WO2025199343A1

WO2025199343A1 - Systems, methods, and devices for mitigating induced stimulation

Info

Publication number: WO2025199343A1
Application number: PCT/US2025/020735
Authority: WO
Inventors: Andrew T. Fried; Thomas L. CHOUINARD; Brett A. Otteson
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2024-03-22
Filing date: 2025-03-20
Publication date: 2025-09-25
Anticipated expiration: 2026-09-22

Abstract

A system may adjust the transfer of inductive energy based on determined induced stimulation. For example, a processing circuitry may be configured to determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device. The processing circuitry may also adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

Description

SYSTEMS, METHODS, AND DEVICES FOR MITIGATING INDUCED STIMULATION

[0001] This application is a PCT application claiming priority to and the benefit of U.S. Provisional Patent Application No. 63/569,086, filed March 22, 2024, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] This disclosure generally relates to mitigating induced stimulation during inductive energy transfer.

BACKGROUND

[0003] When wirelessly recharging an implantable medical device, inductive energy may be transferred by coupling a primary coil in an external recharger to a secondary coil in the implantable medical device via a recharge signal. In this manner, energy can be transferred through tissue of the patient. An implantable medical device can then be recharged as needed to operate over a longer period of time than may be possible with a non-rechargeable power supply. In addition to using inductive coupling for recharging a power supply, the implantable medical device may also utilize inductive coupling to communicate with an external device, such as an external programmer.

SUMMARY

[0004] Examples disclosed herein address issues such as these and others by determining a parameter that is correlated with induced stimulation occurring on a medical lead during the transfer of inductive energy (e.g., recharging energy and/or inductive communication signals) and adjusting the transfer of inductive energy (e.g., a recharging signal or communication signal) based on the parameter to mitigate the induced stimulation. In an example, heat at the implantable medical device may be a parameter that is used as a proxy to determine the presence of problematic induced stimulation that should be mitigated by controlling recharging power. Heat or other parameter considerations that correlate with induced stimulation may be used together with temperature considerations to prevent the high level of recharge that can cause discomfort while temperature is low. In another example, a recharge signal may be modified or combined with a separate signal such that the induced stimulation from the modified recharge signal or separate signal may be measured from the leads by the implantable medical device, where the direct measurement of the modified recharge signal or separate signal is the parameter that correlates to the induced stimulation, to determine if the measured induced stimulation is problematic and should be mitigated by controlling recharging power. In yet another example, the recharge signal itself may be directly measured from the leads as the induced stimulation by the implantable medical device where the direct measurement of the recharge signal as the induced stimulation is the parameter that correlates to the induced stimulation, to determine if the measured induced stimulation is problematic and should be mitigated by controlling recharging power.

[0005] In some example, a method includes: determining, by processing circuitry, a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjusting, by the processing circuitry and based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0006] In some examples, a system includes: processing circuitry configured to: determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0007] In some examples, a non-transitory computer-readable medium includes instructions that, when executed by processing circuitry, causes the processing circuitry to: determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0008] Some examples include systems, devices, and/or methods to provide control of recharging of an implantable medical device. This includes determining a parameter that correlates with an induced stimulation at one or more leads of the implantable medical device during a transfer of recharging power from an implantable medical device recharger to charge the implantable medical device. This also includes adjusting recharging power from the implantable medical device recharger such that the parameter does not exceed a predetermined threshold.

[0009] Examples provide systems, devices, and methods of a medical system. This includes an implantable medical device and an implantable medical device recharger that includes a recharging unit that outputs recharging power where the implantable medical device is inductively coupled to the recharging unit. The implantable medical device includes a memory and a processor, and the memory stores instructions that, when executed by the processor, cause the implantable medical device to determine a parameter that correlates with an induced stimulation at one or more leads of the implantable medical device during a transfer of power from the implantable medical device recharger to charge the implantable medical device. The implantable medical device recharger includes a second memory and a second processor, and the second memory stores instructions that, when executed by the second processor, cause the recharging unit to adjust recharging power from the implantable medical device recharger such that the parameter does not exceed a predetermined threshold.

[0010] Examples provide systems, devices, and methods of a medical system. This includes an implantable medical device and an implantable medical lead. The implantable medical device is coupled to the implantable medical lead and includes a transmit circuit, a memory, and a processor. The memory stores instructions that, when executed by the processor, cause the implantable medical device to determine a parameter that correlates with an induced stimulation into the implantable medical lead during a transfer of recharging power to the implantable medical device and transmit a signal representative of the parameter that correlates with induced stimulation via the transmit circuit.

[0011] Examples provide systems, devices, and methods of an implantable medical device recharger that includes a memory, a processor, a recharge unit, and a receiver circuit. The memory stores instructions that, when executed by the processor, causes the implantable medical device recharge to determine a parameter that correlates with an induced stimulation into an implantable medical lead of an implantable medical device inductively coupled to the recharge unit during a transfer of recharging power from the recharge unit to charge the implantable medical device and adjust recharging power from the recharge unit such that the parameter that correlates with induced stimulation does not exceed a predetermined threshold.

[0012] Examples provide systems, devices, and methods of controlling recharging of an implantable medical device. This includes determining heat induced in the implantable medical device. This also includes determining temperature of one or more portions of the implantable medical device. This also includes determining a recharging power based upon the heat induced in the implantable medical device. This also includes determining a recharging power based upon the temperature of the one or more portions of the implantable medical device. This also includes adjusting recharging power from an implantable medical device recharger based upon the lowest of the power based on heat and the power based on temperature.

[0013] Various examples described herein relate to systems, methods, and devices that determine the presence of induced stimulation on a medical lead during inductive energy transfer, such as recharging a medical device, and adjust recharging to mitigate the induced stimulation. Some examples, may apply to other safety and comfort related considerations of recharging or otherwise transferring inductive energy to implantable medical devices beyond induced stimulation.

DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows an environment for an example medical system.

[0015] FIG. 2 shows an example of a medical system.

[0016] FIG. 3 shows an example of logical operations that may be performed by a medical system to recharge an implantable medical device.

[0017] FIG. 4 shows an example of logical operations that may be performed by a medical system to recharge an implantable medical device that considers a parameter such as heat that correlates with induced stimulation and that also considers the implantable medical device temperature.

[0018] FIG. 5 shows another example of logical operations that may be performed by a medical system to recharge an implantable medical device that considers a parameter such as heat that correlates with induced stimulation and that also considers the implantable medical device temperature.

[0019] FIG. 6 shows an example of a medical system that modifies a recharging signal.

[0020] FIG. 7 shows an example of logical operations that may be performed by a medical system to recharge an implantable medical device by modifying a recharging signal. [0021] FIG. 8 shows another example of logical operations that may be performed by a medical system to recharge an implantable medical device by modifying a recharging signal. [0022] FIG. 9 shows an example of a medical system that modifies a recharging signal by adding a separate signal with the recharge signal. [0023] FIG. 10 shows an example of logical operations that may be performed by a medical system that modifies a recharging signal by adding a separate signal with the recharge signal.

[0024] FIG. 11 shows an example of logical operations that may be performed by a medical system that modifies a recharging signal by skipping pulses in the recharging signal. [0025] FIG. 12 shows a graph of induced stimulation versus time during recharging an implantable medical device system.

[0026] FIG. 13 shows an example of logical operations that may be performed by a medical device system that determines recharging power.

[0027] FIG. 14 shows a normalized plot that shows the correlation of induced stimulation on leads of the implantable medical device and heat at the implantable medical device during recharging.

[0028] FIG. 15 shows an example medical system.

[0029] FIG. 16 shows an example block diagram of an implanted medical device.

[0030] FIG. 17 shows an example block diagram of an example external programmer.

[0031] FIG. 18 shows an example technique for adjusting inductive energy transfer for communication based on induced stimulation.

DETAILED DESCRIPTION

[0032] Examples provide for the determination of a parameter that correlates with induced stimulation of a medical lead during the transfer of inductive energy (e.g., recharging energy or communication signals) and adjustment of the transfer of inductive energy (e.g., a recharging signal) to mitigate induced stimulation.

[0033] Inductive coupling refers to the process in which a primary coil generates a magnetic field that induces current in a secondary coil. In implantable medical device (IMD) systems, the IMD may include one coil and an external device (e.g., recharger or programmer) can include the other coil. Each coil may switch between the primary coil and the secondary coil depending on whether the device is transferring energy or receiving energy. In some examples, each device may include two coils that are configured to only operate as a primary coil or secondary coil. Inductive coupling can be used to transfer energy, and that energy can be used for a variety of purposes. For example, inductive coupling can be used to transfer inductive energy that the receiving device (e.g., the IMD) can use to recharge a battery. In this case, the inductive energy may be referred to as recharge energy. In another example, inductive coupling can be used to transfer inductive energy that is used to transfer information (e.g., data) via modulation of the transferred inductive energy or other methods. Inductive energy can be used for other purposes as well. In any use case, inductive energy can cause other effects to materials or devices affected by the magnetic field. For example, the inductive energy may induce stimulation on implanted components such as the leads and electrodes of the leads.

[0034] In the example of recharging energy, the recharge signal may inductively couple to medical leads that are physically and electrically coupled to the implantable medical device. This may cause unintended or incidental induced stimulation by the leads at the therapy locale. The induced stimulation can adversely affect the patient. For example, the induced stimulation can cause the therapy to deviate from the prescribing physician’s treatment orders. In certain situations, for example with deep brain stimulation (DBS) therapy, induced stimulation can lead to physiological damage to the patient when the induced stimulation exceeds a safety threshold.

