Minimally invasive implantable neurostimulation system

An external medical device generates a drive signal inductively coupled to an implantable coil from an external coil. A regulator module coupled to the implantable coil generates an output signal in response to the inductively coupled signal and a feedback signal correlated to an amplitude of the inductively coupled signal. A signal generator receives the output signal for generating a therapeutic electrical stimulation signal. The control module adjusts the drive signal in response to the feedback signal to control the electrical stimulation signal.

FIELD OF THE DISCLOSURE

The disclosure relates generally to implantable neurostimulation systems and in particular to minimally invasive neurostimulation systems.

SUMMARY

Various exemplary embodiments of a minimally invasive implantable medical device (IMD) system are described. In some embodiments , the IMD system can include an external power supply that is inductively coupled to an IMD. Various exemplary external coil arrangements are described for coupling with an implanted coil for power transmission. A power feedback control signal transmitted from the IMD, which may be embodied as a neurostimulator in some examples, to the external device may be used to control a drive signal applied to an external coil and inductively coupled to an implantable coil. A regulator module of the IMD generates an output signal in response to the inductively coupled signal and provides the output signal to a signal generator for powering generation of a therapeutic electrical signal delivered to a target therapy site. The feedback signal is correlated to the inductively coupled signal and may be generated in response to a measurement of the output signal, the therapeutic electrical signal, or a physiological response to the therapeutic electrical signal in some examples. Adjustments to the therapeutic electrical signal are made by adjusting the drive signal in some embodiments. An activity sensor may be included and, responsive to detection of an activity state, the therapeutic electrical signal may be withheld by inhibiting the drive signal. Other exemplary aspects of the IMD system relating to inductively coupled power, patient management and therapy control are described.

DETAILED DESCRIPTION

Applicants have an appreciation that implantable medical device (IMD) technology is continually advancing as new applications are developed for automated therapy delivery in patients. Such advances may be further enhanced by using devices of reduced size and weight, which makes implantation of such devices less invasive and chronic use more comfortable for the patient. Additionally, applicants recognize that such enhancements such as improved power supply systems, wireless telemetry systems for communication with the implanted device, tools for performing implantation procedures, apparatus and methods for targeting a delivered therapy at desired location, and other system improvements can also enhance therapies in a manner that saves cost, conserves energy and minimizes any burden placed on the patient or clinician. Accordingly, Applicants recognize a need for improved, minimally-invasive implantable medical device systems and associated methods of use for providing patient monitoring and/or therapy delivery. Certain exemplary embodiments disclosed herein may obtain some or all of the aforementioned advantages and enhancements.

In the following description, references are made to illustrative embodiments. Various embodiments of an implantable neurostimulation (INS) system for delivering an electrical stimulation therapy to a targeted neural site are described. However, it is recognized that the various embodiments described herein may be implemented in numerous types of implantable medical device (IMD) systems, including, for example, implantable sensors or monitoring devices, implantable communication devices, and other types of implantable therapy delivery systems. The various embodiments of systems described herein and associated methods of use promote and facilitate minimally invasive INS systems in which the incision size and time required to implant and anchor the device can be minimized. The INS systems are designed to minimize cost, size and invasiveness of the device while providing efficacious therapy delivery (and/or accurate monitoring in a sensing-only device).

FIG. 1is a schematic diagram of a minimally invasive INS system10capable of delivering a neurostimulation therapy. System10includes an IMD20, an external device40enabled for transmitting signals to IMD20, a patient programming device60enabled for bidirectional communication with IMD20and/or external device40, and a physician programming device80according to one illustrative embodiment. In the illustrative embodiments described herein, communication between components included in the INS system10is configured to be bidirectional communication, however it is recognized that in some embodiments communication between two or more system components may be unidirectional.

IMD20includes circuitry for delivering neurostimulation pulses enclosed in a sealed housing and coupled to therapy delivery electrodes. In various embodiments, IMD20may include one or more of a primary battery cell, a rechargeable battery cell, and an inductively coupled power source for providing power for generating and delivering stimulation pulses and powering other device functions such as communication functions.

In some embodiments, IMD20is less than approximately 15 mm in length and less than approximately 1 cc in volume. In illustrative embodiments, the term “approximately” as used herein may indicate a value of ±10% of a stated value or may correspond to a range of manufacturing specification tolerances. In other examples, IMD20may be less than approximately 10 mm in length and may be less than approximately 0.6 cc in volume. IMD20may be approximately 0.1 cc in volume in some embodiments. The embodiments described herein are not limited to a particular size and volume of IMD20, but are generally implemented to enable the use of a reduced size device for minimally invasive implantation procedures and minimized discomfort to a patient. It is recognized, however, that the various INS systems described herein may be implemented in conjunction with a wide variety of IMD sizes and volumes adapted for a particular therapy or monitoring application.

External device40may be a wearable device including a strap42or other attachment member(s) for securing external device40to the patient in operable proximity to IMD20. When IMD20is provided with rechargeable battery cell(s), external device40may be embodied as a recharging unit for transmitting power, for example inductive power transmission from external device40to IMD20. In this embodiment, programming device60may be a patient handheld device that is used to initiate and terminate therapy delivered by IMD20via a bidirectional wireless telemetry link62. Alternatively, programming device60could be operated by a patient for communicating with wearable external device40to control therapy on and off times and other therapy control parameters, which are transmitted to IMD20via communication link21. Programming device60may communicate with wearable external device40via a bidirectional wireless telemetry link41that may establish communication over a distance of up to a few feet or more, enabling distance telemetry such that the patient need not position programming device60directly over IMD20to control therapy on and off times or perform other interrogation or programming operations (e.g., programming of other therapy control parameters).

