Abstract:
The application relates to a stimulation device with power conservation functionality. In implantable devices, power supplies may be limited. Replenishing these power supplies may require costly surgery or periodic recharging depending on the model. A method may be implemented that skips or drops periodic pulses without apparently changing the frequency of the pulses. In this manner, the dropped pulses may be undetected by the patient. On the other hand, the dropped pulse represents power savings. Dropping one in ten pulses may lead to a 10% energy savings. The stimulation device may implement the method with one or more counters implemented in hardware or software.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/627,234, filed Jul. 25, 2003; this application also claims the benefit of (i) U.S. Provisional Patent Application Ser. No. 60/398,704, filed Jul. 26, 2002; (ii) U.S. Provisional Patent Application Ser. No. 60/398,749, filed Jul. 26, 2002; (iii) U.S. Provisional Patent Application Ser. No. 60/398,740, filed Jul. 26, 2002; and (iv) U.S. Provisional Patent Application Ser. No. 60/400,366, filed Aug. 1, 2002, all of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to a method and apparatus for tissue stimulation. More specifically, this invention relates to a method for conserving power in implanted stimulation devices through periodic dropping of pulses. 
       BACKGROUND 
       [0003]    Electronic stimulation systems may be used to control pain or motor disorders. Such systems have also been used to stimulate bone growth. For example, application of an electrical field to spinal nervous tissue can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated tissue. More specifically, applying particularized electrical pulses to the spinal cord associated with regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, in the afflicted bodily regions. This paresthesia can effectively inhibit the transmission of non-acute pain sensations to the brain. 
         [0004]    Electrical energy, similar to that used to inhibit pain perception, may also be used to manage the symptoms of various motor disorders, for example, tremor, dystonia, spacticity, and the like. Motor spinal nervous tissue, or nervous tissue from ventral nerve roots, transmits muscle/motor control signals. Sensory spinal nervous tissue, or nervous tissue from dorsal nerve roots, transmit pain signals. 
         [0005]    Electrical energy may be commonly delivered through electrodes positioned external to the dural layer surrounding a spinal cord. The electrodes are carried by two primary vehicles: the percutaneous lead and the laminotomy lead. 
         [0006]    Percutaneous leads commonly have two or more electrodes and are positioned within an epidural space through the use of an insertion, or Touhy-like, needle. An example of an eight-electrode percutaneous lead is an OCTRODE® lead manufactured by Advanced Neuromodulation Systems, Inc. 
         [0007]    Operationally, an insertion needle is passed through the skin, between the desired vertebrae, and into an epidural space which is defined by a dural layer in combination with the surrounding vertebrae. The stimulation lead is then fed through the bore of the insertion needle and into the epidural space. Conventionally, the needle is inserted at an inferior vertebral position, for example, between vertebrae L1 and L2 (L1/L2), and the stimulation lead is advanced in a superior direction until the electrodes of the stimulation lead are positioned at a desired location within the epidural space, for example, at T10. In a lateral position, percutaneous leads are typically positioned about a physiological midline. 
         [0008]    As an example of application, the above methodology is commonly used for the management of sympathetically maintained pain (SMP). It is generally believed that due to the sympathetic nature of SMP, stimulation leads positioned about a physiological midline provide sufficient electrical energy to interrupt the transmission of SMP signals. However, the above-described conventional technique may be used for the management of sympathetically independent pain (SIP), stimulating bone growth, and treating muscle disorders, among others. 
         [0009]    Spinal Cord Stimulation (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. The internalized power source limits the life of these systems to between one and four years. After the power source is expended, the patient is required to undergo replacement surgery to continue electrical stimulation. 
         [0010]    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 possess greater power resources, thereby enabling RF systems to utilize multiple leads. 
         [0011]    As an alternative to spinal cord stimulation, electrical energy may be delivered to selected peripheral nerves using a peripheral nerve stimulation system. Peripheral nerve stimulation involves administration of electrical energy to a localized group of peripheral nerves through placement of one or more leads at the peripheral nerve site. Unfortunately, if a patient&#39;s pain is widespread, a patient may require a plurality of stimulation leads to be implanted. The surgical procedure necessary for stimulation lead implantation is significant and can be quite painful. Additionally, because peripheral stimulation leads are implanted in “active” areas of the body (e.g., arms and legs), the leads typically lack long-term placement stability. Lead movement, or lead migration, can affect the quality of pain relief. Further, significant lead movement that undermines the intended stimulation effect may require additional corrective surgeries to reposition the stimulation leads. 
