treatment coil remaining unchanged.

These resonant circuit elements can therefore define either successively or simultaneously the current flow in the power circuit and in particular in the treatment coil.

The use of such coupled resonant circuits can thus induce by the generation and the direct succession of half-waves of different duration, even in the tissue a temporal voltage curve or current profile, in which the mean edge steepnesses of the rising edges of the mean edge steepnesses of the falling edges clearly differ

Exemplary embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations provided herein will be omitted to improve the clarity and brevity. FIG. 10 shows a first embodiment of the invention for generating pulse shapes according to FIG. 8. This circuit is based on a direct coupling of two oscillating circuits, which alternately or at times simultaneously determine the time characteristic of the coil current and the coil voltage. For this purpose, the resonant circuits use a common coil 1010, namely the treatment coil, but each use their own capacitors 1030 and 1050 with different capacitance. In each case a capacitor 1030 or 1050 forms with an associated circuit breaker 1020 and 1040, a capacitor-switch unit. The two capacitor switch units are alternately or temporarily also electrically connected to the coil 1010 so that a switching between the capacitors is preferably carried out during the zero crossing of the coil current. In this way, a current waveform can be generated on the coil, which consists of two sine half-waves of different frequency (or of several sections of waves with different frequencies). Alternatively, the sinusoidal half-waves of different frequency can also be generated so that during a half cycle both capacitors 1030 and 1050 are connected to the coil 1010, and during the other half wave only one of the two capacitors 1030 or 1050 is connected to the coil 1010. In this case also capacitors of the same capacity can be used. Furthermore, it is also possible to switch over to a different point in time of the current profile than to the current zero crossing. The two switches 1020 and 1040 can either be controlled so that a single full wave of the coil current (which is composed of two individual half-waves of different frequencies or multiple sections of waves with different frequencies) arises or that produces more than two directly juxtaposed half-waves become.

FIG. 11 shows, by way of example, such a time characteristic of the current I _L in the treatment coil and the coil voltage U _L , as achieved with the circuit according to FIG.

FIG. 12 shows a second embodiment, which is likewise based on the direct coupling of two oscillating circuits, which alternately or at times also simultaneously

Determining the time course of the coil current and the coil voltage. The resonant circuits use a common capacitor 1250, but use their own

Coils 1210 and 1220 with different inductance, wherein one of these coils the

Treatment coil is. The two coil-switch units are alternately electrically connected to the capacitor 1250 so that switching from the first Coil to the second coil is preferably carried out during the zero crossing of the coil current. In this way, a current waveform can be generated on the coil, which is composed of two sine half-waves of different frequency. Alternatively, the sinusoidal half-waves of different frequency can also be generated so that during a half-wave both coils 1210 and 1220 are connected to the capacitor, and during the other half-wave only one of the two coils is connected to the capacitor. In this case, coils of the same inductance can also be used. Furthermore, it is also possible to switch over to a different point in time of the current profile than to the current zero crossing. The two switches 1230 and 1240 can either be controlled so that a single full wave of the coil current (which is composed of two individual half-waves of different frequencies or multiple sections of waves with different frequencies) arises or that produces more than two directly juxtaposed half-waves become.

FIG. 13 shows, by way of example, such a time characteristic of the current I _L in the treatment coil and the coil voltage U _L , as achieved with the circuit according to FIG.

Figure 14 shows a third embodiment, which is based on the direct coupling of several resonant circuits, which alternately determine the time course of the coil current and the coil voltage. For this purpose, the resonant circuits use a common coil 1410, namely the treatment coil, but each use a plurality of own capacitors (n capacitors, where n> 1, of which only two, the capacitors 1430 and 1450 are shown), preferably with different capacitance. A respective capacitor 1430 or 1450 forms one of a total of n capacitor-switch units with an associated power switch 1420 or 1440. These capacitor switch units are alternately or temporarily also electrically connected to the coil 1410 so that switching from a capacitor to a next capacitor is preferably carried out during the zero crossing of the coil current. In this way, a current waveform can be generated in the treatment coil, which is composed of several sine half-waves of different frequency. Furthermore, the sine half-waves of different frequency can also be generated so that during a half-wave, a first group of capacitors is connected to the coil, and during a following half cycle one or more capacitors are connected to the coil, so that their total capacity different from the total capacity of the first group of capacitors. In this Case, capacitors of the same capacity can be used. Furthermore, it is also possible to switch over to a different point in time of the current profile than to the current zero crossing. The switches 1420, 1440 can either be controlled so that a single case of the coil current (which is composed of two individual half-waves of different frequencies or multiple sections of waves with different frequencies) arises or that more than two directly juxtaposed half-waves are generated ,

FIG. 15 shows, by way of example, such a time characteristic of the current I _L in the treatment coil and the coil voltage U _L , as achieved with the circuit according to FIG.