When IMD20includes primary cell(s), a wearable external device40may be optional. Programming of IMD20may be performed by the programming device60, using near- or distance-telemetry technology for establishing bidirectional communication link62for transmitting data between programmer60and IMD20. Programming device60may be used by a patient or clinician to set a therapy protocol that is performed automatically by IMD20. Programming device60may be used to manually start and stop therapy, adjust therapy delivery parameters, and collect data from IMD20, e.g. data relating to total accumulated therapy delivery time or other data relating to device operation or measurements taken by IMD20.

When IMD20is configured as an externally powered device, external device40may be a power transmission device that is worn by the patient during a therapy session to provide power needed to generate stimulation pulses. For example, external device40may be a battery powered device including a primary coil used to inductively transmit power to a secondary coil included in IMD20. External device40may include one or more primary and/or rechargeable cells and therefore may include a power adaptor and plug for re-charging in a standard 110V or 220V wall outlet, for example.

It is contemplated that in some embodiments the functionality required for transmitting power to IMD20when IMD20is embodied as a rechargeable or externally powered device and for programming the IMD20for controlling therapy delivery may be implemented in a single external device. For example, power transmission capability of external device40and programming capabilities of patient programmer60may be combined in a single external device, which may be a wearable or handheld device.

Physician programming device80may include increased programming and diagnostic functionality compared to patient programming device60. For example, physician programming device80may be configured for programming all neurostimulation therapy control parameters, such as but not limited to pulse amplitude, pulse width, pulse shape, pulse frequency, duty cycle, therapy on and off times, electrode selection, and electrode polarity assignments. Patient programming device60may be limited to turning therapy on and/or off, adjusting a start time of therapy, and/or adjusting a pulse amplitude without giving access to the patient to full programming functions such that some programming functions and programmable therapy control parameters cannot be accessed or altered by a patient.

Physician programming device80may be configured to communicate directly with IMD20via wireless, bidirectional telemetry link81, for example during an office visit. Additionally or alternatively, physician programming device80may be operable as remote programming instrument used to transmit programming commands to patient programming device60via a wired or wireless communication network link61, after which patient programming device60automatically transmits programming data to IMD20via bidirectional telemetry link62(or via wearable external device40and link21).

In some embodiments, the patient may be provided with a magnet90for adjusting operation of IMD20. For example, application of magnet90may turn therapy on or off or cause other binary or stepwise adjustments to IMD20operations.

While IMD20is shown implanted along a portion of the lower leg of a patient, IMD20could be implanted at numerous sites according to patient need and the particular medical application. In the illustrative embodiment, IMD20is provided for stimulating the tibial nerve of the patient to treat overactive bladder syndrome and is merely one example of the type of medical application for which INS system10may be used. IMD20may be positioned along a medial portion of the lower leg, e.g. posterior to the medial malleolus and superior to the flexor retinaculum. In another example, IMD20may be implanted to deliver a stimulation therapy to muscles of the pelvic floor, such as periurethral muscles or the external urethral sphincter for treating symptoms of urinary incontinence or overactive bladder syndrome. In such examples, the IMD20may be delivered intravaginally. In other examples, IMD20may be deployed for delivering neurostimulation therapy to an acupuncture point for treatment of a symptom associated with the acupuncture point. IMD20may be implemented in an INS system for providing numerous types of neurostimulation therapies, such as for pain control, autonomic nervous system modulation, functional electrical stimulation, tremor, and more.

FIG. 2is a functional block diagram of IMD20according to one embodiment. IMD20includes a housing34enclosing a control unit22and associated memory24, a telemetry module26, and a pulse generator28coupled to electrodes30. IMD20includes a power supply32, which as described above may include any of a primary battery cell, a rechargeable battery cell, or a secondary coil of an externally powered system.

Control unit22may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or integrated logic circuitry. In some examples, control unit22may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to control unit22herein may be embodied as software, firmware, hardware or any combination thereof. In one example, a neurostimulation therapy protocol may be stored or encoded as instructions in memory24that are executed by controller22to cause pulse generator28to deliver the therapy via electrodes30according to the programmed protocol.

Memory24may include computer-readable instructions that, when executed by controller22, cause IMD20to perform various functions attributed throughout this disclosure to IMD20. The computer-readable instructions may be encoded within memory24. Memory24may comprise non-transitory computer-readable storage media including any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital media, with the sole exception being a transitory propagating signal.

Telemetry module26and associated antenna25are provided for establishing bidirectional communication with wearable external device40, patient programmer60and/or physician programmer80. Examples of communication techniques used by IMD20and a programming device60or80include low frequency or radiofrequency (RF) telemetry, which may be an RF link established via Bluetooth, WiFi, or MICS, for example. Antenna25may be located within, along or extend externally from housing34.

In one embodiment, telemetry module26is implemented as a Near Field Communication (NFC) target device capable of receiving NFC signals and harvesting power from the carrier signal. One example of a commercially available NFC target device is the M24LR16E-R dual interface EEPROM, available from STMicroelectronics, Huntsville, Ala., USA.

NFC is one commercially available, industry standardized short-range inductive communication technology that could be implemented in telemetry module26and an external device communicating with IMD20, however other examples of inductive communication technology that could be used include a passive low frequency interface (PaLFI) device which operates at approximately 135 kHz, such as the TMS37157 Target Board available from Texas Instruments, Dallas Tex., USA, or other radio frequency identity (RFID) devices, e.g. operating at a frequency of 125 kHz. Inductive power transfer can operate at a variety of frequencies. Other standard protocols may operate in the range of 100-200 kHz. Frequencies both above and below this range can be contemplated, with a chosen frequency being some balance between regulatory restrictions, biological interactions and efficiency of energy transfer.

Electrodes30may be located along an exterior surface of housing34and are coupled to pulse generator28via insulated feedthroughs. In other embodiments, electrodes30may be carried by a lead or insulated tether electrically coupled to pulse generator28via appropriate insulated feedthroughs or other electrical connections crossing sealed housing34. In still other embodiments, electrodes30may be incorporated in housing34with externally exposed surfaces adapted to be operably positioned in proximity to a targeted nerve and electrically coupled to pulse generator28.