[0035] Many factors may affect the amount of induced stimulation that occurs. For example, during an implantable medical device implantation surgery, if there is extra lead length, the extra lead length may be wrapped around the can of the implantable medical device. The wrapping of leads around the implantable medical device may cause additional induced stimulation of the recharge signal into the leads. For another example, during unipolar stimulation where the can of the implantable medical device is used as the return for the lead, induced stimulation from the recharge signal with the medical leads may be increased. Although recharge energy generally described herein as an example, inductive energy for other purposes, such as transferring information (e.g., data) between devices may also induce stimulation. The techniques described for recharge can also be applied to any other types of inductive energy transfer.

[0036] Typically, the recharging frequency of an implantable medical device is larger than the frequency of signals measured within the patient body by an implantable medical device. In an example, potential recharge frequencies may include approximately 10 kHz, 20, 30, 40, 50 kHz, 60, 75, 100 kHz, and 150 kHz, and frequencies there between. As such, the implantable medical device typically does not have the required frequency range to measure the induced stimulation from a recharging signal directly. In an example, physiological sensing used for closed loop therapy in deep brain stimulation or spinal cord stimulation or other forms of neuromodulation in low power implantable medical devices may be limited to approximately less than 1 kHz, 5 kHz, or 10 kHz. [0037] Induced stimulation is the unintended or incidental stimulation at the therapy or electrode locale when inductive energy from the recharger unintendedly or incidentally couples to the leads/electrodes in addition to the primary target, the recharge coupling coil associated with the battery in the implant. This induced stimulation often occurs when the leads are wrapped around the implant body during implantation or in the case of unipolar stimulation. Patients may desire a short recharge time of the implantable medical device due to the discomfort of maintaining the recharger on the body of the patient. An aspect of this disclosure may be to allow patients to have a short recharge time for implantable medical devices and configurations susceptible to induced stimulation. Without sensing the induced stimulation directly or otherwise determining an estimation of the induced stimulation, the medical system may need to be conservative in the estimation or controls of the system to mitigate induced stimulation at the therapy delivery target; as a result not all patients may recharge as quickly as possible.

[0038] FIG. 1 shows a typical environment for medical system 100. In this example, medical system 100 may include external medical device 110 and implantable medical system 130 that is present within a patient body 120. The implantable medical system 130 may include an implantable medical device 132. External medical device 110 may include a recharger for recharging the implantable medical device 132. In an example, the external medical device 110 may be an implantable medical device recharger. In some examples, external medical device 110 is an example external device that can transfer inductive energy for purposes other than recharging implantable medical device 132. For example, external medical device 110 may be an external programmer that transmits information to implantable medical device 110 via inductive coupling as shown in example FIG. 15 (or the recharger may also transfer data to implantable medical device 132 via inductive coupling). In this manner, any external device may adjust the transfer of inductive energy to mitigate induced stimulation when the inductive energy is used for one or more different purposes.

[0039] Implantable medical device 132 may determine the parameter that correlates with the induced stimulation from a recharge signal generated by the external medical device 110. Implantable medical device 132 may provide the measure of the parameter or the induced stimulation to the external medical device 110. Additionally or alternatively, implantable medical device 132 may provide the desired recharging power to external medical device 110. In addition to the induced stimulation, the temperature of the implantable medical device 132 and/or the temperature of the tissue of the patient body 120 as measured or estimated by implantable medical device 132 may be used to determine recharging power. [0040] The external medical device 110 may be placed on the patient body 120, such as on the chest of the patient body 120 or another location that is in proximity to the implantable medical system 130. External medical device 110 may be placed on the bare skin of the patient body 120, over clothes on the patient body 120, over medical bandages on the patient body 120, combinations thereof, or any other material that may be between the patient body 120 and external medical device 110 that would allow implantable medical device 132 to be recharged.

[0041] As discussed above, the implantable medical system 130 of this example includes an implantable medical device 132, and the implantable medical device 132 has been implanted into a subcutaneous pocket 140, although other implantation locales may be used depending on the procedure. The implantable medical system further includes at least one implantable medical lead 134, or lead and extension combination, that is routed between a therapy delivery target 142 and the implantable medical device 132. In an example, implantable medical lead 134 may connect one or more therapy delivery targets to the implantable medical device 132. In another example, the implantable medical system 130 may be a leadless design and not include the implantable medical lead 134. In this situation, the induced stimulation may be less due to the lower aperture of a loop in the stimulation circuit within the implantable medical device 132.

[0042] In this example, the implantable medical device 132 is an implantable neurostimulator (INS) configured for adaptive deep brain stimulation, as the implantable medical lead 134 has a distal end 136 and distal electrodes 138 positioned within the brain at the target location for the stimulation to be applied. Other examples of implantable medical devices include but are not limited to neurostimulators for spinal cord stimulation where the implantable medical lead 134 is directed to the spinal cord, peripheral nerve stimulation where the implantable medical lead 134 is directed to a peripheral nerve, sacral nerve stimulation where the implantable medical lead 134 is directed to a sacral nerve, cardiac stimulation where the implantable medical lead 134 is directed to cardiac tissue, tibial neuromodulation where there be no implantable medical lead 134, and the like. Implantable medical system 130 may communicate with the external medical device 110 via wired and/or wireless methods.

[0043] FIG. 2 shows an example of medical system 100. Medical system 100 may include external medical device 110, implantable medical device 132, implantable medical lead 134, and implantable medical lead 134 may be attached to therapy delivery target 142 of the patient. External medical device 110 may include processor 230, memory 232, and recharging unit 234. Memory 232 may store instructions executed by processor 230. External medical device 110 may include one or more processors 230. Implantable medical device 132 may include recharging unit 240, processor 246, and memory 248. Memory 248 may store instructions executed by processor 246. Implantable medical device 132 may include one or more processors 246. Any processor described herein may be referred to as, or including, processing circuitry. In some examples, processing circuitry may be included within the housing of a single device. In some examples, processing circuitry may be referred to collectively as the processing circuitry of multiple different devices, such that each of the devices includes at least a portion of the processing circuitry. In this manner, different aspects of a technique, or even each aspect of the technique, may be distributed amongst different portions of processing circuitry (e.g., processors) of each of the different devices. One example, is that processing circuitry of implantable medical device 132 may perform one or more functions of a technique, and processing circuitry of external medical device 110 may perform one or more other functions of the technique.

[0044] Implantable medical device 132 may optionally include a temperature sensor 242 and/or sense circuit 244. Temperature sensor 242 may measure the temperature of implantable medical device 132 and/or the temperature of the patient body surrounding implantable medical device 132 which may be used for temperature based control of recharging. In an example, implantable medical device 132 may have one or more temperature sensors 242. In another example, one or more temperature sensors 242 may measure one or more portions of implantable medical device 132 and/or the surrounding patient tissue of implantable medical device 132. Additionally or alternatively, temperature control of the recharging may be based in whole or in part on temperature sensing occurring via one or more temperature sensors that may be included at the external medical device 110. Sense circuit 244 may sense one or more signals on implantable medical lead 134 or stimulation current pathway. Each processor may be in the form of a general purpose programmable processor, an application specific processor, hardwired digital logic, combinations thereof, and the like.

[0045] Recharging unit 234 may generate inductive energy (e.g., recharge energy) at a given rate as recharging power 210. Recharging power 210 may be coupled from the external medical device 110 to implantable medical device 132 via recharging unit 240. An unintended consequence of generating recharging power 210 is that part of recharging power 210 may couple to implantable medical lead 134 thus causing induced stimulation at the therapy delivery target 142. The induced stimulation is generally undesirable and could lead to damage to the patient including damage to the therapy delivery target 142 when the induced stimulation is excessive.

[0046] Induced stimulation may be determined by implantable medical device 132 either directly via sensing on the leads or by proxy via determining a parameter that correlates with induced stimulation. In an example, heat at the implantable medical device may be used as the parameter that correlates with induced stimulation such that determining the heat can be a valid proxy for determining induced stimulation. In another example, recharging power 210 may be modified where the modified recharging power is the parameter that correlates with induced stimulation such that determining the modified recharging power on the leads via a direct measurement is a valid proxy for determining induced stimulation at the implantable medical device 132. As used herein, determine, generally, includes estimate, measure, calculate, combinations thereof, and the like. The determination can also include empirical and analytical estimates based on the design and/or testing of the medical device system 100. The design and/or testing of the medical system 100 may be used to configure one or more limits in the medical system 100. In other words, the medical system 100 may determine the induced simulation empirically without actually knowing the magnitude of the induced stimulation level.

