WO1997037721A1 - Techniques for adjusting the locus of excitation of electrically excitable tissue - Google Patents
Techniques for adjusting the locus of excitation of electrically excitable tissue Download PDFInfo
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- WO1997037721A1 WO1997037721A1 PCT/US1997/004908 US9704908W WO9737721A1 WO 1997037721 A1 WO1997037721 A1 WO 1997037721A1 US 9704908 W US9704908 W US 9704908W WO 9737721 A1 WO9737721 A1 WO 9737721A1
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- pulse
- locus
- pulses
- timing relationship
- tissue
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/3605—Implantable neurostimulators for stimulating central or peripheral nerve system
- A61N1/36128—Control systems
- A61N1/36146—Control systems specified by the stimulation parameters
- A61N1/3615—Intensity
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/3605—Implantable neurostimulators for stimulating central or peripheral nerve system
- A61N1/3606—Implantable neurostimulators for stimulating central or peripheral nerve system adapted for a particular treatment
- A61N1/36071—Pain
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/3605—Implantable neurostimulators for stimulating central or peripheral nerve system
- A61N1/36128—Control systems
- A61N1/36146—Control systems specified by the stimulation parameters
- A61N1/36167—Timing, e.g. stimulation onset
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/36014—External stimulators, e.g. with patch electrodes
- A61N1/36017—External stimulators, e.g. with patch electrodes with leads or electrodes penetrating the skin
Definitions
- This invention relates to means of stimulating electrically excitable tissue, and more particularly relates to means for adjusting the locus at which action potentials are induced in such tissue.
- first and second electrodes are implanted adjacent the tissue to be stimulated.
- a first electrical pulse is applied to the first electrode and a second electrical pulse is applied to the second electrode.
- the first and second pulses have a timing relationship such that the combined potentials induced in the locus by the first and second pulses create action potentials in the locus.
- Means are provided for adjusting the timing relationship so that the locus is altered.
- the degree of surgical precision required for the implanting ofthe electrodes is reduced, because the locus at which the nerve fibers are stimulated can be adjusted by merely changing the timing relationship of the pulses applied to the electrodes after the surgical procedure is completed.
- the amplitudes and pulse widths ofthe first and second pulses can be altered, as well as the timing relationship, in order to further alter the locus of the tissue at which action potentials are induced.
- Figure 1 is a diagrammatic view of a patient in which a preferred form of apparatus for SCS made in accordance with the invention has been implanted
- Figure 2 is a cross-sectional view of an exemplary spinal column showing a typical position at which electrodes made in accordance with the preferred practice of the invention have been implanted in the epidural space;
- Figure 3 is a cross-sectional view like Figure 2 showing locus of potential changes induced in the spinal cord from a pulse applied to a first one of two electrodes;
- Figure 4 is a view like Figure 3 showing the locus of potential changes induced in the spinal cord from the application of a pulse to the second ofthe electrodes;
- Figure 5 is a view like Figure 4 showing the combined loci in the spinal cord at which potentials are induced from pulses applied to the first and second electrodes;
- Figure 6 is a view like Figure 5 showing the alteration of the loci due to increase in the amplitude ofthe pulse applied to the first electrode and a decrease in amplitude ofthe pulse applied to the second electrode;
- Figure 7 is a view like Figure 6 showing the alteration ofthe loci due to an increase in amplitude of the pulse applied to the second electrode and a decrease in amplitude ofthe pulse applied to the first electrode;
- Figure 8 is a timing diagram showing pulses applied to the first and second electrodes illustrated in Figure 2 in relationship to the potentials induced in tissue adjacent the electrodes;
- Figures 9 and 10 are timing diagrams illustrating alternative forms of pulses applied to the electrodes illustrated in Figure 2;
- Figure 1 1 is a timing diagram illustrating a preferred form of pulses applied to the electrodes shown in Figure 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS
- a single electrical pulse PI can cause depolarization near a cathode in electrically excitable tissue which includes neural tissue and muscle tissue.
- Neural tissue includes peripheral nerves, the spinal cord surface, deep spinal cord tissue, deep brain tissue, and brain surface tissue.