FIG. 3is a schematic diagram of one embodiment of an INS system100including an IMD120, external device140, and charging unit150. IMD120is an externally powered device or may include a rechargeable battery cell or other rechargeable energy storage device. As such, IMD120includes an electrically conductive coil (not shown inFIG. 3) configured to be inductively coupled to an external coil142included in external device140for inductive power transfer from external device140to IMD120.

External device140is shown as a wearable device, which is an ankle cuff in the illustrative embodiment, for electromagnetic coupling and inductive power transfer to an IMD120implanted along the medial portion of a patient's ankle for delivering an electrical stimulation therapy to the tibial nerve to treat overactive bladder syndrome. It is recognized, however, that the apparatus and techniques described herein may be implemented or adapted for use in a wide variety of IMD systems. The shape and contour of external device140may be adapted for a secure and comfortable fit at a particular body location. For example, when positioned around the ankle, external device140may include a recess or curve to avoid pressure or contact between the external device140and the medial malleolus (inner ankle bone) to prevent patient discomfort.

External device140includes a power source146, which is a rechargeable power source in the illustrative embodiment shown, coupled to at least one primary coil142for transferring power from external power source146to IMD120. External device140includes electrical contacts for electrically coupling to charging unit150for recharging power source146. Charging unit150includes an electrical plug154for plugging into a wall socket for recharging power source146using a standard 110V or 220V outlet for example. Charging unit150includes a receptacle152configured for receiving and retaining external device140during charging. Charging unit150and external device140may be configured with mating geometries including curves, ridges, grooves, varying internal and/or external diameters or other features to promote proper positioning and electrical connection of external device140with charging unit150.

External device140is shown inFIG. 3as a cuff but may be implemented as a variety of wearable structures such as a sock or a boot. In other embodiments, as described further below, external device140is provided as a sleeve or appliance in which a patient positions a foot, ankle, leg, arm, hand, wrist, or other body part corresponding to an implant location of IMD120to establish an electromagnetic field for inductive power transfer.

The external device140may include an adjustable fit device144, which enables the patient or caregiver to adjust the fit of the external device around the patient to reduce a distance from and improve inductive coupling between a primary external coil142and an internal coil. In some embodiments, adjustable fit device144is a button actuated air pump that inflates at least a portion of external device140to provide a snug fit around the patient. In other embodiments, an adjustable button, clip, clasp, buckle or other fastener, a metal or polymeric “slap-on” band, elastic or shape memory material, or any combination thereof may be used to provide an adjustable or conformable fit of external device140to a desired body portion of the patient.

One challenge faced in providing an externally powered or rechargeable IMD120is ensuring adequate positioning of an external coil142relative to the implanted coil of IMD120for efficient power transfer. IMD120may be miniaturized in a minimally invasive system and therefore accurate positioning of an external coil over IMD120may be challenging. IMD120may migrate over time or shift with patient movement causing a change in the relative positioning of IMD120and external device140.

In the embodiment shown, external device140includes a coaxial pair of electrically conductive coils142spaced apart along external device140and encircling the patient's ankle Coils142are wound in the same direction and electrically coupled in parallel to power source146and will provide a uniform electromagnetic field in the patient's ankle for inducing current in the implanted coil to thereby transfer power to the IMD120. Two or more coils extending around the patient's ankle (or other body part) may be used for generating a uniform electromagnetic field over a desired surface area of the patient's body to encompass a likely location of IMD120. By providing a uniform electromagnetic field over a relatively larger portion of the patient's body than the IMD120and encompassing a likely location of the IMD120, the patient's burden in properly aligning or positioning external device140can be reduced.

FIG. 4is a schematic diagram of an external device160including one or more coils162and164having ferrite cores163as opposed to the air core coils142shown inFIG. 3. A ferrite core can enhance the electromagnetic field produced by the coil162or164. Two or more coils162and164may be arranged in a one-dimensional or two dimensional array along external device160and tested independently to determine which coil has the best coupling with the implanted coil based on a power feedback signal as will be described in greater detail below. The coils162and164may be arranged in parallel or at an angle such as the approximate perpendicular angle as shown inFIG. 4.

FIG. 5is a schematic diagram of an alternative embodiment of an external device170including a coil172for power transfer to an IMD. External device170may be a wearable device that allows a patient to be ambulatory, much like a sock or a boot, or may be a stationary boot-like appliance that the patient inserts a foot into during a recharging or therapy delivery session to maintain electromagnetic inductive coupling between the external coil172and an implanted coil. In the example shown, a circular coil172is shown positioned along the device170, e.g. along an interior surface of the device or embedded within the device, in a position that results in approximate alignment with an implanted coil. Numerous external coil configurations could be implemented in a wearable external device or appliance used for transferring power to the IMD and other examples will be described and illustrated herein.

FIG. 6AandFIG. 6Bshow a side and end view, respectively, of an external device180configured as an appliance in which the patient rests or positions a body portion to align an implanted coil with an external coil included in the external device180. The external device180may be sized and contoured to provide a comfortable fit for the patient and for accommodating anatomical features.

The external device180includes one or more primary coils182a,182bfor transmitting power to the implanted device via inductive coupling with an implanted coil. In the illustrative embodiment ofFIG. 6B, two coaxial circular coils182aand182bare shown positioned along a medial wall184of the external device180and along a lateral wall186of the external device such that the patient's ankle is positioned between the coaxial coils182aand182b. In this way, a uniform electromagnetic field is induced between the coils when coils182aand182bare wound in the same direction and driven in phase by an applied current. The uniform electromagnetic field promotes efficient current induction in a coil of the associated IMD implanted in the medial portion of the patient's ankle for stimulating the tibial nerve in this example.