[0047] Implantable medical device 132 may provide a feedback signal 220 to external medical device 110. The feedback signal 220 may include information including the parameter(s) that correlate with induced stimulation due to the recharging, such as an amount of power that has been added to the battery during recharging which directly relates to the heat of the implantable medical device, a direct measurement of the recharging power that has become induced stimulation, a direct measurement of a modified recharge signal that has become induced stimulation, a result of a transfer function of recharging power to induced stimulation, desired recharging power, temperature of implantable medical device 132, and the like. In an example, feedback signal 220 may be provided during recharging. In another example, feedback signal 220 may be provided before recharging and the feedback signal may be used to determine the recharging power. Initially, recharging power may be set to a known safe level while the induced stimulation is characterized and this characterized induced stimulation may be used in subsequent recharges. In an example, feedback signal 220 is optional, such as when external medical device 110 can determine the parameter that correlates with the induced stimulation based on the characteristic of recharging power 210 being output by the external medical device 110. [0048] The measure of induced stimulation such as the determination of a parameter that correlates with induced stimulation may be used to determine recharging power to be output. Recharging power may include any characteristic of a recharge signal, such as magnitude, amplitude, phase, frequency, period, frequency range, bandwidth, time domain response, and the like. In an example, recharging power may be determined such that induced stimulation does not exceed a safety threshold. Other factors may be used to determine an appropriate recharging power to mitigate induced current on the leads and/or to resolve any other recharging related issues. For instance, one additional factor is the measured temperature of the implantable medical device 132. Determination of recharging power may be performed by any combination of external medical device 110 and implantable medical device 132. Furthermore, recharging power control may be based on time. For example, recharging power may be increased during initial recharging before the temperature of a battery of the implantable medical device 132 increases due to the side effects of recharging the battery. In an example, the patient and/or medical practitioner may set a configurable recharging power that is less than the determined recharging power. In this example, when the recharging causes the patient discomfort or other negative side effects, the patient may lower the configurable recharging power. Additionally or alternatively, a medical practitioner may specify a configurable recharging power that the recharging power may not exceed or maximum induced stimulation to not exceed. Recharging power may also be based on the type of therapy being provided, the type of implantable medical device providing the particular type of therapy, as well as the target location of the implantable medical device (e.g., therapy delivery target 142). In another example, the medical practitioner may decide that delivering therapy during recharge is not necessary and configure the implantable medical system 130 to not delivery stimulation therapy during recharging. For example, during recharging, implantable medical system 130 may open circuit the stimulation engine delivering therapy to therapy delivery target 142 via implantable medical lead 134. However, stopping therapy may not be possible in some patients due to the need for continuous therapy. [0049] External medical device 110 may include a first transmit circuit 236 to communicate with a second receiver circuit 252 of the implantable medical device 132. Implantable medical device 132 may include a second transmit circuit 250 to communicate with a first receiver circuit 238 of external medical device 110. Each transmit and receiver circuit may transmit and receive an induced stimulation signal representing induced stimulation into an implantable medical lead 134. While shown as distinct components, each transmit and receive circuit may be implemented as a transceiver. [0050] FIG. 3 shows an example of logical operations that may be performed by a medical system 100 to recharge an implantable medical device 132. Operations of this example may begin by determining a parameter that correlates to the induced stimulation, such as a direct measure of the induced stimulation itself or a proxy, from external medical device 110 to implantable medical lead 134 at operation 3 lOFor example, a measure of the heat occurring in the implanted medical device 132 may be used as the parameter that correlates with induced stimulation at operation 310. In another example, recharging power 210 may be modified such that the parameter that correlates with induced stimulation may be measured by the implantable medical device 132 based on the modification at operation 310. [0051] The recharging power may be adjusted such that the parameter that correlates with the induced stimulation, which serves as a proxy for the direct measure of the induced stimulation, does not exceed a predetermined threshold at operation 320 and this in turn prevents the induced stimulation from reaching a level higher than desired. The predetermined threshold of the parameter may be based on the maximum power level of induced stimulation that therapy delivery target 142 can safely receive and the correlation of the parameter to the level of induced stimulation. In a first example, the predetermined threshold may be a maximum parameter value correlating with the maximum power level of induced stimulation that therapy delivery target 142 can safely receive adjusted by a safety margin. In a second example, a patient may decrease the predetermined threshold when the patient has discomfort from the recharging process. In a third example, the predetermined threshold may be based on the type of stimulation therapy and the type of implantable medical device providing the type of stimulation therapy. In this example, deep brain stimulation (DBS) therapy and the DBS implantable medical device may have a lower predetermined threshold than spinal cord stimulation (SCS) therapy and the SCS implantable medical device. In a fourth example, the predetermined threshold may be based upon the implantable medical lead 134 configuration established in the stimulation circuity of the implantable medical device. In this example, a unipolar stimulation configuration may have a lower threshold than a bipolar stimulation configuration since unipolar stimulation may be more susceptible to induced stimulation. In a fifth example, the recharging power may be determined. In a sixth example, when recharging begins, implantable medical system 130 may switch from a unipolar stimulation to a bipolar stimulation and return to unipolar stimulation when recharging is complete or when the recharging power is below a predetermined value. In a seventh example, external medical device 110 may request the lead configuration from implantable medical system 130 (e.g., unipolar or bipolar stimulation) and set the threshold based on lead configuration.

[0052] FIG. 4 shows an example of logical operations that may be performed by a medical system 100 to recharge implantable medical device 132 that considers a parameter such as implantable medical device heating that correlates with induced stimulation and also considers implantable medical device temperature. While recharging may be temperature controlled in some recharging systems and while this temperature control may eventually provide some level of control of the induced stimulation during recharge, the power in such systems will normally spike to a high level when the temperature is still low. Thus, the temperature control does not offer protection from induced stimulation during these high- level spikes of recharging power. Considering a parameter that correlates with induced stimulation, such as the implantable medical device heating, allows the medical system 100 to avoid these high-level spikes of recharging power.

[0053] Operations of this example may begin by determining a maximum allowable induced stimulation threshold at operation 410 based on finding a maximum heat at the implantable medical device from being recharged where heat at the implantable medical device is a parameter that correlates to the induced stimulation. The maximum allowable induced stimulation threshold may be based on analyzed results of experiments, published literature, and standards.

[0054] Heat recharging power may be determined such that an implantable medical device recharger does not create induced stimulation beyond the maximum allowable induced stimulation threshold at operation 420. The maximum allowable induced stimulation threshold may be empirically measured from experiments and the maximum heat that correlates with the maximum allowed induced stimulation may likewise be empirically measured. Characterization of implantable medical system 130 and/or external medical device 110 may be used to establish a relationship between heat (e.g., implantable medical device 132 heat) and induced stimulation, and the relationship may be used to determine heat recharging power. With reference to FIG. 14, a normalized plot shows an example of the correlation of the induced stimulation at the leads of an implantable medical device to the heat being induced in the implantable medical device during recharging. The y-axis 1420 shows the induced stimulation while the x-axis 14120 shows the heat. It can be seen that the plot line 1430 demonstrates a strong correlation over the entire normalized range of induced current and heat. [0055] In an example, heat at the implantable medical device may be based upon one or more of heat of the recharger primary side, implantable medical device 132 battery current, power into resonant circuit primary side, and temperature of the implantable medical device 132. In another example, implant heat may be determined as power into the resonant circuit (e.g., recharge coil and tuning capacitor) of external medical device 110 minus heat induced in the external medical device 110 minus power into the implantable medical device 132 battery. Specifically, in one example implant heat may be determined with the equation: Q = Ptank - Qprim - Pins batt (eq 1) where

Q is heat of implantable medical device 132

Ptank is power into the LC tank circuit of the external medical device 110 Qprim is heat induced in the external medical device 110

Pins batt is power into the implantable medical device 132 battery

[0056] Temperature recharging power may be determined such that the implantable medical device does not exceed a maximum temperature at operation 430. A side effect of recharging an implantable medical device 132 may be that heat is generated. The temperature of implantable medical device 132 is monitored, and other precautionary actions may also be taken, so that the implantable medical device 132 can never be damaged and/or the patient is never adversely affected by recharging. In an example, the temperature recharging power may be based on an estimate of the temperature applied to the patient’s tissue on the implantable medical device 132.

[0057] Recharging power may be determined based on the heat recharging power and the temperature recharging power at operation 440. In an example, the minimum of the heat recharging power and the temperature recharging power may be the recharging power. In this example, the recharging power of external medical device 110 may be determined such that implantable medical device 132 is within a safe region of operation for both the induced stimulation and temperature of implantable medical device 132, and the patient may be allowed the fastest recharge time safely available. In another example, the recharging power may be set as the lower of the heat recharging power and the temperature recharging power. [0058] FIG. 5 shows another example of logical operations that may be performed by medical system 100 to recharge implantable medical device 132 using induced stimulation and implantable medical device temperature. Operations of this example may begin by determining power based on temperature control at operation 510 and determining power based on heat control at operation 520. In operation 510, the power based on temperature control may be the maximum allowable power for temperature control. In operation 520, heat may be used as the parameter that correlates with the induced stimulation and heat control power may be determined based on a maximum allowable induced stimulation. In operation 520, the power based on heat control may be the maximum allowable power for heat control. In an example, different therapies can have different configurable heat limits. For example, with SCS induced stimulation may not be as high of a safety risk. Operations 510 and 520 may be performed sequentially or in parallel. Recharging power may be set based on the power temperature control and power heat control at operation 530. In an example, recharging power may be set as the lesser of the power temperature control and power heat control. For an initial recharge, a known safe value of any combination of recharging power, power temperature control, and power heat control may be selected.

[0059] A determination may be made if recharging should stop at operation 540. Termination criteria may be used to determine if recharging should stop. Termination criteria may include recharge current dropping below a recharge current threshold, recharger voltage outside limits, fault detected, external medical device 110 outside of recharging range of implantable medical device 132, patient stopping the recharge, and any other condition that could be used as a stop criterion. When it is determined recharging should stop at operation 540, recharging may be stopped at operation 550.