- Muscle tissue includes skeletal (red) muscle, smooth (white) muscle, and cardiac muscle.
- a locus includes a set of points in three-dimensional space and refers to a volume of cells or parts of cells. Due to the electrical characteristics of both the three-dimensional volume conductor and the membrane properties, the potentials outside and inside a neuron respond to the depolarization, usually with exponential-type increases and then attenuation over time.
- the time constant for an isolated neuron membrane typically is 5-15 milliseconds (Nerve, Muscle and Synapse by Bernard Katz, circa 1972). For myelinated axons or muscle cells, it may be considerably shorter.
- the local depolarization from a single pulse PI results in a transmembrane potential PT1 between times TI and T3.
- the peak of potential PT1 is below the transmembrane potential threshold TPT.
- the pulse fails to produce an action potential in that cell.
- Action potential is an all-or-none, nonlinear phenomenon, caused by opening of sodium gates, inrush of sodium of ions, and a delayed opening of potassium gates and a restoration ofthe membrane potential.
- a certain amount of charge must be passed at the electrodes (amplitude [Volts] / resistance [Ohms] x pulse width
- Electrode Basic neurophysiological principles, called “electrotonus”, show that in any volume of electrically excitable tissue in which two or more pulses, each of which alone is insufficient to bring the cells to threshold, arrive closely together in time, at least part of their effect is additive, i.e., the memory ofthe first pulse is still present when the second pulse arrives. If the sum ofthe potentials (distorted by resistive and capacitive properties of the surroundings and the cell membranes) can get some cells depolarized to threshold, then an action potential will start in those cells.
- FIG. 8 is a schematic view of a patient 10 having an implant of a neurological stimulation system employing a preferred fo ⁇ n ofthe present invention to stimulate spinal cord 12 ofthe patient.
- the preferred system employs an implantable pulse generator 14 to produce a number of independent stimulation pulses which are sent to spinal cord 12 by insulated leads 16 and 18 coupled to the spinal cord by electrodes 16A and 18A ( Figure 2). Electrodes 16A and 18A also can be attached to separate conductors included within a single lead.
- Implantable pulse generator 14 preferably is a modified ITREL II implantable pulse generator available from Medtronic, Inc. with provisions for multiple pulses occurring either simultaneously or with one pulse shifted in time with respect to the other, and having independently varying amplitudes and pulse widths.
- This preferred system employs a programmer 20 which is coupled via a conductor 22 to a radio frequency antenna 24. This system permits attending medical personnel to select the various pulse output options after implant using radio frequency communications. While the preferred system employs fully implanted elements, systems employing partially implanted generators and radio-frequency coupling may also be used in the practice ofthe present invention (e.g., similar to products sold by Medtronic, Inc. under the trademarks X-trel and Mattrix).
- Figure 2 is a cross-sectional view of spine 12 showing implantation of the distal end of insulated leads 16 and 18 which terminate in electrodes 16A and 18A within epidural space 26.
- the electrodes may be conventional percutaneous electrodes, such as PISCESD model 3487A sold by Medtronic, Inc. Also shown is the subdural space 28 filled with cerebrospinal fluid (cfs), bony vertebral body 30, vertebral arch 31, and dura mater 32.
- the spine also includes gray matter 34 and dorsal horns 36 and 37 and white matter, for example, dorsal columns 46 and dorsal lateral columns 47.
- pulse P 1 is applied to electrode 18A ( Figure 2) and pulse P2 is applied electrode 16A ( Figure 2).
- Pulses PI and P2 have a timing relationship. For example, the end of pulse PI at time T2 and the start of pulse P2 at time T3 are displaced by a predetermined time period less than 500 microseconds, and preferably less than 50 microseconds.
- Amplitude Al of PI is adjustable independently from amplitude A2 of pulse P2.
- the pulse widths of pulses PI and P2 also are independently adjustable. Widening the pulse widths of each pulse (i.e., PI and P2) can also expand the loci of depolarizations, just like increasing amplitude, either voltage or current amplitude.
- the pulses P 1 and P2 also could have other timing relationships in order to accomplish the goals ofthe present invention.
