Feedforward control system for spinal cord stimulation system and method of use - Patent Application 20070122997

Abstract

The system incorporates a feedforward control system that automatically adjusts the mean stimulation current to maintain a constant current dosage applied to the spinal cord, even as the spinal cord moves relative to the epidural electrode array. Optical boundary conditions are obtained using a sample-and-hold circuit when the spinal cord is at its most dorsal position (patient supine) and its most ventral position (prone or sitting). During setup, the optimal mean stimulation current for these two ordinal positions is manually set. During operation, the mean current is actively adjusted by interpolating the mean current between two current boundary conditions using a nominally inversely linear relationship to the instantaneous optical reflectance, which is limited by the optical boundary conditions.

Description

[Technical Field]

[0001] The present invention relates generally to spinal cord stimulation systems. [Background technology]

[0002] Neuromodulation is defined by the International Society for Neuromodulation as "altering neural activity through the targeted delivery of stimuli, such as electrical or chemical impulses, to specific neural sites in the body." In its broadest sense, neuromodulation refers to anything that modulates neural activity (e.g., neurotransmitters, magnetic fields), but in clinical settings, the term most commonly refers to spinal cord stimulation (SCS) therapy using implanted electrical devices.

[0003] SCS alters nerve function by stimulating the spinal cord. Electrodes are surgically implanted into the spine near the spinal cord and are used to deliver stimulation signals that trigger complex electrochemical reactions within the nervous system that can produce a pain-relieving effect.

[0004] SCS is typically delivered via an implantable pulse generator (IPG). Most IPGs are battery-powered and must be periodically charged or replaced. A handheld remote device is used to control the IPG via wireless signals. The IPG provides stimulation signals via one or more implanted leads containing one or more electrodes.

[0005] The electrodes are exposed contacts fixed to the distal ends of the leads that can be individually activated as cathodes or anodes and selectively programmed to activate defined electrode patterns to transmit any number of waveform signals.

[0006] Leads can be percutaneous leads or paddle arrays. One or more percutaneous lead arrays can be inserted through the skin using a Touhy needle. They are usually cylindrical and only 1-2 mm in diameter.

[0007] Paddle arrays are larger than percutaneous leads and contain flexible plastic sheets with embedded electrodes. They are placed via a laminectomy.

[0008] Figure 1 shows details of an electrode array 30, which includes electrode contacts 35 sealed in an elastomeric housing 36. Each electrode contact has a separate electrical conductor in the electrode lead 31, allowing for independent control of the current to each contact. Independent control allows for the stimulation signal to be varied from top to bottom and left to right along the array.

[0009] In Figure 2, the spinal column 1 is shown to have a number of vertebrae divided into four sections or types: lumbar 2, thoracic 3, cervical 4, and sacral 5. The cervical vertebrae 4 include the first cervical vertebra (C1) through the seventh cervical vertebra (C7). Directly below the seventh cervical vertebra are the first of twelve thoracic vertebrae 3, including the first thoracic vertebra (T1) through the twelfth thoracic vertebra (T12). Directly below the twelfth thoracic vertebra are five lumbar vertebrae 2, including the first lumbar vertebra (L1) through the fifth lumbar vertebra (L5), which are attached to the sacral vertebrae 5 (S1-S5). The sacral vertebrae 5 are naturally fused in adults.

[0010] Figures 3 and 4 show a representative thoracic vertebra 10, sharing several notable features with the lumbar vertebrae 2 and cervical vertebrae 4. The thick, oval bony portion forming the anterior surface of the vertebra 10 is the vertebral body 12. The vertebral body 12 is attached to the bony vertebral arch 13, through which the spinal nerves 11 pass. The vertebral arch 13, forming the posterior portion of the vertebra 10, is composed of two pedicles 14, short, stout processes extending from the lateral sides of the vertebral body 12 and from the vertebral discs 15 on either side. The pedicles 14 project into wide, triangular plates that join to form the hollow, arched spinal canal 16. Spinous processes 17 project from the junctions of the vertebral discs 15 on either side. Transverse processes 18 project from the junctions of the pedicles 14 and the vertebral discs 15 on either side. The vertebral arch structure protects the spinal cord 20 and the spinal nerves 11 that pass through the spinal canal. Surrounding the spinal cord 20 is the dura mater 21, which contains cerebrospinal fluid (CSF) 22. The epidural space 24 is the space within the spinal canal outside the dura mater.

