Recharging power supply for implantable medical device

Abstract

In some examples, a medical device system includes a first implantable medical device. The first implantable medical device (IMD) can include circuitry configured to at least one of deliver therapy to a patient or sense a physiological signal from the patient; generate stimulation deliverable to the patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device. The medical device system can include processing circuitry configured to control charging of the first rechargeable power source based on a charge status of a second rechargeable power source of a second IMD.

Description

Technical Field

[0001] The present disclosure relates to medical devices, and more particularly, to systems and techniques for recharging a power source of one or more implantable medical devices. Background Art

[0002] Implantable medical devices can be used to monitor patient conditions and / or deliver therapy to patients. In chronic or long-term use, implantable medical devices may include a rechargeable power source (e.g., including one or more capacitors or batteries) that extends the operating life of the medical device by weeks, months, or even years over non-rechargeable devices.

[0003] When the energy stored in the rechargeable power source has been depleted, the patient can recharge the power source using an external charging device. Because the rechargeable power source is implanted in the patient and the charging device is external to the patient, this charging process may be referred to as transcutaneous charging. In some examples, transcutaneous charging can be performed via inductive coupling between a primary coil in the charging device and a secondary coil in the implantable medical device. When current is applied to the primary coil and the primary coil is aligned with the secondary coil, current is induced in the secondary coil in the patient's body. Therefore, the external charging device does not need to be physically connected to the rechargeable power source for charging. Summary of the Invention

[0004] This disclosure describes systems, devices, and techniques for recharging a power source for one or more medical devices. When multiple implantable medical devices receive power from an external charging device, at least one of the medical devices and / or the external charging device can manage at least one aspect of the charging process to account for differences in the charge state of each medical device. In this way, the power source of a first medical device and the power source of a second medical device can be recharged simultaneously.

[0005] For example, an external charging device can transcutaneously deliver energy to one or more rechargeable power sources of one or more corresponding IMDs. The external charging device can query each IMD regarding the power source charge state and, prior to charging, control the one or more devices with a higher charge to consume more power so that the IMDs begin charging at a similar charge state to the corresponding power source. In other examples, an IMD can directly receive communication regarding the charge state from another IMD and independently increase power consumption to equalize the power source charge state with that of the other IMD before charging. In other examples, an IMD can stop charging the power source by independently detecting a full charge state or in response to receiving a command from the external charging device, while continuing to deliver power through the external charging device. An IMD can interrupt charging the power source by disconnecting the power source from the secondary coil receiving power or configuring the circuitry to prevent current from flowing in the IMD's secondary coil or associated charging circuitry.

[0006] In one example, the present disclosure relates to a medical system that includes a first implantable medical device (IMD) comprising: a stimulation circuit system configured to generate stimulation deliverable to a patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; and a processing circuit system configured to control charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second IMD.

[0007] In another example, the present disclosure relates to a method for controlling charging of a first rechargeable power source of a first implantable medical device (IMD) within a patient, the method comprising: receiving energy from a primary coil of an external charging device via inductive coupling at a secondary coil of the first IMD; and controlling the charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second IMD by a processing circuit system.

[0008] In another example, the present disclosure is directed to a medical system that includes a first implantable medical device (IMD) including: stimulation circuitry configured to generate stimulation deliverable to a patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; and processing circuitry; a second IMD including: stimulation circuitry configured to generate stimulation deliverable to the patient; a second rechargeable power source; and a secondary coil coupled to a second rechargeable power source, the secondary coil configured to charge the second rechargeable power source via inductive coupling with a primary coil of an external charging device; the processing circuitry configured to determine a charge state of the first rechargeable power source and a charge state of the second rechargeable power source, control the first IMD to achieve a target charge state of the first rechargeable power source based on the charge state of the second rechargeable power source of the second IMD, and control energy delivery from the external charging device to the secondary coil coupled to the first rechargeable power source and the secondary coil coupled to the second rechargeable power source.

[0009] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of examples according to the disclosure will become apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a conceptual diagram illustrating an example of a medical system having multiple stimulation leads implanted in a patient's brain.

[0011] Figure 2 yes Figure 1 A block diagram of an example of an implantable medical device.

[0012] Figure 3 yes Figure 1 A block diagram of an example of an external charging device.

[0013] Figure 4 is a flow chart illustrating an example technique for controlling charging of a power source of a medical device via an external charging device.

[0014] Figure 5 is a flow chart illustrating an example technique for controlling charging of a power source of a medical device via an external charging device.

[0015] Figure 6 is a flow chart illustrating an example technique for controlling charging of a power source of a medical device via an external charging device. DETAILED DESCRIPTION

[0016] The present disclosure describes systems (e.g., including one or more devices, components, subsystems, or assemblies) and techniques (e.g., methods or processes) for recharging one or more power sources of one or more corresponding medical devices. An external charging device is configured to transmit energy to an implantable medical device (IMD), and when multiple medical devices are implanted within range of the external charging device, the medical devices can receive the energy to charge corresponding rechargeable power sources.

[0017] An IMD may include a rechargeable power source to extend the operational life of the medical device. The IMD may receive power transcutaneously from an external charging device via a wireless charging scheme (such as inductive coupling). Typically, only a single IMD is positioned within the patient to receive energy from the external charging device. In some cases, two IMDs may be positioned within the patient, but when the distance between the IMDs prevents an external charging device from delivering energy to both IMDs simultaneously, each IMD may be charged separately. However, if two or more IMDs are positioned close enough together, or otherwise close enough to an external charging device, the multiple IMDs will simultaneously receive energy from the external charging device and potentially charge their respective rechargeable power sources simultaneously. This scenario may pose challenges during the charging process. For example, if the first rechargeable power source of a first IMD (e.g., "IMD1") reaches a fully charged state before the second rechargeable power source from a second IMD (e.g., "IMD2"), the first IMD may need to process the additional charging current as heat and potentially expose surrounding tissue to undesirable heat. Any examples described herein with reference to “IMD” or “IMD1 ” may also apply to IMD2 or both IMD1 and IMD2 .

[0018] As described herein, one or more devices can operate during charging to reduce the temperature of the IMD and / or provide more efficient recharging when multiple IMDs are inductively coupled to the same external charging device. As discussed above, multiple medical devices (e.g., two IMDs, such as two neurostimulators) can be implanted proximate to one another or disposed outside a patient’s body such that both devices receive recharging energy from a common primary coil. When energy is transmitted via inductive coupling, for example, the secondary coils will subsequently be inductively coupled to the primary coil of the external charging device. In other words, the magnetic field of the primary coil will induce a current in the two respective secondary coils of the IMDs. By using the techniques described herein, the external charging device and the IMDs can safely charge the respective power sources of the multiple devices. For example, these techniques can reduce overheating of the IMDs and, thus, undesirable heating of tissue surrounding the devices. In examples, by using the techniques described herein, multiple power sources of multiple medical devices can be charged more efficiently (e.g., faster) while increasing safety for the patient (e.g., better monitoring of the IMDs or tissue temperature). Examples of the techniques described herein include controlling charging of a first power source of a first IMD while still applying full power from the charging device and preventing overheating of tissue proximate to the first and second IMDs when a second power source of a second IMD is proximate to a target state of charge (e.g., charging complete, fully charged, or another desired or appropriate state of charge).

[0019] In examples, two IMDs can be close enough to one another such that charging energy from the charging device reaches both devices. In other words, the recharging circuitry of both IMDs can receive charging energy from the charging device at the same time. In such cases, the primary coil of the charging device can couple with both respective secondary coils of the two IMDs. In some instances, each IMD can receive a different amount of charging energy. Simultaneous charging of multiple IMDs can reduce the amount of time required to charge all of the IMDs of a patient relative to charging each of the multiple IMDs separately and independently of one another. For example, the system can be configured to monitor how each IMD is being charged to manage excess heat. In some examples, one or more of the IMDs can individually manage the charging process to avoid overcharging or heating when multiple IMDs are being charged simultaneously. In other examples, one or more of the IMDs can receive communications from other IMDs regarding the respective state of charge of the power sources and control charging of the power sources based on the state of charge of the other IMDs. In other examples, the external charging device can receive information from the IMDs and control the charging power and / or transmit instructions to one or more of the IMDs to take actions to reduce the state of charge of one or more power sources, reduce the rate of charging of one or more power sources, and / or terminate charging of one or more power sources. In this way, one or more devices of the system can communicate to coordinate charging among all of the affected IMDs.

[0020] In one example, a medical system includes processing circuitry configured to determine a charge state of a first rechargeable power source of a first IMD (e.g., “IMD1”) and / or determine a charge state of a second rechargeable power source of a second IMD (e.g., “IMD2”). IMD1 and IMD2 can be structurally identical or have different components or different capabilities. IMD1 and IMD2 can be configured to provide the same therapy, different therapies, or even provide different functions such as therapy delivery or monitoring services. Although described with reference to IMD1 and IMD2, the systems and techniques can also apply to more than two devices (e.g., three or more medical devices). In some examples, IMD1 and IMD2 can communicate with each other via communication circuitry. The communication circuitry can use wireless telemetry to transmit and / or receive information. For example, each IMD can be configured for bidirectional communication, or in other examples, different IMDs can be configured to only transmit or only receive information. Each IMD in the system can communicate with one or more other devices such as an external charging device or a programmer device. Any one device or combination of devices described herein can implement the techniques described herein. In one example, IMD1 can include processing circuitry configured to control charging of one or more devices (e.g., including IMD1). In another example, an external charging device can include processing circuitry configured to control charging of one or more devices.

[0021] Generally, the processing circuitry can control charging of the IMDs prior to a recharge session or during a recharge session. In this way, processing circuitry within one or more of the IMDs in the patient, processing circuitry of an external charger, or some combination thereof can control aspects of delivering charging power to the IMDs, such as when to charge and at what power level to charge. Because the charge states of the respective power sources of IMD1 and IMD2 can be unbalanced, for example, the processing circuitry can control one or both IMDs to balance the respective charge states prior to a recharge session or during a recharge session. Balancing the charge states of the IMDs can reduce the likelihood that one of the IMDs reaches a fully charged state before the other. In this disclosure, the charge state of a power source can also be referred to as the charge state of an IMD because each IMD can include a respective power source.

