Abstract:
An electronic stimulation system is used to control pain over multiple regions of a patient&#39;s body. The system has one or more percutaneous leads, each having multiple electrodes, implanted within the patient&#39;s epidural space parallel to the axis of the spinal cord. The leads are connected to either a totally implanted system or a radio frequency system. The system is able to treat pain over different regions of a patient&#39;s body by “simultaneously” stimulating the patient with at least three different stimulation settings. “Simultaneous” stimulation involves sequentially stimulating the patient with the multiple stimulation settings such that the patient receives the cumulative effect of each stimulation setting, while not perceiving the transition from one stimulation setting to another.

Description:
FIELD OF THE INVENTION 
     This invention relates to an electronic tissue stimulator. More specifically, the invention relates to an improved neuromodulation system for managing various diffuse and multi-focal neurological and/or motor disorders. 
     BACKGROUND OF THE INVENTION 
     The concept of using electronic stimulation systems to control pain by nerve or muscle stimulation is well known. Spinal cord stimulation (SCS) is a technique that has been used for pain management since the 1960s. SCS systems feature a pulse generator, discussed further below, coupled to one or more percutaneous leads having a plurality of electrodes (systems may also use a paddle-type lead that requires insertion by laminectomy). The leads are positioned within a patient&#39;s epidural space, parallel to the axis of the spinal cord. The leads&#39; electrodes are used to deliver a particularized electric field to a specific region of the spinal cord or surrounding tissue. Applying an electric field across one or more nerve bundles and/or nerve roots can produce paresthesia, or a subjective sensation of numbness, tingling or “pins and needles,” at the affected nerves&#39; dermatomes. This paresthesia, if properly directed and produced at the necessary levels, can “mask” certain forms of chronic pain. 
     The focus, characteristics and intensity of the generated electric field are determined by the electrode configuration (i.e., the polarity, if any, assumed by each electrode) and the electric pulse waveform (collectively “stimulation setting”). The waveform properties include, at least, a stimulation frequency, a stimulation pulse width and phase information. 
     SCS systems are of two types. The most common system is a totally implanted pulse generator (IPG). An IPG consists of a surgically implanted, internally-powered pulse generator and, typically, a single multi-electrode lead. Once implanted, the IPG may be activated and controlled (programmed) by an outside telemetry source. The patient, being largely relieved of daily interaction with the system, uses a small magnet to both turn the system on and off and limitedly control the stimulation settings. The internalized power source limits the life of these systems to between two and four years. After the power source is expended, the patient is required to undergo replacement surgery to continue electrical stimulation. 
     The second type of SCS system is a radio frequency (RF) system. An RF system consists of a surgically implanted, passive receiver and a transmitter which is worn externally. The transmitter is connected to an antenna which is positioned, externally, over the site of the implanted receiver. In operation, the transmitter communicates, through an RF signal, to the implanted receiver. Just as with the IPG system, electrical stimulation is delivered via implanted leads. Differing from an IPG, however, RF systems typically posses greater power resources, thereby enabling RF systems to utilize multiple leads. An RF system, like the one described herein, is disclosed in U.S. Pat. No. 4,612,934, issued Sep. 23, 1986, to Borkan. 
     Although existing systems have proven effective, these systems provide only qualified relief to patients who experience multi-focal or complex pain. Current SCS systems can address, at a maximum, two distinct pain patterns—a “pain pattern” being a dermatome, dermatome segment or series of dermatomes afflicted by pain. One current system features two percutaneous leads, wherein the user can elect to address up to two unilateral pain patterns or a single non-complex, non-migrating bilateral pain pattern. 