[0011] 2, 3, and 4, the IPG 39 typically includes a pulse generator 32 operatively connected to a digital controller 33. The pulse generator 32 delivers electrical stimulation to the spinal cord, typically in the thoracic region, via electrode leads 31 to an electrode array 30. The electrode array 30 is typically positioned in the epidural space 24 between the dura mater 21 and the wall of the spinal canal 16, toward the dorsal side of the spinal canal nearest the bilateral lamina 15 and spinous processes 17.

[0012] Controlling the amplitude of the stimulation current is crucial for the success of spinal cord stimulation. Insufficient current will not depolarize the target neurons and result in a therapeutic effect. Conversely, excessive current will depolarize the target neurons but also stimulate additional cell populations that may perceive noxious stimuli.

[0013] Establishing consistent, therapeutically effective, and non-toxic stimulation levels requires establishing an ideal current density within the target neurons of the spinal cord. Essentially, this should be a simple matter of establishing an optimal electrode current, taking into account the local bulk conductivity of the surrounding tissue. However, in practice, the optimal electrode current varies with the patient's position and activity due to spinal cord movement as the spinal cord is suspended in cerebrospinal fluid within the spinal canal. Significant changes have been shown to occur in the distance between the epidural electrode array and the target spinal neurons. Therefore, it is preferable to dynamically adjust the electrode stimulation current as a function of the distance between the electrode array and the spinal cord.

[0014] Dynamically adjusting the electrode current of a spinal cord stimulator as a function of the distance between the electrode array and the spinal cord has several advantages: Avoiding stimulation currents that are too high reduces the potential for harmful stimulation and potentially reduces device power consumption; Avoiding stimulation currents that are too low eliminates periods of insufficient stimulation and reduced therapeutic efficacy.

[0015] One such system for dynamically adjusting stimulation signals is described in U.S. Patent No. 9,550,063 to Wolf II, which is incorporated herein by reference for all purposes. Wolf describes an IPG that delivers current pulses to an electrode array to stimulate target neurons in the ascending tracts of the spinal cord. Generally, the amplitude of the stimulation signal is controlled by an optical feedback signal that indicates how far the spinal cord is from the electrodes. Summary of the Invention [Problem to be solved by the invention]

[0016] A challenge in SCS treatment is setting patient-specific stimulation parameters, such as amplitude, frequency, and pulse width. Vertebral and spinal column dimensions can vary by as much as 20%–25% from patient to patient, requiring adjustment and optimization of these parameters. These variations directly affect the stimulation current density at the spinal cord, making calibration of stimulation current levels challenging. Anatomical variations, such as blood vessels, epidural fat, and scar tissue, can affect both the bulk resistance and the optical environment within the epidural space. Therefore, a calibration process for IPGs is necessary, using an optical control system to automatically adjust the stimulation current. [Means for solving the problem]

[0017] Disclosed herein is an IPG system that communicates with an external system manager to deliver stimulation signals. The IPG incorporates a novel control system that automatically adjusts stimulation signal current and addresses optical calibration to improve analgesia and extend IPG battery life. A control system for IPGs is disclosed. The control system requires both optical and stimulation boundary conditions. Upper and lower boundary conditions for optical reflectivity occur in the supine and prone positions, respectively. Other patient positions that result in extreme optical reflectivity may be substituted. In the context of this disclosure, the term "prone position" refers to the patient position in which the spinal cord is in its most ventral position and farthest from the reflectometer. Similarly, the term "supine position" refers to the patient position in which the spinal cord is in its most dorsal position and closest to the reflectometer. Each boundary condition requires a single optical measurement that solicits patient feedback to determine the optimal stimulation current required to produce an analgesic effect. The stimulation current is then limited at each upper and lower boundary condition to ensure patient safety and extend battery life. Alternatively, the stimulation current may be limited only at the upper boundary condition.

