Apparatus and methods for stimulating tissue
Apparatus and methods for stimulating tissue employing local current imbalance to facilitate more effective stimulation regimens.
1. Field of Inventions
The present inventions relate generally to neurostimulation systems.
2. Description of the Related Art
Neurostimulation systems, such as spinal cord stimulation (SCS) systems, deep brain stimulation systems and peripheral nerve stimulation systems, include at least one electrode positioned to enable stimulation of neural elements that are the target tissue (i.e. the tissue that, when sufficiently stimulated, will create the desired therapeutic effect). The electrodes are commonly mounted on a carrier and, in many instances, a plurality of electrodes are mounted on a single carrier. These carrier/electrode devices are sometimes referred to as “leads”. The electrodes may be used to cause nerves to fire action potentials (APs) that propagate along the neural fibers. More specifically, supplying stimulation energy to an electrode functioning as a cathode creates an electric potential field that causes depolarization of the neurons adjacent to the electrode. When the field is strong enough to depolarize (or “stimulate”) the neurons beyond a threshold level, the neurons will fire APs.
Stimulation energy may be delivered to the electrodes during and after the lead placement process in order to verify that the electrodes are stimulating the target neural elements and to formulate the most effective stimulation regimen. The regimen will dictate which of the electrodes are sourcing or returning current pulses at any given time, as well as the magnitude and duration of the current pulses. The stimulation regimen will typically be one that provides stimulation energy to all of the target tissue that must be stimulated in order to provide the therapeutic benefit (e.g., pain relief), yet minimizes the volume of non-target tissue that is stimulated. Thus, certain types of neurostimulation leads are typically implanted with the understanding that the stimulus pattern will require fewer than all of the electrodes on the leads to achieve the desired clinical effect; in the case of SCS, such a clinical effect is “paresthesia,” i.e., a tingling sensation that is effected by the electrical stimuli applied through the electrodes.
The present inventor has determined that conventional stimulus regimens, and the manner in which they are formulated, may be susceptible to improvement. For example, there are instances where the target tissue is not directly adjacent to an electrode and, because electrical field strength decreases exponentially with distance from the electrode, a relatively strong electric field must be created to generate APs in the target neural fibers. The electric field may, however, result in the generation of APs in the non-target fiber bundles between the electrode and the target fibers. The generation of APs in the non-target tissue may, in turn, lead to undesirable outcomes (e.g., discomfort) for the patient. The present inventor has determined that it may also be desirable in, for example, the context of leads that are oriented transverse to the target neural fibers, to selectively control the shape of the AP generating region in order to prevent the generation of APs in non-target fibers.
SUMMARY OF THE INVENTIONSApparatus and methods in accordance with some of the present inventions involve the creation of APs in neural fibers and the selective blocking of the APs in some of the neural fibers in which APs are created. Such apparatus and methods are advantageous for a variety of reasons. For example, such apparatus and methods facilitate stimulation regimens that create APs in tissue that is not directly adjacent to the depolarizing electrode(s) while preventing APs from propagating in the tissue therebetween that produce undesirable outcomes for the patient.
Apparatus and methods in accordance with some of the present inventions involve the use of local current imbalances and the sinking of current at a remote cathode(s). Such apparatus and methods are advantageous for a variety of reasons including, but not limited to, facilitation of the selective control of the width and depth of AP generating regions. For example, the programmer may increase the current sourced at one or more electrodes within the stimulation site, which tends to reduce the width of the AP generating and propagating region, without a corresponding increase in the current sunk at one or more other electrodes within the stimulation site (which would increase the depth of the AP generating region).
The above described and many other features of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGSDetailed description of exemplary embodiments of the inventions will be made with reference to the accompanying drawings.
The following is a detailed description of the best presently known modes of carrying out the inventions. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the inventions. The detailed description is organized as follows:
I. Exemplary Neurostimulation Systems
II. Exemplary Neurostimulation Regimens
The section titles and overall organization of the present detailed description are for the purpose of convenience only and are not intended to limit the present inventions.