     “Unilateral pain” is said to be that pain which is localized on one side of the patient&#39;s body or the other. Unilateral pain is most efficiently addressed through a “unilateral electrode array,” or a lead which is positioned to one side or the other of the physiological midline of the spine, e.g., an electrode positioned to the left of the physiological midline typically addresses pain located on the left side of the patient&#39;s body. Therefore, logically, “bilateral pain” is that pain which affects both sides of the patient&#39;s body, for example, lower back pain is often considered bilateral in nature. A bilateral electrode array generates an electric field to address bilateral pain. A bilateral electrode array may take two forms: (i) a single multi-electrode array positioned on or immediately about the physiological midline of the patient; or (ii) two parallel multi-electrode leads positioned to either side of the physiological midline, in which the leads produce a single electric field which transverses the spinal cord. As began above, the system of this example can be configured to address two unilateral pain patterns or a single bilateral pain pattern. The limitation inherent with this system is that a patient can experience only “either-or” pain management. Therefore, the patient is restricted to the simplest form of “multi-focal” stimulation applications. 
     For those patients whose pain does not conform to the non-yielding stricture of prior art systems, it would be desirable to provide an improved SCS system, whether an IPG or RF system, which could accommodate three or more stimulation settings to address diffuse, multi-focal pain, whether of a unilateral or bilateral nature or any combination thereof. A further desire would be to allow a patient, at will, to tailor a stimulation treatment from a group of programmed stimulation settings, wherein the patient may select: (i) a single stimulation setting, (ii) any number of stimulation settings from the programmed group, the selected settings being administered “simultaneously”, or (iii) “simultaneous” stimulation of all programmed stimulation settings. “Simultaneous” stimulation being a mode of operation wherein each selected stimulation setting is delivered to the patient, the patient receiving the cumulative effect of each stimulation setting, and not substantially perceiving the transition from one stimulation setting to another. 
     In addition to the use of this technology for pain management, some researchers believe that SCS may have beneficial application in obtaining relief from and/or controlling the physical effects of peripheral vascular disease (PVD), angina pectoris, and various motor disorders. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the invention to provide an improved SCS system, the improved system being capable of being programmed with three or more stimulation settings to generate a corresponding number of electrical stimulation pulses. 
     It is another object of the invention to provide an improved SCS system which allows a patient, at will, to tailor a stimulation treatment from a group of programmed stimulation settings, wherein the user may select: (i) a single stimulation setting, (ii) any number of stimulation settings from the programmed group, the selected settings being administered “simultaneously”, or (iii) “simultaneous” stimulation of all programmed stimulation settings. 
     These and other objects of the invention are obtained by providing a microcomputer controlled system. The improved system is capable of storing and delivering at least three stimulation settings, each stimulation setting potentially addressing a differing region of the patient&#39;s body. As well, each stimulation, setting can produce, if the system possesses more than one multi-electrode catheter, electric fields characteristic of either a unilateral or bilateral electrode array. 
     For example, for an RF system, the transmitter may store a plurality of stimulation settings. Stimulation settings include data concerning, at least, an electrode configuration (the defined electric polarity of each electrode, if any), a stimulation amplitude, a stimulation frequency, a stimulation pulse width and signal phase information. The treatment information is encoded in the transmitter and impressed on an RF carrier signal which is broadcast through a transmission antenna to the system&#39;s implanted receiver. 
     An RF transmitter embodying the present invention is configured to include three or more setting data registers. Each of these data registers can be programmed to store an independent stimulation setting. Each independent stimulation setting can potentially target distinct regions of the patient&#39;s body to relieve pain or address other conditions such as motor disorders. Associated with each of the different stimulation settings is a stimulation amplitude. Independent amplitude registers store each of the amplitude values. Since each amplitude is associated with a stimulation setting, this embodiment includes an equal number of setting data registers and amplitude registers. Each of the setting data registers are connected to a setting select multiplexer which is used to select a particular stimulation setting to be broadcast by the transmitter. Similarly, an amplitude select multiplexer is used to select the amplitude information associated with the selected stimulation setting. 
     To control the stimulation setting and associated amplitude broadcast to the receiver, the transmitter includes a programmable setting time generator which is controlled by the microcomputer. The setting time generator generates a treatment interval which is sent to a programmable setting counter. The treatment interval is the interval that a particular stimulation setting is broadcast before the transmitter switches to the next stimulation setting. In the “simultaneous” operations mode, the treatment modality is set such that the patient cannot discern the switching between stimulation setting intervals, or pulses, and feels only the cumulative effect of all settings. The setting counter uses the treatment interval to control the select lines of the setting and amplitude multiplexers. The counter allows the setting counter to cycle through the desired stimulation settings substantially sequentially and ensures that all elected settings are broadcast. 