[0018] In use, a light signal VP is injected into an optical fiber in an electro-optic lead that is directed towards the spinal canal. Upon reaching the spinal canal, a portion of the light is reflected by the spinal cord and travels back along the same optical fiber towards a reflectometer, such as a photodiode. The reflectometer generates a signal R(t) that indicates the intensity of the reflected signal. The reflected signal is measured as the optical reflectance R in the prone position. prone The first sample-and-hold circuit for calibrating the local minimum optical boundary condition (LOB) and the optical reflectance R in the supine position. supine The signal is routed to a second sample-and-hold circuit for calibrating the local maximum optical boundary conditions.

[0019] In the addition block, R(t) is converted to R prone to remove the baseline reflectance offset, R(t) corr With the patient in the prone position, the average stimulation current across the electrode array is manually programmed to the patient's preference to optimize the analgesic effect. At this point, the stimulation current S high The third sample-and-hold circuit is set to indicate the local maximum stimulation current boundary condition. The current is then slowly increased while monitoring whether the patient shows signs of just noticeable difference stimulation (JND). high The difference in current tojnd is recorded as

[0020] When the patient is in a supine position, a second sample-and-hold circuit measures the optical reflectance R supine The second summation block is set to record R supine From R prone Subtract R range Next, determine R(t) corr R range Dividing by r leads to a normalized signal nominally ranging from 0 to 1. Spinal cord acceleration or momentum can push the spinal cord beyond the physical position used to define the supine or prone optical boundary conditions. Therefore, the reflectance output is clipped to the respective supine or prone value to arrive at R′. R′ is then inverted (subtracted from 1) to provide the signal (1-R′). In the supine position, the stimulation current is manually slowly increased, and the patient is again monitored for signs of a slightly noticeable difference.

[0021] When the patient is in the supine position, the average stimulation current across the electrode array is manually programmed to suit the patient's preferences to optimize the analgesic effect in this position. A fourth sample-and-hold circuit is set to control the stimulation current S low (Local minimum stimulation current boundary condition).

[0022] S low S high is subtracted from S range becomes.

[0023] Next, (1-R') is S range Multiply by S low to generate the signal S(t).

[0024] A signal S(t) responsive to the reflectometer signal R(t) is used to drive a current source, which in turn generates a current I(t), which is used to drive an electrode. [Brief explanation of the drawings]

[0025] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings. [Figure 1] FIG. 1 shows a conventional spinal cord stimulation paddle lead. [Figure 2] FIG. 2 is a lateral view of the human spine showing the approximate location of a conventional spinal cord stimulation electrode array. [Figure 3] FIG. 3 is an axial view of the thoracic spine showing the location of the spinal cord and a conventional spinal cord stimulation electrode array. [Figure 4] FIG. 4 is a sagittal cross-sectional view of the human spine showing the approximate location of a conventional spinal cord stimulation electrode array. [Figure 5] FIG. 5 is a schematic diagram of a preferred embodiment IPG and external control system. [Figure 6A] FIG. 6A is an architectural diagram of a preferred embodiment of the IPG. [Figure 6B] FIG. 6B is an architecture diagram of a preferred embodiment of the external control system. [Figure 7] FIG. 7 is an architectural diagram showing the signal flow through the analog circuitry of the preferred embodiment. [Figure 8] FIG. 8 is a graph showing the preferred relationship between reflectometer current and stimulation current. [Figure 9A] FIG. 9A is a state diagram of the preferred system. [Figure 9B] FIG. 9B is a flow chart of a preferred embodiment of the calibration state. [Figure 9C] FIG. 9C is a flow chart of a preferred embodiment of the Run state. [Figure 9D] FIG. 9D is a flow chart of a preferred embodiment of the Stop state. DETAILED DESCRIPTION OF THE INVENTION

[0026] In the following description, like parts are numbered the same throughout the specification and figures. The figures are not necessarily drawn to scale and may show exaggerated or generalized shapes for clarity and conciseness. Unless otherwise specified, all use of the term "about" refers to ±20%.