[0022] In one example, before a recharge session, if IMD1 has a higher state of charge than IMD2, processing circuitry within IMD1, IMD2, and / or an external charging device can control IMD1 to increase its power consumption until the state of charge of IMD1 is balanced with that of IMD2 (e.g., equal, substantially equal, or within a tolerance of being equal). Once the states of charge are balanced, the external charging device can begin delivering power to IMD1 and IMD2 during the recharge session. In some examples, the external charger can withhold charging during the recharge session until the states of charge of IMD1 and IMD2 are balanced, and then begin or continue charging during the recharge session until each IMD has reached a target state of charge. In some examples, an IMD can increase its power consumption by activating a power-consuming feature, where the power-consuming feature may not affect the therapeutic or monitoring functions provided by the IMD. Examples of power-consuming features that can be initiated to consume power include: activating wireless telemetry circuitry, executing one or more programs by the processing circuitry of the IMD, and / or shunting energy from a power source through a resistive load. IMD 1 may increase its power consumption in these or other ways and, thereby, reduce the state of charge of the power source. The command instructing IMD 1 to consume additional power may be sent from processing circuitry within IMD 1, from processing circuitry within another IMD (such as IMD 2), or from processing circuitry within an external charging device. In some examples, control of IMD 1 may be shared or distributed among multiple devices.

[0023] In addition to or as an alternative to initial power consumption by IMDs having a higher state of charge, a system of multiple IMDs receiving recharging power can use other strategies to control the state of charge of the IMDs. For example, during a recharging session, if IMD1 will reach or is expected to reach a target state of charge (e.g., fully charged) before IMD2’s target state of charge, IMD1 can reduce the amount of recharging current reaching its power source. In this way, IMD1’s power source can receive relatively less recharging energy (or none at all), while IMD2 continues to receive recharging energy from the same external charging device. IMD 1 can reduce the amount of recharging energy reaching IMD1’s power source for a desired amount of time or until the state of charge of the respective power sources of IMD1 and IMD2 are balanced, such as described herein. In one example, IMD1 can reduce the amount of recharging current reaching IMD1’s power source by detuning the circuitry of IMD1’s secondary coil in which current is induced by the external charging device. In some examples, detuning the circuitry of the coil is performed as described in U.S. Patent No. 9,042,995 (e.g., “opening a tuning switch”). In another example, IMD1 can disable IMD1’s self-tuning oscillator to reduce or prevent current from reaching the power source. In another example, IMD1 can shunt recharging energy through a load (e.g., a resistive load) other than the first power source (e.g., other than a battery) to convert the undesired current into heat rather than power stored in the power source.

[0024] In examples in which the charging circuitry of the secondary coil is detuned, less energy can be transferred from the primary coil in the external charging device to the secondary coil of IMD 1. However, this detuning of the charging circuitry can result in a smaller current and lower heat generation compared to the normal tuning of the charging circuitry that is intended to generate a higher current for charging the rechargeable power source. In one example, detuning the charging circuitry of IMD 1 can include changing the resonant frequency of an oscillating circuit, where the oscillating circuit includes the secondary coil of IMD 1. The charging circuitry can include the oscillating circuit and other circuits such as rectification circuitry and / or filtering circuitry. By detuning the resonant frequency of the oscillating circuit and changing it to be different from the frequency from the external primary coil, a smaller current can be generated in the secondary coil that will be used to charge the rechargeable power source. In other examples, IMD 1 can include a self-tuning oscillator coupled across the oscillating circuit. IMD 1 can detune the oscillating circuit by disabling the self-tuning oscillator, such as switching the self-tuning oscillator out of the oscillating circuit. In other examples, IMD 1 can detune the rectifier circuit to detune the charging circuitry and reduce the amount of direct current (DC) generated in IMD 1 from alternating current (AC) power provided by the external charging device. For example, IMD 1 can switch from full-wave rectification to half-wave rectification to detune the rectifier circuit.

[0025] In some examples, the charging device communicates a command instructing IMD 1 to open a circuit coupled to or as part of the secondary coil. In other examples, IMD 1 can proactively open the circuit coupled to or as part of the secondary coil. IMD 1 can communicate with the charging device 20 to inform the charging device 20 that IMD 1 has opened the circuit that prevents charging of the power source of IMD 1. By creating an open circuit associated with the secondary coil, the energy applied by the external primary coil can not induce a current in the secondary coil. The communicated command can also instruct an associated timer to start in response to opening the circuit. For example, the command can instruct IMD 1 to open the circuit associated with the secondary coil and start a countdown for IMD 1 in which the circuit remains open. In some examples, the charging device can also track the countdown. Once the countdown of the timer expires, IMD 1 can close the circuit and re-enable charging using the secondary coil, or the charging device can again request that IMD 1 open the circuitry associated with the secondary coil of IMD 1 if the charge status of IMD 1 remains greater than the charge status of IMD 2. The processing circuitry of the medical system can be configured to control one or more of these steps. In one example, a relay or solid state switch can be included in the IMD to control opening and closing the circuit associated with the secondary coil.

[0026] In some examples, the systems and techniques described herein may utilize thermal modeling or monitoring. For example, an IMD may include a temperature sensor that transmits data representing the temperature to processing circuitry, such as described further below. The processing circuitry of the IMD may thus receive a temperature signal from the temperature sensor or from multiple temperature sensors. The processing circuitry may determine a thermal model of the IMD and / or surrounding tissue based on one or more temperature signals. In other examples, the IMD or other device may generate a thermal dose (e.g., energy delivered over a period of time) to be delivered to the patient's tissue based on the temperature signals and / or the known power output by an external charging device. These temperature signals may be generated by one or more temperature sensors of the IMD. In some examples, the processing circuitry may track the temperature of the device or surrounding tissue over time based on the one or more temperature signals, thereby monitoring the thermal state of the IMD and / or tissue surrounding the IMD. This thermal modeling or monitoring may enable the IMDs and / or external devices described herein to further reduce the likelihood that an implanted device will deliver excessive heat to a patient. The systems and techniques described herein may enable charging of multiple IMDs while receiving power from a single external charging device, while avoiding overcharging one of the IMDs (which could result in excessive heat exposure to surrounding tissue). For example, a charging device can deliver a relatively high charging power, which can result in a faster IMD charging rate because IMD1 can decouple from the charging energy (e.g., due to a certain charge state or temperature state), while IMD2 remains coupled to continue charging. In this way, the IMDs can determine whether to reduce charging or continue charging based on the temperature information and charge state of the power supply in the IMDs. This ability to adjust how and / or when each IMD receives power can reduce the need for the external charging device to reduce charging power due to one of the IMDs reaching a fully charged state before other IMDs receiving power from the same external charging device.

[0027] Although descriptions of charging (also referred to as "recharging") an IMD may refer to charging an implantable neurostimulator, the systems and techniques described herein may be used with other types of medical devices or systems. For example, the devices, systems, and techniques described herein may be used with systems including medical devices that deliver electrical stimulation therapy to a patient's heart (e.g., pacemakers and pacemaker-cardioverter-defibrillators), drug pumps, monitoring devices, or other therapeutic, monitoring, or diagnostic devices.

[0028] While the present disclosure generally describes examples of deep brain stimulation, features and techniques of the systems and techniques described herein can be used to deliver other types of electrical stimulation therapies (e.g., spinal cord stimulation, peripheral nerve stimulation, sacral nerve stimulation, pelvic nerve stimulation, gastric nerve stimulation, or vagus nerve stimulation), stimulation of at least one muscle or muscle group, stimulation of at least one organ such as gastric system stimulation, stimulation accompanying gene therapy, and generally stimulation of any tissue of a patient. In examples, the techniques described herein can be used with any system that includes multiple rechargeable power sources that can be charged from a single or common charging device.

[0029] Figure 1 is a conceptual diagram illustrating an example of a medical system 10 including a plurality of stimulation leads 15A and 15B configured to be implanted in the brain 18 of a patient 12. Figure 1 In an example, medical system 10 includes a charging device 20 configured to deliver energy to one or more implantable medical devices (IMDs) 14A and 14B, such as via inductive coupling. For ease of description, IMD 14A and IMD 14B may be collectively referred to as "IMD 14." Similarly, for ease of description of two example IMDs, IMD 14A may be referred to as "IMD1" and IMD 14B may be referred to as "IMD2." In an example, IMD 14 may be at least partially implanted within patient 12 or completely implanted within patient 12. IMD 14 may include or be coupled to corresponding leads (e.g., lead 15A coupled to IMD 14A, and lead 15B coupled to IMD 14B). One or more electrodes of leads 15A and leads 15B are configured to provide electrical signals (e.g., pulses or analog signals) to surrounding anatomical regions of brain 18 in treatment to alleviate a condition of patient 12. In some examples, one or both of IMDs 14 may be coupled to more than one lead implanted in brain 18 of patient 12 to stimulate multiple anatomical regions of the brain. Figure 1 As shown, system 10 may include two IMDs 14, each including leads. However, in other examples, more than two IMDs may be positioned within patient 12.

[0030] Deep brain stimulation (DBS) delivered by one or both of IMDs 14 can be used to treat dysregulated neuronal activity in the brain that manifests as a disease or condition such as Huntington’s disease, Parkinson’s disease, or a movement disorder. Certain anatomical regions of the brain 18 can be responsible for producing symptoms of such brain conditions. As one example, stimulating an anatomical region in the brain 18 such as the substantia nigra can reduce the number and / or amplitude of tremors experienced by the patient 12. Other anatomical regions that can be receptive to stimulation therapy can include the subthalamic nucleus, the medial globus pallidus, the ventral intermediate body, and the zona inserta. During pre-operative planning and lead implantation, the clinician targets anatomical regions such as these. In other words, the clinician can attempt to position the lead 15A and the lead 15B as close as possible to these regions for DBS therapy.