Figure 16 shows a fourth embodiment, which is also based on the direct coupling of several resonant circuits, which alternately determine the time course of the coil current and the coil voltage. The resonant circuits use a common capacitor 1650 for this purpose, but use several coils (n coils, with n> 1, of which only two, the coils 1610 and 1620 are shown), preferably with different inductance, one of these coils being the treatment coil. In each case a coil 1610 or 1620 forms with an associated circuit breaker 1630 or 1640 one of a total of n coil-switch units. These coil-switch units are alternately or temporarily also so electrically connected to the capacitor 1650 that a switch from one coil to the next coil is preferably carried out during the zero crossing of the respective coil current. In this way, a current waveform can be generated in the treatment coil, which is composed of several sine half-waves of different frequency. Alternatively, the sine half-waves of different frequency can also be generated so that during a half-wave, a first group of coils is connected to the capacitor, and during another half-wave, one or more coils are connected to the capacitor, so that their total inductance different from the total inductance of the first group of coils. In this case, coils of the same inductance can also be used. Furthermore, it is also possible to switch over to a different point in time of the current profile than to the current zero crossing. The switches 1630, 1640 can either be controlled so that a single full wave of the coil current (which is composed of two individual half-waves of different frequencies or multiple sections of waves with different frequencies) arises or that more than two directly juxtaposed half-waves are generated , FIG. 17 shows by way of example such a time characteristic of the current I _Ln in the nth coil, the treatment coil and the coil voltage UL, as achieved with the circuit according to FIG.

Figure 18 shows a fifth embodiment based on a combination of the third and fourth embodiments. The resonant circuits use m capacitors and n coils, where m and n are integers greater than one. In particular, in the illustrated embodiment according to Figure 18, in addition, the capacitors have been extended by further switches, so that in each case the current and voltage direction can be switched at the capacitors. Alternatively, this switching can also take place on the coils (of which only two, the coils 1810 and 1820 are shown), if they are each extended by correspondingly more switches. This can be formed by appropriate switching on and off of capacitors (for example via the capacitor switch units 1850, 1860) and / or coils a time course of the current in the treatment coil (eg coil 1810), which consists of several sine half-waves of different frequency composed. Preferably, a changeover takes place from one coil to the next, or from one capacitor to the next, during the zero crossing of the respective current to be switched. Alternatively, it is also possible to switch over to other times of the current profile as the current zero crossing. The switches 1830, 1840, 1850 and 1860 can either be controlled so that a single full wave of the coil current (which is composed of two individual half-waves of different frequencies or multiple sections of waves with different frequencies) arises or that more than two directly strung half waves are generated.

FIG. 19 shows a sixth embodiment which comprises a capacitor 1920 as a first energy store, which can be supplied with energy by an external charging circuit 210, and a coil 1910, preferably the treatment coil as a further energy store, which is connected to the first energy store via a special triggering circuit is. The special trigger circuit consists of four switching elements 1930, 1940, 1950 and 1960, which on the one hand initiate the discharge of the first energy storage in the further energy storage, as well as again allow a recharge in the first energy storage. The switches are preferably switched in pairs, so that each opposite switch closed and the remaining switches are open. A switch from one pair of switches to the other is preferably carried out at the zero crossing of Spuienstromes. In this way, at first positive polarity of the capacitor charge by closing the two switches 1930 and 1940 (with switches open 1950 and 1960) a sine half wave with positive current direction can be generated by the coil until the magnetic field energy of the coil back into the capacitor 1920th fed back, but now with negative polarity. Subsequently, by closing the two switches 1950 and 1960 (with switches 1930 and 1940 open) in turn a half-wave can be generated with also positive current direction through the coil. By alternately switching the pairs of switches 1930, 1940 and 1950, 1960 thus pulses can be generated in the coil, which consist of several current half waves of the same polarity. Thus, this Ausführuπgsform generates temporal current curves in the treatment coil in such a way that a time course of the induced electric field strength results, in which the mean edge steepnesses of the rising edges of the mean edge steepnesses of the falling edges significantly different. From the circuit of the third embodiment, one arrives at this sixth embodiment, for example, with three capacitances C1, C2 and C3, wherein for the initial voltages of the capacitances U _C i = U _C 3 = -Uc2 and for the second capacitance a Limes formation C2 → 0 is performed.