[0027] Referring now to FIG. 5, a preferred SCS system 500 consists of an IPG 510 implanted subcutaneously below the skin surface 530 .

[0028] In summary, the IPG 510 comprises a controller 505 operatively connected to an external system manager 516. The IPG and external system manager communicate via transcutaneous wireless signals transmitted between RF antennas 532 and 534, as described below.

[0029] The IPG 510 is preferably battery-powered and housed in a sealed case 507 that allows for long-term subcutaneous implantation. The IPG 510 includes a controller 505 operatively connected to a light processing assembly 543. The light processing assembly 543 is operatively connected to leads 512A and 512B. The leads 512A and 512B terminate in electrode arrays 545A and 545B on the paddle array 514. In another embodiment, the electrode arrays may be on percutaneous leads, as previously described. The leads 512A and 512B also include optical transmission fibers (not shown) that transmit optical signals from the light processing assembly 543 to the electrode arrays, where the optical signals illuminate the spinal cord and are reflected back to the light processing assembly. The light processing assembly converts the reflected optical signal into a variable current signal, which is used to determine the distance from the spinal cord to the electrode array. The controller 505 uses the optical signal to modulate electrical stimulation signals sent to the electrodes via the leads, as described in more detail below.

[0030] The external system manager 516 includes a controller 520 operatively connected to an RF antenna 534 .

[0031] In use, the controller 520 contains a set of instructions that assist in gathering feedback from the patient regarding the efficacy of various stimulation signal types. The feedback is processed to generate a set of operating parameters that are transmitted wirelessly back to the IPG via the RF antenna 532, as will be described in more detail below.

[0032] Referring to FIG. 6A, the controller 505 is further described. The controller 505 includes a CPU 602 with on-board memory 604. The memory contains instructions that, when executed, provide the functionality of the IPG. The controller 505 is operatively connected to a control circuit 603 for monitoring reflectometer signals, as described below. The control circuit 603 is preferably implemented using the threshold function of a multimodal front-end, part number ADP4100, available from Analog Devices, Inc., Wilmington, Massachusetts. The controller 505 is also operatively connected to an optical processing assembly 543 for use in modulating stimulation signals and an RF transceiver 610 for transmitting status signals and receiving control parameters. In certain alternative embodiments, the CPU 602 is further connected to a pulse modulator 608 and a pulse generator 606 for generating and transmitting stimulation signals to the electrodes. All components are operatively connected to a battery 612, which provides the current for operating the IPG. The CPU 602 receives real-time optical reflectance information using a feedforward control system to automatically set the stimulation current level for each electrode. The stimulation current levels are calculated digitally and sent to the pulse generator 606 and pulse modulator 608. The pulse modulator 608 then provides the required current to each electrode. The stimulation current levels can also be calculated and generated automatically by an analog version of the control circuitry, as will be described in more detail below.

[0033] Referring to FIG. 6B, the controller 520 is further described. The controller 520 includes a CPU 632 connected to an RF transceiver 638, a display 642, an input device 640, and a memory 634. In a preferred embodiment, the display 642 is a low-power liquid crystal display adapted to display the current operating state of the system. The input device 640 is a simple push-button contact array that is constantly monitored by the CPU 632. The memory 634 is preferably resident on the CPU 632 and stores instructions that, when executed, operate an external system manager. In a preferred embodiment, the RF transceiver 638 is a low-power transmitter / receiver combination. In a preferred embodiment, all components of the controller are powered by a battery 644.

[0034] In another preferred embodiment, the components of controller 520 may be included in a personal computer such as a laptop or cell phone that sends and receives RF signals containing data and instructions via MICS, WiFi, infrared, or Bluetooth protocols.