The external device180may include a passive or active cooling system184to prevent overheating of the external device180during power transfer, which might otherwise cause patient discomfort. In the embodiment shown, cooling system184is a passive cooling system including a network of fluid channels184that allow heat to be conducted away from the patient. In alternative embodiments, heat absorbing materials may be incorporated along an outer portion of external device180, such as a wax or other phase change material (PCM) to provide heat sinks away from the patient. Active cooling systems could include fluid pumps that circulate air or another fluid through a system of channels formed in external device180. Heat management techniques in external device180may include any active and/or passive cooling techniques and/or insulation. Among other heat management techniques that may be used are Peltier cooling elements, external ice/cold packs, fans, thermally conductive and insulation material/members.

External device180may be a foldable device for packing and storing for convenience. For example, medial wall184and lateral wall186may be coupled to base188at rotatable hinges190allowing walls184and186to be folded down on base188when not in use. External device180may be a battery powered device or powered using a standard 110V or 220V outlet. In some embodiments, external device180includes a rechargeable cell or energy storage device that is recharged by plugging external device into a standard 110V or 220V outlet, directly or via a charging unit as described above.

FIGS. 7-11are schematic diagrams of alternative embodiments of an external electrically conductive coil included in an external device for inductive power transfer to an IMD. The various embodiments of external coils described herein may be incorporated in a wearable external device such as a cuff, boot, sock or clip-on type device or an external device intended for stationary use such as a boot, stand or appliance like the external device shown inFIGS. 6A and 6B. Each of the various coil shapes may be implemented singly or in any combination, including ordered linear or circular arrays, random, concentric or opposing arrangements. The coils may be printed on a printed circuit board or flexible substrate or other conformable electronic substrate or be wound and mechanically coupled to a surface or embedded within layers of the external device. Examples of conductive materials that may be included in an external or implantable coil in various embodiments herein include those comprising copper, nickel, gold, platinum, niobium, tantalum, titanium, alloys thereof or alloys such as MP35N or titanium alloyed with molybdenum, and the like. Materials may be inherently biostable/biocompatible, or they may be clad with biostable/biocompatible materials (such as silver cored wire clad with MP35N) or may be coated, overmolded or potted with polymeric or ceramic material, or enclosed in a hermetic or sealed enclosure.

FIG. 7depicts a two-dimensional array202of coils204which are each shown of equal size inFIG. 7, but may alternatively vary in size. In the various embodiments shown inFIGS. 7-11, individual external coils are generally larger in diameter than the IMD itself. Typical sizes may range from approximately a half inch to several inches in diameter, with sizes between one to three inches perhaps being most common. An external coil configuration for use in power transmission as described herein is not intended to be limited to any particular coil size, however. Optimal inductive coupling is generally achieved when a primary coil radius is approximately 1.4 times the distance to the secondary coil. To illustrate, if an implanted coil is between 1 and 2 cm beneath the skin, an external air core coil may have a diameter in the range of approximately 1 to 2.5 inches. Different embodiments may require larger coils depending on the depth of an implanted coil beneath the skin and the proximity of an external coil included in an external device to the skin when properly positioned for power transmission. When multiple concentric coils or coil arrays are included, the coil sizes may range in size. A number of windings included in a coil can vary depending on a chosen carrier frequency and may range between one turn and more than 100 turns.

The coils204are shown as air-core, circular coils or loops arranged in a circular array. In alternative embodiments, coils of the same or varying size may be arranged in a linear, rectangular or circular array of coils with or without a ferrite core. Coils arranged in a two-dimensional array along the external device may be linear coils, coils shaped into a circle (as shown inFIG. 7), polygonal, spiral or other shapes. The two dimensional array promotes optimal coupling with an implanted coil over a range of horizontal and vertical positions of the external device to mitigate misalignment of an external device with the IMD.

The coils204may be coupled to a drive signal source independently, all simultaneously or in any combination. When driven independently or in different combinations, a power transfer feedback signal received from the IMD may be used to select one or more coils204providing the highest or most efficient power transfer. The use of a power transfer feedback signal for optimizing coupling between one or more external coils and an implanted coil will be described in greater detail below.

FIG. 8depicts a two-dimensional coil array210in which coils212are overlapping. Similarly to the array ofFIG. 7, the coils212may be operated independently or in any combination to achieve optimal coupling for power transfer to an IMD. The coils212may be circular or polygonal loops or linear coils and may have air or ferrite cores.

FIG. 9is a circular array220of differently sized circular coils222and224. A relatively large center coil222is circumferentially surrounded by relatively smaller circular coils224. The smaller coils224may be tested independently one at a time and a power transfer feedback signal may be used to identify which of the smaller coils224is optimally aligned with the implanted coil. This location of the optimally aligned coil is used to provide directional feedback to the patient or a caregiver for adjusting the position of array220relative to the IMD. Once the array220is optimally positioned, any one or combination of coils may be used for power transfer. For example, relatively larger coil222may be used alone, or, if optimally positioned, a smaller coil224may provide more efficient power transfer.

FIG. 10is a concentric array230of n circular coils232athrough232n. The concentric coils may be selected one at a time to determine proximity to the implanted coil. Adjustment of the position of array230may be made based on a power transfer feedback signal. The concentric coils232a-nmay then be selected in any combination for optimal coupling during power transfer. For example, the smallest coil having the best coupling may be selected for the most efficient power transfer.

FIG. 11Ais a spiral coil240that may be used individually, in a concentric pair, or in an array of coils in an external device. The spiral coil240may be circular as shown or have a polygonal spiral shape, such as a spiraling square as shown inFIG. 11Bor hexagonal shape as shown inFIG. 11Cfor example. The spiral coil240may be printed on a circuit board or flexible substrate.

