The present disclosure is generally related to electrical stimulation of a subject, more particularly, to an apparatus and method for electrical stimulation using an interferential current pattern for treating certain conditions.
Electrical stimulation of the posterior spinal cord, spinal cord stimulation (SCS), has developed into an effective therapeutic tool for treating chronic pain conditions. However, very little is known about the sites of activation or the neural mechanisms evoked by SCS that relieve pain and promote changes in the function of somatic and visceral structures.
Spinal Cord Stimulation is most commonly used for patients with chronic intractable pain syndromes. It has also been useful for treating movement disorders and is occasionally used following head injuries. However, one complication with SCS is that of accommodation or habituation to the stimulation signal. Accommodation is when the body habituates or becomes accustomed to an activity or signal and then starts to ignore or “tune it out”. By varying the signal or keeping the focal point of the signal moving, accommodation can be minimized.
Dorsal Column Stimulation (DCS) or SCS using an electrical current pattern has shown to be beneficial in treating chronic pain disorders in patients. Traditional SCS stimulation can be limited because of a spread of the stimulating electrical field within cerebral spinal fluid as intensity of stimulation increases. This is due to the highly conductive nature of cerebral spinal fluid (CSF) as compared to the less conductive nature of the spinal cord tissue itself. Frequently, patient satisfaction with electrical stimulation is compromised by the recruitment of adjacent neuronal structures that, when activated, can create discomfort, motor contractions, and outright pain. The efficacy of the therapy is thus limited.
Electrical stimulation has also been shown to be useful to treat certain other conditions. Success of the treatment often is limited to an ability at which the stimulation can be effectively delivered and maintained to a location of pain in the subject.
Within examples, a method for electrical stimulation of a subject is described, comprising creating multiple circuits using implantable electrodes positioned in the subject, transmitting a signal of a first frequency through a first circuit of the multiple circuits and the first circuit generates a first electrical field, and transmitting a signal of a second frequency through a second circuit of the multiple circuits and the second circuit generates a second electrical field. The implantable electrodes are positioned in a substantially linear configuration along a same axis such that the first electrical field and the second electrical field are in an axial bias configuration, and the first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
In other examples, a method for electrical stimulation of a subject is described, comprising transmitting a signal of a first frequency through a first circuit created between a first pair of implantable electrodes positioned in the subject and the first circuit generates a first electrical field, and transmitting a signal of a second frequency through a second circuit created between a second pair of implantable electrodes positioned in the subject and the second circuit generates a second electrical field. The first pair of implantable electrodes and the second pair of implantable electrodes are positioned in a substantially linear configuration along a same axis such that the first electrical field and the second electrical field are in an axial bias configuration, and the first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
In other examples, an electrical stimulator for electrical stimulation of a subject is described, comprising an interferential current generator which generates an interferential alternating current output comprising first signals and second signals, and multiple circuits created using implantable electrodes. The implantable electrodes have a first end and a second end, and the first ends are coupled to the interferential current generator and the second ends are configured to be positioned in the subject, The first signals are transmitted through a first circuit of the multiple circuits to generate a first electrical field, the second signals are transmitted through a second circuit of the multiple circuits to generate a second electrical field, and the implantable electrodes are positioned in a substantially linear configuration along a same axis such that the first electrical field of the first circuit and the second electrical field of the second circuit are in an axial bias configuration. The first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.
Many aspects of the disclosure can be understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Example methods and systems are described herein. It should be understood that the words “example,” “exemplary,” and “illustrative” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as being an “example,” being “exemplary,” or being “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
Examples described herein provide an apparatus and method for electrical stimulation of a subject, such as for many different types of treatment and applications. Within examples, an electrical stimulator is provided that includes implantable electrodes, and interferential stimulation is used to produce a beat frequency signal that is directionally controlled to appropriate targets within the subject. An effective area of stimulation is controlled by the quantity of electrodes, and positioning of the electrodes and electrode interference pattern orientation.
Interferential current provides directional control, decreased accommodation or habituation, and increased depth of penetration in comparison to other standard implantable stimulation systems and accompanying surgical leads. Amplitudes of outputs in respective circuits may be modulated to increase an area of targeted stimulation. Within examples, to target specific areas of the subject using modulation of the circuit outputs, the beat frequency signal would be directionally controlled and/or depths of penetration are controlled.