FIG. 20 shows, by way of example, such a time characteristic of the current I _L in the treatment coil and the coil voltage U _L , as achieved with the circuit according to FIG. 19.

In particular, in the fifth and sixth embodiments, the switches can be further controlled so that the one or more capacitors are each operated only in a polarity direction of the voltage. For this purpose, care must be taken in particular during the discharging processes of the respective capacitor occurring within the pulses that the current direction across the switches is reversed at the latest when the capacitor is completely discharged, so that the capacitor voltage does not assume negative values, but instead instead continues to increase to positive values. By this measure, it is possible to use electrolytic capacitors with high energy density in the power circuits.

In all embodiments it may be advantageous to periodically recharge the respective capacitors after each generated half-sine wave. This periodic recharge can be via another electrically coupled Oscillating circuit system consisting of at least one switch, at least one further coil and at least one further capacitor.

In all the cases described, the switches can be designed as power semiconductors, such as, for example, thyristors, IGBTs or MOSFETs. Depending on the embodiment, the switches can additionally have a rectifying characteristic, so that they are either reverse-conducting or reverse-blocking. In addition, these switches can also act as self-activating erasers, for example by increasing their conductivity when applied current or voltage characteristics have certain properties. This includes, for example, the polarity or a rapid increase in voltage.

Furthermore, instead of the switch power semiconductors with controllable electrical resistance, such as IGBTs or MOSFETs can be used so that the current profile in the treatment coil can be controlled in addition to this controllable electrical resistance.

Claims

claims

1. A device for generating short strong current pulses in a coil, the coil generates magnetic field pulses with a duration of 20 to 3000 microseconds duration and a thickness of 0.1 to 5 Tesla, according to the principle of s electromagnetic induction in the body tissue electrical stimulation currents to

Cause irritation of nerve and / or muscle cells, characterized

that the device comprises at least one capacitor for storing and delivering the energy required for the field pulses and a suitable charging circuit for charging this capacitor; and

that the coil is made to be positioned close enough to the body tissue to be stimulated so that the magnetic field generated by the coil falls within the intended target area at most to one tenth of the thickness at the coil surface; and

that the electrical stimulation currents caused by the magnetic field of the coil are at least one-tenth and at most five times the stimulation currents required for stimulation of the cells; and

in that the device generates in the coil a current pulse whose time characteristic is such as to induce from the coil an electric field in which the mean edge steepness of rising edges of the middle one

Slope slope of falling edges is different.

2. Apparatus according to claim 1, characterized in that in the electronic circuit for generating the magnetic field pulses components are used for controlling the coil current, on the one hand trigger the field pulse on the coil and can terminate and on the other hand, the different mean edge slopes from increasing to falling edge of the induced electric field.

3. Apparatus according to claim 1 or 2, characterized in that the electronic circuit for generating the pulses has a resonant structure, so that the energy required for the field pulse quickly passed from one or more capacitors in one or more coils and from this one or more coils can be routed back into one or more capacitors.

4. The device according to claim 3, characterized in that the resonant structure is such that at least two electrical resonant circuits s consisting of at least one capacitor and at least one coil in the

Are coupled together that they determine alternately or together the time course of the current of the coil, thus generating magnetic field pulses, which are composed of parts of sine waves of different frequency.

5. Apparatus according to claim 4, characterized in that a plurality of electrical resonant circuits of the resonant structure are coupled in such a way that during the magnetic field pulse, a corresponding switching of the coil current to other capacitors takes place.

6. The device according to claim 4, characterized in that a plurality of electrical ls resonant circuits of the resonant structure are coupled in such a way that takes place during the magnetic field pulse, a corresponding switching of the coil current to other coils.

7. The device according to claim 4, characterized in that a plurality of electrical resonant circuits of the resonant structure are coupled in such a way that 0 during the magnetic field pulse, a corresponding switching of

Coil current to other capacitors and / or to other coils is done.