[0060] When it is determined recharging should continue at operation 540, operations 560 and 570 may be performed. Temperature of implantable medical device 132 may be read at operation 560 and loading on a recharging unit of external medical device 110 may be sensed at operation 570. In an example, heat at the implantable medical device may be measured as discussed above, for instance by equation 1. Operations 560 and 570 may be performed sequentially or in parallel. The applied temperature may be estimated at operation 580. Applied temperature may be measured by one or more temperature sensors in implantable medical device 132 and/or external medical device 110. After operation 580, operation 510 may be performed. Heat may be estimated in operation 590. As noted, heat may be measured in one example by equation 1. After operation 590, operation 520 may be performed. The order of operations may be rearranged so long as the overall function is similar. For example, the stop recharge determination at operation 540 may occur before setting recharging power in operation 530.

[0061] FIG. 6 shows an example of medical system 100 that modifies a recharging signal to allow for determining the parameter that correlates with induced stimulation where measurement of the modified recharging signal from the leads is the parameter. Medical system 100 may include external medical device 110, implantable medical device 132, implantable medical lead 134, and implantable medical lead 134 may be attached to therapy delivery target 142 of the patient. External medical device 110 may include processor 630, memory 632, and recharging unit 634. Memory 632 may store instructions executed by processor 630. External medical device 110 may include one or more processors 630. Implantable medical device 132 may include recharging unit 640, processor 646, and memory 648. Memory 648 may store instructions executed by processor 646. The external medical device 110 may include a transmit circuit 636 and a receive circuit 638 to communicate signals with the implantable medical device 132 when determining the induced stimulation on the leads. As with the example in FIG. 2, the transmit and receive circuits may be implemented as distinct components or as a transceiver.

[0062] Implantable medical device 132 may include one or more processors 646. Implantable medical device 132 may optionally include a temperature sensor 642 and/or sense circuit 644. Temperature sensor 642 may measure the temperature of implantable medical device 132 and/or the temperature of the patient body surrounding implantable medical device 132. Sense circuit 644 may sense one or more signals on implantable medical lead 134. Each processor may be in the form of a general purpose programmable processor, an application specific processor, hardwired digital logic, combinations thereof, and the like. The implantable medical device 110 may include a transmit circuit 650 and a receive circuit 652 to communicate signals with the external medical device 110 when determining the parameter that correlates with the induced stimulation on the leads. As with the example in FIG. 2, the transmit and receive circuits may be implemented as distinct components or as a transceiver.

[0063] Recharging unit 634 may generate recharging power 610. Recharging power 610 may be coupled from the external medical device 110 to implantable medical device 132 via recharging unit 640 and implantable medical lead 134. Although implantable medical device 132 may measure a signal from the therapy delivery target 142 of the patient with a sense circuit 644, in general, as the implantable medical device 132 sense circuit 644 may have a lower frequency range than the frequency range of the recharge signal, the implantable medical device 132 may not be able to measure induced stimulation directly as the parameter that correlates with induced stimulation. In an example, a signal that is different than the recharge signal and resulting induced stimulation, such as a different frequency than the recharge signal and resulting induced stimulation, may be added to the recharge signal and this different frequency signal may be measured on the implantable medical device 132 by sense circuit 644 to determine the parameter that correlates with the induced stimulation. The different frequency signal may be selected such that the implantable medical device 132 sense circuit 644 may measure the different frequency signal. Additionally or alternatively, the sensing hardware of implantable medical device 132 sense circuit 644 may have the frequency response increased such that the recharge signal frequency, and hence the induced stimulation itself, may be measured directly as the parameter that correlates with induced stimulation. For example, the sense circuit 644 may be selected to have a frequency range of twice the recharging frequency. Additionally or alternatively, another sensing circuit may be added to implantable medical device 132 that includes a high frequency response and the other sensing circuit could be used during recharging to sense the recharging signal as the parameter that correlates to the induced stimulation during recharging.

[0064] Additionally, or alternatively, the recharging power 610 may be filtered by external medical device 110 to introduce a signal that may be measured by implantable medical device 132 as the parameter that correlates with induced stimulation. For example, the external medical device 110 may skip recharge cycles or individual pulses to induce a frequency component into recharging power 610 that is different than the recharge signal frequency, either higher or lower The frequency may be one that may be sensed by one or more electrodes on the lead according to system capabilities. For example, certain leads may be designed to sense bioelectric signals (evoked action potentials, compound muscle potentials, local field potentials) received at certain frequencies. A selection may be made of the frequency of the signal that is sent from the external device that can be sensed in a similar manner and detected by the leads. In determining the parameter that correlates with the induced stimulation, the sense circuit 644 may apply a filter, such as a bandpass filter, to the sensed signal or may perform a digital operation on the sensed signal, such as Fast Fourier Transform (FFT) of the time domain signal.

[0065] Implantable medical device 132 may provide a feedback signal 620 to external medical device 110. In an example, feedback signal 620 is optional. The feedback signal 620 may be the same or similar to feedback signal 220.

[0066] FIG. 7 shows an example of logical operations that may be performed by medical system 100 to recharge implantable medical device 132 by modifying a recharging signal. The recharging power 610 may be modified by external medical device 110 such that a sense circuit 644 of implantable medical device 132 may measure the modified recharge signal as the parameter that correlates with the induced stimulation at operation 710. In an example, the sense circuit 644 may also measure signals within the body of the patient. [0067] Implantable medical device 132 may measure the recharge signal as the parameter that correlates with the induced stimulation at implantable medical lead 134 at operation 720. In an example, a known relationship between the different frequency signal and the recharge signal along with the measured different frequency signal may be used to determine parameter that correlates with the induced stimulation from the recharge signal. External medical device 110 may adjust the recharging power such that the parameter that correlates with the induced stimulation does not exceed a predetermined amount at operation 730. [0068] FIG. 8 shows another example of logical operations that may be performed by medical system 100 to recharge implantable medical device 132 by modifying a recharging signal. Operations of this example may begin by determining power based on temperature control at operation 810 and determining power based on the parameter that correlates with induced stimulation for induced stimulation control at operation 820. In operation 810, the power based on temperature control may be the maximum allowable power for temperature control. In operation 820, the power based on the parameter that correlates with induced stimulation for induced stimulation control may be the maximum allowable power for induced stimulation. Operations 810 and 820 may be performed sequentially or in parallel. Recharging power may be set based on the power temperature control and induced stimulation control at operation 830. In an example, recharging power may be set as the minimum of power temperature control and induced stimulation control. For an initial recharge, a known safe value of any combination of recharging power, power temperature control, and power induced stimulation may be selected.

[0069] A determination may be made if recharging should stop at operation 840. Termination criteria may be used to determine if recharging should stop. Termination criteria may include recharge current dropping below a recharge current threshold, recharger voltage outside limits, fault detected, external medical device 110 outside of recharging range of implantable medical device 132, patient stopping the recharge, and any other condition that could be used as a stop criterion. When it is determined recharging should stop at operation 840, recharging may be stopped at operation 850.

[0070] When it is determined recharging should continue at operation 840, operations 860 and 870 may be performed. Temperature of implantable medical device 132 may be read at operation 860 and an induced stimulation signal may be sensed at operation 870. Operations 860 and 870 may be performed sequentially or in parallel. The applied temperature may be estimated at operation 880. Temperature may be measured by one or more temperature sensors in implantable medical device 132 and/or in the external medical device 110. After operation 880, operation 810 may be performed. Induced stimulation at therapy delivery target 142 may be estimated in operation 890. After operation 890, operation 820 may be performed. In an example, after operation 870, operation 820 may be performed, such as when the parameter that correlates with induced stimulation is the induced stimulation being sensed directly. The order of operations may be rearranged so long as the overall function is similar. For example, the stop recharge determination at operation 540 may occur before setting recharging power in operation 530.

[0071] FIG. 9 shows an example of medical system 100 that modifies a recharging signal by adding a different frequency signal onto the recharge signal, such as by superimposing or interspersing the different frequency signal in relation to the recharge signal. Medical system 100 may include external medical device 110, implantable medical device 132, implantable medical lead 134, and implantable medical lead 134 may be attached to therapy delivery target 142 of the patient. External medical device 110 may include recharge driver 930 and different frequency driver 940. Implantable medical device 132 may include stimulation engine 950 and sense circuit 960. Implantable medical device 132 may optionally include a temperature sensor 980. Temperature sensor 980 may measure the temperature of implantable medical device 132 and/or the temperature of the patient body surrounding implantable medical device 132. As previously discussed, temperature of the external medical device 110 may additionally or alternatively be considered for the temperature control of the recharge.

[0072] Recharging power 910 may be coupled from the external medical device 110 to implantable medical device 132 via recharging unit 970 and implantable medical lead 134. While recharge driver 930 generates a recharge signal to provide recharge power, different frequency driver 940 may generate a different frequency signal relative to the recharge signal. [0073] The recharge signal generated by recharge driver 930 and the different frequency signal generated by different frequency driver 940 may be combined to further create recharging power 910. Although a two driver configuration is disclosed, any circuit capable of superimposing, or interspersing, or otherwise combining a recharge signal and a different frequency signal may be used.

[0074] Sense circuit 960 may measure the parameter that correlates with the induced stimulation from the different frequency signal generated by different frequency driver 940. The known relationship between the different frequency signal generated by different frequency driver 940 and the recharge signal generated by recharge driver 930 along with the measured different frequency signal induced on the implantable medical lead 134 may be used to determine the parameter that correlates with the induced stimulation from recharging power 910 to implantable medical lead 134.