The electrical stimulator 100 described herein may be fully implanted into a subject, or portions of the electrical stimulator 100 may be implanted and portions remain exterior of the subject. As an example, the implantable electrodes 108 may be implantable, as described, and the interferential current generator 102 and a power source can be external and coupled to the implanted electrodes 108 through wires. In other examples, coupling may occur through a wireless link (e.g., radio frequency (RF) link) from the interferential current generator 102 to the implantable electrodes 108, such that the electrodes are implanted and the interferential current generator 102 is not implanted. The RF carrier frequency can be in the MHz, GHz or THz range and will induce a current in an implanted receiver that is linked or connected to the implantable electrodes 108. The RF carrier frequency can range from about 1 MHz through about 20 THz.
In still other examples, the interferential current generator 102 is implantable in the subject (and a power source connected to the interferential current generator 102 may be implanted as well), and the implantable electrodes 108 are further implanted. The interferential current generator 102 may be implanted near or in the brachial plexus, or near or underneath the 12th rib bone, for example.
In operation of the electrical stimulator 100, the first signals 104 are transmitted through a first circuit of the multiple circuits to generate a first electrical field, the second signals 106 are transmitted through a second circuit of the multiple circuits to generate a second electrical field, and the implantable electrodes 108 are positioned in a substantially linear configuration along a same axis such that the first electrical field of the first circuit and the second electrical field of the second circuit are in an axial bias configuration. The first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
In some examples, the electrical stimulator 100 also includes a processor 116 coupled to the interferential current generator 102, and the processor 116 is programmed to cause the interferential current generator 102 to send the first signals 104 and the second signals 106 at selected frequencies, voltage levels, and time periods.
The interferential current generator 102 includes a pulse generator 118 that generates digital signal pulses, and the processor 116 connects to or is in communication with the pulse generator 118 to cause generation of digital signal pulses to approximate a sine-wave-like output waveform. For example, the output may be a sinewave, pseudo sinewave, or some sine-wave-like continuous waveform that are in-phase. In other examples, the output includes a square wave.
The pulse generator 118 generates individual pulses of differing widths and resultant amplitudes. In some examples, the pulse width is set in a range from about 0 to about 2.5 microseconds (ms), from about 2.5 ms to about 5 ms, or from about 5 ms to about 10 ms. When those differing pulses are driven into a transformer (not shown), the pseudo-sine-wave is produced.
The pulse generator 118 also generates a range of outputs, such as amplitudes within a range of about 5 mA to about 9 mA, about 9 mA to about 10 mA, and about 10 mA to about 18 mA, for example, depending on the patient's needs for pain treatment.
The processor 116 may be or include a field-programmable gate array (FPGA) used to shape multiple pulsatile waveforms to approximate the output of a sine-wave generator instead of or in addition to a digital signal processor. The FPGA is an integrated circuit that can be programmed in the field after it is manufactured and allows its user to adjust the circuit output as desired. Thus, in an alternative example, the processor 116 may be replaced with the FPGA. An FPGA device can allow for complex digital signal processing applications such as finite impulse response filters, forward error correction, modulation-demodulation, encryption and applications.
The processor 116 may include internal memory (non-transitory memory as well as buffer/transitory type memory) to store instructions for execution to cause the electrical stimulator 100 to perform functions as described herein. In addition or alternatively, in one example the electrical stimulator 100 includes discrete internal memory to which the processor is in communication (through a traditional bus communication), and the internal memory stores instructions for execution to cause the electrical stimulator 100 to perform functions as described herein.
The electrical stimulator 100 may include further components as well, such as a power source and other circuitry to perform functions described herein.
Within examples, as mentioned above, the processor 116 is in communication with the interferential current generator 102 to cause the interferential current generator 102 to send different signals at different time periods for waveform generation for electrical stimulation treatment.
In operation, the current generator 102 generates an interferential output including the first signals 104 and the second signals 106 having different first and second frequencies. Selected electrodes of the implantable electrodes 108 carry one of the first signals 104 and the second signals 106 to create separate circuits. Where a first circuit (created between two electrodes) and a second circuit (created between two electrodes) interfere, a resultant beat frequency will be a difference between frequencies of the two circuits, and an amplitude will be additive and greater than either circuit alone. Within other examples, the resultant beat frequency signal may have a frequency within a range of more than 250 Hz to about 15,000 Hz.