8. The device according to claim 3, characterized in that during the generation of the magnetic field pulse by switching components, the direction of the coil current can be changed so that a temporal5 course of the field induced by the coil results, in which the middle

Slope slopes of rising to falling edge of the induced electric field differ.

9. The device according to claim 8, characterized in that the resonant structure of a capacitor, a coil and at least three switches um0 polarity of the current consists, so that a time course of the current in the

Coil can be generated during the magnetic field pulse, resulting from at least two juxtaposed half sine waves of the same polarity composed.

10. Device according to one of claims 2 to 9, characterized in that the components for controlling the coil current are controlled so that at least at a zero crossing of the current in the coil a short interruption of

Vibration occurs, so that during these interruptions from the coil no magnetic field is generated.

11. The device according to claim 3, characterized in that the components for controlling the coil current switch the currents of the resonant circuit components in such a way that the polarity of the voltage in the capacitor always remains the same.

12. Device according to one of claims 2 to 11, characterized in that the components for controlling and switching the coil current are electronic or mechanical switches.

13. Device according to one of claims 2 to 11, characterized in that the components for controlling and switching the coil current are electronic components with controllable electrical resistance.

14. The apparatus of claim 12 or 13, characterized in that the components for controlling and switching the coil current even in the off state conduct the current in one direction.

15. A method for irritating nerve and / or muscle cells, in which magnetic field pulses are generated with a duration of 20 to 3000 microseconds duration and a thickness of 0.1 to 5 Tesla, according to the principle of electromagnetic induction in the body tissue electrical stimulation currents cause, characterized

that the magnetic field pulses are generated by a coil that is so close to the body tissue to be stimulated that the field generated by the coil within the intended target area drops at most to one tenth of the strength at the coil surface; and that the induced electrical stimulation currents are at least one-tenth and at most five times the stimulation currents required for stimulation of the lines; and

in that the time characteristic of the electric field induced by the coil during the field pulse is such that the average edge steepness of rising edges differs from the mean edge steepness of falling edges.

16. The method according to claim 15, characterized in that the time profile of the magnetic field pulse is generated according to the principle of a resonant resonant circuit, wherein by selectively changing the

Oscillating circuit parameter is changed during the pulse of the time course of the magnetic field pulse in such a way that the field pulses are composed of parts of sine waves of different frequency.

17. The method according to claim 15, characterized in that the time course of the magnetic field pulse according to the principle of a plurality of coupled resonant

Oscillation circuits is generated, which is changed by targeted change of the resonant circuit parameters during the pulse of the time course of the magnetic field pulse in such a way that the field pulses composed of parts of sine waves of different frequency.

18. The method according to claim 16 or 17, characterized in that the time profile of the current in the coil during the magnetic field pulse of two juxtaposed half sine waves of different frequency and different polarity composed.

19. The method of claim 16 or 17, characterized in that the time profile of the current in the coil during the magnetic field pulse from more than two juxtaposed half sine waves composed, each differing in the frequencies and the polarities of successive half sine waves.

20. The method of claim 16 or 17, characterized in that the time profile of the current in the coil during the magnetic field pulse from at least two juxtaposed half sine waves of the same polarity composed.

21. The method according to claim 15, characterized in that the temporal course of the magnetic field pulse is such that within the field pulse successively a plurality of rising and falling edges of the induced electric field strength arise, wherein the mean edge steepness of the rising edges of the mean edge steepness of falling down flanks.

22. The method according to any one of claims 16 to 21, characterized in that at least at a zero crossing of the current in the coil, a brief interruption of the oscillation process takes place, so that no magnetic field is generated during these interruptions from the coil.

23. The method according to claim 16 or 17, characterized in that the currents of the resonant circuit components are controlled in such a way that occur in one or more capacitors used for energy storage only voltages of one polarity.

24. The method according to any one of claims 16 to 22, characterized in that the currents are influenced in the resonant circuit in such a way that occur in at least one inductance used for energy storage only current flows of one direction.

25. The method according to claim 24, characterized in that the influencing of the currents is effected by a choice of a plurality of current paths.

26. The method according to claim 24, characterized in that the influencing of the currents is effected by switches or rectifiers.

27. The method according to any one of claims 24 to 26, characterized in that it is at least one of said coils to treatment coils of the method.