[0075] The different frequency may be selected such that the different frequency is within the frequency range of sense circuit 960. In an example, the different frequency signal may be selected in the range of 100-1000 Hz, thus lower than the frequency of the recharge frequency. In another example, sense circuit 960 may be capable of sensing up to 1 kHz signal or in yet another example up to 10 kHz signal. The different frequency may be selected in order to minimize the interference with a stimulation signal generated by stimulation engine 950. In an example, when the stimulation signal is selected in 100 Hz increments, the different frequency signal may be selected as a non-increment of 100 Hz, such as the prime number 701 Hz. The different frequency and a stimulation frequency of implantable medical device 132 may be selected such that aliasing is reduced between the different frequency and the stimulation frequency. The different frequency may be selected based on the stimulation frequency. For example, when a stimulation frequency is set in implantable medical device 132, the different frequency may be determined based on the stimulation frequency.

[0076] Implantable medical device 132 may provide a feedback signal 920 to external medical device 110. In an example, feedback signal 920 is optional. The feedback signal 920 may be the same or similar to feedback signal 220 and/or feedback signal 620. The implantable medical device 132 and the external device 110 of FIG. 9 may include components like those of FIGS. 2 and 6 above, including transmit and receive circuits for exchanging the feedback signal 920.

[0077] FIG. 10 shows an example of logical operations that may be performed by medical system 100 that modifies a recharging signal by superimposing a different frequency signal onto the recharge signal. Operations of this example may begin by external medical device 110 superimposing, interspersing, or otherwise combining a different frequency signal generated by different frequency driver 940 with a recharge signal generated by recharge driver 930 at operation 1010. The parameter that correlates with the induced stimulation may be determined based on the sensed different frequency signal by sense circuit 960 at operation 1020. External medical device 110 may adjust the recharging power such that parameter that correlates with the induced stimulation does not exceed a predetermined amount at operation 1030.

[0078] FIG. 11 shows an example of logical operations that may be performed by medical system 100 that modifies a recharging signal by skipping pulses in the recharging signal. Operations of this example may begin by external medical device 110 skipping pulse in the recharging signal to create a different frequency signal at operation 1110. In an example, the recharge signal may be multiplied by a square wave to skip pulses. In another example, a signal may be subtracted from the recharger signal. The parameter that correlates with the induced stimulation may be determined based on the sensed different frequency signal by sense circuit 960 at operation 1120. External medical device 110 may adjust the recharging power such that the parameter that correlates with the induced stimulation does not exceed a predetermined amount at operation 1130.

[0079] FIG. 12 shows a graph of induced stimulation versus time during recharging an implantable medica device. Axis 1210 may be time, axis 1220 may be magnitude of the parameter that correlates with the induced stimulation, and curve 1230 may be the parameter that correlates with the induced stimulation over time for recharging an implantable medical system 130. At time 1240, recharging an implantable medical system 130 may begin. Curve 1230 may begin at a high level for the initial charging. The high level of initial charging may be allowed because the battery of implantable medical system 130 may initially have a low temperature before recharging. Line 1250 may be an unsafe threshold for the parameter that correlates with the induced stimulation. In particular, above line 1250 may be an unsafe level of the parameter that correlates with induced stimulation while below line 1250 may be a safe level for the parameter that correlates with the induced stimulation. Line 1250 may be considered a safe or unsafe parameter level that correlates with the induced stimulation level depending on how the line 1250 is defined. In an example, any of the induced stimulation apparatuses and/or methods described herein may be used to limit the initial induced stimulation. For example, the apparatuses and/or methods may limit the parameter that correlates with the induced simulation to a safe level.

[0080] FIG. 13 shows another example of logical operations that may be performed by a medical device system that determines recharging power. Heat induced in the implantable medical device may be determined at step 1310. Temperature of one or more portions of the implantable medical device may be determined at step 1320. A recharging power target based upon the heat induced in the implantable medical device may be determined at step 1330 such as by a look-up table or calculation. A recharging power target based upon the temperature of the one or more portions of the implantable medical device may be determined at step 1340 such as by a look-up table or calculation. Adjusting recharging power from an implantable medical device recharger based upon the lowest of the target power based on heat and the target power based on temperature may be performed at step 1350.

[0081] FIG. 15 shows an example medical system 1500. As shown in FIG. 15, medical system 1500 includes IMD 1506, lead extension 1510, leads 1514A and 1514B (collectively leads 1514”), and electrodes 1516 and 1518, all of which can be configured to be implanted within patient 1523. Electrodes 1516 and 1518 may be implanted within brain 1520 of cranium 1522, but leads and electrodes may be implanted in any location within the patient, such as the spinal cord, pelvic floor, peripheral nerves, tibial nerve, etc. In addition, external programmer 1504 may be an example external device that can communicate with IMD 1506 via inductive energy 1520. Inductive energy 1520 may represent the inductive energy, or magnetic field, that can be generated by programmer 1504 and/or IMD 1506 to send information between the devices.

[0082] Medical system 1500 may be similar to system 100 of FIG. 1, as medical system 1500 may also be configured to determine a parameter that correlates with an induced stimulation at one or more of leads 1514 of IMD 1506 during a transfer of inductive energy 1530 from external programmer 1504 to IMD 1506. For example, IMD 1506 may be similar to IMD 132, and programmer 1504 may have similar capabilities to recharger 110, particularly with respect to adjusting inductive energy transfer based on induced stimulation. In addition, external programmer 1504 and/or IMD 1506 may be configured to adjust, based on the parameter, the transfer of the inductive energy from external programmer 1504 such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold. External programmer 1504 or IMD 1506 may be configured to sense an aspect of the inductive energy transfer, such as loading on a primary coil, heat, etc., and estimate the induced stimulation at one or more leads/electrodes. Based on this parameter, external programmer 1504 or IMD 1506 may reduce the power of the inductive energy if needed to maintain communication while also mitigating any possible induced stimulation.

[0083] External programmer 1504 may be a patient programmer or clinician programmer that can transfer inductive energy 1530 to IMD 1506. Inductive energy 1530 may include inductive communication that transmits operational information to IMD 1506. The operational information may include one or more parameters that define stimulation therapy, cycling information, recharging instructions, or any other commands regarding operation of IMD 1506. [0084] FIG. 16 shows an example block diagram of IMD 1506 of FIG. 15. IMD 1506 of FIG. 16 may be configured to deliver DBS therapy and/or sensing signals from the patient. In the example shown in FIG. 16, IMD 1506 includes processor 1610, memory 1611, stimulation generator 1602, sensing module 1604, telemetry module 1608, and power source 1620. Each of these modules may be or include electrical circuitry configured to perform the functions attributed to each respective module. For example, processor 1610 may include processing circuitry, sensing module 1604 may include sensing circuitry, and telemetry module 1608 may include telemetry circuitry. Switch module 1604 may not be necessary for multiple current source and sink configurations. Memory 1611 may include any volatile or non-volatile media, such as a random-access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. Memory 1611 may store computer-readable instructions that, when executed by processor 1610, cause IMD 1506 to perform various functions. Memory 1611 may be a storage device or other non-transitory medium.

[0085] Stimulation generator 1602, under the control of processor 1610, generates stimulation signals for delivery to patient 1512 via selected combinations of electrodes 1516, 1518. An example range of electrical stimulation parameters believed to be effective in DBS to manage a movement disorder of patient include:

[0086] 1. Pulse Rate, i.e., Frequency: between approximately 0.1 Hertz and approximately 500 Hertz, such as between approximately 0.1 to 10 Hertz, approximately 40 to 185 Hertz, or such as approximately 140 Hertz.

[0087] 2. In the case of a voltage controlled system, Voltage Amplitude: between approximately 0.1 volts and approximately 50 volts, such as between approximately 2 volts and approximately 3 volts.

[0088] 3. In the alternative case of a current controlled system, Current Amplitude: between approximately 0.2 milliamps to approximately 100 milliamps, such as between approximately 1.3 milliamps and approximately 2.0 milliamps.

[0089] 4. Pulse Width: between approximately 10 microseconds and approximately 5000 microseconds, such as between approximately 100 microseconds and approximately 1000 microseconds, or between approximately 180 microseconds and approximately 450 microseconds.

[0090] Accordingly, in some examples, stimulation generator 202 generates electrical stimulation signals in accordance with the electrical stimulation parameters. Other ranges of therapy parameter values may also be useful, and may depend on the target stimulation site within patient 112. While stimulation pulses are described, stimulation signals may be of any form, such as continuous-time signals (e.g., sine waves) or the like. Stimulation signals configured to elicit ECAPs or other evoked physiological signals may be similar or different from the above parameter value ranges.

[0091] Processor 1610 may include fixed function processing circuitry and/or programmable processing circuitry, and may comprise, for example, 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), discrete logic circuitry, or any other processing circuitry configured to provide the functions attributed to processor 1610 herein may be embodied as firmware, hardware, software or any combination thereof. Processor 1610 may control stimulation generator 1602 according to therapy programs stored in memory 1611 to apply particular stimulation parameter values specified by one or more of programs, such as voltage amplitude or current amplitude, pulse width, or pulse rate.