- pulses P3 and P4, having different rise times could be used.
- P3 has a rise time from TI to T8 and P4 has a rise time from TI to T9.
- pulses P5 and P6, having different fall times could be used.
- P5 has a fall time from T10 to TI 1
- P6 has a fall time from T10 to T12.
- the weighted average WA3 of pulse P3 ( Figure 9) is displaced from the weighted average WA4 of pulse P4 by a predetermined time period of less than 500 microseconds and preferably less than 50 microseconds.
- the peak PK3 of pulse P3 is displaced from the peak PK4 of pulse P4 by a predetermined time period of less than 500 microseconds and preferably less than 50 microseconds. Objectives ofthe invention also can be achieved using combinations of the foregoing timing relationships.
- line Ll represents the edge of a three-dimensional locus L1A in which pulse PI applied to electrode 18A induces a potential PT1 between times TI and T3 that is less than the transmembrane potential threshold TPT for cells of interest in that locus.
- line L2 represents the edge of another three-dimensional locus L2A in which the application of pulse P2 ( Figure 8) to electrode 16A induces a depolarizing potential less than the transmembrane potential threshold TPT for cells of interest in that locus.
- Figure 5 illustrates a locus L3A representing the intersection of loci L1A and L2A in which the combined potentials induced in locus L3A from pulses PI and P2 create an action potential in cells of interest in locus L3A as illustrated by potential PT3 in Figure 8.
- the potential induced in locus Ll A outside locus L3A is illustrated by potential PT1 ( Figure 8). Since PT1 is lower than the transmembrane potential threshold TPT, there is no action potential created in locus Ll A outside L3A.
- potential PT2 Figure 8).
- line L4 represents the edge of another three-dimensional locus L4A resulting from the application of a pulse PI to electrode 18A having an amplitude greater than amplitude Al ( Figure 8), and line L5 represents the edge of another three-dimensional locus L5A resulting from the application of a pulse P2 to electrode 16A having an amplitude less than amplitude A2.
- the intersection of loci L4A and L5A creates a locus L6A in which action potentials are induced. Locus L6A is moved mostly to the right relative to locus L3A shown in Figure 5. Action potentials are not induced outside locus L6A.
- line L8 represents the edge of another three-dimensional locus L8A resulting from the application of a pulse P2 to electrode 16A having an amplitude greater than amplitude A2 ( Figure 8).
- line L7 represents the edge of another three-dimensional locus L7A resulting from the application of a pulse PI to electrode 18 A having an amplitude less than amplitude Al .
- the intersection of loci L7A and L8A creates a locus L9A in which action potentials are induced. It will be noted that the locus L9A is moved to the left compared with locus L3A shown in Figure 5. Action potentials are not induced outside locus L9A.
- the ability to move the locus in which action potentials are induced is an important feature. In many therapies, it is important to prevent action potentials being induced in gray matter 34 or dorsal horns 36 and 37, dorsal roots 38 and 40, dorsal lateral columns 47 or peripheral nerves 42 and 44 in order to minimize the possibility of causing pain, motor effects, or uncomfortable paresthesia.
- the locus in which action potentials are induced e.g., L3A, L6A or L9A
- the ability to move the locus in which action potentials are induced drastically reduces the accuracy necessary for surgically implanting electrodes 16A and 18A, and may eliminate the need for surgical lead revisions.
- Figure 1 1 illustrates a preferred timing relationship between pulse P7 applied to electrode 18A and pulse P8 applied to electrode 16A.
- pulse generators use a biphasic pulse to insure no net direct current flows into the tissue.
- pulse P8 has a net charge delivered of A2*(T4-T3).
- This injected charge is balanced by the negative pulse PI 0, whose charge is A3*(T5-T4), where A3 «A2 and (T5-T4)»(T4-T3). Similar principles apply even if the first and second pulses are not of constant amplitude.
- pulse P7 may be generated with a trailing negative pulse P9 from time T4 to time T5, so that the output on electrode 18A is substantially at neutral or 0 potential until the termination of pulse P8 at time T4. Having this delay in charge balancing prevents the loss of potential in adjacent tissue that otherwise would occur if pulse P9 immediately followed pulse P7 and overlapped with pulse P8, thus offsetting the benefit of pulse P8.