[0035] Referring now to FIG. 7, a block diagram 700 illustrating the signal flow of a preferred analog embodiment of control circuit 603 will now be further described.

[0036] The current detection circuit 704 includes a photodiode current source 701, I PD, and a photodiode load 702. A current detection circuit 704 generates a voltage signal R(t) indicative of the amount of light incident on the photodiode. The current detection circuit 704 is operatively connected to a sample and hold circuit 706, a sample and hold circuit 708, and a subtraction circuit 714, thereby distributing the R(t) signal to each of these circuits. The command input of the sample and hold circuit 706 is further connected to a switch 710, which causes R(t) to be momentarily sampled during application of a digital logic "sample" command and to be in a "hold" state otherwise. Similarly, the command input of the sample and hold circuit 708 is further connected to and similarly controlled by a switch 712.

[0037] The output of sample and hold circuit 706 is operatively connected to subtraction circuit 714 and subtraction circuit 716. When the patient is in the prone position, the input of the sample and hold circuit is momentarily asserted to "sample" and then returned to "hold" to capture the light reflectance at the prone patient position RP. Signal RP is indicative of the light incident on the photodiode when the patient is in the prone position and is distributed to subtraction circuit 714 and subtraction circuit 716. Similarly, when the patient is supine, sample and hold circuit 708 generates a voltage signal R indicative of the light incident on the photodiode when the patient is supine. S is stored and distributed to the subtraction circuit 716. P and R S are the optical boundary conditions corresponding to the minimum and maximum reflectance, respectively.

[0038] The subtraction circuit 714 calculates R P The voltage signal R is the difference between the R(t) signal and the R(t) signal. L (t), which varies with time. Similarly, subtraction circuit 716 generates R S Signal and R P The voltage signal R is the difference between the signals R This difference indicates the extent to which the reflected light signal changes between prone and supine positions.

[0039] Divider circuit 718 is operatively connected to subtractor circuit 714 and subtractor circuit 716. Divider circuit 718 calculates R L (t) Signal to R R Divide by the signal, thereby producing a signal normalized to 1.

[0040] The output of the divider circuit 718 is connected to a clipping circuit 719. The clipping circuit 719 limits the output signal R'(t) to the range between 0 and 1.

[0041] The output of clipping circuit 719 is operatively connected to subtraction circuit 720, thereby delivering the R'(t) signal thereto. Subtraction circuit 720 is further operatively connected to voltage reference source VCC 711. Subtraction circuit 720 generates a voltage output signal (1-R'(t)) that is the difference between 1 and R'(t) and delivers that signal to multiplication circuit 722, which will be further described below. The subtraction circuit effectively inverts the R'(t) signal to account for the fact that the stimulation current should be approximately inversely proportional to the reflected light signal.

[0042] The current sensing circuit 728 senses the stimulation current source 724, I SD (t). Current sense circuit 728 is further connected to electrode array load 726. Current sense circuit 728 generates a voltage signal S(t) indicative of the average current through the electrodes and distributes that signal to sample and hold circuit 730 and sample and hold circuit 732.

[0043] The sample and hold circuit 730 is operatively controlled by a switch 734. The sample and hold circuit 730 generates a voltage signal VP indicative of the optimal average stimulation current required when the patient is in the prone position and distributes that signal to a subtraction circuit 738.

[0044] Similarly, sample and hold circuit 732 is operatively controlled by switch 736. Sample and hold circuit 732 generates a voltage signal Vs indicative of the optimal stimulation current required when the patient is supine and distributes that signal to subtraction circuit 738 and summation circuit 740, as will be further described below.

[0045] The subtractor circuit 738 calculates the signal S, which is the difference between the VP and VS signals. range Generate S range The signal is distributed to the multiplication circuit 722. range indicates the range in which the stimulation current changes between prone and supine positions.