     The system further includes a clock to provide a signal at a continuous frequency. This frequency is altered by a frequency divider according to the microcomputer, in accordance with the selected stimulation setting, to produce the desired stimulation frequency. The stimulation frequency is sent to a pulse width modulator which modifies the stimulation frequency to add the selected pulse width. All of the treatment information is combined at an RF modulator which impresses the combined treatment information on an RF carrier for broadcasting to the receiver. 
    
    
     The above embodiment is but one example and such example shall not be construed as limiting the scope of the present invention. In an alternative form, the present invention may be embodied in an IPG system. Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a functional block diagram of partially implanted electronic tissue stimulation system; 
     FIG. 2 is a frontal view of the transmitter used in the partially implanted electronic stimulation system; 
     FIG. 3 is a side view of the transmitter shown in FIG. 2; 
     FIG. 4 is a top view of the transmitter shown in FIG. 2; and 
     FIG. 5 is a functional block diagram of the circuit used to implement the transmitter used in the partially implanted electronic stimulation system. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, FIG. 1 illustrates a simplified block diagram of one embodiment of an electronic tissue stimulation system. The embodiment depicted is a radio frequency (RF) system and, particularly, a multi-channel neurostimulator having two multi-electrode catheters  20 ,  22 . Stimulation system  10  essentially includes transmitter  12  and receiver  18 . Receiver  18 , including reception antenna  16 , and multi-electrode catheters  20 ,  22  are surgically implanted beneath a patient&#39;s skin  32 . Transmitter  12  combines programmed stimulation settings with an RF carrier signal prior to passing the combination to the transmission antenna  14 . From transmission antenna  14 , the RF carrier signal/stimulation settings are transmitted through patient&#39;s skin  32  to reception antenna  16  and receiver  18 . 
     The programmed stimulation settings specifically define and characterize the administered electric stimulation. In one embodiment, each stimulation setting is comprised of an electrode configuration and stimulation amplitude, stimulation frequency, stimulation pulse width and signal phase information. The electrode configuration defines whether each electrode is on or off and, if on, the polarity of such electrode. The amplitude is the intensity of the applied electric pulse. The frequency is the number of times the electrodes are turned on each second. The pulse width is the amount of time the electrodes are left on during each cycle. Finally, the signal phase setting defines the stimulation waveform as “monophasic” (either a positive or negative pulse) or “biphasic” (an alternating negative-positive or positive-negative pulse). 
     Receiver  18  demodulates the carrier signal and decodes the stimulation settings. Receiver  18  generates electrical pulses in accordance with the demodulated stimulation settings. The electrical pulses are realized at the distal ends of multi-electrode catheters  20 ,  22  through electrodes  24   a-h  and  26   a-h . The generated electric pulses, assuming the characteristics of the active stimulation setting, may utilize any combination of unilateral or bilateral electrode arrays. 
     FIG. 2 is a frontal view of transmitter  12 . Transmitter  12  includes case  40  which houses the electronics (not shown) and battery  41 . Case  40  includes display  42  which preferably includes a liquid crystal display (LCD) as is well known in the art. Display  42  allows the electronics of transmitter  12  to display the current settings for the transmitter and to prompt a user for input via a menu driven series of informational display screens. Display  42  has backlighting capabilities, allowing display  42  to be viewable in dim lighting. To save power and increase battery life, the backlighting feature operates only briefly each time the user presses either plus key  54 , minus key  52  or scroll/enter key  56 . Access door  44  conceals an inner compartment that includes a 4-pin serial port connector  50  and a battery receptacle, for receiving a common alkaline battery  41  or other power source. 
     FIG. 3 illustrates a side view of transmitter  12 . Clip  46  is removably coupled to case  40  to effectively secure transmitter  12  to a user&#39;s belt, pocket or the like. Antenna connector  48  connects transmitter  12  to antenna  14  (FIG.  1 ). 