Within many examples described below, multiple circuits are created between the implantable electrodes 108 in a number of ways. For example, multiple circuits can be created using three electrodes, where one electrode is common among two circuits. In other examples, multiple circuits can be created using four electrodes, so that separate circuits are created between separate pairs of electrodes. Still further, multiple circuits can be created using electrodes on a single lead, or multiple circuits can be created using two separate leads positioned in the substantially linear configuration approximately end-to-end, and a distance, measured perpendicular to the same axis, between the first lead and the second lead is less than about 2 mm.
Thus, in some examples, the implantable electrodes 108 are included on a single lead, and the implantable electrodes 108 are independently controllable to be arranged as positive and negative electrode pairs for creation of the first circuit and the second circuit using a single lead. Further, using a single lead, multiple circuits can be created so that a first circuit is between a first implantable electrode and a second implantable electrode and a second circuit is between the first implantable electrode and a third implantable electrode, and the first circuit and the second circuit have a common implantable electrode. In other examples, using a single lead, multiple circuits can be created so that a first circuit is between a first implantable electrode and a second implantable electrode and a second circuit is between a third implantable electrode and a fourth implantable electrode.
In still other examples, the implantable electrodes include a first pair of implantable electrodes and a second pair of implantable electrodes positioned in the substantially linear configuration along the same axis.
In summary, the multiple circuits are created in many ways including using three electrodes on a single lead, using four electrodes on a single lead, using more than four electrodes on a single lead (such as for more than two circuits), using three electrodes from two different leads, using four electrodes from two different leads, or using more than four electrodes from two different leads. Examples are described and shown in Figures below.
Each of the implantable electrodes 132a-d is independently controllable to be operated as a cathode or anode, and any combination of the implantable electrodes 132a-d can be selected to create one or more circuits. For physiological purposes, a nerve has a negative internal charge and is polarized at rest so as to be ready to fire, and the electrons (negative internal charge) attract positive charge on an outside of the nerve resulting in depolarization. Thus, physiologically, a cathode is considered a negative contact, and an anode is where the negative charge accumulates so that the anode is considered a positive contact that attracts negative charge.
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The interferential current generator 120 is operated in many ways to transmit the first signals 104 and the second signals 106 of different frequencies. In one example, transmitting the signal of the first frequency across the first circuit includes transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz, and transmitting the signal of the second frequency across the second circuit includes transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz. For generation of the beat signal, the first frequency is different from the second frequency.
Frequencies of signals may be transmitted through the first circuit and the second circuit within ranges of about 0 to about 20,000 Hz, or any ranges than can result in the beat signal having a frequency in a range of more than 0 Hz to about 5,000 Hz, for example. The beat signal frequency results from interference of the two signals from the first circuit and the second circuit (e.g., for a frequency of 10,000 Hz at the first circuit creating a first electrical field interfering with a second electrical field generated by the second circuit due to a frequency of 12,000 Hz results in a beat signal frequency of about 2,000 Hz).
Based on combinations of the frequencies used and transmitted in the first circuit and the second circuit, the beat signal may be in a range of more than 0 Hz to about 5,000 Hz. Thus, within examples, signals are transmitted in a range of frequencies between about 12,000 Hz to about 15,000 Hz, a range of frequencies between about 13,000 Hz to about 15,000 Hz, a range of frequencies between about 14,000 Hz to about 15,000 Hz, a range of frequencies between about 10,000 Hz to about 15,000 Hz, a range of frequencies between about 6,000 Hz to about 9,000 Hz, a range of frequencies between about 7,000 Hz to about 9,000 Hz, a range of frequencies between about 8,000 Hz to about 9,000 Hz, a range of frequencies between about 9,000 Hz to about 12,000 Hz, a range of frequencies between about 10,000 Hz to about 12,000 Hz, a range of frequencies between about 11,000 Hz to about 13,000 Hz, a range of frequencies between about 13,000 Hz to about 15,000 Hz, a range of frequencies between about 3,000 Hz to about 5,000 Hz, a range of frequencies between about 3,000 Hz to about 7,000 Hz, a range of frequencies between about 3,000 Hz to about 6,000 Hz, a range of frequencies between about 5,000 Hz to about 8,000 Hz, a range of frequencies between about 1,000 Hz to about 5,000 Hz, or any other ranges between 1,000 Hz to about 20,000 Hz.