[0092] Electrodes 1516, 1518 on respective leads 1514 may be constructed of a variety of different designs. For example, one or both of leads 1514 may include two or more electrodes at each longitudinal location along the length of the lead, such as multiple electrodes at different perimeter locations around the perimeter of the lead at each of the locations A, B, C, and D. On one example, the electrodes may be electrically coupled to a switch module via respective wires that are straight or coiled within the housing the lead and run to a connector at the proximal end of the lead. In another example, each of the electrodes of the lead may be electrodes deposited on a thin film. The thin film may include an electrically conductive trace for each electrode that runs the length of the thin film to a proximal end connector. The thin film may then be wrapped (e.g., a helical wrap) around an internal member to form the lead 1514. These and other constructions may be used to create a lead with a complex electrode geometry. Sense circuit 1644 may sense one or more signals on implantable medical leads 1514 or stimulation current pathway. Sense circuit 1644 may be part of sensing module 1604 or in communication with sensing module 1604 in various examples.

[0093] Telemetry module 1608 supports wireless communication between IMD 1506 and an external programmer 1504 or another computing device under the control of processor 1610. Processor 1610 of IMD 1506 may receive, as updates to programs, values for various stimulation parameters such as magnitude and electrode combination, from programmer 1504 via telemetry module 1608. The updates to the therapy programs may be stored within memory 1611. In addition, processor 1610 may control telemetry module 1608 to transmit alerts or other information to programmer 1504 that indicate a lead moved with respect to tissue. Telemetry module 1608 in IMD 1506, as well as telemetry modules in other devices and systems described herein, such as programmer 1504, may accomplish communication by radiofrequency (RF) communication techniques. In addition, telemetry module 1608 may communicate with external medical device programmer 1504 via proximal inductive interaction (e.g., transfer of inductive energy 1530) of IMD 1506 with programmer 1504. Accordingly, telemetry module 1608 may send information to external programmer 1504 on a continuous basis, at periodic intervals, or upon request from IMD 1506 or programmer 1504.

[0094] Telemetry module 1608 may transmit and/or receive information via one or more antennas and using different communication modalities. For example, telemetry module 1608 may communicate with external programmer 1504 or other external, or implanted, device, via the transfer of inductive energy through one or more antennas. Transmit circuit 1630 may be configured to transmit information via inductive energy transfer and receive circuit 1632 may be configured to receive information via inductive energy transfer.

Transmit circuit 1630 and receive circuit 1632 may be similar to transmit circuit 250 and receive circuit 252, respectively, of IMD 132 of FIG. 2.

[0095] Power source 1620 delivers operating power to various components of IMD 1506. Power source 1620 may include a small rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD 1506. In some examples, power requirements may be small enough to allow IMD 1506 to utilize patient motion and implement a kinetic energy-scavenging device to trickle charge a rechargeable battery. In other examples, traditional batteries may be used for a limited period of time.

[0096] FIG. 17 shows an example block diagram of an example external programmer 1504. Although programmer 1504 may generally be described as a hand-held device, programmer 1504 may be a larger portable device or a more stationary device. In some examples, programmer 1504 may be referred to as a tablet computing device. In addition, in other examples, programmer 1504 may be included as part of a bed-side monitor, an external charging device or include the functionality of an external charging device. As illustrated in FIG. 17, programmer 1504 may include a processor 1710, memory 1711, user interface 1702, telemetry module 1708, and power source 1720. Memory 1711 may store instructions that, when executed by processor 1710, cause processor 1710 and external programmer 1504 to provide the functionality ascribed to external programmer 1704 throughout this disclosure. Each of these components, or modules, may include electrical circuitry that is configured to perform some or all of the functionality described herein. For example, processor 1710 may include processing circuitry configured to perform the processes discussed with respect to processor 1710.

[0097] In general, programmer 1504 comprises any suitable arrangement of hardware, alone or in combination with software and/or firmware, to perform the techniques attributed to programmer 1504, and processor 1710, user interface 1702, and telemetry module 1708 of programmer 1504. In various examples, programmer 1504 may include one or more processors, which may include fixed function processing circuitry and/or programmable processing circuitry, as formed by, for example, one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Programmer 1504 also, in various examples, may include a memory 1711, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, a CD-ROM, comprising executable instructions for causing the one or more processors to perform the actions attributed to them. Moreover, although processor 1710 and telemetry module 1708 are described as separate modules, in some examples, processor 1710 and telemetry module 1708 may be functionally integrated with one another. In some examples, processor 1710 and telemetry module 1708 correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

[0098] Memory 1711 (e.g., a storage device) may store instructions that, when executed by processor 1710, cause processor 1710 and programmer 1504 to provide the functionality ascribed to programmer 1504 throughout this disclosure. For example, memory 1711 may include instructions that cause processor 1710 to obtain a parameter set from memory, select a spatial electrode movement pattern, provide an interface that recommends or otherwise facilitates parameter value selection, or receive a user input and send a corresponding command to IMD 1506, or instructions for any other functionality. In addition, memory 1711 may include a plurality of programs, where each program includes a parameter set that defines stimulation therapy.

[0099] User interface 1702 may include a button or keypad, lights, a speaker for voice commands, a display, such as a liquid crystal (LCD), light-emitting diode (LED), or organic light-emitting diode (OLED). In some examples the display may be a touch screen. User interface 1702 may be configured to display any information related to the delivery of stimulation therapy, identified patient behaviors, sensed patient parameter values, patient behavior criteria, or any other such information. User interface 1702 may also receive user input via user interface 1702. The input may be, for example, in the form of pressing a button on a keypad or selecting an icon from a touch screen.

[0100] Telemetry module 1708 may support wireless communication between IMD 1506 and programmer 1504 under the control of processor 1710. Telemetry module 1708 may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired connection. In some examples, telemetry module 1708 provides wireless communication via an RF or proximal inductive medium (e.g., via the transfer of inductive energy). In some examples, telemetry module 1708 includes an antenna, which may take on a variety of forms, such as an internal or external antenna. In some examples, IMD 1506 and/or programmer 104 may communicate with remote servers via one or more cloud-services in order to deliver and/or receive information between a clinic and/or programmer.

[0101] Telemetry module 1708 may transmit and/or receive information via one or more antennas and using different communication modalities. For example, telemetry module 1708 may communicate with IMD 1506, or other implanted or external devices, via the transfer of inductive energy through one or more antennas. Transmit circuit 1730 may be configured to transmit information via inductive energy transfer and receive circuit 1732 may be configured to receive information via inductive energy transfer. Transmit circuit 1730 and receive circuit 1732 may be similar to transmit circuit 236 and receive circuit 232, respectively, of recharger 110 of FIG. 2.

[0102] Examples of local wireless communication techniques that may be employed to facilitate communication between programmer 1504 and IMD 1506 include RF communication according to the 802.11 or Bluetooth specification sets or other standard or proprietary telemetry protocols. In this manner, other external devices may be capable of communicating with programmer 1504 without needing to establish a secure wireless connection. As described herein, telemetry module 1708 may be configured to transmit a spatial electrode movement pattern or other stimulation parameter values to IMD 1506 for delivery of stimulation therapy.

[0103] FIG. 18 shows an example technique for adjusting inductive energy transfer for communication based on induced stimulation. The technique of FIG. 18 will be described with respect to external programmer 1506 and IMD 1504 of FIG. 15, but the same techniques may be performed by other devices and applicable to other uses of induced energy transfer. [0104] As shown in the example of FIG. 18, processing circuitry 1710 can control transmit circuit 1730 of telemetry module 1708 to transmit information to IMD 1506 via inductive coupling (1800). For example, transmit circuit 1730 cam modulate current on a primary coil antenna to generate a magnetic field that induces current within a secondary coil antenna of IMD 1506. During transmitting of inductive energy, transmit circuit can sense the amount of loading from IMD 1506 and determine the amount of loading on the transmit circuit (1802). In some examples, processing circuitry 1710 may determine the amount of loading based on a loading signal generated by transmit circuit 1730.

[0105] Processing circuitry 1710 can then determine a parameter correlated with induced stimulation caused on one or more of leads 1514 of IMD 1506 based on the amount of loading (1804). In some examples, IMD 1506 may transmit a signal indicating the amount of loading at the secondary coil. In some examples, processing circuitry 1710 may determine the parameter based on a received signal strength indictor (RSSI), such as an RSSI value received from IMD 1506. Programmer 1504 or IMD 1506 may perform the sensing of loading or other characteristic correlated with induced stimulation prior to the transmission of data and/or on an ongoing basis during transmission of data using inductive coupling.

[0106] Processing circuitry 1710 can then control, based on the parameter correlated with induced stimulation, the power of transmit circuit 1730 to change the inductive energy used to transmit the information to IMD 1506 (1806). For example, if the parameter is higher (e.g., there is higher loading that is likely causing induced stimulation on leads 1514), processing circuitry 1710 may control transmit circuit 1730 to reduce the transmit power for the inductive energy. Processing circuitry 1710 may compare the determined parameter to a parameter threshold and adjust the inductive power in response to the parameter exceeding a parameter threshold indicative of induced stimulation (or stimulation that is undesirable for the patient). Put another way, processing circuitry 1710 and/or transmit circuit 1730 may iteratively adjust inductive energy transfer in order to provide sufficient energy to transfer data while mitigating any induced stimulation. In some examples, transmit circuit 1730 may gradually and/or iteratively increase transmit power of the inductive energy until IMD 1506 confirms that the signal is received, and then continue to transmit power at that level to reduce the likelihood of transmitting energy at an unnecessarily high level. The process of FIG. 18 may continue in a loop during inductive energy transfer to monitor energy transfer. [0107] The following examples are described herein.