[0031] A typical DBS lead includes one or more electrodes placed along the longitudinal axis of the lead, such as can be seen on the lead 15A and the lead 15B. In one example, each electrode can be a ring electrode that resides at one axial location on the lead along the entire circumference of the lead. Thus, current from a ring electrode propagates in all directions from the active electrode. The resulting stimulation field reaches anatomical regions of the brain 18 within some distance of the lead in all directions.

[0032] In other examples, the lead 15A or the lead 15B can have a complex electrode array geometry. A complex electrode array geometry includes multiple electrodes positioned at different axial locations along the longitudinal axis of the lead and multiple electrodes positioned at different angular locations around the circumference of the lead, which can be referred to as electrode segments. In some examples, the present disclosure can be applicable to leads with all ring electrodes, or a combination of one or more ring electrodes and electrode segments at different axial and angular locations around the circumference of the lead. In this way, electrodes can be selected along the longitudinal axis of the lead 15A and the lead 15B and along the circumference of the lead. A complex electrode array geometry can allow for activation of a subset of the electrodes of the lead 15A and the lead 15B to produce a customizable stimulation field that can be directed to a particular side of the lead 15A or the lead 15B in order to isolate the stimulation field around a target anatomical region of the brain 18.

[0033] The IMD 14 can be implanted on the skull 16, such as Figure 1 The IMD 14 can be positioned at other locations on the skull 16, such as Figure 1The shown are closer together or farther apart. The precise placement of IMD 14 can be determined to allow lead 15 A and lead 15B to be implanted at desired locations within respective hemispheres of brain 18. In examples, IMD 14 can be positioned at least partially within respective holes or notches of skull 16. In examples, IMD 14 can be implanted at other locations within patient 12. For example, one or more IMDs 14 can be implanted in the heart of patient 12 or within the thoracic space of patient 12. Regardless of the location of IMD 14, leads 15A and 15B can be connected to respective IMDs 14A and 14B, and the distal ends of each of leads 15A and 15B can be disposed through a drill hole in skull 16 and implanted at selected predetermined locations within brain 18 to deliver DBS or to monitor brain activity.

[0034] Medical system 10 can also include multiple leads or electrodes on other shapes and sizes of leads. In some DBS patients, two leads are implanted at symmetric locations within brain 18 for bilateral stimulation to respective hemispheres. Specifically, a first lead is placed in the right hemisphere of brain 18 and a second lead is placed at a mirror image location within the left hemisphere of the brain. Programmer 19 can receive input from a clinician defining a desired stimulation field for the first lead, and programmer 19 can generate a mirror image field for the second lead, for example. The clinician can input fine adjustments to programmer 19 to finely adjust either stimulation field to accommodate slight anatomical regional differences between the left and right hemispheres of brain 18.

[0035] Although lead 15A and lead 15B are described as being used in DBS applications as examples throughout this disclosure, lead 15A and lead 15B or other leads can be implanted at any other location within patient 12. For example, lead 15A or lead 15B can be implanted near the spinal cord, pudendal nerve, sacral nerve, or any other nerve or muscle tissue that can be stimulated, with IMDs also implanted away from skull 16 in these examples.

[0036] The medical system 10 may include an external programmer 19, which may be a handheld device, a portable computer, or a workstation that provides a user interface to the clinician. The user interface may include a display to present information to the user. Typically, the user can interact with the user interface. In an example, the processing circuit system may provide information to the user interface (e.g., a signal corresponding to the charging status of one or more power supplies). In some examples, the user interface includes a keyboard, a keypad, a touch screen, a mouse, etc. for receiving input from the user. The user interface may include a light or a speaker that can be used to provide an indication or alarm to the user. For example, if the temperature sensor senses a temperature of the IMD that meets the maximum limit, the processing circuit system described herein can control the user interface to initiate a flashing light or an audible sound to alert the clinician of the information or other relevant information.

[0037] The clinician can interact with the user interface to program stimulation parameters. The clinician can also interact with the user interface to manually select and program certain electrodes of lead 15A or lead 15B and use the anatomical region as a guide to adjust the resulting stimulation field, or to limit one or more stimulation fields to affect only the anatomical region of interest. In an example, the clinician can interact with the user interface to determine the charge state of the rechargeable power supply of IMD 14. For example, the charge state can be presented as a percentage or a numerical value, a visual representation such as a symbol, or as an alert (e.g., a recharge indicator).

[0038] Medical system 10 may provide the clinician with additional tools that allow the clinician to program charging device 20 , IMD 14A, or IMD 14B. Figure 1 A communication link is shown between charging device 20 and programmer 19. The communication link can represent a wired connection or a wireless connection. In some examples, the communication link represents telemetry, as further described herein. Although not shown, any device of medical system 10 can be configured to communicate with any other device of medical system 10. For example, external programmer 19 can be configured to communicate with IMD 14A, IMD 14B, and / or charging device 20. For example, charging device 20 can be configured to communicate with IMD 14A, IMD 14B, and programmer 19.

[0039] In some examples, the techniques described herein can be performed by one or more devices. In one example, the processing circuitry described herein for controlling the charging of IMD 14 can be within programmer 19 or within charging device 20. In another example, more than one device in medical system 10 includes processing circuitry configured to perform the techniques described herein. In another example, IMD 14A includes processing circuitry configured to perform the techniques described herein. Because two or more devices in medical system 10 can communicate, medical system 10 can utilize multiple devices to perform portions of the processing and control for charging IMD 14.

[0040] Medical system 10 may include a charging device 20 configured to deliver power to each of IMDs 14 for recharging a power source within each IMD. Typically, IMDs 14 may include a power source (e.g., a rechargeable power source). The power source may include a rechargeable battery and / or a capacitor. The power source may be coupled to a coil (e.g., a secondary coil), such as via charging circuitry. The secondary coil may be connected to a primary coil 48 (e.g., a secondary coil) of charging device 20. Figure 3 14). Charging device 20 can inductively deliver energy, such as through the skin of patient 12 or other tissue or anatomical structures, to recharge the power source of IMD 14. When IMD 14 is implanted in patient 12, charging device 20 can be used to recharge one or more rechargeable power sources of IMD 14. Charging device 20 can be a handheld device, a portable device, or a stationary charging system. In any case, charging device 20 may include the components necessary to charge one or more rechargeable power sources through the tissue of patient 12. In other examples, charging device 20 may include an external programmer (e.g., programmer 19) or other device configured to perform additional functions. For example, when implemented as an external programmer, charging device 20 can transmit programming commands to IMD 14 in addition to charging the rechargeable power sources. In another example, charging device 20 can communicate with IMD 14 to transmit or receive information related to the charging of the rechargeable power sources. For example, IMD 14A and IMD 14B can transmit temperature information or charge status information of their respective rechargeable power sources. Other information may include information related to, for example, the rate of charge consumption during use, or any other information relevant to power consumption and recharging of IMD 14 .

[0041] Charging device 20 and IMD 14 can utilize any wireless power transfer technology capable of recharging the rechargeable power source of IMD 14 while IMD 14 is implanted in patient 14. In one example, medical system 10 can utilize inductive coupling between a coil of charging device 20 and a corresponding coil of IMD 14A or IMD 14B coupled to the corresponding rechargeable power source. In inductive coupling, charging device 20 is placed near implanted IMD 14 so that the primary coil of charging device 20 is aligned with (e.g., positioned above) the secondary coil of IMD 14A, IMD 14B, or both. Charging device 20 can then generate a current in the primary coil based on the power level selected for charging the rechargeable power source. The current in the primary coil creates a magnetic field that, when the primary and secondary coils are aligned, induces a current in the secondary coil within one or both of IMDs 14. The primary coil can generate electromagnetic energy (e.g., radio frequency (RF) energy) that is received by the secondary coil depending on the distance and alignment from the primary coil. Because the secondary coil is associated with and electrically coupled to the rechargeable power source, the induced current can be used to increase the voltage or charge level of the rechargeable power source. Although inductive coupling is generally described herein, any type of wireless energy transfer can be used to charge one or more rechargeable power sources.

[0042] like Figure 1 As shown, IMDs 14 may need to be placed on skull 16 in a position where each of leads 15 can reach the appropriate target stimulation site within brain 18. However, this may result in IMDs 14 being too close together for charging device 20 to charge only one at a time. In other words, the electric field generated by the primary coil of charging device 20, which is used to charge the power source of IMD 14A, may also induce at least some current in the secondary coil of IMD 14B. This arrangement offers the benefit that a single charging device 20 can be used to charge both IMDs 14. However, simultaneously charging two separate IMDs can present challenges with regard to adequate charging rates for each IMD and the cessation of energy delivery if one IMD is fully charged and the other still requires more charging. While IMDs 14 may include mechanisms for diverting excess current from a fully charged power source to a resistor or other device for heat dissipation, the heat generated in one IMD to remove the excess current while the other IMD is also receiving charging energy may result in undesirable patient temperatures.

[0043] As described herein, system 10 can employ one or more mechanisms for enabling the recharging of multiple IMDs using a single charging device. For example, charging device 20 can control the higher-powered IMD to reduce the residual charge to create approximately equal charge levels for both IMDs 14. As a result, each IMD 14 can be fully charged and reach full charge at approximately the same time. In other examples, the IMD that reaches full charge first can be detuned or even have its charging circuitry open circuited to reduce or stop the current generated in the secondary coil and delivered to the rechargeable power source. In this way, IMDs still needing additional charging can continue to receive charging power without causing excessive heat to be generated by the IMD with the already fully charged rechargeable power source.

[0044] Figure 2 is a block diagram illustrating example components of IMD 14. IMD 14 may correspond to IMD 14A, IMD 14B, or other medical devices. Figure 2 In the example shown, IMD 14 includes processing circuitry 22, power source 24 (e.g., a rechargeable power source), charging circuitry 26, coil 28 (also referred to as secondary coil 28), temperature sensor 30, memory 32, stimulation circuitry 34, communication circuitry 36, and timer circuitry 38. In other examples, IMD 14 may include a greater or lesser number of components.