         [0012]    In each of these cases, the stimulation device may be coupled to one or more leads with one or more electrodes. Depending on the application and the purpose of the stimulation, varying stimulation patterns and electrical fields may be desired. An applied electrical field is defined by the polarity of each electrode of the stimulation lead. Conventionally, each electrode is set as an anode (+), cathode (−), or neutral (off). For a four electrode percutaneous lead there exists approximately 50 electrode combinations. For an eight electrode percutaneous lead, the number of possible electrode combinations grows to approximately 6050. Further, various combinations of pulses and pulse frequencies may be using with sets of electrodes. 
         [0013]    Since many typical stimulation devices are implanted in a patient, these stimulation devices have a limited power source or require periodic charging with an RF charger. In a unit having a limited power source, costly surgery is performed to service the unit and replace the power source. In RF charged units, patients must remember to periodically charge the unit. 
         [0014]    In a typical stimulation device, patients are encouraged to turn the units off as often as possible. Alternately, the units are cycled on and off so that the tissue is stimulated for a period of time, then not. When the stimulation is used to mask pain, turning the unit off or cycling the unit on and off may cause considerable discomfort. Further, the patient may simply ignore the request to turn the unit off. 
         [0015]    As such, many typical stimulation devices suffer from limited power sources or periodic recharging requirements. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein. 
       SUMMARY 
       [0016]    The application relates to a stimulation device with power conservation functionality. In implantable devices, power supplies may be limited. Replenishing these power supplies may require costly surgery or periodic recharging depending on the model. A method may be implemented that skips or drops periodic pulses without apparently changing the frequency of the pulses. In this manner, the dropped pulses may be undetected by the patient. On the other hand, the dropped pulse represents power savings. Dropping one in ten pulses may lead to a 10% energy savings. The stimulation device may implement the method with one or more counters implemented in hardware or software. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram depicting a stimulation device. 
           [0018]      FIG. 2  is a pictorial depicting an exemplary embodiment of a implanted stimulation device. 
           [0019]      FIG. 3  is a schematic block diagram depicting an exemplary embodiment of a stimulation device. 
           [0020]      FIG. 4A  is a graph depicting an exemplary embodiment of a typical pulse set as delivered by the stimulation device seen in  FIG. 3 . 
           [0021]      FIG. 4B  is a graph depicting an exemplary embodiment of a power conserving pulse set as delivered by the stimulation device seen in  FIG. 3 . 
           [0022]      FIG. 4C  is a graph depicting another exemplary embodiment of a power conserving pulse set as delivered by the stimulation device seen in  FIG. 3 . 
           [0023]      FIG. 5  is a schematic block diagram of an exemplary embodiment of a controller for use in the stimulation device seen in  FIG. 3 . 
           [0024]      FIG. 6  is a schematic block diagram of an exemplary embodiment of the system as seen in  FIG. 3 . 
           [0025]      FIG. 7  is a block flow diagram of an exemplary method for use by the stimulation device as seen in  FIG. 3 . 
       
    
    
       [0026]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION  
       [0027]    Several conditions may benefit from electrical pulse stimulation or modulation of tissue. These conditions may include pain, bone growth, cardiac arrest and arrhythmias, peripheral vascular disease (PVD), angina pectoris, and various motor disorders. The electrical pulse stimulation may be delivered by a lead with several electrodes placed near the tissue to be stimulated. The lead may be connected to a stimulation device which is either implanted corporally or external to the body. 
         [0028]      FIG. 1  is an exemplary implanted stimulation system  10 . The device  12  may be implanted in a patient. Attached to the device  12  may be a lead  14  which may terminate in a set or array of electrodes  16 . Such devices  12  may be used to treat various conditions such as arrhythmias, muscle tremors, tissue damage, and chronic pain, among others. 
         [0029]    The device  12  may take various forms. These forms may include implantable pulse generators, neurostimulators, muscle stimulators, and defibrillators, among others. Moreover, the device may have a limited power supply. 