FIG. 12is a schematic diagram of an external device250including a wearable cuff252carrying a two-dimensional array of circular or ring coils254. As described above, each of the coils254in the array may be controlled independently to identify a coil having optimal coupling to an implanted coil. This information can be used as feedback for adjusting the position of cuff252and/or in selecting one or more of coils254for applying a drive signal for inducing an electromagnetic field. The array shown inFIG. 12is arranged in a two-dimensional rectangular array on a conformable or contoured wearable cuff. In other embodiments, multiple coils may be arranged in a one-dimensional linear array extending vertically, horizontally or at any angle along cuff252. The coils may be embodied as any of the coil configurations described herein.

FIG. 13is a schematic diagram of an alternative embodiment of an external device280including a wearable cuff282, a rotatable dial284and a linear coil286. Coil286is wound on a ferrite core288. The angular orientation of linear coil286relative to an implantable coil may be adjusted by rotating dial284. In some embodiments, dial284is a clip-on device that may be attached to cuff282, or optionally to any garment the patient is wearing over the location of the IMD. The angular orientation may be adjusted until optimal power transfer is achieved, for example based on a power transfer feedback signal. The rotatable dial may include pre-determined positions established by interfacing stops configured between the dial and a face plate285that the rotatable dial284is mounted on such that the degree of rotation of the dial is controlled. In some embodiments, dial rotation and selection of dial position for power transmission could be an automated process controlled by a control module receiving the power transfer feedback signal and configured to control an actuator or motor for turning dial284.

FIG. 14is a functional block diagram of an IMD system300according to one embodiment. IMD system300includes an IMD310, an external device340, a remote sensing device302, and a remote database/programming device380. IMD310includes controller312and associated memory314, a power monitoring and regulator module316and associated implantable secondary coil315, a telemetry module320and associated antenna321, and signal generator322coupled to at least one pair of electrodes330. IMD310may include a charge storage device318and one or more sensors324.

Controller312controls IMD functions and may be implemented as a microprocessing device executing instructions and using operating parameters stored in memory314. Signal generator322receives a regulated voltage signal from power monitoring and regulator module316and/or charge storage device318for generating a therapeutic electrical signal delivered to a targeted therapy site via electrodes330. Telemetry module320is used for bidirectional communication with external device340and may be used to receive signals from one or more remote sensors302.

Power monitoring and regulator module316is coupled to a secondary coil315that is inductively coupled to external coil352of external device340when a drive signal is applied to external coil352. Power transmission is performed by inductive coupling between implanted coil315and external coil352. External coil352may be implemented according to any of the coil configurations described herein. Power monitoring and regulator module316measures the power transmitted from external device340or a signal correlated to the inductively coupled signal and generates a power transfer feedback control signal transmitted via telemetry320back to external device340. As further described below, this feedback signal is used by external device340to control a drive signal applied to external primary coil352to control and optimize the power transfer. In some embodiments, power transmission via inductive coupling between antennas using a Near Field Communication (NFC) signal or other inductive communication technique is performed. Methods described herein for using a power transmission feedback signal may be adapted for use with any inductive power transmission technique.

Power monitoring and regulator module316may provide a rectified voltage output signal to signal generator322. Signal generator322uses the rectified voltage signal to generate stimulation output signals. A pulse amplitude, pulse width, pulse frequency or other stimulation control parameter may be adjusted by controller312or signal generator322in response to the received amplitude or signal pattern of the inductively coupled signal.

The inductively coupled signal may also be used to provide power to controller312, telemetry module320and other IMD circuitry. A data bus325couples IMD components and carries an output signal from power monitoring and regulator module316to other IMD components. In this way, power monitoring and regulator module316may provide inductively received power for all or any portion of IMD functions. IMD310may include a charge storage device318, e.g. a rechargeable cell, capacitor or supercapacitor, for storing power transferred from external device340to IMD310through inductive coupling, in which case power monitoring and regulator module316provides a rectified voltage output signal to charge storage device318. Charge storage device318may be used to provide power to any other IMD circuitry components requiring a voltage input signal.

A feedback control signal is correlated to the inductively coupled signal and is generated by power monitoring and regulator module316by measuring the inductively coupled signal received from implantable coil315, measuring an output signal from regulator module316, measuring a therapeutic electrical stimulation signal output from signal generator322, and/or measuring a physiological sensor signal measuring a response to the electrical stimulation. As such, a signal output measurement from signal generator322may be carried back to power monitoring and regulator module316via data bus325. The feedback control signal is transmitted to external device340by telemetry module320via link370and used by external device340to control and optimize power transfer for charging a charge storage device318. The feedback control signal may correspond to an amplitude of a rectified Vout signal from power monitoring and regulator module316and/or the amplitude of a therapy signal output from signal generator322. The external device340can adjust a drive signal applied to external coil352up or down to adjust the transmitted power, i.e. the inductively coupled signal induced in coil315, accordingly.

IMD310may include one or more sensors324for use in detecting a need for therapy delivery, monitoring a response to therapy delivery, controlling therapy delivery on/off times, and/or providing feedback to a patient to indicate that re-positioning of external device340and/or the patient's body is required. In some embodiments, a physiological response signal may be used by external device340to adjust a power transmission signal. Among the sensors that may be included in sensors324are electrodes for sensing an electromyogram (EMG) signal and/or a nerve signal, an activity or motion sensor, a posture sensor, and an acoustical sensor.

External device340includes, controller342and associated memory344, a user interface346, display348, power transfer control module350and associated primary coil352, telemetry module354and associated antenna355, networked patient services module356, sensors358, a network communication device360and auxiliary functions module362. A power supply364, which may be a rechargeable or primary cell, provides power to the external device circuitry.

The functionality described and attributed to external device340may be implemented in a single external device or may be distributed across two or more external devices enabled for telemetric communication with each other or with other system components in order to seamlessly provide the described functionality. For example, some of the functions attributed to external device340shown inFIG. 14may be implemented in a patient handheld device while other functions are implemented in a wearable external device.