     FIG. 4 is a top view of transmitter  12  and shows the user inputs which allow the user to interface with and program transmitter  12 . Three position switch  58  allows the user to turn transmitter  12  off, or to place transmitter  12  in one of two operating states. When transmitter  12  is in the “on” position, the user may adjust the treatment information (i.e., stimulation settings) in transmitter  12  using the three input buttons  52 ,  54 ,  56  and display  42  as described below. However, when transmitter  12  is in the “lock” position, the user may review the treatment information on display  42 , but cannot change any of the settings. 
     Scroll/enter key  56  allows each of the stimulation setting parameters (electrode configuration, amplitude, frequency, pulse width and phase) to be scrolled through, or called up sequentially, for programming. In this embodiment, scroll/enter key  56  also acts as an enter key when held down for at least two seconds. Plus key  54  and minus key  52  are used to adjust all parameter values by incrementing the parameter values up or down, respectively, when the specific parameter is displayed in display  42 . 
     As an alternative to using transmitter controls  52 ,  54 ,  56 , transmitter  12  may be connected to a specially programmed computer  28 . Cable  30  (FIG. 1) electrically couples transmitter  12 , through serial connection port  50 , to computer  28 . In addition to merely providing an alternative means for programming transmitter  12 , computer  28  can enable data collection, stimulation setting optimization, electrode catheter placement feedback, and other functions associated with the pre-, intra-, and post-operative implantation of system  10 . A specially programmed computer  28  could be the computer system described in the co-pending patent application Ser. No. 081,659,874 filed Jun. 7, 1996, now U.S. Pat. No. 5,938,690 which is incorporated herein by reference. 
     It should be recognized that the present invention is not limited to RF systems. Rather, the present invention may also be implemented in the form of a totally implantable pulse generator (IPG). For an IPG, an external telemetry source would transmit programmable stimulation settings to the implanted component of the system. 
     FIG. 5 is a block diagram of the circuit used to implement the present invention. Circuit  70  includes microcomputer  74  which is used to control the various components of circuit  70 . 
     A user interacts with system  10 , and specifically microcomputer  74 , through display and keyboard interface  72 . For the RF system described above, display  42  and transmitter controls  52 ,  54 ,  56  collectively represent display and keyboard interface  72 . For an IPG system, for example, a programmable telemetry source (not shown) provides a medium by which a user may communicate with the system  10 . 
     Circuit  70  includes setting data registers  82 , also referred to as parameter registers. Each individual setting data register  82  stores information concerning electrode configuration(s), stimulation frequency, stimulation pulse width and signal phase. For a dual lead system, the stored electrode configuration will define a unilateral or bilateral electrode array. The preferred configuration of circuit  70  includes twenty-four individual setting data registers  82  to store up to twenty-four stimulation settings. Notwithstanding the preferred embodiment, one skilled in the art shall understand circuit  70  is not limited to the number of setting data registers shown by this specific embodiment. Further, setting data registers  82  can assume any form of memory, memory partitioning, or storage configuration to allow storage of stimulation setting data without departing from the scope of this invention. 
     Setting data registers  82  are individually connected to setting select multiplexer  86  which is used to select a particular simulation setting, excluding stimulation amplitude. The frequency and pulse width information are fetched by microcomputer  74  for operations that will be detailed below. The selected electrode configuration and phase information are sent to modulator  98  for combination with the setting&#39;s processed amplitude, frequency and pulse width information. 
     Amplitude registers  84 , also referred to as parameter registers store the stimulation amplitudes associated with each of the stimulation settings stored in setting data registers  82 . Accordingly, circuit  70  should be configured to include the same number of amplitude registers  84  as setting data registers  82  which, as stated above, is twenty-four in the preferred configuration. Amplitude select multiplexer  88  is used to select the amplitude corresponding to the selected stimulation setting. The selected amplitude is sent to digital-to-analog converter  90  where the digital amplitude information is converted into analog as required by modulator  98 . One skilled in the art will understand that the amplitude registers  84  could be a part of the stimulation setting registers  82 , or may assume some other storage configuration without departing from the scope of this invention. 