- both negative pulses P9 and P10 begin in order to maintain the charge balance in tissue adjacent to the respective electrodes 18A and 16A.
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- Engineering & Computer Science (AREA)
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- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Radiology & Medical Imaging (AREA)
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Abstract
A first electrical pulse and a second electrical pulse are transmitted to one or more implanted leads (16, 18) including first and second electrodes (16A, 18A), respectively. The first and second pulses have a timing relationship such that the combined potentials induce action potentials in a certain locus of electrically excitable tissue (12). Means are provided for adjusting the timing relationship and pulse parameters so that the locus is altered.
Description
TECHNIQUES FOR ADJUSTING THE LOCUS OF EXCITATION OF ELECTRICALLY EXCITABLE TISSUE
BACKGROUND OF THE INVENTION Field of the Invention
This invention relates to means of stimulating electrically excitable tissue, and more particularly relates to means for adjusting the locus at which action potentials are induced in such tissue.
Description of the Related Art Two major practical problems reduce the efficacy of epidural spinal cord stimulation (SCS) for pain control. One is the difficulty of directing the stimulation- induced paresthesia to the desired body part and the other is the problem of disagreeable sensations or motor responses to the stimulation, which reduce the comfortable amplitude range ofthe stimulation. It is generally agreed that in SCS, for chronic pain, paresthesia should cover the whole pain region. With present stimulation methods and equipment, only highly skilled and experienced practitioners are able to position a stimulation lead in such a way that the desired overlap is reached and desired results are obtained over time with minimal side effects. It requires much time and effort to focus the stimulation on the desired body region during surgery and, with single channel approaches, it is difficult to redirect it afterwards, even though some readjustments can be made by selecting a different contact combination, pulse rate, pulse width or voltage.
Redirecting paresthesia after surgery is highly desirable. Even if paresthesia covers the pain area perfectly during surgery, the required paresthesia pattern often changes later due to lead migration, or histological changes (such as the growth of connective tissue around the stimulation electrode) or disease progression. The problem of lead placement has been addressed by U.S. Patent No. 5,121,754 by the use of a lead with a deformable distal shape. These problems are not only found with SCS, but also with peripheral nerve stimulation (PNS), depth brain stimulation (DBS), cortical stimulation and also muscle or cardiac stimulation.
A system capable of some adjustment of spinal cord excitation is described in PCT International Publication No. WO 95/19804. However, that system requires three electrodes, optimally spaced, which is a serious handicap during the surgical procedure required in order to place these electrodes in the body. Three electrodes may require the use of a paddle arrangement which is surgically difficult to manipulate adjacent the spinal cord. In addition, that system has only limited adjustment capability, dependent on the distance from the electrodes to the spinal cord.
SUMMARY OF THE INVENTION The present invention can be used to advantage for altering the locus in electrically excitable tissue at which action potentials are induced. According to a preferred embodiment, first and second electrodes are implanted adjacent the tissue to be stimulated. A first electrical pulse is applied to the first electrode and a second electrical pulse is applied to the second electrode. The first and second pulses have a timing relationship such that the combined potentials induced in the locus by the first and second pulses create action potentials in the locus. Means are provided for adjusting the timing relationship so that the locus is altered.
By using the foregoing system, the degree of surgical precision required for the implanting ofthe electrodes is reduced, because the locus at which the nerve fibers are stimulated can be adjusted by merely changing the timing relationship of the pulses applied to the electrodes after the surgical procedure is completed.