Power transfer control module350transmits power through inductive coupling between external coil352and implanted coil315. In some embodiments, the power transmission signal, i.e. a drive signal, is applied to external coil352in a pattern, e.g. frequency, amplitude and/or duty cycle, that establishes stimulation control parameters such as pulse amplitude, pulse width, pulse frequency and/or duty cycle. In this way, the power transmission signal is used to provide power to IMD310and to set the stimulation control parameters instead of programming therapy control parameters into IMD310. Therapy control is achieved by adjustment of the power transmission signal rather than by the implanted device itself. For example, if the external device340transfers bursts of power at a therapy pulse rate, with a therapy pulse width, and with some relative therapy delivery amplitude, the IMD310could rectify the power signal and deliver it directly to the electrodes. In this way, the IMD310is nearly fully passive, and all the therapy control is implemented in the external device340by controlling the power transmission signal.

External device340receives a power transfer feedback signal from power monitoring and regulator module316via telemetry link370. In some embodiments, power transfer control module350adjusts a drive signal applied to coil352in response to the feedback signal. The drive signal may be increased or decreased to control a desired level of power transmission while minimizing the power expended by external device340.

The power monitoring and regulator module316generates a DC voltage that is proportional to the power that is transferred. The signal generator322is functions like a switch that gates the DC voltage to the electrodes330, creating a stimulation pulse. By measuring the DC voltage, which is proportional to the transferred power, and providing a feedback signal to the external device340indicating the DC voltage amplitude, the transferred power can be increased or decreased as needed to control the DC voltage to maintain a desired stimulation voltage delivered to electrodes330. The DC voltage measurement point can be at the output of power monitor/regulator326or the stimulation pulse amplitude output by signal generator322.

Variation in the transferred power, e.g. due to variation in the placement of the external controller340, and changes in programmed stimulation voltage amplitudes can all be controlled in one feedback loop. The feedback signal can be based on a DC signal measurement as described above or a physiological sensor signal from sensors324, sensors358, or remote sensors302that measures a physiological response, such as EMG or muscle motion due to nerve capture or actual nerve fibers firing due to stimulation. The feedback signal is then used to control the power transmission to achieve a desired physiological response

Alternatively, the power transfer feedback signal may be used by control342to control display348to generate a display to a user to indicate the power transfer efficiency. The power transfer efficiency may be reduced when the external device340is not optimally positioned for inductive coupling between external coil352and implanted coil315. A user may adjust the position of external device340or adjust a position or orientation of a body part relative to external device340until display348indicates an improved or optimal power transfer efficiency. Display348may indicate the power transfer efficiency by way of an LED display, e.g. a number of LEDs illuminated relative to a total number of LEDs not illuminated indicates a relative power transfer efficiency, an audible signal, text signal, visible icon, or other user perceptible signal. By maximizing the power transfer efficiency, the drain on power supply364can be reduced, increasing longevity of a primary cell in the external device340or increasing time between or reducing the number of recharges of a rechargeable cell in the external device340. Various methods for controlling power transfer with the use of a power transfer feedback signal will be further described below.

External device340includes a user interface346which may enable a patient to manually adjust stimulation control parameters or turn external device340on and off. In one embodiment, user interface346includes a therapy activation button347that enables a patient to manually start a stimulation therapy or stop a stimulation therapy that is already in progress.

User interface346may additionally be used by the patient to enter patient data, such as patient diary information relating to symptoms or events associated with the treated condition and therapy being delivery. In the example of tibial nerve stimulation for treating overactive bladder syndrome, a patient may enter fluid intake, voiding times, wetting events, medications taken, or other data. Display348may prompt the patient at regular intervals to enter patient diary data. Alternatively display348may prompt the patient to enter data when an expected data entry has not been received. Memory344may store patient data343entered by the patient or automatically acquired by external device sensors358and/or remote sensors302.

In some embodiments, external device340includes one or more sensors358for providing feedback signals that may be used in optimizing power transmission and/or acquiring patient and therapy related data. Sensors358may include electromyogram (EMG) sensing electrodes, an activity sensor, and/or a postural sensor though other sensors may be used depending on the information relevant to a particular therapy application.

EMG sensing electrodes may be used to provide a signal to controller342and/or power transfer control350for use in controlling power transferred to IMD310. The EMG signal response may be used to control the amplitude of delivered power that in turn controls the amplitude of delivered therapeutic electrical stimulation pulses. By increasing or decreasing the transferred power signal, by adjusting the drive signal applied to external primary coil352, the therapy pulse amplitude may be increased or decreased and the result on the stimulated nerve is monitored by measuring a feature of the EMG signal. An EMG signal may be acquired using implanted or external (surface) electrodes, and EMG sensing may be performed during delivery of a stimulation pulse.

Additionally or alternatively, the EMG signal may be used to monitor and quantify therapy delivery time intervals, e.g. times of day of therapy delivery, frequency of therapy delivery, duration of therapy delivery intervals, and total time that therapy is delivered cumulatively or over a predetermined time interval such as daily or weekly. This therapy delivery data may be stored in therapy/device data345of memory344and transmitted to remote database/programmer380for use by a clinician in evaluating therapy effectiveness, assessing patient compliance, and making adjustments to a therapy protocol as needed.

An EMG signal (or another sensed signal that varies in response to therapeutic stimulation) may be transmitted to a patient hand-held device in some embodiments to provide a patient a feedback display of therapy activity. The patient will be aware therapy is in progress and efficacious stimulation pulses are being delivered. This allows a patient to stop a therapy in progress if needed, adjust therapy delivery parameters if desired, and may simply provide reassurance to the patient that therapy is being delivered effectively.

A posture sensor, e.g. a 3-dimensional accelerometer, included in sensors358may be used to determine the position, e.g. upright, prone, semi-prone, left-lying, right-lying, etc., of the patient's body portion on which external device340is positioned. In some cases, the body position may influence the position of the IMD310relative to the external device340, which may affect power transfer efficiency. Body position may also influence the relative position of electrodes330to a target nerve. Accordingly, body position may be monitored using a posture sensor, included in implanted sensors324or external sensors358. Feedback to the patient to adjust body position may be provided via display348as required.