I. Exemplary Neurostimulation Systems
The present inventions have application in a wide variety of neurostimulation systems. Although the present inventions are not so limited, examples of such systems are illustrated in
The exemplary neurostimulation system 100 illustrated in
The exemplary IPG 110 includes an outer case 122 that may be formed from an electrically conductive, biocompatible material such as titanium and, in some instances, will function as an electrode. The IPG 110 is typically programmed, or controlled, through the use of an external (non-implanted) programmer 124. The external programmer 124 is coupled to the IPG 110 through a suitable communications link, represented by the arrow 126, that passes through the patient's skin 128. Suitable links include, but are not limited to, radio frequency (RF) links, inductive links, optical links and magnetic links. The programmer 124 or other external device may also be used to couple power into the IPG 110 for the purpose of operating the IPG or replenishing a power source, such as a rechargeable battery, within the IPG. Once the IPG 110 has been programmed, and its power source has been charged or otherwise replenished, the IPG may function as programmed without the external programmer 124 being present.
With respect to the stimulus regimens provided during operation of the exemplary neurostimulation system 100, electrodes that are selected to receive stimulation energy are referred to herein as “activated,” while electrodes that are not selected to receive stimulation energy are referred to herein as “non-activated.” Electrical stimulation will occur between two (or more) electrodes, one of which may be the IPG case, so that the electrical current associated with the stimulus has a path through the tissue from one or more electrodes configured as anodes to one or more electrodes configured as cathodes, or return electrodes. The return electrode(s) may be one or more of the electrodes 106 on the leads 102 and 104 or may be the IPG case 122. Stimulation energy may be transmitted to the tissue in monopolar, bipolar, or multipolar fashion, as examples. Monopolar stimulation occurs when a selected one of the lead electrodes 106 is activated along with the case 122. Bipolar stimulation occurs when two of the lead electrodes 106 are activated. The lead electrodes 106 may be on the same lead, or on different leads. For example, electrode E3 on lead 102 may be activated as an anode at the same time that electrode E4 on lead 102, or electrode E11 on lead 104, is activated as a cathode. Tripolar stimulation occurs when three of the lead electrodes 106 are activated on the same lead, or on different leads. For example, electrodes E4 and E6 on lead 102 may be activated as anodes at the same time that electrode E5 on lead 102, is activated as a cathode. Generally speaking, multipolar stimulation occurs when multiple lead electrodes 106 are activated.
Turning to
The IPG programming will dictate which of the electrodes, i.e. the lead electrodes 106 and the IPG case 122, will act as source(s) and sink(s) at any particular time. To that end, the IPG 110 is provided with a programmable current control circuit 134 that causes selected dual current sources 130 to operate as an anode or a cathode, at specified times, to source or sink current having predetermined amplitude (and other parameters). In the illustrated embodiment, where there are eight (8) electrodes 106 on lead 102 (labeled E1-E8), eight (8) electrodes on lead 104 (E9-E16), and an IPG case 122 that can function as an electrode (labeled Ecase), there are seventeen individually operable dual current sources 130. The control circuit 134, which typically operates in accordance with stored control data that is received from the programmer 124, also turns off the selected dual current sources 130 at specified times. Alternative implementations may, for instance, employ fewer dual current sources than there are electrodes. Here, at least some of the dual current sources will be connected to more than one electrode. Alternative implementations may also be configured such that the IPG case 122 only functions as an anode, or such that the IPG case only functions as a cathode
The operation of the control circuit 134 may be explained in the context of the following example. Referring to
As another example, the control circuit 134 may be used to cause a portion of the current sourced from one or more lead electrodes to be sunk by one (or more) lead electrodes and the remainder of the current to be sunk at the IPG case. Turning to