According to another embodiment of the invention, the amplitudes and pulse widths ofthe first and second pulses can be altered, as well as the timing relationship, in order to further alter the locus of the tissue at which action potentials are induced. BRIEF DESCRIPTION OF THE DRAWINGS
These and other advantages and features of the invention will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which:
Figure 1 is a diagrammatic view of a patient in which a preferred form of apparatus for SCS made in accordance with the invention has been implanted;
Figure 2 is a cross-sectional view of an exemplary spinal column showing a typical position at which electrodes made in accordance with the preferred practice of the invention have been implanted in the epidural space;
Figure 3 is a cross-sectional view like Figure 2 showing locus of potential changes induced in the spinal cord from a pulse applied to a first one of two electrodes;
Figure 4 is a view like Figure 3 showing the locus of potential changes induced in the spinal cord from the application of a pulse to the second ofthe electrodes; Figure 5 is a view like Figure 4 showing the combined loci in the spinal cord at which potentials are induced from pulses applied to the first and second electrodes;
Figure 6 is a view like Figure 5 showing the alteration of the loci due to increase in the amplitude ofthe pulse applied to the first electrode and a decrease in amplitude ofthe pulse applied to the second electrode; Figure 7 is a view like Figure 6 showing the alteration ofthe loci due to an increase in amplitude of the pulse applied to the second electrode and a decrease in amplitude ofthe pulse applied to the first electrode;
Figure 8 is a timing diagram showing pulses applied to the first and second electrodes illustrated in Figure 2 in relationship to the potentials induced in tissue adjacent the electrodes;
Figures 9 and 10 are timing diagrams illustrating alternative forms of pulses applied to the electrodes illustrated in Figure 2; and
Figure 1 1 is a timing diagram illustrating a preferred form of pulses applied to the electrodes shown in Figure 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 8, a single electrical pulse PI can cause depolarization near a cathode in electrically excitable tissue which includes neural tissue and muscle tissue. Neural tissue includes peripheral nerves, the spinal cord surface, deep spinal cord tissue, deep brain tissue, and brain surface tissue. Muscle tissue includes skeletal (red) muscle, smooth (white) muscle, and cardiac muscle. A locus includes a set of
points in three-dimensional space and refers to a volume of cells or parts of cells. Due to the electrical characteristics of both the three-dimensional volume conductor and the membrane properties, the potentials outside and inside a neuron respond to the depolarization, usually with exponential-type increases and then attenuation over time. The time constant for an isolated neuron membrane typically is 5-15 milliseconds (Nerve, Muscle and Synapse by Bernard Katz, circa 1972). For myelinated axons or muscle cells, it may be considerably shorter.
As shown in Figure 8, the local depolarization from a single pulse PI results in a transmembrane potential PT1 between times TI and T3. The peak of potential PT1 is below the transmembrane potential threshold TPT. As a result, the pulse fails to produce an action potential in that cell.
Action potential is an all-or-none, nonlinear phenomenon, caused by opening of sodium gates, inrush of sodium of ions, and a delayed opening of potassium gates and a restoration ofthe membrane potential. In general, a certain amount of charge must be passed at the electrodes (amplitude [Volts] / resistance [Ohms] x pulse width
[time]) in order to cause enough depolarization for an action potential to begin. There is a reciprocal relationship between amplitude and pulse width: the product must reach a certain value before the threshold is reached. This relationship does not reach the Volts = 0 axis. There is a certain minimum voltage needed, called rheobase, before an action potential can happen.
Basic neurophysiological principles, called "electrotonus", show that in any volume of electrically excitable tissue in which two or more pulses, each of which alone is insufficient to bring the cells to threshold, arrive closely together in time, at least part of their effect is additive, i.e., the memory ofthe first pulse is still present when the second pulse arrives. If the sum ofthe potentials (distorted by resistive and capacitive properties of the surroundings and the cell membranes) can get some cells depolarized to threshold, then an action potential will start in those cells.
Still referring to Figure 8, the inducement of an action potential in a cell is illustrated by a transmembrane depolarizing potential PT3 reaching the transmembrane potential threshold TPT at time T4.
Figure 1 is a schematic view of a patient 10 having an implant of a neurological stimulation system employing a preferred foπn ofthe present invention to stimulate spinal cord 12 ofthe patient. The preferred system employs an implantable pulse generator 14 to produce a number of independent stimulation pulses which are sent to spinal cord 12 by insulated leads 16 and 18 coupled to the spinal cord by electrodes 16A and 18A (Figure 2). Electrodes 16A and 18A also can be attached to separate conductors included within a single lead.