Thus, any signals in a range of frequency between about 1,000 Hz and 20,000 Hz can be used and transmitted to the first circuit and the second circuit to caused interference of electrical fields resulting in a beat signal generated that is in a range of about 0-5,000 beats per second (BPS).
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In other examples, a dual lead arrangement is implemented so that the first lead 140 and the second lead 142 are positioned in the substantially linear configuration approximately end-to-end, and a distance (d), measured perpendicular to the same axis, between the first lead 140 and the second lead 142 is less than about 2 mm. In other examples, the distance (d) is less than about 1 mm, less than about 1 mm-2 mm, or less than about 0.5-1 mm.
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In some examples, the first circuit is created using the implantable electrodes on the first lead 140, and the second circuit is created using the implantable electrodes on the second lead 142. By positioning the first lead 140 and the second lead 142 along the same axis as shown in
Thus, within examples described herein, an axial bias configuration can be implemented to generate a beat signal useful for electrical stimulation. The axial bias configuration can be established using three electrodes on a single lead, using four electrodes on a single lead, using three electrodes from two different leads, or using four electrodes from two different leads, for example.
In still further examples, functions of methods described herein are performed by circuitry (processor) executing instructions stored on non-transitory computer-readable medium to cause the electrical stimulator to provide stimulation treatment.
It should be understood that for this and other processes and methods disclosed herein, flowcharts show functionality and operation of one possible implementation of present embodiments. Alternative implementations are included within the scope of the example embodiments of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.
At block 202, the method 200 includes creating multiple circuits using implantable electrodes positioned in the subject.
In some examples, creating multiple circuits using implantable electrodes positioned in the subject comprises creating the first circuit between a first implantable electrode and a second implantable electrode, and creating the second circuit between the first implantable electrode and a third implantable electrode. In these examples, the first circuit and the second circuit have a common implantable electrode.
In some examples, creating multiple circuits using implantable electrodes positioned in the subject comprises creating the first circuit between a first implantable electrode and a second implantable electrode, and creating the second circuit between a third implantable electrode and a fourth implantable electrode.
In some examples, creating multiple circuits using implantable electrodes positioned in the subject comprises creating the first circuit and the second circuit using the implantable electrodes on a single lead. The single lead includes a plurality of electrodes arranged in a linear electrode array, and the method 200 optionally includes altering selection of a first electrode of the first circuit on the single lead to alter a longitudinal positioning of the beat signal. In addition, the method 200 optionally includes altering a longitudinal positioning of the beat signal by changing a configuration of the first circuit and the second circuit to be operated from among the plurality of electrodes of the linear electrode array.
In some examples, creating multiple circuits using implantable electrodes positioned in the subject comprises creating the first circuit using the implantable electrodes on the first lead, and creating the second circuit using the implantable electrodes on the second lead.
At block 204, the method 200 includes transmitting a signal of a first frequency through a first circuit of the multiple circuits, and the first circuit generates a first electrical field.
At block 206, the method 200 includes transmitting a signal of a second frequency through a second circuit of the multiple circuits, and the second circuit generates a second electrical field. The implantable electrodes are positioned in a substantially linear configuration along a same axis such that the first electrical field and the second electrical field are in an axial bias configuration, and the first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
In one example, the first lead and the second lead are positioned in the substantially linear configuration approximately end-to-end, wherein a distance, measured perpendicular to the same axis, between the first lead and the second lead is less than about 2 mm.
In one example, the implantable electrodes are independently controllable to be arranged as positive and negative electrode pairs for creation of the first circuit and the second circuit.
In some examples, the method 200 includes transmitting the signal of the first frequency comprises transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz, and transmitting the signal of the second frequency comprises transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz, wherein the first frequency is different from the second frequency. In some examples, the beat signal has a frequency within a range of more than 0 Hz to about 5,000 Hz.
It should be understood that for this and other processes and methods disclosed herein, flowcharts show functionality and operation of one possible implementation of present embodiments. Alternative implementations are included within the scope of the example embodiments of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.
At block 212, the method 210 includes transmitting a signal of a first frequency through a first circuit created between a first pair of implantable electrodes positioned in the subject, and the first circuit generates a first electrical field.
At block 214, the method 210 includes transmitting a signal of a second frequency through a second circuit created between a second pair of implantable electrodes positioned in the subject, and the second circuit generates a second electrical field.