[0045] In general, IMD 14 may include any suitable arrangement of hardware, alone or in combination with software and / or firmware, for performing the various techniques described herein as being attributed to IMD 14 or processing circuitry 22. In various examples, IMD 14 may include one or more processors (e.g., processing circuitry 22), such as 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 combination of such components. In various examples, IMD 14 may also include memory 32, such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, that includes executable instructions for causing one or more processors (e.g., processing circuitry) to perform the actions attributed thereto. Furthermore, while processing circuitry 22, stimulation circuitry 34, charging circuitry 26, and communication circuitry 36 are described as separate, in some examples, processing circuitry 22, stimulation circuitry 34, charging circuitry 26, and communication circuitry 36 are physically and / or functionally integrated. In some examples, processing circuitry 22, stimulation circuitry 34, charging circuitry 26, and communication circuitry 36 correspond to respective hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

[0046] Memory 32 may be configured to store therapy programs or other instructions specifying therapy parameters for therapy deliverable by stimulation circuitry 34 and IMD 14. In some examples, memory 32 may also store temperature data from temperature sensor 30, temperature thresholds, instructions for rechargeable power source 24, circuit models, open-circuit voltage models, tissue models, thresholds, instructions for communication between IMD 14 and programmer 19 or charging device 20, or any other instructions necessary to perform tasks attributed to IMD 14. In this manner, memory 32 may be configured to store the charge state of one or more rechargeable power sources. Processing circuitry 22 may be configured to determine whether an IMD (e.g., IMD 14) has a higher or lower charge state than another IMD by comparing the two charge states. In response to this comparison, processing circuitry 22 may control charging circuitry 26 of the higher-charged IMD, for example, to open circuits in charging circuitry 26 until processing circuitry 22 determines that the two IMDs have similar charge states or are within an appropriate threshold of each other.

[0047] In general, stimulation circuitry 34 can be configured to generate and deliver electrical stimulation under the control of processing circuitry 22. In some examples, processing circuitry 22 controls stimulation circuitry 34 by accessing memory 32 to selectively access at least one of the stimulation programs and load it to stimulation circuitry 34. For example, in operation, processing circuitry 22 can access memory 32 to load one of the stimulation programs to stimulation circuitry 34. In such examples, the relevant stimulation parameters can include voltage amplitude, current amplitude, pulse rate, pulse width, duty cycle, or a combination of electrodes 17A, 17B, 17C, and 17D (or fewer or more electrodes) used by stimulation circuitry 34 to deliver an electrical stimulation signal. Although stimulation circuitry 34 can be configured to generate and deliver electrical stimulation therapy via one or more of electrodes 17A, 17B, 17C, and 17D of a lead (e.g., lead 15A or lead 15B), stimulation circuitry 34 can be configured for providing different therapies to patient 12. For example, stimulation circuitry 34 can be configured for delivering a drug delivery therapy via a catheter. These and other therapies can be provided by IMD 14. In this way, stimulation circuitry 34 can be an example of a therapy model configured to generate and / or deliver a therapy such as electrical stimulation or a drug therapy. In examples in which IMD 14 delivers a drug to patient 12, the therapy model can include a drug pump. In some examples, stimulation circuitry 34 can also be configured to sense a physiological signal from brain or any other tissue of patient 12 (e.g., an electrical signal from the brain such as an electroencephalogram (EEG) or an electrocorticogram (ECoG), an electrical signal from other tissue, pressure, temperature, tissue chemistry, etc.). In some examples, in addition to stimulation circuitry 34, IMD 14 can include sensing circuitry configured to sense one or more physiological signals from patient 12 and generate electrical signal representations of the one or more physiological signals.

[0048] IMD 14 also includes components configured to receive power from charging device 20 to recharge power source 24, such as when power source 24 has been at least partially depleted. As shown, IMD 14 includes secondary coil 28 and charging circuitry 26 coupled to power source 24. Charging circuitry 26 can be configured to charge power source 24 using power received from external charging device 20. In some examples, power generated by external charging device 20 is generated according to a selected power level determined by processing circuitry 22 or charging device 20. Although processing circuitry 22 can provide some commands to charging circuitry 26 in some examples, processing circuitry 22 can not need to control any aspects of recharging in other examples. Figure 2

[0049] ​The secondary coil 28 can include a coil of wire or other device in which a current can be induced via inductive coupling with a primary coil disposed external to the patient 12. Although the secondary coil 28 is shown as a single loop in Figure 2 FIG. 1, the secondary coil 28 can include multiple turns of wire. The secondary coil 28 can include a winding of wire configured such that a current can be induced within the secondary coil 28 from a magnetic field generated by an external primary coil. The induced current can then be used by the IMD 14 to recharge the power source 24. In this way, a current can be induced in the secondary coil 28 associated with the power source 24. The induction of current can be caused by a magnetic field generated by a current in the primary coil of the charging device 20 and based on the selected power level. The coupling between the secondary coil 28 and the primary coil of the charging device 20 can depend on the alignment of the two coils. Generally, the coupling efficiency increases when the two coils share a common axis and are in close proximity to one another.

[0050] Although inductive coupling is generally described as a method for recharging the power source 24, other wireless energy transfer techniques can additionally or alternatively be used. Any of these techniques can generate heat in the IMD 14 that can be monitored, e.g., by the temperature sensor 30.

[0051] The charging circuitry 26 can include one or more circuits that filter and / or transform the electrical signal induced in the secondary coil into an electrical signal that can be used to recharge the power source 24. For example, in alternating current induction, the charging circuitry 26 can include a half-wave rectifier circuit and / or a full-wave rectifier circuit configured to convert the alternating current from the induction into direct current for the power source 24. Full-wave rectifier circuits can be more efficient in converting the induced energy for the power source 24. However, half-wave rectifier circuits can be used to store energy in the power source 24 at a slower rate. In some examples, the charging circuitry 26 can include both a full-wave rectifier circuit and a half-wave rectifier circuit, thereby enabling the charging circuitry 26 to switch between each circuit to control the rate of charging of the power source 24 and the temperature of the IMD 14. As discussed above, the charging circuitry 26 can be detuned by changing the rectifier circuitry from full-wave rectification to half-wave rectification to reduce the amount of DC power sent to the power source 24.

[0052] In some examples, charging circuitry 26 may include an oscillating circuit that may include a secondary coil 28. The oscillating circuit may be tuned to an external primary coil to generate current for charging power source 24. However, in some cases, IMD 14 may include circuitry configured to change the resonant frequency of the oscillating circuit or tune the oscillating circuit as needed. The resonant frequency of the oscillating circuit may be altered by variable reactance provided by a variable capacitor. For example, IMD 14 may include a tuning switch that receives a control signal from processing circuitry 22 to change state and ultimately change the reactance of the oscillating circuit including secondary coil 28. The tuning switch may be opened or closed to remove or add a capacitor in parallel with a hardwired capacitor in series with secondary coil 28. In this way, the tuning switch may tune the oscillating circuit for recharging or tune the oscillating circuit to a resonant frequency different from the recharging frequency to provide power management by reducing the power received during recharging (e.g., detuning the oscillating circuit). Other types of circuitry may also be used by charging circuitry 26 in order to detune coil 28 and vary the current generated by coil 28 from the power output by the external primary coil.

[0053] In other examples, IMD 1 may include an autotuning oscillator coupled to both ends of the tank circuit. For example, an oscillator, such as a sinusoidal power amplifier, may be coupled to the tank circuit to drive the tank circuit at a target frequency for inductive coupling with primary coil 48 of charging device 20. Processing circuitry 22 may detune the tank circuit by disabling the autotuning oscillator, such as by switching the autotuning oscillator out of the tank circuit when less charging current is desired to be induced by the secondary coil. In some examples, disabling the autotuning oscillator may not reduce the power generated in IMD 1 as much as adding or removing capacitors, as discussed above.

[0054] In some examples, charging circuitry 26 may include measurement circuitry (e.g., a coulomb counter) configured to measure the current and / or voltage induced in IMD 14 during inductive coupling. This measurement may be used to measure or calculate the power delivered from charging device 20 to power source 24 of IMD 14. In some examples, charging circuitry 26 or other circuitry may include an electrometer, a fuel gauge, or a coulomb counter that may measure the charging current applied to power source 24 and communicate the charging current to processing circuitry 22. In some examples, processing circuitry 22 may control charging circuitry 26 to open the circuit of charging circuitry 26 to prevent electrical induction and / or detune coil 28 of IMD 14, thereby generating less power from charging device 20.

[0055] Power supply 24 may include one or more capacitors, batteries, and / or other energy storage devices. Power supply 24 may then deliver operating power to the components of IMD 14. In some examples, power supply 24 may include power generation circuitry for generating the operating power. Power supply 24 may be configured to operate through hundreds or thousands of discharge and recharge cycles. Power supply 24 may also be configured to provide operating power to IMD 14 during the recharging process. In some examples, power supply 24 may be constructed of materials that reduce the amount of heat generated during charging. In other examples, IMD 14 may be constructed of materials that help dissipate heat generated by power supply 24, charging circuitry 26, and / or secondary coil 28 over a larger surface area of ​​the housing of IMD 14.

[0056] Although power source 24, charging circuitry 26, and secondary coil 28 are shown as being contained within the housing of IMD 14, at least one of these components may be disposed outside the housing. For example, secondary coil 28 may be disposed outside the housing of IMD 14 to facilitate better coupling between secondary coil 28 and the primary coil of charging device 20. These different configurations of IMD 14 components may allow IMD 14 to be implanted in different anatomical spaces or facilitate better inductive coupling alignment between the primary and secondary coils.