[0046] The multiplication circuit 722 multiplies the signal (1-R'(t)) normalized to 1 by S range The signal product, V(t), is generated and distributed to summing circuit 740. Multiplier circuit 722 effectively scales the range of the stimulation current to match the inverse of the reflected light signal.

[0047] The summing circuit 740 sums the VS signal with the VT signal to generate a voltage signal S(t) and distributes that signal to a voltage-driven current source 742 .

[0048] A voltage-driven current source 742 generates an average current signal I(t) that is proportional to the voltage signal S(t). The I(t) current signal is used to drive the electrode array, as will be described in more detail below.

[0049] Next, referring to Figure 8, the stimulation current "I S ” and the photodiode current “I PD The feedforward relationship between the light reflectance and the

[0050] Graph 800 is I PD on the x-axis, and I S is plotted on the y-axis. The photodiode current IPD and the stimulation current I SThe relationship can be modeled as linear with an inverse slope. Line 802 is defined by two points. The first point is the photodiode current in the prone position, "I PDprone ” and the optimized stimulation current “I Sprone The second point is defined by the photodiode current in the supine position, I PDsupine ” and the stimulation current in the supine position “I Ssupine " is defined as:

[0051] The equation for line 802 is: TIFF2025525557000002.tif52135

[0052] 9A, the state chart 900 is further described. The state chart 900 defines the various states that the system may be in during operation. Preferably, the external system manager 516 displays the various states that the system is active in, sends instructions to the IPG 510, and receives feedback from the IPG 510 confirming the state of the system.

[0053] Upon power-up, both the IPG 510 and the external system manager 516 enter a wait state 905. While in wait state 905, the external system manager 516 displays a menu on the display 642 indicating either a stop state 907, a run state 909, or a calibrate state 913. The IPG 510 simply waits for a command. If a stop selection is received, the external system manager enters the stop state 907 and returns to the wait state 905. Similarly, if a run selection is received, the external system manager 516 enters the run state 909 and returns to the wait state 905. If a calibrate selection is received, the external system manager 516 enters the calibrate state 913 and returns to the wait state 905.

[0054] Referring now to FIG. 9B, a preferred embodiment of the calibration state 913 will be further described.

[0055] In step 902 , the IPG 510 is in a standby state and polls the RF transceiver 610 for instructions from the external system manager 516 .

[0056] In step 904, the patient is positioned on their back. Preferably, the patient's position is indicated to the external system manager by a selection received from the input device 640. This selection is communicated wirelessly from the external system manager to the IPG.

[0057] In step 906, the IPG 510 measures the photodiode current I PD (t) and write it as "I PDsupine " and store it in memory.

[0058] In step 908, the stimulation current I Ssupine is manually adjusted to the patient's supine position preference through input to the external system manager 516 and then communicated to the IPG 510. The IPG 510 then Ssupine Save the value of

[0059] At step 910, the external system manager 516 receives an indication of whether paresthesia-based stimulation is to be used. If yes, the method proceeds to step 914. If no, the method proceeds to step 912.

[0060] In step 914, the stimulation current I S is manually increased until the patient notices a change in perceived stimulation intensity. This change can be thought of as the "just noticeable difference stimulus" or "JND." When such a change is indicated, the external system manager receives the input and forwards it to the IPG. The IPG then adjusts the stimulation current to I JND This is recorded as I S -I Ssupine The method then proceeds to step 916.

[0061] In step 912, I JND is set to the resolution of the pulse modulator, preferably 0.1 mA.

[0062] At step 916, the patient assumes a prone or forward-facing sitting position. The external system manager 516 preferably receives a signal from the input device 640 indicating that the patient has assumed such a position. The external system manager 516 then sends a signal to the IPG 510 indicating that the patient has assumed a prone or forward-facing sitting position.

[0063] In step 918, the IPG 510 measures the photodiode current I PD (t) and write it as "I PDprone " and store it in memory.