[0108] Example 1. A method comprising: determining, by processing circuitry, a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjusting, by the processing circuitry and based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0109] Example 2. The method of example 1, wherein determining the parameter that correlates with the induced stimulation is based at least partially on a characterization of a relationship between the inductive energy of the external device and the induced stimulation to the one or more leads.

[0110] Example 3. The method of any of examples 1 or 2, further comprising generating a low frequency signal separate from the inductive energy; and wherein determining the parameter that correlates with the induced stimulation includes detecting the low frequency signal at the one or more leads of the implantable medical device.

[0111] Example 4. The method of example 3, wherein the implantable medical device is configured to measure a frequency range comprising the low frequency signal.

[0112] Example 5. The method of any of examples 3 or 4, further comprising: generating, by a first driver, a recharge signal; and generating, by a second driver, the low frequency signal.

[0113] Example 6. The method of any of examples 3 through 5, wherein the low frequency signal is selected to reduce aliasing into a stimulation frequency range of the implantable medical device.

[0114] Example 7. The method of any of examples 3 through 6, wherein: stimulation is provided at a stimulation frequency by the implantable medical device; and the low frequency signal is selected such that: interference between the stimulation frequency and the additional low frequency signal is reduced, or that interaction of the low frequency signal with physiological response is minimal.

[0115] Example 8. The method of any of examples 3 through 7, further comprising determining a maximum power such that the parameter that correlates with induced stimulation does not exceed the predetermined threshold; and wherein adjusting the transfer of the inductive energy comprises adjusting the inductive energy to a level that is less than the maximum power.

[0116] Example 9. The method of any of examples 1 through 8, further comprising detecting, by a sense circuit, the induced stimulation; and wherein the sense circuit has a frequency range to measure the inductive energy being induced onto the one or more leads. [0117] Example 10. The method of any of examples 1 through 9, wherein the inductive energy includes skipped pulses to create a different frequency component being induced onto the one or more leads.

[0118] Example 11. The method of any of examples 1 through 10, wherein the predetermined threshold is based at least partially on at least one of a type of the implantable medical device and a therapy delivery target location of a patient.

[0119] Example 12. The method of any of examples 1 through 11, wherein the external device comprises an implantable medical device recharger, wherein the inductive energy comprises a recharging power that charges the implantable medical device, and wherein adjusting the transfer of the inductive energy comprises the recharging power from the implantable medical device recharger.

[0120] Example 13. The method of example 12, wherein determining the parameter that correlates with the induced stimulation is based at least partially on heat.

[0121] Example 14. The method of any of examples 12 or 13, wherein determining the parameter that correlates with induced stimulation is based at least partially on modifying a recharging signal of the recharging power with a signal that is different from the recharging signal included in the recharging power and sensing by the implantable medical device the signal that is different from the recharging signal at the one or more leads.

[0122] Example 15. The method of any of examples 12 through 14, further comprising: determining a first maximum recharging power based at least partially upon the parameter that correlates with induced stimulation; determining a second maximum recharging power based at least partially upon a measured temperature; and wherein adjusting recharging power includes adjusting the recharging power based at least partially upon the first maximum recharging power and the second maximum recharging power.

[0123] Example 16. The method of example 15, wherein adjusting recharging power includes selecting the lower of the first maximum recharging power and the second maximum recharging power.

[0124] Example 17. The method of any of examples 1 through 11, wherein the external device is an external programmer, wherein the inductive energy comprises inductive communication that transmits operational information from the external device to the implantable medical device.

[0125] Example 18. A system comprising: processing circuitry configured to: determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0126] Example 19. The system of example 18, wherein determining the parameter that correlates with the induced stimulation is based at least partially on a characterization of a relationship between the inductive energy of the external device and the induced stimulation to the one or more leads.

[0127] Example 20. The system of any of examples 18 or 19, further comprising generating a low frequency signal separate from the inductive energy; and wherein determining the parameter that correlates with the induced stimulation includes detecting the low frequency signal at the one or more leads of the implantable medical device.

[0128] Example 21. The system of example 20, wherein the implantable medical device is configured to measure a frequency range comprising the low frequency signal.

[0129] Example 22. The system of any of examples 20 or 21, further comprising: generating, by a first driver, a recharge signal; and generating, by a second driver, the low frequency signal.

[0130] Example 23. The system of any of examples 20 through 22, wherein the low frequency signal is selected to reduce aliasing into a stimulation frequency range of the implantable medical device.

[0131] Example 24. The system of any of examples 20 through 23, wherein: stimulation is provided at a stimulation frequency by the implantable medical device; and the low frequency signal is selected such that: interference between the stimulation frequency and the additional low frequency signal is reduced, or that interaction of the low frequency signal with physiological response is minimal.

[0132] Example 25. The system of any of examples 20 through 24, further comprising determining a maximum power such that the parameter that correlates with induced stimulation does not exceed the predetermined threshold; and wherein adjusting the transfer of the inductive energy comprises adjusting the inductive energy to a level that is less than the maximum power.

[0133] Example 26. The system of any of examples 18 through 25, further comprising detecting, by a sense circuit, the induced stimulation; and wherein the sense circuit has a frequency range to measure the inductive energy being induced onto the one or more leads. [0134] Example 27. The system of any of examples 18 through 26, wherein the inductive energy includes skipped pulses to create a different frequency component being induced onto the one or more leads.

[0135] Example 28. The system of any of examples 18 through 27, wherein the predetermined threshold is based at least partially on at least one of a type of the implantable medical device and a therapy delivery target location of a patient.

[0136] Example 29. The system of any of examples 18 through 28, wherein the external device comprises an implantable medical device recharger, wherein the inductive energy comprises a recharging power that charges the implantable medical device, and wherein adjusting the transfer of the inductive energy comprises the recharging power from the implantable medical device recharger.

[0137] Example 30. The system of example 29, wherein determining the parameter that correlates with the induced stimulation is based at least partially on heat.

[0138] Example 31. The system of any of examples 29 or 30, wherein determining the parameter that correlates with induced stimulation is based at least partially on modifying a recharging signal of the recharging power with a signal that is different from the recharging signal included in the recharging power and sensing by the implantable medical device the signal that is different from the recharging signal at the one or more leads.

[0139] Example 32. The system of any of examples 29 through 31, further comprising: determining a first maximum recharging power based at least partially upon the parameter that correlates with induced stimulation; determining a second maximum recharging power based at least partially upon a measured temperature; and wherein adjusting recharging power includes adjusting the recharging power based at least partially upon the first maximum recharging power and the second maximum recharging power.

[0140] Example 33. The system of example 32, wherein adjusting recharging power includes selecting the lower of the first maximum recharging power and the second maximum recharging power.

[0141] Example 34. The system of any of examples 18 through 33, wherein at least one of the external device or the implantable medical device comprises at least a portion of the processing circuitry.

[0142] Example 35. The system of any of examples 18 through 34, wherein the external device is an external programmer, wherein the inductive energy comprises inductive communication that transmits operational information from the external device to the implantable medical device. [0143] Example 36. The system of any of examples 18 through 35, further comprising the external device.

[0144] Example 37. The system of any of examples 18 through 36, further comprising the implantable medical device.

[0145] Example 38. The system of any of examples 18 through 37, further comprising the one or more leads.

[0146] Example 39. A non-transitory computer-readable medium comprising instructions that, when executed by processing circuitry, causes the processing circuitry to: determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0147] Example 101. A method of controlling recharging of an implantable medical device comprising: determining a parameter that correlates with an induced stimulation at one or more leads of the implantable medical device during a transfer of recharging power from the implantable medical device recharger to charge the implantable medical device; and adjusting recharging power from the implantable medical device recharger such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0148] Example 102. The method of example 101, wherein determining the parameter that correlates with the induced stimulation is based at least partially on heat.

[0149] Example 103. The method of example 101, wherein determining the parameter that correlates with the induced stimulation is based at least partially on a characterization of a relationship between recharging power of the implantable medical device recharger and induced stimulation to the one or more leads.

[0150] Example 104. The method of example 101, further comprising generating a low frequency signal separate from the recharging power; and wherein determining the parameter that correlates with the induced stimulation includes detecting the low frequency signal at the one or more leads of the implantable medical device.

[0151] Example 105. The method of example 104, wherein the low frequency signal is within a frequency range that can be measured by the implantable medical device.

[0152] Example 106. The method of example 104, further comprising: generating, by a first driver, a recharge signal; and generating, by a second driver, the low frequency signal. [0153] Example 107. The method of example 104, wherein the low frequency signal is selected so as to reduce aliasing into a stimulation frequency range of the implantable medical device.

[0154] Example 108. The method of example 104, wherein stimulation is provided at a stimulation frequency by the implantable medical device; and wherein the low frequency signal is selected such that interference between the stimulation frequency and the additional low frequency signal is reduced or that interaction of the low frequency signal with physiological response is minimal.

[0155] Example 109. The method of example 104, further comprising determining a maximum power such that the parameter that correlates with induced stimulation does not exceed the predetermined threshold; and wherein adjusting the recharging power comprises adjusting the recharging power to a level that is less than the maximum power.

[0156] Example 110. The method of example 101, further comprising detecting, by a sense circuit, the induced stimulation; and wherein the sense circuit has a frequency range to measure the recharging power being induced onto the one or more leads.

[0157] Example 111. The method of example 101, wherein the recharging power includes skipped pulses to create a low frequency component being induced onto the one or more leads.