[0057] IMD 14 may also include a temperature sensor 30. Temperature sensor 30 may include one or more temperature sensors (e.g., thermocouples or thermistors) configured to measure the temperature of IMD 14. Temperature sensor 30 may be disposed within the housing of IMD 14, in contact with the housing, formed as a part of the housing, or disposed externally to the housing. Temperature sensor 30 is positioned within the IMD and may sense the internal temperature of the IMD. In an example, temperature sensor 30 may sense the temperature of the housing of the IMD. In other examples, temperature sensor 30 may be positioned on the housing of the IMD and may sense the temperature of tissue surrounding the IMD. In some examples, multiple temperature sensors may be positioned on or within the IMD.

[0058] As described herein, temperature sensor 30 can be used to directly measure the temperature of IMD 14 and / or the temperature of tissue surrounding and / or in contact with the housing of IMD 14. Processing circuitry 22 or charging device 20 can use this temperature measurement as the tissue temperature to determine a temperature model of IMD 14 or a temperature model of tissue surrounding IMD 14. Although a single temperature sensor can be sufficient, multiple temperature sensors can provide a better temperature gradient or average temperature of IMD 14. Various temperatures of IMD 14 can also be modeled. Although processing circuitry 22 can continuously measure the temperature using temperature sensor 30, processing circuitry 22 can conserve energy by measuring the temperature only during recharging sessions. Further, the temperature can be sampled at a rate to determine sufficient temperature measurements or a model, but the sampling rate can be reduced to conserve power when appropriate.

[0059] Processing circuitry 22 can also use communication circuitry 36 to control the exchange of information with charging device 20 and / or an external programmer. Communication circuitry 36 can be configured to wirelessly communicate using a radio frequency protocol or an inductive communication protocol. For example, communication circuitry 36 can include one or more antennas configured to communicate with external device 20. Processing circuitry 22 can transmit operational information and receive therapy programs or therapy parameter adjustments via communication circuitry 36. Also, in some examples, IMD 14 can communicate with other implanted devices, such as stimulators, control devices, or sensors, via communication circuitry 36. Additionally, communication circuitry 36 can be configured to transmit, for example, measured tissue temperatures from temperature sensor 30, a charge state of power source 24 (e.g., a respective charge state from each of the power sources associated with IMD 14A and IMD 14B). The communication circuitry of each of IMD 14A and IMD 14B can communicate information (e.g., power source charge state information) to each other and to other devices, such as programmer 19, charging device 20, or others. In some examples, the tissue temperature can be measured proximate to power source 24.

[0060] In other examples, processing circuitry 22 can transmit additional information related to the operation of power source 24 to charging device 20. For example, charging circuitry 22 can use communication circuitry 36 to transmit an indication that power source 24 is fully charged, power source 24 is fully discharged, how much charge (e.g., charging current) is being applied to power source 24, a charge capacity of power source 24, a state of charge (SOC) of power source 24, or any other charging information of power source 24. Processing circuitry 22 can also transmit information to charging device 20 indicating any issues or errors of power source 24 that can prevent power source 24 from providing operational power to components of IMD 14.

[0061] Processing circuitry 22 may determine the state of charge of power source 24. For example, processing circuitry 22 may include a voltage tester circuit coupled to power source 24 to determine the state of charge (e.g., voltage level) of power source 24. In some examples, processing circuitry 22 determines the state of charge as a voltage measurement, as a percentage of full capacity, relative to another power source state of charge (e.g., higher, the same, similar, lower), or any combination thereof. In some examples, a user interface (e.g., Figure 3 The user interface 54) indicates the charging status of one or more power sources. For example, the user interface can display a bar graph, a graphic, a value, a light, or any other indication of the charging status of the power source.

[0062] In an example, processing circuitry 22 may control timer circuitry 38 to start a countdown (such as during a recharging session). In an example, processing circuitry 22 may control one or more devices to perform a specific task for a specific duration, such as may be timed via timer circuitry 38. For example, processing circuitry 22 may control charging circuitry 26 to open a circuit for a desired amount of time (e.g., in seconds, minutes, or hours). Once the countdown expires, processing circuitry 22 may control charging circuitry 26 to close the circuit, such as to tune the IMD to the charging device (e.g., change from a detuned state of the IMD).

[0063] Figure 3 is a block diagram of an example of an external charging device 20. Although the charging device 20 may generally be described as a handheld device, the charging device 20 may be a larger portable device or a more stationary device. Additionally, in other examples, the charging device 20 may be included as an external programmer (e.g., Figure 1 The charging device 20 may be configured to communicate with an external programmer. Figure 3 As shown, charging device 20 may include a primary coil 48, processing circuitry 50, memory 52, a user interface 54, communication circuitry 56, charging circuitry 58, and a power source 60. Memory 52 may store instructions that, when executed by processing circuitry 50, cause processing circuitry 50 and external charging device 20 to provide the functionality attributed to external charging device 20 throughout this disclosure.

[0064] In general, charging device 20 includes any suitable hardware arrangement, alone or in combination with software and / or firmware, to perform the techniques attributed to charging device 20, as well as its processing circuitry 50, user interface 54, communication circuitry 56, and charging circuitry 58. In various examples, charging device 20 may include one or more processors (e.g., processing circuitry 50), such as one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components. In various examples, charging device 20 may also include memory 52, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, or a CD-ROM, containing executable instructions for causing the one or more processors to perform the actions attributed to them. Furthermore, while processing circuitry 50 and communication circuitry 56 are depicted as separate, in some examples, processing circuitry 50 and communication circuitry 56 are functionally integrated. In some examples, processing circuitry 50 , communication circuitry 56 , and charging circuitry 58 correspond to respective hardware units, such as an ASIC, DSP, FPGA, or other hardware units.

[0065] Memory 52 may store instructions that, when executed by processing circuitry 50, cause processing circuitry 50 and charging device 20 to provide the functionality attributed to charging device 20 throughout this disclosure. For example, memory 52 may include instructions for causing processing circuitry 50 to control charging circuitry 58, communicate with IMD 14, or for any other functionality. Additionally, memory 52 may include a record of selected power levels, calculated estimated energy transfers, or any other data related to charging rechargeable power source 24. Processing circuitry may, upon request, send any of this stored data in memory 52 to another computing device for review or further processing.

[0066] In some examples, memory 52 may be configured to store data measured over time regarding the state of charge of one or more power supplies of one or more IMDs, the aging of power supply 24, and / or any other factors that may affect the voltage of power supply 24. In some examples, memory 52 may be configured to store data representing an energy absorption tissue model used by processing circuitry 50 to determine energy absorption by tissue at a particular operating frequency. In some examples, memory 52 may be configured to store data representing a tissue model used by processing circuitry 50 to calculate tissue temperature based on the tissue model and the power delivered to rechargeable power supply 24 over a period of time. The tissue model may indicate how the temperature of tissue surrounding IMD 14 changes over time.

[0067] User interface 54 may include buttons or a keypad, lights, a speaker that generates audible sounds, a microphone that detects voice commands, and a display (such as a liquid crystal (LCD), a light emitting diode (LED), or a cathode ray tube (CRT)). In some examples, the display may be a touch screen. As discussed in this disclosure, processing circuitry 50 may present and receive information related to the charging of rechargeable power source 24 via user interface 54. For example, user interface 54 may indicate when charging is occurring, the quality of the alignment between secondary coil 28 and primary coil 48, the selected power level, the current charge level of rechargeable power source 24, the duration of the current recharging session, the expected remaining time of the charging session, or any other information. In some examples, processing circuitry 50 may receive some of the information displayed on user interface 54 from IMD 14.

[0068] User interface 54 may also receive user input via user interface 54. The input may be, for example, in the form of pressing a button on a keyboard or selecting an icon from a touch screen. The input may include a request to start or stop a recharging session, a desired charge level, or one or more statistics related to charging rechargeable power source 24 (e.g., estimated energy transfer). In this manner, user interface 54 may receive charging commands and / or allow a user to view information related to charging of rechargeable power source 24.

[0069] Charging device 20 also includes components for transferring power to recharge rechargeable power source 24 associated with IMD 14. Figure 3 As shown, the charging device 20 includes a primary coil 48 and a charging circuit system 58 coupled to a power source 50. The charging circuit system 58 can be configured to generate a current in the primary coil 48 from a voltage stored in the power source 60. Figure 3 14. Although shown as a single loop in the example of FIG14, primary coil 48 may include multiple turns of wire. Charging circuitry 58 may generate current based on a power level selected by processing circuitry 50 based on the estimated energy transfer. As described herein, processing circuitry 50 may select a high power level, a low power level, or a variety of different power levels (e.g., three or more different power levels) to control the recharging rate in rechargeable power source 24. In some examples, the power level may be selected based on a determined temperature of one or more of IMDs 14. In some examples, processing circuitry 50 may control charging circuitry 58 based on the power level selected by processing circuitry 22 of at least one of IMDs 14.

[0070] Primary coil 48 may comprise a coil of wire (e.g., having multiple turns) or other device capable of inductively coupling with secondary coil 28 disposed within patient 12. Primary coil 48 may comprise windings of wire configured such that current generated within primary coil 48 can generate a magnetic field configured to induce a current within secondary coil 28. Primary coil 48 may be configured with certain dimensions and / or driven to generate electromagnetic energy having a specific frequency selected for secondary coil 28. The induced current may then be used to recharge rechargeable power source 24. In this manner, current may be induced in secondary coil 28 associated with rechargeable power source 24. The coupling efficiency between secondary coil 28 and primary coil 48 of charging device 20 may depend on the alignment of the two coils. Generally, coupling efficiency increases when the two coils share a common axis and are in close proximity to one another. Therefore, if the respective secondary coils of two IMDs 14 receive power from a single primary coil 48, one IMD may receive more power than the other. Primary coil 48 can be configured to couple with multiple secondary coils at once. For example, primary coil 48 can be sized to couple with corresponding secondary coils of multiple IMDs to recharge the power supplies of the IMDs. User interface 54 of charging device 20 can provide one or more audible tones or visual indications of alignment.