After time period T1, the control circuit 134 will typically switch the polarities of the electrodes during a second time period T2. Thus, an electrode that was functioning as an anode during time period T1 will function as a cathode during time period T2, and an electrode that was functioning as a cathode during time period T1 will function as an anode during time period T2. Operating the control circuit 134 in this manner produces a biphasic stimulation pulse that is characterized by a first phase (period T1) of one polarity followed by a second phase immediately or shortly thereafter (period T2) of the opposite polarity. The electrical charge associated with the first phase should be equal to the charge associated with the second phase to maintain charge balance during the stimulation, which is generally considered an important component of stimulation regimes, although this is not required by the present inventions. Referring to FIG. 7, the charge balance of a biphasic stimulation pulse 136 may be achieved by making the amplitudes of the first and second phases, as well as the periods T1 and T2, substantially equal. Charge balance may also be achieved using other combinations of phase duration and amplitude. For example, the amplitude of the second phase may be equal to one-half of the amplitude of the first phase and the period T2 may be equal to twice the period T1, as is the case in the biphasic stimulation pulse 136′ illustrated in
Neurostimulation systems in accordance with the present inventions may also employ the alternative IPG 110′ illustrated in
The dual voltage sources 130′ and control circuit 134′ may be used to produce the biphasic stimulation pulses that are characterized by a first phase (period T1) of one polarity followed by a second phase immediately or shortly thereafter (period T2) of the opposite polarity applied between any two or more electrodes. Charge balance of the biphasic stimulation pulse may be achieved by making the amplitudes of the first and second phases, as well as the periods T1 and T2, equal. Charge balance may also be achieved using other combinations of phase duration and amplitude. For example, the amplitude of the second phase may be equal to one-half of the amplitude of the first phase and the period T2 may be equal to twice the period T1.
Additional details concerning IPGs may be found in U.S. Pat. No. 6,516,227 and U.S. Pub. App. 2003/0139781, which are incorporated herein by reference. It also should be noted that the block diagrams illustrated in
The present inventions also have application in non-implantable neurostimulation systems. For example, the present inventions may be embodied in, and/or performed using, transcutaneous electrical nerve stimulation (“TENS”) systems. In TENS systems, the sourcing and sinking electrodes are placed on the patient's skin. Current is sourced into the neural tissue by way of the skin. Current is also sunk, both locally and remotely, by way of the skin.
II. Exemplary Neurostimulation Regimens
The neurostimulation systems described above with reference to
Conventional stimulation regimens for use with a lead that is generally parallel to the neural fibers, which serve as a reference for certain stimulation regimens in accordance with the present inventions, are illustrated in FIGS. 10 and 11. In
E1ectrodes E1 and E3, which are functioning as anodes in the stimulation regimen illustrated in
Turning to
In both of the regimens described above, the generation of APs in the fibers within the second fiber bundle FB2 will require an increase in the depolarizing electric field generated by electrode E2 over that illustrated in
As illustrated in
The inventor herein has determined that sinking all of the current sourced by electrodes E1 and E3 at electrode E2 could result in a depolarizing electric field that would meet or exceed the depolarization threshold DPT in fiber bundles well beyond the second fiber bundle FB2. In those instances where the creation of APs beyond the second fiber bundle FB2 is undesirable, a portion of the current sourced by the electrodes E1 and E3 will be sunk at an electrode that is located remotely from stimulation site, thereby creating a local current imbalance at the stimulation site. Sinking some of the current at a remote electrode allows the intensity of the depolarizing electric field created by electrode E2 to be reduced to a level where the hyperpolarization threshold HPT will not be met in fibers within the second fiber bundle FB2.
The portion of the current in the exemplary stimulation regimen illustrated in
It should be noted here that there are a variety ways to remotely sink current. One example is, as discussed above, sinking current at the remotely located case electrode Ecase. Current may also be sunk, for example, at some or all of the electrodes on a remotely implanted lead. Another example is sinking current at a dedicated, and preferably spherical, remotely implanted electrode on the end of a lead.