[0158] Example 112. The method of example 101, wherein determining the parameter that correlates with induced stimulation is based at least partially on modifying a recharging signal of the recharging power with a signal that is different from the recharging signal included in the recharging power and sensing by the implantable medical device the signal that is different from the recharging signal at the one or more leads.

[0159] Example 113. The method of example 101, further comprising: determining a first maximum recharging power based at least partially upon the parameter that correlates with induced stimulation; determining a second maximum recharging power based at least partially upon a measured temperature; and wherein adjusting recharging power includes adjusting the recharging power based at least partially upon the first maximum recharging power and the second maximum recharging power.

[0160] Example 114. The method of example 113 wherein adjusting recharging power includes selecting the lower of the first maximum recharging power and the second maximum recharging power. [0161] Example 115. The method of example 101, wherein the predetermined threshold is based at least partially on at least one of a type of the implantable medical device and a therapy delivery target location of a patient.

[0162] Example 116. A medical system comprising: an implantable medical device; an implantable medical device recharger comprising a recharging unit that outputs recharging power; wherein the implantable medical device is inductively coupled to the recharging unit; wherein the implantable medical device includes a memory and a processor, and the memory stores instructions that, when executed by the processor, cause the implantable medical device to determine a parameter that correlates with an induced stimulation at one or more leads of the implantable medical device during a transfer of recharging power from the implantable medical device recharger to charge the implantable medical device; and wherein the implantable medical device recharger includes a second memory and a second processor, and the second memory stores instructions that, when executed by the second processor, cause the recharging unit to adjust recharging power such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

[0163] Example 117. The medical system of example 116, wherein the implantable medical device determines the parameter that correlates with the induced stimulation based at least partially on heat occurring at the implantable medical device.

[0164] Example 118. The medical system of example 116, wherein the recharging power comprises a signal that is different from a recharge signal of the recharging power and that is used to determine the parameter that correlates with the induced stimulation.

[0165] Example 119. The medical system of example 116, wherein the instructions of the second memory, when executed, further causes the recharging unit to generate a low frequency signal; and wherein the implantable medical device determines the parameter that correlates with the induced stimulation by detecting the low frequency signal at the one or more leads of the implantable medical device.

[0166] Example 120. The medical system of example 116, further comprising a sense circuit; wherein the sense circuit is coupled to the implantable medical device; and wherein the sense circuit has a frequency range to measure the recharging power being induced onto the one or more leads.

[0167] Example 121. The medical system of example 116, wherein the instructions of the second memory, when executed, further causes the recharging unit to output the recharging power by skipping pulses to create an additional low frequency component within the recharging power being induced onto the one or more leads. [0168] Example 122. The medical system of example 116, wherein the implantable medical device determines the parameter that correlates with the induced stimulation based at least partially on a modified recharging signal of the recharging power and by the implantable medical device sensing the modified recharging signal at the one or more leads.

[0169] Example 123. A medical system comprising: an implantable medical device; an implantable medical lead; wherein the implantable medical device includes a transmit circuit; wherein the implantable medical device is coupled to the implantable medical lead; and wherein the implantable medical device includes a memory and a processor, and the memory stores instructions that, when executed by the processor, cause the implantable medical device to: determine a parameter that correlates with an induced stimulation into the implantable medical lead during a transfer of recharging power from an implantable medical device recharger to charge the implantable medical device; and transmit a signal representative of the parameter that correlates with the induced stimulation via the transmit circuit.

[0170] Example 124. The medical system of example 123, wherein the implantable medical device determines the parameter that correlates with the induced stimulation based at least partially on heat.

[0171] Example 125. The medical system of example 123, wherein the implantable medical device determines the parameter that correlates with the induced stimulation based at least partially on recharging power modified with a signal that is different than a recharge signal of the recharging power.

[0172] Example 126. The medical system of example 123, wherein the implantable medical device further comprises a sense circuit and determines the parameter that correlates with the induced stimulation by the sense circuit measuring an induced stimulation signal at the implantable medical lead.

[0173] Example 127. A implantable medical device recharger comprising: a memory; a processor; a recharge unit; a receiver circuit; and wherein the memory stores instructions that, when executed by the processor, cause the processor to: determine a parameter that correlates with an induced stimulation into an implantable medical lead of an implantable medical device inductively coupled to the recharge unit during a transfer of recharging power from the recharge unit to charge the implantable medical device; and adjust recharging power from the recharge unit such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold. [0174] Example 128. The implantable medical device recharger of example 127, wherein the instructions, when executed, further causes the recharge unit to generate a low frequency signal separate from the recharging power; and wherein the processor determines the parameter that correlates with induced stimulation by detecting the low frequency signal at the lead of the implantable medical device.

[0175] Example 129. The implantable medical device recharger of example 128, wherein the low frequency signal is selected such that interference between a stimulation frequency of an implantable medical device and the additional low frequency signal is reduced.

[0176] Example 130. The implantable medical device recharger of example 127, wherein the instructions, when executed, further causes the recharging unit to output the recharging power by skipping pulses to create a low frequency component within the recharging power being induced onto the lead.

[0177] Example 131. The implantable medical device recharger of example 127, wherein the instructions, when implemented, cause determination of the parameter that correlates with the induced stimulation based at least partially on heat at the implantable medical device.

[0178] Example 132. The implantable medical device recharger of example 127, wherein determining the parameter that correlates with the induced stimulation into the implantable medical lead of the implantable medical device comprises receiving an induced stimulation signal from the implantable medical device where the induced stimulation signal represents the induced stimulation.

[0179] Example 133. A method of controlling recharging of an implantable medical device comprising: determining heat induced in the implantable medical device; determining temperature of one or more portions of the implantable medical device; determining a recharging power target based upon the heat induced in the implantable medical device; determining a recharging power target based upon the temperature of the one or more portions of the implantable medical device; and adjusting recharging power from an implantable medical device recharger based upon the lowest of the recharging power target based on heat and the recharging power target based on temperature.

[0180] Example 134. The method of any of examples 101-115, further comprising stopping delivery of stimulation therapy during recharging.

[0181] Example 135. The method of any of examples 101-115, wherein adjusting recharging power further comprises: configuring the implantable medical device for bipolar stimulation when recharging; and configuring the implantable medical device for unipolar stimulation when not recharging. [0182] The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, such as fixed function processing circuitry and/or programmable processing circuitry, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit comprising hardware may also perform one or more of the techniques of this disclosure.

[0183] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0184] The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

[0185] While examples have been particularly shown and described, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: processing circuitry configured to: determine a parameter that correlates with an induced stimulation at one or more leads of an implantable medical device during a transfer of inductive energy from an external device to the implantable medical device; and adjust, based on the parameter, the transfer of the inductive energy from the external device such that the parameter that correlates with the induced stimulation does not exceed a predetermined threshold.

2. The system of claim 1, wherein determining the parameter that correlates with the induced stimulation is based at least partially on a characterization of a relationship between the inductive energy of the external device and the induced stimulation to the one or more leads.

3. The system of any of claims 1 or 2, further comprising generating a low frequency signal separate from the inductive energy; and wherein determining the parameter that correlates with the induced stimulation includes detecting the low frequency signal at the one or more leads of the implantable medical device.

4. The system of claim 3, wherein the implantable medical device is configured to measure a frequency range comprising the low frequency signal.

5. The system of any of claims 3 or 4, further comprising: generating, by a first driver, a recharge signal; and generating, by a second driver, the low frequency signal.

6. The system of any of claims 3 through 5, wherein the low frequency signal is selected to reduce aliasing into a stimulation frequency range of the implantable medical device.

7. The system of any of claims 3 through 6, wherein: stimulation is provided at a stimulation frequency by the implantable medical device; and the low frequency signal is selected such that: interference between the stimulation frequency and the additional low frequency signal is reduced, or that interaction of the low frequency signal with physiological response is minimal.

8. The system of any of claims 3 through 7, further comprising determining a maximum power such that the parameter that correlates with induced stimulation does not exceed the predetermined threshold; and wherein adjusting the transfer of the inductive energy comprises adjusting the inductive energy to a level that is less than the maximum power.

9. The system of any of claims 1 through 8, further comprising detecting, by a sense circuit, the induced stimulation; and wherein the sense circuit has a frequency range to measure the inductive energy being induced onto the one or more leads.

10. The system of any of claims 1 through 9, wherein the inductive energy includes skipped pulses to create a different frequency component being induced onto the one or more leads.

11. The system of any of claims 1 through 10, wherein the external device comprises an implantable medical device recharger, wherein the inductive energy comprises a recharging power that charges the implantable medical device, and wherein adjusting the transfer of the inductive energy comprises the recharging power from the implantable medical device recharger.

12. The system of claim 11, wherein determining the parameter that correlates with the induced stimulation is based at least partially on heat.

13. The system of any of claims 11 or 12, wherein determining the parameter that correlates with induced stimulation is based at least partially on modifying a recharging signal of the recharging power with a signal that is different from the recharging signal included in the recharging power and sensing by the implantable medical device the signal that is different from the recharging signal at the one or more leads.

14. The system of any of claims 11 through 13, further comprising: determining a first maximum recharging power based at least partially upon the parameter that correlates with induced stimulation; determining a second maximum recharging power based at least partially upon a measured temperature; and wherein adjusting recharging power includes adjusting the recharging power based at least partially upon the first maximum recharging power and the second maximum recharging power.

15. The system of any of claims 1 through 14, wherein the external device is an external programmer, wherein the inductive energy comprises inductive communication that transmits operational information from the external device to the implantable medical device.