         [0030]    The lead  14  and electrodes  16  may take various forms. These forms may include cylindrical leads and electrodes, paddles, and lamitrodes, among others. The lead  14  may have one or more electrodes  16  and these electrodes  16  may be shaped in accordance with various functions. Furthermore, more than one lead  14  may be attached to device  12 . 
         [0031]    The stimulation device  12  may be configured to stimulate one or more sets of electrodes with one or more pulses having various pulse characteristics. Together, the sets of electrodes and pulse characteristics make stimulation settings. For each stimulation setting, each electrode is set as an anode (+), cathode (−), or neutral (off). For a four electrode percutaneous lead there exists approximately 50 electrode combinations. For an eight electrode percutaneous lead, the number of possible electrode combinations grows to approximately 6050. These electrode settings are combined with pulse characteristics to form stimulation settings. An array of stimulation settings may be used to create a cycle. Further a set of cycles or pulses with or without variations within the cycles or among the pulses may form a repeating pattern. The repeating pattern may typically provide stimulation at frequencies between 2 and 500 HZ. However, the frequency may be more or less than this range. 
         [0032]    If the repeating pattern includes periodically dropped or skipped pulses or cycles, energy savings may be realized without discomfort to the patient. For example, a repeating pattern of 10 cycles may have nine stimulation cycles and one dropped cycle. This pattern would result in a 10% energy saving. Alternately, the pattern may have more or less than 10 cycles. Further, the pattern may include more than one dropped cycle. In another exemplary embodiment, pulses associated with stimulation settings may be dropped within cycles. 
         [0033]    For example the device may be act to stimulate the heart muscle, bone, spinal nervous tissue, other muscle tissue, and other nervous tissue, among others.  FIG. 2  depicts an exemplary embodiment of a neurostimulator implanted in the torso  30  of an individual. In this exemplary embodiment, the device  32  may be installed such that the lead  34  extends into the spinal foramen  36  as defined by the vertebrae  38 . The lead  34  may terminate in one or more electrodes. These electrodes may be used to stimulate or modulate nervous tissue. The stimulation or modulation may function to prevent muscle tremor and/or mask pain. The function and location of the effect may be affected by the location and stimulation characteristics of the electromagnetic pulses delivered by the device  32 . 
         [0034]      FIG. 3  is an exemplary embodiment of a stimulation device power conservation functionality. The device  50  may have a receiver  52 , transmitter  58 , power storage  54 , controller  55 , switching circuitry  56 , memory  57 , pulse generators  60  and  62 , and processor  63 , among others. Further, the device  50  may be coupled to one or more leads  64  and  66 . These leads may terminate in one or more electrodes  65  and  67 . However, some, all, or none of the components may be included in the device  50 . Further, these components may be together, separate, or in various combinations, among others. 
         [0035]    The receiver  52  may take various forms. These forms may include a circuitry, antenna, or coil, among others. The receiver  52  may or may not function to receive instructions and data. Further, the receiver  52  may or may not function to receive power that may be used by the device and/or stored in the power storage  54 . Similarly, the transmitter  58  may take various forms including a circuitry, antenna, or coil, among others. The transmitter  58  may function to transmit data and/or instructions. However, the receiver  52  and transmitter  58  may or may not be included or may be together, separate, combine various components, among others. 
         [0036]    The power storage  54  may take various forms. These forms may include various batteries. In an implanted device, the power is limited by the capacity of the source. Thus, power conservation may function to reduce the frequency of recharge or costly replacement. 
         [0037]    The controller  55  may take various forms. These forms may include those discussed in  FIG. 4  or other means for modulating and controlling pulses and signals. Further, aspects of the controller  55  may be implemented as software, hardware, or a combination of software and hardware. 
         [0038]    The switching circuitry  56  may take various forms. These forms may include various contacts, relays, and switch matrices, among others. Further, the switching circuitry  56  may or may not include one or more blocking capacitors associated with connections to the leads. These blocking capacitors may block direct connection to the leads and/or function to build charge that may be discharged between signal pulses. Furthermore, the switching circuitry  56  in combination with the microprocessor  63  and/or the controller  55  may function to drop, skip, or repeat stimulation patterns. 
         [0039]    The memory  57  may take various forms. These forms may include various forms of random access memory, read-only memory, and flash memory, among others. The memory may be accessible by the controller  55 , the switching circuitry  56 , and/or the processor  63 . Further, the memory  57  may store various stimulation settings, repetition parameters, skipping parameters, programs, instruction sets, and other parameters, among others. 