Another exemplary stimulation regimen in accordance with a present invention, which may be employed when AP block is only desired in a single direction, is illustrated in
Additionally, in those instances where the creation of APs in fibers beyond the second fiber bundle FB2 is undesirable, a portion of the current sourced by electrode E1 will be sunk at an electrode that is located remotely from the stimulation site, thereby creating a local current imbalance at the stimulation site. As noted above, this reduces the intensity of the depolarizing electric field created by electrode E2 to a level where the hyperpolarization threshold HPT will not be met beyond the second fiber bundle FB2. In the illustrated regimen, the current from electrode E1 that is not sunk at electrode E2 is sunk at the IPG case electrode Ecase. Although the relative amounts may vary to suit particular situations, a majority of the current is sunk at E2 in the illustrated example. More specifically, 60% of the current sourced by electrode E1 is sunk at electrode E2 and the remaining 40% is sunk at electrode Ecase.
Turning to stimulation regimens for use with a lead that is oriented generally transverse to the neural fibers, and as illustrated for example in
The present inventor has determined that locally current balanced stimulation regimens, such as that illustrated in
As illustrated in
Current steering techniques may also be employed with local current imbalances to further control the locus of stimulation LOS. Referring for example to
Stimulation regimens that involve the local current imbalances of the type described above with reference to
Although the inventions disclosed herein have been described in terms of the preferred embodiments above, numerous modifications and/or additions to the above-described preferred embodiments would be readily apparent to one skilled in the art. By way of example, but not limitation, the present inventions include neurostimulation systems that also comprise at least one neurostimulation lead. It is intended that the scope of the present inventions extend to all such modifications and/or additions and that the scope of the present inventions is limited solely by the claims set forth below.
Claims
1. A method, comprising the steps of:
- generating action potentials in neural fibers in first and second neural fiber bundles with a first electrode that is a first distance from the first neural fiber bundle and is a second distance, that is greater than the first distance, from the second neural fiber bundle; and
- blocking at least some of the action potentials in the first neural fiber bundle with a second electrode that is the first distance from the first neural fiber bundle and the second distance from the second neural fiber bundle.
2. A method as claimed in claim 1, wherein
- generating action potentials comprises sinking a portion of current from the second electrode at the first electrode;
- and further comprising the step of:
- sinking another portion of the current from the second electrode at a remote electrode.
3. A method as claimed in claim 1, wherein blocking at least some of the action potentials comprises blocking at least some of the action potentials in the first neural fiber bundle with second and third electrodes that are each the first distance from the first neural fiber bundle and the second distance from the second neural fiber bundle and are located on opposite sides of the first electrode.
4. A method as claimed in claim 3, wherein
- generating action potentials comprises sinking a portion of current from the second and third electrodes at the first electrode;
- and further comprising the step of:
- sinking another portion of the current from the second and third electrode at a remote electrode.
5. A neurostimulation system for use with a first implantable lead including a plurality of lead electrodes, the neurostimulation system comprising:
- an implanted pulse generator (IPG) including a lead connector;
- circuitry, operably connected to the lead connector, to generate electrical waveforms that create action potentials in neural fibers in first and second neural fiber bundles with a first lead electrode, the first neural fiber bundle being a first distance from the first implantable lead and the second neural fiber bundle being a second distance, that is greater than the first distance, from the first implantable lead; and
- circuitry, operably connected to the lead connector, that generates electrical waveforms to block at least some of the action potentials in the first neural fiber bundle with a second lead electrode.
6. A neurostimulation system as claimed in claim 5,
- further comprising a remote electrode;
- wherein the circuitry generating electrical waveforms to block at least some of the action potentials comprises circuitry to source current at the second lead electrode; and
- wherein the circuitry to generate electrical waveforms to create action potentials comprises circuitry to sink a portion of the current from the second lead electrode at the first lead electrode and to sink a portion of the current from the second lead electrode at the remote electrode.