[0071] Charging circuitry 58 may include one or more circuits that generate an electrical signal and current within primary coil 48. In some examples, charging circuitry 58 may generate alternating current of a specific amplitude and frequency. In other examples, charging circuitry 58 may generate direct current. In any case, charging circuitry 58 may be configured to generate an electrical signal that, in turn, causes primary coil 48 to generate a magnetic field that delivers various power levels to IMD 14. In this manner, charging circuitry 58 may be configured to charge rechargeable power source 24 of IMD 14 using any desired power level.

[0072] The power level may specify wattage, current amplitude, voltage amplitude, current in primary coil 48 or secondary coil 28, or any other parameter that may be used to modulate the power delivered from coil 48. The parameters of the power level may be selected based on the hardware characteristics of charging device 20 and / or IMD 14.

[0073] Power supply 60 can deliver operating power to the components of charging device 20. Power supply 60 can also deliver operating power to drive primary coil 48 during the charging process. Power supply 60 can include a battery and power generation circuitry to generate operating power. In some examples, the battery can be rechargeable to allow for extended portable operation. In other examples, power supply 60 can draw power from a limited voltage source, such as a consumer or commercial electrical outlet.

[0074] Although the power source 60 and charging circuitry 58 are shown as being within the housing of the charging device 20, and the primary coil 48 is shown as being external to the charging device 20, different configurations may be used. For example, the primary coil 48 may also be placed within the housing of the charging device 20. In another example, the power source 60, charging circuitry 58, and primary coil 48 may all be located outside the housing of the charging device 20 and coupled to the charging device 20.

[0075] Communication circuitry 56, under the control of processing circuitry 50, supports wireless communication between IMD 14, charging device 20, and / or programmer 19. Communication circuitry 56 may also be configured to communicate with another computing device via wireless communication techniques, or directly via a wired connection. In some examples, communication circuitry 56 may be substantially similar to communication circuitry 36 of IMD 14 described herein, thereby providing wireless communication via RF or proximal inductive media. In some examples, communication circuitry 56 may include an antenna, which may take various forms, such as an internal or external antenna. In some examples, communication to IMD 14 may occur via modulation of power from primary coil 48, which is detectable by IMD 14.

[0076] Examples of local area wireless communication technologies that may be used to facilitate communication between charging device 20 and IMD 14 include RF communication according to the 802.11 or Bluetooth specification sets or other standard or proprietary telemetry protocols. In this way, other external devices may be able to communicate with charging device 20 without establishing a secure wireless connection.

[0077] Figure 4 is a flow chart illustrating an example of a technique for controlling the charging of a power source (e.g., power source 24) of a medical device by an external charging device. The charging circuitry 50 of the charging device 20 is described as generally performing an example Figure 4 However, in other examples, Figure 4 The techniques described herein may be performed by processing circuitry 22 of IMD 14, processing circuitry of another IMD, processing circuitry of external programmer 19, or by any processing circuitry of any individual device described herein, or any combination thereof. In other words, some functions may be performed by a distributed computing process. In some examples, one or both of programmer 19 and charging device 20 receive information from IMD 14. For example, processing circuitry 50 may control IMD 14A and IMD 14B before and during charging. For example, processing circuitry 50 may control IMD 14A to shunt energy through a resistive load before a recharging session.

[0078] like Figure 4As shown in the example of FIG, processing circuitry 50 of charging device 20 may receive data indicating respective charging states from a first IMD and a second IMD (e.g., IMD1 and IMD2 or IMD 14A and IMD 14B) (102). In some examples, communication circuitry 36 of the respective IMDs transmits data indicating the charging state of each power source 24 to charging device 20. Processing circuitry 50 may then determine the charging state of the first power source of IMD1 and the charging state of the second power source of IMD2 based on information such as the received data (104).

[0079] The processing circuitry may control IMD1 based on the state of charge of IMD2 to achieve a target state of charge (106). In an example, if IMD2 has a state of charge that is less than the state of charge of IMD1, the processing circuitry may control the circuitry of IMD1 (e.g., processing circuitry 22 or charging circuitry 26 of IMD1) to achieve a target state of charge, such as a state of charge similar to the state of charge of IMD2. In some examples, the target state of charge of IMD1 is within a threshold of the state of charge of IMD2 (e.g., within about 5% to about 10% of the state of charge of IMD2, or within a threshold voltage value of IMD2). Processing circuitry 50 may transmit a command to IMD1 to perform an action that will achieve the target state of charge (e.g., reduce the state of charge of power supply 24 of IMD1). For example, processing circuitry 50 may transmit an instruction to IMD1 to turn on a power-consuming feature of IMD1, such as powering a communication antenna, powering a sensor, or for processing circuitry 22 to perform a calculation. Typically, these power consumption characteristics are selected so as not to affect therapy delivery or other therapeutic or sensing functions. In some examples, processing circuitry 50 may initiate a telemetry session, run a program on a microprocessor (such as processing circuitry 50), shunt energy through a resistive load, or another task. If processing circuitry 50 determines that IMD 1 has not yet reached the target charge state (the "no" branch of block 107), processing circuitry 50 continues to control IMD 1 to achieve the target charge state (106). If processing circuitry 50 determines that IMD 1 has reached the target charge state (the "yes" branch of block 107), charging device 20 may deliver energy to the first and second IMDs (108). Typically, charging device 20 may deliver energy to the first and second IMDs (108) before, during, or after the aforementioned steps.

[0080] The charging device 20 can perform Figure 5The technology can be used as part of any recharging of an IMD implanted in patient 12. Alternatively, when multiple IMDs 14 are receiving power from charging device 20, external programmer 19 can be connected between charging device 20 and IMDs 14 to relay data and / or commands to one or more of IMDs 14, sending data related to the current charge state of their respective power sources 24 and / or causing IMDs 14 to perform actions intended to equalize the charge states. In some examples, this process can occur before charging begins. In other examples, when each of IMDs 14 may receive a different amount of power with primary coil 48 displaced relative to a different secondary coil of IMD 14, equalization of the charge states can be achieved during a charging session. Charging device 20 can periodically ping each IMD 14 to obtain charge state information, and / or each IMD 14 can periodically report the charge state during a charging session.

[0081] In other examples, IMDs 14 may communicate with each other and / or partially or fully control the balancing of charge states among IMDs 14. For example, IMD1 may act as a master device that receives charge state data from IMD2, determines which of IMD1 or IMD2 needs to perform a power consumption function to equalize the charge states, and transmits a command to IMD2 to perform the function as needed. Figure 5 As shown in the example of FIG, multiple IMDs 14 receive energy (110) via inductive coupling with a charging device 20. For example, primary coil 48 and the corresponding secondary coils of IMDs 14 are not necessarily coupled in the same manner. In some cases, charging device 20 may be closer to one of the two or more IMDs. In some cases, primary coil 48 may be oriented to better couple with the secondary coil of one IMD than with the secondary coil of another IMD. By using the systems and methods described herein, two or more IMDs can be safely and efficiently recharged regardless of the various distances between the IMDs and the charging device.

[0082] Processing circuitry 22 of IMD1 may determine a charge state of a first rechargeable power source (e.g., IMD1's power source) and a charge state of a second rechargeable power source (e.g., IMD2's power source) (112). Processing circuitry 22 of IMD1 may then control charging of IMD1's first power source based on the charge state of IMD2's second power source (114). For example, during a recharging session, if IMD1 approaches a target charge state (e.g., fully charged) before IMD2, IMD1 may consume more power to reduce the charge state and / or reduce the amount of recharging current reaching its own power source, such as described herein. For example, IMD1 may detune its charging circuitry 28 or open the circuit of its secondary coil to reduce the amount of current reaching the power source. Alternatively, if IMD2 has a higher charge state than IMD1, IMD1 may send a command directly to IMD2 to reduce the charge state of IMD2's power source and / or reduce the power reaching IMD2's power source. IMD1 and IMD2 may communicate directly or via charging device 20 and / or external programmer 19. During a recharging session from charging device 20, IMD1 may continue to control IMD1 and / or IMD2 to manage power consumption and / or received charging power based on the determined charge status from each IMD (e.g., blocks 112 and 114).

[0083] Figure 6 is a flow chart of an example technique for controlling charging of a power source of a medical device (e.g., IMD 14) by an external charging device (e.g., charging device 20) based on the temperature of IMD 14. Figure 6 14A or IMD 14B, or any combination thereof, may perform the processing circuitry 50 of charging device 20. Figure 6 characteristics.

[0084] exist Figure 6 In the example of FIG1 , charging device 20 delivers energy to IMD 14 via inductive coupling (116). As described herein, multiple IMDs 14 may receive recharging energy, and each IMD may be monitored for the current state of charge and temperature of its respective power source. Processing circuitry 50 may control charging of power source 24 of IMD1 (e.g., IMD 14A) based on the state of charge of the power source of IMD2 (e.g., IMD 14B). For example, the power source of IMD2 may not charge quickly enough due to inefficient inductive coupling or the state of charge of IMD2 may initially be lower than the state of charge of IMD1.

[0085] During a charging session, processing circuitry 50 may determine whether the temperature of IMD1 or IMD2 exceeds a maximum limit. IMD1 and IMD2 may periodically transmit the sensed temperature of the respective IMD. If processing circuitry 50 determines that the temperature of either IMD (or, in other examples, patient tissue) has not reached the maximum temperature limit (the "no" branch of block 120), processing circuitry 50 continues to deliver energy for charging both IMDs, such as until both IMDs have reached a target charge state (118). If the temperature of either IMD1 or IMD2 has exceeded the maximum temperature limit (the "yes" branch of block 120), processing circuitry 50 controls the IMD that has exceeded the temperature limit to reduce the temperature of the IMD to an acceptable level while charging device 20 continues to deliver energy via inductive coupling (122). For example, processing circuitry 50 may transmit a command to IMD1 via communication circuitry 56 (or via modulated power delivery from primary coil 48) to perform one or more functions that may reduce the temperature of IMD1. The commands may instruct IMD 1 to detune or even open the circuit of secondary coil 28 in order to reduce or eliminate the current induced in secondary coil 28. In this way, charging device 20 may continue to charge IMD 2 while also reducing the risk of IMD 1 overheating or delivering undesirable temperatures to patient 12. In some examples, processing circuitry 50 may control charging within IMD 1 and / or IMD 2 based on the thermal dose to patient tissue and the charge state of the power supply of each respective IMD 1 and IMD 2.