         [0040]    The processor  63  may take various forms. These forms may include logic circuitry or microprocessors, among others. The processor  63  may function to monitor, deliver, and control delivery of the modulation or stimulation signal. Further, the processor  63  may manipulate the switching circuitry  56 . This manipulation may or may not be in conjunction with the controller  55 . 
         [0041]    The one or more pulse generators  60  and  62  may take various forms. These forms may include a clock driven circuitry, or an oscillating circuitry, among others. The pulse generator(s)  60  and  62  may deliver a electric or electromagnetic signal through the switching circuitry  56  to the leads  64  and  66  and electrodes  65  and  67 . The signal may be modulated by circuitry associated with the switching circuitry  56 , the controller  55 , and/or the processor  63  to manipulate characteristics of the signal including amplitude, frequency, polarity, and pulse width, among others. 
         [0042]    In one exemplary embodiment, the microprocessor  63  may interact with the switching circuitry  56  to establish electrode configurations. The pulse generator may then generate a pulse and, in combination with the microprocessor  63  and the switching circuitry  56 , stimulate the tissue with a number of pulses or cycles having desired characteristics. The controller  55  may then direct the skipping or dropping of one or more pulses associated with settings in the array of settings or one or more cycles of the array. The controller may be implemented as software for use by the microprocessor or in hardware for interaction with the microprocessor and switching circuitry, among others. 
         [0043]      FIGS. 4A ,  4 B, and  4 C are graphs depicting optional pulse patterns for a single stimulation setting. However more than one stimulation setting may be used. As such, the pattern in the graphs may also represent a pattern of pulses for an individual stimulation setting in an array of stimulation settings or cycles of an array of stimulation settings. 
         [0044]      FIG. 4A  depicts a pulse set. In this example, the pulse set has 5 pulses.  FIG. 4B  depicts the skipping or dropping of the fifth pulse. In this case, a 20% power conservation may be seen with limited impact on the pattern of pulses. Further, more than one pulse may be skipped in a set as seen in  FIG. 4C . Similarly, dropping one pulse in ten may conserve 10% power and skipping one pulse in three may conserve 33%. The set may be larger or smaller than 10 and 3, as well. However, smaller sets may be noticeable by patients. For example if one in two pulses were skipped, the patient may perceive a change in frequency. 
         [0045]      FIG. 5  is a schematic block diagram depicting an exemplary embodiment of a controller. Controller  110  may have one or more stimulation counters  112 , one or more drop counters  114 , stimulation parameters  116 , drop parameters  118 , and an interface  120 . 
         [0046]    In one embodiment, the one or more stimulation counters  112  counts the pulses or cycles to determine the completion of a set of stimulation pulses or cycles. In coordination, stimulation parameters  116  determines the number of stimulation pulses or cycles in a pattern. For example, a set of nine (9) stimulation pulses or cycles may be counted. However, a set of 3, 5, 20, 100 or other numbers may be counted as well. 
         [0047]    Drop counter  114  may count dropped pulses or cycles within a set or pattern. In accordance with drop parameters  118 , drop counter  114  determines the number of dropped pulses or cycles within a set or pattern. For example, counter  114  may count to one (1) dropped pulse in accordance with the drop parameter  118  before the system continues the set or pattern. Alternately, counter  114  may count to two (2) or more dropped pulses. 
         [0048]    Together, counters  112  and  114  may be used to create patterns of stimulated and dropped pulses and/or cycles. For example, stimulation counter  112  may count nine (9) cycles. Then, the drop counter  114  may count to one (1) dropped cycle. 
         [0049]    Both counters  112  and  114  may be reset upon completion of a pattern. Counters  112  and  114  may be implemented in hardware, software, or a combination of hardware and software. Further, the functionality of counters  112  and  114  may be combined in a single counter that uses stimulation parameter  116  and drop parameters  118 . For example, skipping one pulse out of 10 may be effectively achieved by counting nine pulses and skipping the next pulse. Alternately, a more complex skipping pattern could be created using an array of parameters or a randomly generated parameter. However, various configurations may be envisaged. 
         [0050]    Interfaces  120  may aid in communication with the microprocessor, switching circuitry, and pulse generators. When controller  110  has a hardware implementation, the interfaces may be communicative couplings between circuitries. In a software implementation, the interfaces may be software interfaces. Further, the interfaces may be combination of these. 