In the method 210, the first pair of implantable electrodes and the second pair of implantable electrodes are positioned in a substantially linear configuration along a same axis such that the first electrical field and the second electrical field are in an axial bias configuration, and the first electrical field and the second electrical field interfere with each other at an area of overlap to produce a beat signal.
In some examples, the first pair of implantable electrodes and the second pair of implantable electrodes are aligned vertically along a longitudinal axis of the spinal cord to form the first circuit and the second circuit and the first circuit is positioned on the same axis as the second circuit.
In some examples, the first pair of implantable electrodes and the second pair of implantable electrodes are included on a single lead, and the first pair of implantable electrodes and the second pair of implantable electrodes are independently controllable to be arranged as positive and negative electrode pairs for creation of the first circuit and the second circuit. In some examples, the single lead includes a plurality of electrodes arranged in a linear electrode array, and the method 210 further comprises altering selection of a first electrode of the first pair of implantable electrodes on the single lead to alter a longitudinal positioning of the beat signal.
In some examples, the first pair of implantable electrodes are included on a first lead and the second pair of implantable electrodes are included on a second lead, and the first lead and the second lead are positioned in the substantially linear configuration approximately end-to-end, such that a distance (d), measured perpendicular to the same axis, between the first lead and the second lead is less than about 2 mm.
In some examples, the substantially linear configuration approximately end-to-end comprises at least one electrode on the first lead positioned adjacent to at least one electrode on the second lead.
In some examples, the method 210 includes transmitting the signal of the first frequency comprises transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz, and transmitting the signal of the second frequency comprises transmitting the signal at a frequency between about 1,000 Hz to about 20,000 Hz, wherein the first frequency is different from the second frequency. In some examples, the beat signal has a frequency within a range of more than 0 Hz to about 5,000 Hz.
The electrical stimulation described herein may be used for many different types of treatment or applications. In one example, the methods described herein include positioning the first pair of implantable electrodes to a dura matter in an epidural space proximate to a spinal cord of the subject, and positioning the second pair of implantable electrodes to the dura matter in the epidural space proximate to the spinal cord of the subject in order to provide spinal cord stimulation treatment. In such examples, the first pair of implantable electrodes and the second pair of implantable electrodes are aligned vertically along a longitudinal axis of the spinal cord to form the first circuit and the second circuit and the first circuit is positioned on the same axis as the second circuit.
Other example applications exist as well and the implantable electrodes may be positioned accordingly, such as proximal to the spinal cord and supportive tissues (Glia and Microglia, interstitial tissue, etc.), transforaminal stimulation of the spinal nerve(s) and spinal nerve root(s) separately or simultaneously and supportive tissues, vertebrae nerves and supportive tissues, peripheral nerves and supportive tissues, and Vagus Nerves and supportive tissues. Still other example applications including for treatment and application to sympathetic and parasympathetic nerves outside the spinal canal may be implemented by positioning the implantable electrodes proximal to paravertebral locations, such as cervical including superior cervical ganglion, the middle cervical ganglion, the cervicothoracic ganglion (stellate ganglion), thoracic, and lumbar or prevertebral locations, such as coeliac, superior mesenteric, inferior mesenteric, and ganglion impar.
Example indications and intended uses of the electrical stimulation include pain treatment (both chronic and acute), blood pressure modulation, blood sugar level modulation (diabetes modulation), inflammation, heart rate and cardiac neuromodulation, neuromodulation of breathing, neuromodulation of other vegetative functions (sympathetic and parasympathetic systems), and anxiety.
As such, within example methods described herein, the methods optionally include positioning the implantable electrodes to space proximate to nervous tissue of the subject, positioning the implantable electrodes to space proximate to vertebral nerves of the subject, positioning the implantable electrodes to space proximate to a dorsal root ganglia of the subject, positioning the first pair of implantable electrodes and positioning the second pair of implantable electrodes to space proximate to Vagus nerves of the subject, or positioning the implantable electrodes to space proximate sympathetic and parasympathetic nerves.
Within yet further examples, system and methods described herein are useful for operation of the electrical stimulator as well as for programming operation of the electrical stimulator 100. To program the electrical stimulator 100 and select electrodes from among the implantable electrodes 108 for use, circuits are created (as described with references to the methods in
By the term “about” and/or the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.