[0086] Although the charging device 20 is described as performing Figure 6 While some examples may include features of IMD 1, in other examples, the processing circuitry of one or more IMDs may implement these features. For example, the processing circuitry of IMD 1 may self-monitor the temperature of IMD 1 during a charging session and, in response to detecting that the temperature exceeds a temperature limit, take steps to reduce the temperature. In this way, if the inductive coupling causes the temperature of IMD 1 to exceed the limit, IMD 1 may proactively reduce the charging current induced from charging device 20. When the power supply of IMD 1 has reached a fully charged state and / or if the inductive coupling is generating too much current within IMD 1, the increase in temperature may be caused by resistive shunting of energy. This may occur due to inefficient coupling and / or the patient covering the IMD during charging, preventing the IMD from dissipating heat through the patient's tissue.

[0087] The following numbered examples illustrate one or more aspects of the present disclosure.

[0088] Example 1: A medical device system comprises: a first implantable medical device (IMD) comprising: a stimulation circuit system configured to generate stimulation deliverable to a patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; and a processing circuit system configured to control charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second IMD.

[0089] Example 2: In some examples of the medical device system of Example 1, the processing circuit system is further configured to: identify the start of a charging session; determine that the charge state of the first rechargeable power source is greater than the charge state of the second rechargeable power source; and in response to the determination, increase the consumption of charge stored by the first rechargeable power source by the first IMD by controlling until the charge states of the first rechargeable power source and the second rechargeable power source are substantially equal.

[0090] Example 3: In some examples of the medical device system of Example 1 or 2, the processing circuit system is further configured to: determine that the charge state of the first rechargeable power supply is greater than the charge state of the second rechargeable power supply; and in response to the determination, control the charging current to the first rechargeable power supply to be reduced.

[0091] Example 4: In some examples of the medical device system of Example 3, the processing circuit system controls the charging current reduced to the first rechargeable power source by at least one of: tuning a rectifier circuit of the charging circuit system to a frequency different from the frequency of the recharging energy delivered by the external charging device, controlling an oscillator to generate a frequency different from the frequency of the recharging energy, or diverting the recharging energy through a resistive load in the first IMD.

[0092] Example 5: In some examples of the medical device system of Examples 1-4, the processing circuitry controls charging of the first rechargeable power source by opening a circuit coupled to a secondary coil of the first IMD to prevent current from being induced in the secondary coil.

[0093] Example 6: In some examples of the medical device system of Example 5, the medical device system further includes a timer circuit system configured to initiate a countdown when the processing circuit system opens the secondary coil, and wherein, in response to the end of the countdown, the processing circuit system is configured to close the circuit coupled to the secondary coil.

[0094] Example 7: In some examples of the medical device system of any of examples 1-6, the medical device system further includes a temperature sensor coupled to the processing circuitry, wherein the processing circuitry controls charging of the first rechargeable power source based on a temperature of the first IMD, and wherein, in response to the temperature sensor sensing that the temperature of the first IMD satisfies a maximum temperature limit, the processing circuitry is configured to at least one of: control a reduction in consumption of charge stored by the first rechargeable power source by the first IMD, or close a circuit coupled to a secondary coil of the first IMD.

[0095] Example 8: In some examples of the medical device system of any of examples 1-7, the medical device system further includes communication circuitry coupled to the processing circuitry, the communication circuitry configured to receive a first signal corresponding to a charge state of the first rechargeable power source and a second signal corresponding to a charge state of the second rechargeable power source, and wherein the processing circuitry is configured to control charging of the first rechargeable power source and the second rechargeable power source based on the first signal and the second signal.

[0096] Example 9: In an example, a method for controlling charging of a first rechargeable power source of a first implantable medical device (IMD) within a patient includes: receiving energy at a secondary coil of the first IMD from a primary coil of an external charging device via inductive coupling; controlling, by processing circuitry, charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second IMD.

[0097] Example 10: In some examples of the method of example 9, the method further includes: identifying, by the processing circuitry, a charging session; determining, by the processing circuitry, that the charge state of the first rechargeable power source is greater than the charge state of the second rechargeable power source; and in response to the determination, controlling, by the processing circuitry, an increase in consumption of charge stored by the first rechargeable power source by the first IMD until the charge states of the first rechargeable power source and the second rechargeable power source are substantially equivalent.

[0098] Example 11: In some examples of the method of example 9 or 10, the method further includes: determining, by the processing circuitry, that the charge state of the first rechargeable power source is greater than the charge state of the second rechargeable power source; and in response to the determination, controlling, by the processing circuitry, a reduction in charging current to the first rechargeable power source.

[0099] Example 12: In some examples of the method of example 11, controlling the reduction in charging current includes at least one of: tuning a rectifier circuit of the charging circuitry to a different frequency than a frequency of recharging energy delivered by the external charging device, controlling an oscillator, or shunting recharging energy through a resistive load in the first IMD.

[0100] Example 13: In some examples of the method of any of examples 9-12, the method further includes opening a circuit coupled to the secondary coil of the first IMD to prevent current from being induced in the secondary coil.

[0101] Example 14: In some examples of the method of example 13, the method further includes initiating a countdown when the circuit of the secondary coil is open, and closing the circuit coupled to the secondary coil in response to an end of the countdown.

[0102] Example 15: In some examples of the method of any of examples 9-14, the method further includes controlling charging of the first rechargeable power source based on a temperature of the first IMD; and in response to the temperature of the first IMD satisfying a maximum temperature limit, performing at least one of: controlling, by the processing circuitry, a reduction in consumption of charge stored by the first rechargeable power source by the first IMD, or closing, by the processing circuitry, the circuit coupled to the secondary coil of the first IMD.

[0103] Example 16: In some examples of the method of any of examples 9-15, the method further includes receiving, at the communication circuitry, a first signal corresponding to a charge state of the first rechargeable power source and a second signal corresponding to a charge state of the second rechargeable power source, and controlling, by the processing circuitry, charging of the first rechargeable power source and the second rechargeable power source based on the first signal and the second signal.

[0104] Example 17: In an example, a medical system includes: a first implantable medical device (IMD) including: stimulation circuitry configured to generate stimulation deliverable to a patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; a second IMD including: stimulation circuitry configured to generate stimulation deliverable to a patient; a second rechargeable power source; and a secondary coil coupled to the second rechargeable power source, the secondary coil configured to charge the second rechargeable power source via inductive coupling with the primary coil of the external charging device; and processing circuitry configured to: determine a charge state of the first rechargeable power source and a charge state of the second rechargeable power source; control the first IMD to achieve a target charge state of the first rechargeable power source based on the charge state of the second rechargeable power source of the second IMD; and control delivery of energy from the external charging device to the secondary coil coupled to the first rechargeable power source and the secondary coil coupled to the second rechargeable power source.

[0105] Example 18: In some examples of the medical system of Example 17, the processing circuit system is further configured to: identify the start of a charging session; determine that the charge state of the first rechargeable power source is greater than the charge state of the second rechargeable power source; and in response to the determination, control an increase in consumption of charge stored by the first rechargeable power source by the first IMD until the charge states of the first rechargeable power source and the second rechargeable power source are substantially equal.

[0106] Example 19: In some examples of the medical system of Example 17 or 18, the processing circuit system is further configured to: determine that the charge state of the first rechargeable power source is greater than the charge state of the second rechargeable power source; and in response to the determination, control the charging current to be reduced to the first rechargeable power source by at least one of the following: tuning a rectifier circuit of the charging circuit system to a frequency different from the frequency of the recharging energy delivered by the external charging device, controlling the oscillator to generate a frequency different from the frequency of the recharging energy, or diverting the recharging energy through a resistive load.

[0107] Example 20: In some examples of the medical system of any of Examples 17-19, the processing circuit system is further configured to: open a circuit coupled to the secondary coil of the first IMD to prevent current from being induced in the secondary coil of the first IMD; and the medical system further includes a timer circuit system that is configured to initiate a countdown when the processing circuit system opens the secondary coil of the first IMD, and wherein, in response to the end of the countdown, the processing circuit system is configured to close the circuit coupled to the secondary coil.

[0108] Example 21: In an example, a method for controlling charging of a first rechargeable power supply of a first implantable medical device (IMD) within a patient's body includes: determining, by a processing circuit system, a charge state of the first rechargeable power supply and a charge state of a second rechargeable power supply of a second IMD; controlling, by the processing circuit system, the first IMD to achieve a target charge state of the first rechargeable power supply based on the charge state of the second rechargeable power supply of the second IMD; and delivering energy to the first IMD and the second IMD through a primary coil and via inductive coupling.

[0109] Example 22: In some examples of the method of Example 21, the method further includes: identifying, by the processing circuit system, the start of a charging session; determining, by the processing circuit system, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and in response to the determination, controlling, by the processing circuit system, an increase in consumption of charge stored by the first rechargeable power source by the first IMD until the states of charge of the first rechargeable power source and the second rechargeable power source are substantially equal.

[0110] Example 23: In some examples of the method of Example 21 or 22, the method further includes: determining, by the processing circuit system, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and in response to the determination, controlling, by the processing circuit system, the charging current reduced to the first rechargeable power source by at least one of the following: tuning a rectifier circuit of the charging circuit system to a frequency different from the frequency of the recharging energy delivered by the external charging device, controlling an oscillator to generate a frequency different from the frequency of the recharging energy, or diverting the recharging energy through a resistive load.

[0111] Example 24: In some examples of the method of any one of Examples 21-23, the method further includes: opening the circuit of the secondary coil of the first IMD to prevent current from being induced in the secondary coil; when the circuit of the secondary coil is opened, initiating a countdown by the timer circuit system, and closing the circuit of the secondary coil in response to the end of the countdown.