     Microcomputer  74  is connected to and controls setting time generator  78 . Setting time generator  78  is programmable and used to implement a selected time interval provided by microcomputer  74  (based on the then active stimulation setting), which controls the amount of time an individual stimulation setting and amplitude are: selected. For example, in the preferred embodiment, a stimulation setting runs for at least two pulses and shall not run less than 10 milliseconds. Alternatively, each pulse could represent a differing stimulation setting, with no significant time delay between each pulse. The selected time interval provided by setting time generator  78  is sent to setting counter  80 . Setting counter  80  is programmable by microcomputer  74  and is used to select the proper stimulation settings and associated amplitudes corresponding to both a programmed sequence set, controlled by microcomputer  74 , and to the time interval from the setting time generator  78 . The count modulus of setting counter  80  is set by microcomputer  74  according to the number of individual stimulation settings to be used. Counter  80  is cycled such that each elected stimulation setting and amplitude is transmitted to receiver  18  (FIG. 1) for the time interval programmed into setting time generator  78 . Time generator  78  and counter  80  accomplish the selection and switching by controlling the select line of setting select multiplexer  86  and amplitude select multiplexer  88 , thereby controlling which stimulation setting and amplitude are sent and for how long each is sent to modulator  98 . 
     Clock  92  is a standard oscillator which provides a known frequency to frequency divider  94 . Frequency divider  94  modifies the signal from clock  92  according to the commands from microcomputer  74  to produce the desired treatment frequency. The desired treatment frequency is then sent from frequency divider  94  to pulse width modulator  96 . Pulse width modulator  96  imposes the pulse width received from microcomputer  74  on the desired frequency. As stated earlier, the frequency of the treatment is the number of times the selected electrode combination is activated each second, while the pulse width of the treatment is the amount of time the electrode combination is on every time it is activated. The frequency and pulse width signal are sent from pulse width modulator  96  to modulator  98  where they are combined with (i) the electrode configuration and phase information from setting select multiplexer  86  and (ii) the analog amplitude information from digital-to-analog converter  90 . In addition to combining this treatment information, modulator  98  encodes the combined treatment information on an RF carrier signal. The RF signal with the treatment information is sent from modulator  98  to RF oscillator  100 . The output of oscillator  100  is delivered to antenna  14  where it is transmitted to receiver  18 . As receiver  18  of this embodiment possesses no internalized power source, the transmission from antenna  14  includes that power necessary for receiver  18  to generate the defined electrical pulses. 
     Alternatively, receiver  18  may possess a plurality of registers similar to the configuration of FIG. 5. A receiver of this nature could assume the form of an IPG system or an RF system wherein the receiver  18  contains an internalized power source to maintain the content of the registers during non-transmission. The latter configuration would allow the reduction of the quantity of information transmitted between the transmitter  12  and receiver  18 , thereby increasing the longevity of the transmitter power source. 
     In operation, microcomputer  74  can be programmed to administer any combination of stimulation settings. In a first mode, a user, through microcomputer  74 , selects a single stimulation setting. The user may choose to deliver the single stimulation setting contiguously or intermittently at a predefined or manually defined interval. In a second mode, the user, through microcomputer  74 , selects any number of stimulation settings from a group of stored stimulation settings. As an example, user could select stimulation settings  1 ,  5 ,  7  and  12  of stimulation setting population  1 - 24 . The selected stimulation settings are delivered for their respective time intervals in a continuous, substantially sequential manner. The period between each stimulation setting, if any, is minimal, or the stimulation settings may be made to overlap, so that the patient cannot substantially detect the transition from one stimulation setting to the next, or at least does not find the transition annoying. This stimulation technique allows the patient to perceive “simultaneous” stimulation in those regions subject to the stimulation settings. Moreover, stimulation of multiple regions may be accomplished with a minimal burden on system power resources. In a third mode, user selects all the stored stimulation settings. System  10  administers each stimulation setting in the same “simultaneous” approach as discussed above. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.