7. A neurostimulation system as claimed in claim 5, wherein
- the IPG includes a case electrode;
- the circuitry generating electrical waveforms to block at least some of the action potentials comprises circuitry to source current at the second lead electrode; and
- the circuitry to generate electrical waveforms to create action potentials comprises circuitry to sink a portion of the current from the second lead electrode at the first lead electrode and to sink a portion of the current from the second lead electrode at the case electrode.
8. A neurostimulation system as claimed in claim 5, wherein
- the circuitry generating electrical waveforms to block at least some of the action potentials comprises circuitry to generate electrical waveforms to block at least some of the action potentials in the first neural fiber bundle with second and third lead electrodes located on opposite sides of the first lead electrode.
9. A neurostimulation system as claimed in claim 8, wherein
- the circuitry generating electrical waveforms to block at least some of the action potentials comprises circuitry to source current at the second and third lead electrodes; and
- the circuitry to generate electrical waveforms to create action potentials comprises circuitry to sink a portion of the current from the second and third lead electrodes at the first lead electrode and to sink a portion of the current from the second and third lead electrodes at a remote electrode.
10. A neurostimulation system as claimed in claim 8, wherein
- the IPG includes a case electrode;
- the circuitry generating electrical waveforms to block at least some of the action potentials comprises circuitry to source current at the second and third lead electrodes; and
- the circuitry to generate electrical waveforms to create action potentials comprises circuitry to sink a portion of the current from the second and third lead electrodes at the first lead electrode and to sink a portion of the current from the second and third lead electrodes at the case electrode.
11. A neurostimulation system for use with a first implantable lead including a plurality of lead electrodes, the neurostimulation system comprising:
- an implanted pulse generator (IPG) including a lead connector and a case electrode;
- circuitry, operably connected to the lead connector, to source current at a first lead electrode; and
- circuitry, operably connected to the lead connector and the case electrode, to sink a portion of the current from the first lead electrode at a second lead electrode and to sink a portion of the current from the first lead electrode at the case electrode.
12. A neurostimulation system as claimed in claim 11, wherein
- the circuitry to source current comprises circuitry to source current at first and third lead electrodes located on opposite sides of the second lead electrode; and
- the circuitry to sink current comprises circuitry to sink a portion of the current from the first and third lead electrodes at the second lead electrode and to sink another portion of the current from the first and third lead electrodes at the case electrode.
13. A neurostimulation system as claimed in claim 12, wherein
- the circuitry to source current comprises circuitry to source equal amounts of current at the first and third lead electrodes.
14. A method, comprising the steps of:
- sourcing current into neural tissue with a first electrode on an implantable lead;
- sinking a portion of the current from the first electrode at a second electrode on the implantable lead; and
- sinking another portion of the current from the first electrode at a remote electrode.
15. A method as claimed in claim 14, wherein
- sourcing current into neural tissue comprises sourcing current into neural tissue with first and third electrodes located on the implantable lead and on opposite sides of the second electrode.
16. A method as claimed in claim 15, wherein
- all of the current sourced at the first and third electrodes is sunk at the second electrode and the remote electrode.
17. A method as claimed in claim 14, wherein
- sinking a portion of the current from the first electrode at a second electrode comprises sinking current sufficient to generate action potentials in the neural tissue at the second electrode.
18. A method as claimed in claim 14, wherein
- sourcing current into neural tissue with first electrode comprises sourcing current sufficient to block action potentials at the first electrode.
19. A method as claimed in claim 14, wherein
- sinking another portion of the current from the first electrode comprises sinking another portion of the current from the first electrode at a case electrode.
20. A method as claimed in claim 14, wherein the neural tissue comprises elongate fibers, the method further comprising the step of:
- orienting the implantable lead transverse to the elongate fibers.
Type: Application
Filed: Dec 15, 2005
Publication Date: Jun 21, 2007
Inventor: Kerry Bradley (Glendale, CA)
Application Number: 11/300,963
International Classification: A61N 1/18 (20060101);