[0064] In step 920, the stimulation current for prone or leaning forward position is programmed to the patient's preference. The external system manager 516 preferably receives an input to incrementally increase the stimulation current. This input is wirelessly transmitted to the IPG 510, which increases the stimulation current accordingly. Once the patient's preference is reached, the external system manager receives a signal and forwards it to the IPG. The IPG includes a stimulation current level I Sprone is saved.

[0065] In step 922, the linear coefficients M and B are calculated by the IPG as described above and stored in memory.

[0066] In step 924, the IPG calculates the optical change associated with the minimum perceptible difference stimulus according to the following formula: TIFF2025525557000003.tif17135

[0067] At step 926, the method ends and both the IPG and the external system manager return to a standby state.

[0068] The "Run" state 909 is further described with reference to FIG. 9C.

[0069] At step 940, the method begins.

[0070] In step 942, the controller 505 calculates the photodiode current I PD Get (t).

[0071] In step 944, the controller calculates the photodiode current I PD Stimulation current I as a function of (t) S The appropriate transfer function is described by the following set of equations: TIFF2025525557000004.tif69135

[0072] where M and B have the form described above.

[0073] In step 946, the controller determines the stimulation current value I S to the current source, thereby activating the stimulation current to the electrode.

[0074] In step 948, the controller sets the light threshold comparator boundary of the control circuit 603 according to the following equation: Upper optical threshold = I PD(t) +I PDjnd Lower optical threshold = I PD(t) -I PDjnd In step 950, the controller enables the light threshold comparator interrupt of the control circuit 603 as previously described.

[0075] The controller waits for the control circuit to send an optical comparator interrupt at step 952. Upon receiving such an interrupt, the controller returns to step 942 and repeats the process.

[0076] The "Stop" state 907 is further described with reference to FIG. 9D.

[0077] In step 982, the method begins.

[0078] In step 983 , the external system manager 516 receives a “stop” selection from the input device 640 .

[0079] In step 984 , the external system manager 516 sends a stop command to the IPG 510 .

[0080] In step 986, the CPU 602 deactivates the pulse modulator 608.

[0081] In step 987, the CPU 602 deactivates the pulse generator 606.

[0082] In step 988, CPU 602 deactivates control circuitry 603.

[0083] In step 989, the IPG 510 sends a confirmation signal to the external system manager 516 indicating the system has stopped.

[0084] At step 990, the method ends and both the external system manager and the IPG return to a standby state.

Claims

1. It is a spinal cord stimulation system, A controller having memory, A reflectometer operatively connected to the controller, A stimulating electrode operatively connected to the controller, A set of instructions stored in the memory and, when executed, causes the system to perform the following steps, wherein the steps are: A step of saving the lower reflex current boundary and upper stimulation current boundary associated with the patient's prone position, A step of saving the upper limit reflexometer current boundary and the lower limit stimulation current boundary associated with the patient's supine position, A step of deriving the relationship between the lower limit reflectometer current boundary, the upper limit reflectometer current boundary, the lower limit stimulation current boundary, and the upper limit stimulation current boundary, A step of adjusting the stimulation current value based on the aforementioned relationship and the reflectometer current signal, A step of transmitting a stimulation signal to the stimulation electrode based on the stimulation current value, An instruction set having, A system that has

2. In the system described in claim 1, the relationship is linear.

3. In the system according to claim 1, when the instruction set is executed, The system further includes an instruction causing the system to perform the step of clipping the reflectometer current signal at the upper reflectometer current boundary and the lower reflectometer current boundary, thereby maintaining the stimulus signal between the lower stimulus current boundary and the upper stimulus current boundary.

4. In the system according to claim 1, when the instruction set is executed, The system further includes an instruction causing the system to perform the step of monitoring a processor interrupt condition for one of the upper reflectometer current boundary and the lower reflectometer current boundary.

5. In the system according to claim 4, when the instruction set is executed, A system further comprising an instruction causing the system to execute a step of changing the stimulus current value when the aforementioned processor interrupt condition occurs.

6. In the system according to claim 1, when the instruction set is executed, The system further includes an instruction causing the system to perform the step of setting the optical threshold comparator of the controller to respond to a range of the reflectometer current signal.