Implantable pulse generator 14 preferably is a modified ITREL II implantable pulse generator available from Medtronic, Inc. with provisions for multiple pulses occurring either simultaneously or with one pulse shifted in time with respect to the other, and having independently varying amplitudes and pulse widths. This preferred system employs a programmer 20 which is coupled via a conductor 22 to a radio frequency antenna 24. This system permits attending medical personnel to select the various pulse output options after implant using radio frequency communications. While the preferred system employs fully implanted elements, systems employing partially implanted generators and radio-frequency coupling may also be used in the practice ofthe present invention (e.g., similar to products sold by Medtronic, Inc. under the trademarks X-trel and Mattrix).
Figure 2 is a cross-sectional view of spine 12 showing implantation of the distal end of insulated leads 16 and 18 which terminate in electrodes 16A and 18A within epidural space 26. The electrodes may be conventional percutaneous electrodes, such as PISCESD model 3487A sold by Medtronic, Inc. Also shown is the subdural space 28 filled with cerebrospinal fluid (cfs), bony vertebral body 30, vertebral arch 31, and dura mater 32. The spine also includes gray matter 34 and dorsal horns 36 and 37 and white matter, for example, dorsal columns 46 and dorsal lateral columns 47.
Referring to Figure 8, pulse P 1 is applied to electrode 18A (Figure 2) and pulse P2 is applied electrode 16A (Figure 2). Pulses PI and P2 have a timing relationship. For example, the end of pulse PI at time T2 and the start of pulse P2 at time T3 are displaced by a predetermined time period less than 500 microseconds, and
preferably less than 50 microseconds. Amplitude Al of PI is adjustable independently from amplitude A2 of pulse P2. The pulse widths of pulses PI and P2 also are independently adjustable. Widening the pulse widths of each pulse (i.e., PI and P2) can also expand the loci of depolarizations, just like increasing amplitude, either voltage or current amplitude.
The pulses P 1 and P2 also could have other timing relationships in order to accomplish the goals ofthe present invention. Referring to Figure 9, pulses P3 and P4, having different rise times, could be used. P3 has a rise time from TI to T8 and P4 has a rise time from TI to T9. Referring to Figure 10, pulses P5 and P6, having different fall times, could be used. P5 has a fall time from T10 to TI 1 , and P6 has a fall time from T10 to T12. The weighted average WA3 of pulse P3 (Figure 9) is displaced from the weighted average WA4 of pulse P4 by a predetermined time period of less than 500 microseconds and preferably less than 50 microseconds. Similarly, the peak PK3 of pulse P3 is displaced from the peak PK4 of pulse P4 by a predetermined time period of less than 500 microseconds and preferably less than 50 microseconds. Objectives ofthe invention also can be achieved using combinations of the foregoing timing relationships.
Referring to Figure 3, line Ll represents the edge of a three-dimensional locus L1A in which pulse PI applied to electrode 18A induces a potential PT1 between times TI and T3 that is less than the transmembrane potential threshold TPT for cells of interest in that locus.
Referring to Figure 4, line L2 represents the edge of another three-dimensional locus L2A in which the application of pulse P2 (Figure 8) to electrode 16A induces a depolarizing potential less than the transmembrane potential threshold TPT for cells of interest in that locus.
Figure 5 illustrates a locus L3A representing the intersection of loci L1A and L2A in which the combined potentials induced in locus L3A from pulses PI and P2 create an action potential in cells of interest in locus L3A as illustrated by potential PT3 in Figure 8. The potential induced in locus Ll A outside locus L3A is illustrated by potential PT1 (Figure 8). Since PT1 is lower than the transmembrane potential
threshold TPT, there is no action potential created in locus Ll A outside L3A. The potential created in locus in L2A outside L3A is illustrated by potential PT2 (Figure 8). Since potential PT2 is less than the transmembrane potential threshold TPT, there is no action potential created in locus L2A outside locus L3A. Referring to Figure 6, line L4 represents the edge of another three-dimensional locus L4A resulting from the application of a pulse PI to electrode 18A having an amplitude greater than amplitude Al (Figure 8), and line L5 represents the edge of another three-dimensional locus L5A resulting from the application of a pulse P2 to electrode 16A having an amplitude less than amplitude A2. The intersection of loci L4A and L5A creates a locus L6A in which action potentials are induced. Locus L6A is moved mostly to the right relative to locus L3A shown in Figure 5. Action potentials are not induced outside locus L6A.