An activity sensor, which may be embodied as an accelerometer or piezoelectric crystal, or other motion sensor included in sensors358and/or324may be used to sense muscular motion caused by therapy delivery and used as a therapy delivery feedback signal, similar to the use of an EMG signal as described above.

Alternatively, an activity sensor may be used in controlling therapy delivery by stopping or starting therapy delivery based on an activity signal. When a patient activity is detected that corresponds to an activity state during which therapy delivery is undesirable, therapy may be stopped. Depending on the target site and therapy intensity, therapy delivery may cause altered motor activity that could be undesirable during certain patient activities, such as operating a motor vehicle, walking, jogging, running, stair climbing, cycling etc.

Accordingly, controller342may be configured to perform an activity sensor signal analysis for detecting and discriminating between activity states and automatically inhibit or enable therapy delivery according to activity state. At times, therapy delivery may be automatically inhibited to avoid undesired motor activity during a particular patient activity. At other times, when a patient activity is detected during which therapy is desired, such as a resting state, therapy delivery may be automatically enabled. In still other cases, an activity sensor signal may be analyzed to detect a particular pattern of a patient movement performed intentionally by the patient to start or stop therapy delivery.

In one embodiment, the external device is configured to position the external primary coil for inducing an electromagnetic field along a region of the tibial nerve, e.g. as shown inFIGS. 3-6for example. The IMD having associated electrodes is adapted to deliver therapeutic electrical stimulation signal to the tibial nerve, for example through a deep fascia tissue layer, superior to the flexor retinaculum. A detected activity state that corresponds to an intrinsic activation of the tibial nerve, stair climbing or driving an automobile, may cause a drive signal applied to the external coil to be withheld to inhibit the therapeutic electrical stimulation in response to the detected activity state.

As mentioned previously, IMD310may include one or more sensors324. Accordingly, acquiring a sensor signal, analysis of a sensor signal, and control of IMD operation based on the sensor signal as generally described above with regard to external sensors358may all or in part be implemented in IMD310or based on an implanted sensor signal being transmitted via telemetry unit320.

External sensors358may include a camera positioned to provide a visualization of the positioning of external device340relative to a patient's body, e.g. relative to an anatomical marker such as the medial malleolus. A camera image may be transmitted via a networked communication device360to remote database/programmer/expert services380to enable a remote technician or clinician to aid a patient in trouble-shooting when power transmission or communication between external device340and IMD310is not optimized.

External device340includes a network communication device360to enable communication between external device340and other devices on a wired or wireless network, e.g. a personal area network (PAN), body area network (BAN), body sensor network (BSN), local area network (LAN) or a wide area network (WAN), such as a WiFi wireless technology network, BLUETOOTH® wireless technology network, or ZIGBEE® wireless technology network. For example, external device340may communicate with remote database/programmer/expert services380via communication link382for transferring data from memory344or in real time to enable a clinician or technician to evaluate patient data, therapy data, or device related data (such as battery life) for programming external device340and/or IMD310remotely, prescribing therapy protocol adjustments or giving other patient care instructions.

External device340may include a networked patient services module356configured to perform services for the patient such as aiding in troubleshooting, providing social connectedness such as linking the patient to other patients or experts in a help line or chat line type of format, locating restroom facilities, providing patients with incentives for compliance, or other services related to the treated patient condition but somewhat peripheral to the therapy delivery itself.

External device340may include auxiliary functions module362that provides added functionality in a multi-use device that may be unrelated or indirectly related to the therapy delivery itself. For example, auxiliary functions module362may include a pedometer to provide exercise monitoring or other functionality that relates to patient wellness.

In other embodiments, system300may include one or more remote sensors302configured to transmit a sensor signal to IMD310and/or to external device340for use in controlling IMD function and/or accumulating patient or therapy related data. A remote sensor may be used to detect a need for therapy and/or a therapeutic response at a target organ. Remote sensor(s)302may include implanted and/or external sensors. For example, in the application of tibial nerve stimulation for treating overactive bladder syndrome, a remote sensor302may be implanted for sensing bladder activity, bladder volume or another indication of a likely urge event. The remote sensor may transmit a signal continuously to the IMD310for analysis by controller312or transmit a signal that an event or condition warranting a change in therapy is detected. In response, controller312may control IMD310to start, stop or adjust therapy intensity (e.g. increase or decrease a pulse amplitude, pulse width, pulse frequency, duty cycle or other therapy control parameter).

Remote sensor(s)302may transmit a signal to external device340for accumulating patient or therapy-related data for assessing therapy effectiveness and compliance and/or for use by controller342and/or power transfer control350in controlling IMD therapy delivery functions. Remote sensors302may include a posture sensor, activity sensor, acoustical sensor, pressure sensor, EMG sensor, nerve activity sensor, impedance sensor, volume sensor or the like.

In some embodiments, system300is configured to characterize a patient's urinary urge pattern to enable the system300to automatically control signal generator322to optimally deliver therapy to alleviate the intensity and/or frequency of urges and/or prevent urge incontinence. Characterization of a patient's urge pattern may be performed by controller342and/or remote database/programmer/expert services380using input stored in patient data343and therapy/device data345, which may include patient data input by the patient, sensor signal data, and therapy delivery data. In this way, the therapy delivery may be optimized to achieve maximum benefit to the patient while conserving power and avoiding patient inconvenience and burden.

FIG. 15is a flow chart400of a method for controlling power transmission from an external device340to IMD310. At block402, a power transmission signal is generated by the external device340under the control of power transfer control350. The power transmission signal may be started manually, e.g., by a user interacting with user interface346, automatically on a scheduled basis or in response to a sensor signal indicating a need for therapy, or automatically in response to detecting the IMD310within transmission range. IMD310may be detected as being in transmission range in response to a telemetry communication signal, e.g., confirmation of receipt of a telemetry wake-up signal or other techniques.