7. In the system according to claim 6, the range is associated with the minimum perceptual difference of the stimulus signal.

8. A method for controlling a spinal cord stimulator, A controller having memory executes the instruction set stored in that memory, A process of receiving the reflectometer current signal acquired from the reflectometer, A step of storing the lower reflex current boundary and upper stimulation current boundary associated with the patient's prone position in the memory, A step of storing the upper reflex current boundary and lower stimulation current boundary associated with the patient's supine position in the memory, A step of deriving the relationship between the lower limit reflectometer current boundary, the upper limit reflectometer current boundary, the lower limit stimulation current boundary, and the upper limit stimulation current boundary, A step of calculating the stimulation current value based on the relationship and the reflectometer current signal, A step of controlling the stimulation signal supplied to the stimulation electrode based on the stimulation current value, A method having the following characteristics.

9. A method according to claim 8, wherein the relationship is linear.

10. In the method of claim 8, when the instruction set is executed, A method further comprising a command causing the controller to perform the step of clipping the reflectometer current signal at one of the upper reflectometer current boundary and the lower reflectometer current boundary.

11. In the method of claim 8, when the instruction set is executed, A method further comprising an instruction causing the controller to perform the step of monitoring a processor interrupt condition for one of the upper reflectometer current boundary and the lower reflectometer current boundary.

12. In the method according to claim 11, when the instruction set is executed, The aforementioned processor interrupt conditions A method further comprising a command to cause the controller to perform a step of changing the stimulation current value when it occurs.

13. In the method of claim 8, when the instruction set is executed, A method further comprising a command causing the controller to perform the step of setting the optical threshold comparator of the controller to respond to a range of the reflectometer current signal.

14. A method according to claim 13, wherein the range is related to the minimum perceptual difference of the stimulus signal.

15. It is a spinal cord stimulation system, A first sample-and-hold circuit operatively connected to the photodiode current level, A second sample-and-hold circuit is operationally connected to the photodiode current level, The first sample-and-hold circuit and the first subtraction circuit operatively connected to the photodiode current level, A second subtraction circuit operatively connected to the first sample-and-hold circuit and the second sample-and-hold circuit, A division circuit operatively connected to the first subtraction circuit and the second subtraction circuit, A third subtraction circuit is operationally connected to the division circuit and logic "1", A third sample-and-hold circuit is operationally connected to the stimulation current level, A fourth sample-and-hold circuit operatively connected to the stimulation current level, A fourth subtraction circuit operatively connected to the third sample-and-hold circuit and the fourth sample-and-hold circuit, A multiplication circuit operationally connected to the third subtraction circuit and the fourth subtraction circuit, An adder circuit operatively connected to the multiplication circuit and the fourth sample-and-hold circuit, A voltage-driven current source is operationally connected to the summing circuit and the spinal cord stimulation electrode set, A spinal cord stimulation system having the following features.

16. In the system according to claim 15, further A system having a clipping circuit operationally connected between the division circuit and the third subtraction circuit.

17. In the system described in claim 16, The first latch signal from the first sample-and-hold circuit is associated with a low photodiode current boundary. The second latch signal from the second sample-and-hold circuit is associated with a high photodiode current boundary. The third latch signal from the third sample-and-hold circuit is associated with a high-stimulation current boundary. The fourth latch signal from the fourth sample-and-hold circuit is associated with a low-stimulation current boundary in the system.

18. In the system described in claim 17, The clipping circuit clips to the maximum stimulation current level by referencing the first latch signal and to the minimum stimulation current by referencing the second latch signal, in this system.

19. In the system described in claim 17, The first latch signal, the second latch signal, the third latch signal, the fourth latch signal, and the photodiode current level drive the stimulation current level from the voltage-driven current source, in a system.

20. The system according to claim 17, wherein the first latch signal, the second latch signal, the third latch signal, and the fourth latch signal define a linear relationship between the photodiode current level and the stimulation current level.

Images