Referring to Figure 7, line L8 represents the edge of another three-dimensional locus L8A resulting from the application of a pulse P2 to electrode 16A having an amplitude greater than amplitude A2 (Figure 8). and line L7 represents the edge of another three-dimensional locus L7A resulting from the application of a pulse PI to electrode 18 A having an amplitude less than amplitude Al . The intersection of loci L7A and L8A creates a locus L9A in which action potentials are induced. It will be noted that the locus L9A is moved to the left compared with locus L3A shown in Figure 5. Action potentials are not induced outside locus L9A.
The ability to move the locus in which action potentials are induced is an important feature. In many therapies, it is important to prevent action potentials being induced in gray matter 34 or dorsal horns 36 and 37, dorsal roots 38 and 40, dorsal lateral columns 47 or peripheral nerves 42 and 44 in order to minimize the possibility of causing pain, motor effects, or uncomfortable paresthesia. In the described techniques, the locus in which action potentials are induced (e.g., L3A, L6A or L9A) can be manipulated to a desired area of the dorsal columns 46 without inducing action potentials in dorsal horns 36 and 37, gray matter 34 or dorsal lateral columns 47. Moreover, the ability to move the locus in which action potentials are induced
drastically reduces the accuracy necessary for surgically implanting electrodes 16A and 18A, and may eliminate the need for surgical lead revisions.
Figure 1 1 illustrates a preferred timing relationship between pulse P7 applied to electrode 18A and pulse P8 applied to electrode 16A. Currently available pulse generators use a biphasic pulse to insure no net direct current flows into the tissue.
This is known as charge-balanced pulsing, and is accomplished by driving the pulse negative for a duration of time. For example, in Figure 1 1, pulse P8 has a net charge delivered of A2*(T4-T3). This injected charge is balanced by the negative pulse PI 0, whose charge is A3*(T5-T4), where A3«A2 and (T5-T4)»(T4-T3). Similar principles apply even if the first and second pulses are not of constant amplitude.
In a preferred embodiment, pulse P7 may be generated with a trailing negative pulse P9 from time T4 to time T5, so that the output on electrode 18A is substantially at neutral or 0 potential until the termination of pulse P8 at time T4. Having this delay in charge balancing prevents the loss of potential in adjacent tissue that otherwise would occur if pulse P9 immediately followed pulse P7 and overlapped with pulse P8, thus offsetting the benefit of pulse P8. At time T4 both negative pulses P9 and P10 begin in order to maintain the charge balance in tissue adjacent to the respective electrodes 18A and 16A.
The foregoing techniques also may be applied to all of the electrically excitable tissue described previously. Those skilled in the art will recognize that the preferred embodiments may be altered and amended without departing from the true spirit and scope ofthe appended claims.
Claims
1. A system for altering the locus of electrically excitable tissue in which action potentials are induced comprising in combination: a first electrode adapted to be implanted adjacent said tissue; a second electrode adapted to be implanted adjacent said tissue; means for applying a first electrical pulse to said first electrode and a second electrical pulse to said second electrode, said first and second pulses having a timing relationship such that the combined potentials induced in said locus by said first and second pulses create action potentials in said locus; and means for adjusting said timing relationship so that said locus is altered.
2. A system, as claimed in claim 1 , wherein the first electrical pulse has insufficient amplitude to induce an action potential at a desired locus of electrically excitable tissue.
3. A system, as claimed in claim 2, wherein the second electrical pulse has insufficient amplitude to induce an action potential at a desired locus of electrically excitable tissue.
4. A system, as claimed in claim 1 , and further comprising means for altering the amplitudes of said first and second pulses.
5. A system, as claimed in claim 1 , and further comprising means for altering the widths of said first and second pulses.