A signal is measured at block404for generating a power transmission feedback signal. In one embodiment, therapy delivery occurs when power transmission is occurring. In this embodiment, after starting the power transmission, the IMD power monitoring and regulator module316provides a rectified DC output signal to signal generator322for generating and delivering therapy. In other words, the power required by signal generator for generating and delivering a therapeutic signal is provided by power monitoring and regulator module316during inductive power transmission and when power transmission stops or is insufficient to power signal generator322, therapy is not delivered.

In this embodiment, a feedback signal may be a measured amplitude of the delivered therapy pulses. Accordingly, the output pulse amplitude of therapy pulses generated by signal generator322may be measured and this amplitude may be transmitted as a feedback signal to the external device340at block406. The feedback signal is used by power transfer control350at block408to adjust the transmitted power signal up or down as needed to regulate the output therapy pulse amplitude to a desired amplitude or within a range of a desired output amplitude. In some embodiments, the desired amplitude range is established based on other sensor feedback, e.g. an EMG signal. In this way, the control of output pulse amplitude is achieved through power transmission regulation using a closed-loop feedback signal. Variations in external device position, power status of external device340or other factors that may influence inductive coupling between external coil352and implanted coil315and variation in net power transmission to IMD310may be mitigated by adjusting the power transmission signal to maintain the pulse amplitude output at a desired level.

The feedback signal may additionally be used to generate a user display at block410to provide feedback to a user to notify the user that a therapy is in progress. The feedback signal display may be used to notify the user than an adjustment of body position and/or external device position is required to optimize power transmission.

In an alternative embodiment, an amplitude of the signal received by implanted coil315or the amplitude of a rectified Vout signal provided by monitoring and regulator module316may be measured at block404for generating a feedback signal transmitted to the external device at block406. The power transfer control module350may adjust the power transmission signal to achieve a targeted received power by the IMD310. In some cases, the power transmission signal may be reduced and still maintain a desired level of power transmission, thereby conserving the external power supply364.

The feedback control signal may be provided on a continuously sampled basis or may be provided at regular intervals during a power transmission. In some embodiments, the feedback control signal may be requested by external device340via telemetry354when a change in patient activity, patient posture, EMG signal or other sensor signal is detected from external device sensors358, IMD sensors324, and/or remote sensors302.

Power transmission feedback signal data may be stored in memory344for transmission to remote database/programmer/expert services380. In some embodiments, the feedback signal may be transmitted to remote database/programmer expert services380in real or delayed time to enable an expert to assess the power transmission and therapy delivery functions for patient monitoring or troubleshooting purposes.

FIG. 16is a flow chart of a method500for controlling a therapy delivered by IMD310according to one embodiment. At block502, if a stimulation therapy is not currently being delivered, therapy trigger signals are monitored at block504. A therapy trigger signal may be a manual trigger entered by a user using external interface346or transmitted from remote database/programmer/expert services380. A therapy trigger may be an automatic trigger generated in response to analysis of a sensor signal from IMD sensor(s)324, external device sensor(s)358and/or remote sensors(s)302. A sensor signal may indicate a need for therapy, e.g. an event detected by analysis of a sensor signal that meets a therapy delivery criterion, such as bladder activity or pressure. A sensor signal may alternatively indicate appropriate conditions for therapy delivery, such as a patient activity and/or posture condition that is/are desired for therapy delivery episodes.

A therapy trigger may additionally or alternatively be an automatic trigger provided by external device340or IMD controller312on a scheduled basis and/or upon external device340and IMD310coming into communication and power transmission range. Accordingly, multiple therapy trigger signals may be monitored for initiating a therapy and criteria for starting therapy may require one therapy trigger condition to be met or multiple trigger conditions to be detected in combination.

If a need for therapy is detected based on detecting a therapy trigger, as determined at block506, the system300may evaluate one or more sensor signals or other device related conditions to determine if a therapy override condition is detected at block508. If a therapy is undesirable, as determined at block510, the therapy delivery is inhibited at block514. If no therapy override condition is detected, therapy is delivered at block512by the IMD.

Therapy is delivered until a therapy episode of a predetermined time duration has expired or until a need for therapy is no longer detected at block506. The therapy override conditions may be monitored throughout therapy delivery, and the therapy may be inhibited during therapy delivery if an undesirable therapy delivery condition is detected. Similarly, if therapy is inhibited at block514, prior to starting or during therapy delivery, and a therapy override condition changes, as determined at blocks508and510, therapy may be started or restarted if a therapy trigger is still being detected or a therapy session has not expired.

Therapy override conditions monitored at block508for detecting undesirable therapy delivery conditions at block510may include a patient activity state, patient posture, an EMG or nerve signal indicating intrinsic motor activity or other sensor-based condition, power transmission status, a power supply status or other conditions that would make therapy delivery undesirable for the sake of patient safety, patient convenience, therapy effectiveness or otherwise. The override condition may be detected from IMD sensors324, remote sensor302and/or external device sensors358. In some embodiments, the override condition may be manually entered by a user. The external device340and IMD310are therefore configured to cooperatively detect an activity state in response to an activity sensor signal and inhibit the therapeutic electrical stimulation by withholding the drive signal applied to the external coil352in response to a detected activity state corresponding to a previously defined therapy override condition.

Thus, various embodiments of a minimally invasive IMD system have been presented in the foregoing description with reference to specific embodiments. The various features and aspects of the IMD system described herein may be implemented in any combination other than the particular combinations shown in the illustrative embodiments, which may include adding or omitting some features. It is appreciated that various modifications to the referenced embodiments may be made without departing from the scope of the disclosure as set forth in the following claims.