         [0051]      FIG. 6  is a schematic block diagram depicting an exemplary embodiment of the system. This exemplary embodiment  70  may have a microprocessor  74 , an interface  72 , a program memory  76 , a clock  78 , a magnet control  80 , a power module  84 , a voltage multiplier  86 , a pulse amplitude and width control  88 , a CPU RAM  82 , and a multi-channel switch matrix  90 . However, these components may or may not be included and may be together, separate, or in various combinations. 
         [0052]    The microprocessor  74  may take the form of various processors and logic circuitry. The microprocessor  74  may function to control pulse stimulations in accordance with settings 1 through N stored in the CPU RAM  82 . Further, the microprocessor may function in accordance with programs stored in the program memory  76 . 
         [0053]    The program memory  76  may take various forms. These forms may include RAM, ROM, flash memory, and other storage mediums among others. Further, the program memory  76  may be programmed using interfaces  72 . 
         [0054]    These interfaces  72  may be accessed prior to implanting to program the microprocessor  74 , program memory  76 , and or CPU RAM  82 . These forms may include ports or connections to handheld circuitry, computers, keyboards, displays, and program storage, among others. Alternately, the interfaces  72  may include means for interaction and programming after implanting. 
         [0055]    A clock  78  may be coupled to the microprocessor  74 . The clock may provide a signal by which the microprocessor operates and/or uses in creating stimulation pulses. 
         [0056]    A magnet control  80  may also interface with the microprocessor. The magnet control  80  may function to turn the implantable stimulation device on or off. Alternately, a receiver or other means may be used. This receiver may or may not function to provide programming instruction, charge, and on/off signals. 
         [0057]    The system  70  may also have a power supply or battery  84 . This power supply  80  may function to power the various circuitries such as the clock  78 , microprocessor  74 , program memory  76 , and CPU RAM  82 , among others. Further, the power supply  80  may be used in generating the stimulation pulses. As such, the power supply may be coupled to the microprocessor  74 , a voltage multiplier, and/or a switch matrix  90 . 
         [0058]    The CPU RAM  82  may store stimulation settings 1 through N. These stimulation settings may include electrode configuration, pulse frequency, pulse width, pulse amplitude, and other limits and control parameters. The stimulation and drop parameters may or may not be stored in the CPU RAM  82  and may or may not be associated with each of the stimulation settings 1 through N. The microprocessor  74  may uses these stimulation settings and parameters in configuring the switch matrix  90 , manipulating the pulse amplitude and pulse width control  88 , and producing stimulation pulses. 
         [0059]    The switch matrix  90  may or may not permit more than one lead with more than one electrode to be connected to the system  70 . The switch matrix  90  may function with other components to selectively stimulate varying sets of electrodes with various pulse characteristics. 
         [0060]    In this exemplary embodiment, the controller may be implemented in software for interpretation by the microprocessor  74 . Alternately, a hardware implementation may be coupled to the microprocessor  74 , pulse amplitude controller  88 , and switch matrix  90 . However, various embodiment of the controller system, and implementation may be envisaged. 
         [0061]      FIG. 7  is a block flow diagram of an exemplary method for use by the stimulation device. In method  130 , a counter is decremented with a pulse stimulation as seen in a block  132 . In this case, the completion of a stimulation set would be determined if the counter reaches zero as seen in a block  134 . 
         [0062]    If the pulse marks the end of a set, a second counter may be decremented as seen in a block  136 . This second counter may function to instigate and count dropped pulses as seen in a block  138  while the counter is greater than zero. Once the counter reaches zero, the set of dropped pulses or cycles is complete as seen in block  138 . Both counters may then be reset or values may be loaded into the counters as seen in a block  142 . 
         [0063]    However, incrementing counters may also be used and the decision made upon reaching a predetermined number. Further, more complex patterns may be created using an array of counter values per counter or an array of counters with associated counter values. 
         [0064]    This method may also be implemented with a single counter in which the decision as to resetting or dropping a pulse is made in accordance with parameters. The pulse may be dropped through communication with the microprocessor, switching circuitry, and/or pulse generator, among others. 
         [0065]    As such, a stimulation device with power conservation functionality is described. In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention as set forth in the claims which follow.