6. A system, as claimed in claim 1 , wherein said timing relationship comprises the time period between the end of the first pulse and the beginning ofthe second pulse.
7. A system, as claimed in claim 1 , wherein said timing relationship comprises the time period between the weighted mean of said first pulse and the weighted mean of said second pulse.
8. A system, as claimed in claim 1 , wherein said timing relationship comprises the time period between the peak of said first pulse and the peak of said second pulse.
9. A system, as claimed in any of claims 6, 7 or 8, wherein said time period is adjustable from 0 to 500 microseconds.
10. A system, as claimed in any of claims 6, 7 or 8, wherein said time period is adjustable from 0 to 50 microseconds.
11. A system, as claimed in claim 1 , wherein said timing relationship comprises the rise time of said first and second pulses.
12. A system, as claimed in claim 1 , wherein said timing relationship comprises the fall time of said first and second pulses.
13. A system, as claimed in claim 1 , wherein the amplitude of said first and second pulses decreases during the duration of said first and second pulses and wherein said timing relationship comprises a time period between the beginning of said second pulse and the end of said first pulse.
14. A system, as claimed in claim 13, wherein said means for applying comprises means for generating a neutral potential tail portion of said first pulse.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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AU24239/97A AU2423997A (en) | 1996-04-04 | 1997-03-28 | Techniques for adjusting the locus of excitation of electrically excitable tissue |
Applications Claiming Priority (2)
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US62757896A | 1996-04-04 | 1996-04-04 | |
US08/627,578 | 1996-04-04 |
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WO1997037721A1 true WO1997037721A1 (en) | 1997-10-16 |
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PCT/US1997/004908 WO1997037721A1 (en) | 1996-04-04 | 1997-03-28 | Techniques for adjusting the locus of excitation of electrically excitable tissue |
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WO (1) | WO1997037721A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7930037B2 (en) | 2003-09-30 | 2011-04-19 | Medtronic, Inc. | Field steerable electrical stimulation paddle, lead system, and medical device incorporating the same |
WO2020128748A1 (en) * | 2018-12-20 | 2020-06-25 | Galvani Bioelectronics Limited | Nerve stimulation system |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4813418A (en) * | 1987-02-02 | 1989-03-21 | Staodynamics, Inc. | Nerve fiber stimulation using symmetrical biphasic waveform applied through plural equally active electrodes |
US5121754A (en) * | 1990-08-21 | 1992-06-16 | Medtronic, Inc. | Lateral displacement percutaneously inserted epidural lead |
WO1995019804A1 (en) * | 1994-01-24 | 1995-07-27 | Medtronic, Inc. | Multichannel apparatus for epidural spinal cord stimulation |
-
1997
- 1997-03-28 AU AU24239/97A patent/AU2423997A/en not_active Abandoned
- 1997-03-28 WO PCT/US1997/004908 patent/WO1997037721A1/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4813418A (en) * | 1987-02-02 | 1989-03-21 | Staodynamics, Inc. | Nerve fiber stimulation using symmetrical biphasic waveform applied through plural equally active electrodes |
US5121754A (en) * | 1990-08-21 | 1992-06-16 | Medtronic, Inc. | Lateral displacement percutaneously inserted epidural lead |
WO1995019804A1 (en) * | 1994-01-24 | 1995-07-27 | Medtronic, Inc. | Multichannel apparatus for epidural spinal cord stimulation |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7930037B2 (en) | 2003-09-30 | 2011-04-19 | Medtronic, Inc. | Field steerable electrical stimulation paddle, lead system, and medical device incorporating the same |
US9867980B2 (en) | 2003-09-30 | 2018-01-16 | Medtronic, Inc. | Field steerable electrical stimulation paddle, lead system, and medical device incorporating the same |
WO2020128748A1 (en) * | 2018-12-20 | 2020-06-25 | Galvani Bioelectronics Limited | Nerve stimulation system |
US12036413B2 (en) | 2018-12-20 | 2024-07-16 | Galvani Bioelectronics Limited | Nerve stimulation system |
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AU2423997A (en) | 1997-10-29 |
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