[0112] Example 25: In some examples, a system includes: a device for determining a charge state of a first rechargeable power supply of a first implantable medical device (IMD) and a charge state of a second rechargeable power supply of a second IMD; a device for controlling the first IMD to achieve a target charge state of the first rechargeable power supply based on the charge state of the second rechargeable power supply of the second IMD; and a device for delivering energy to the first IMD and the second IMD.

[0113] Example 26: In some examples, a non-transitory computer-readable storage medium includes instructions that, when executed, cause one or more processors to: determine a charge state of a first rechargeable power supply of a first implantable medical device (IMD) and a charge state of a second rechargeable power supply of a second IMD; control the first IMD to achieve a target charge state of the first rechargeable power supply based on the charge state of the second rechargeable power supply of the second IMD; and deliver energy to the first IMD and the second IMD.

[0114] The techniques described in this disclosure (including those attributed to system 10, IMD 14, charging device 20, and programmer 19, as well as various component parts) may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, aspects of these techniques may be implemented within one or more processors or processing circuitry, including one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components, remote servers, remote client devices, or other devices. 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.

[0115] Such hardware, software, firmware can 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 can 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 can be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0116] The techniques or processes described in this disclosure can also be implemented or encoded in an article of manufacture including a computer readable storage medium encoded with instructions for performing at least a portion of the techniques described herein. Instructions embedded or encoded in an article of manufacture including a computer readable storage medium can cause one or more programmable processors, or other processors, to perform at least a portion of the techniques described herein, such as when instructions included or encoded in a computer readable storage medium are executed by one or more processors. Example computer readable storage media that can be encoded with instructions to perform at least a portion of the techniques described herein include random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), ferroelectric random access memory (FRAM), flash memory, hard disk drive, compact disk ROM (CD-ROM), floppy diskette, tape, magnetic media, optical media, or any other computer readable storage media or tangibly embodied computer readable medium. Computer readable storage media can also be referred to as a storage device.

[0117] In some examples, a computer readable storage medium includes a non-transitory medium. The term "non-transitory" can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can change over time (e.g., in RAM or cache).

[0118] Various examples have been described in this document. Any combination of the described operations or functions is contemplated. These and other examples are within the scope of the following claims.

Claims

1. A medical system comprising: A first implantable medical device, comprising: a circuit system configured to at least one of deliver therapy to a patient or sense a physiological signal from the patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; and processing circuitry configured to control charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second implantable medical device, The processing circuitry is further configured to: Identifies the start of a charging session; determining that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and In response to the determination, control increases consumption of charge stored by the first rechargeable power source by the first implantable medical device until the states of charge of the first and second rechargeable power sources are substantially identical.

2. The medical system according to claim 1, wherein: The state of charge includes a percentage of full capacity.

3. The medical system according to claim 1, wherein: The processing circuitry is further configured to: determining that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and In response to the determination, control reduces charging current to the first rechargeable power source.

4. The medical system according to claim 3, wherein: The processing circuit system controls the reduction of charging current to the first rechargeable power source by at least one of tuning a rectifier circuit of the charging circuit system to a frequency different from the frequency of the recharging energy delivered by the external charging device, controlling an oscillator to generate a frequency different from the frequency of the recharging energy, or shunting the recharging energy through a resistive load in the first implantable medical device.

5. The medical system according to any one of claims 1 to 4, characterized in that: The processing circuitry controls charging of the first rechargeable power source by opening a circuit coupled to the secondary coil of the first implantable medical device to prevent current from being induced in the secondary coil.

6. The medical system of claim 5, further comprising a timer circuit system configured to initiate a countdown when the processing circuit system opens the secondary coil, and wherein In response to completion of the countdown, the processing circuitry is configured to close the circuit coupled to the secondary coil.

7. The medical system of any of claims 1-4, further comprising a temperature sensor coupled to the processing circuitry, wherein the processing circuitry controls charging of the first rechargeable power source based on a temperature of the first implantable medical device, and wherein In response to the temperature sensor sensing that the temperature of the first implantable medical device meets a maximum temperature limit, the processing circuit system is configured to at least one of: control a reduction in consumption of charge stored by the first rechargeable power source by the first implantable medical device, or close a circuit coupled to the secondary coil of the first implantable medical device.

8. The medical system of any one of claims 1-4, further comprising communication circuitry coupled to the processing circuitry, the communication circuitry configured to receive a first signal corresponding to a charge state of the first rechargeable power source and a second signal corresponding to a charge state of the second rechargeable power source, and wherein the processing circuitry is configured to control charging of the first rechargeable power source and the second rechargeable power source based on the first signal and the second signal.

9. A method for controlling charging of a first rechargeable power source of a first implantable medical device within a patient, the method comprising: receiving energy at the secondary coil of the first implantable medical device from a primary coil of an external charging device via inductive coupling; controlling, by processing circuitry, charging of the first rechargeable power source based on a charge state of a second rechargeable power source of a second implantable medical device; identifying, by the processing circuitry, a charging session; determining, by the processing circuitry, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; as well as In response to the determination, increasing consumption of charge stored by the first rechargeable power source by the first implantable medical device is controlled by the processing circuitry until the states of charge of the first and second rechargeable power sources are substantially identical.

10. The method of claim 9, wherein the state of charge comprises a percentage of full capacity.

11. The method of claim 9, further comprising: determining, by the processing circuitry, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; as well as Responsive to the determination, a charging current to the first rechargeable power source is controlled by the processing circuitry to be reduced.

12. The method according to claim 11, wherein Controlling the reduction in charging current includes at least one of tuning a rectifier circuit of the charging circuit system to a frequency different from the frequency of the recharging energy delivered by the external charging device, controlling an oscillator, or shunting the recharging energy through a resistive load in the first implantable medical device.

13. The method of any one of claims 9 to 12, further comprising: An electrical circuit coupled to the secondary coil of the first implantable medical device is opened to prevent current from being induced in the secondary coil.

14. The method of claim 13, further comprising: A countdown is initiated when the circuit of the secondary coil is opened, and in response to completion of the countdown, the circuit coupled to the secondary coil is closed.

15. The method of any one of claims 9 to 12, further comprising: controlling charging of the first rechargeable power source based on a temperature of the first implantable medical device; as well as In response to the temperature of the first implantable medical device satisfying a maximum temperature limit, at least one of the following is performed: controlling, by the processing circuit system, a reduction in consumption of charge stored by the first rechargeable power source by the first implantable medical device, or closing, by the processing circuit system, a circuit coupled to the secondary coil of the first implantable medical device.

16. The method of claim 9, further comprising: A first signal corresponding to a charge state of the first rechargeable power source and a second signal corresponding to a charge state of the second rechargeable power source are received at the communication circuitry, and charging of the first and second rechargeable power sources is controlled by the processing circuitry based on the first and second signals.

17. A medical system comprising: A first implantable medical device, comprising: a first circuit system configured to at least one of deliver a first therapy to a patient or sense a first physiological signal from the patient; a first rechargeable power source; and a secondary coil coupled to the first rechargeable power source, the secondary coil configured to charge the first rechargeable power source via inductive coupling with a primary coil of an external charging device; A second implantable medical device, the second implantable medical device comprising: a second circuit system configured to at least one of deliver a second therapy to the patient or sense a second physiological signal from the patient; a second rechargeable power source; and a secondary coil coupled to the second rechargeable power source, the secondary coil configured to charge the second rechargeable power source via inductive coupling with the primary coil of the external charging device; and processing circuitry configured to: determining a state of charge of the first rechargeable power source and a state of charge of the second rechargeable power source; controlling the first implantable medical device to achieve a target state of charge for the first rechargeable power source based on the state of charge of the second rechargeable power source of the second implantable medical device; and controlling the delivery of energy from the external charging device to the secondary coil coupled to the first rechargeable power source and the secondary coil coupled to the second rechargeable power source, wherein the processing circuitry is further configured to: Identifies the start of a charging session; determining that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and In response to the determination, control increases consumption of charge stored by the first rechargeable power source by the first implantable medical device until states of charge of the first and second rechargeable power sources are substantially equal.

18. The medical system according to claim 17, wherein: The state of charge includes a percentage of full capacity.

19. The medical system according to any one of claims 17-18, characterized in that The processing circuitry is further configured to: determining that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; and In response to the determination, a charging current to the first rechargeable power source is controlled to be reduced by at least one of tuning a rectifier circuit of the charging circuitry to a frequency different from a frequency of recharging energy delivered by the external charging device, controlling an oscillator to generate a frequency different from the frequency of the recharging energy, or shunting the recharging energy through a resistive load.

20. The medical system according to any one of claims 17-18, characterized in that The processing circuitry is further configured to: opening a circuit coupled to the secondary coil of the first implantable medical device to prevent current from being induced in the secondary coil of the first implantable medical device; and The medical system further includes a timer circuit system configured to initiate a countdown when the processing circuit system opens the secondary coil of the first implantable medical device, and wherein, in response to the end of the countdown, the processing circuit system is configured to close the circuit coupled to the secondary coil.

21. A method for controlling charging of a first rechargeable power source of a first implantable medical device within a patient, the method comprising: determining, by processing circuitry, a charge state of the first rechargeable power source and a charge state of a second rechargeable power source of a second implantable medical device; controlling, by the processing circuitry, the first implantable medical device based on the charge state of the second rechargeable power source of the second implantable medical device to achieve a target charge state of the first rechargeable power source; delivering energy to the first implantable medical device and the second implantable medical device through a primary coil and via inductive coupling; identifying, by the processing circuitry, the start of a charging session; determining, by the processing circuitry, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; as well as In response to the determination, increasing consumption of charge stored by the first rechargeable power source by the first implantable medical device is controlled by the processing circuitry until the states of charge of the first and second rechargeable power sources are substantially identical.

22. The method of claim 21, wherein the state of charge comprises a percentage of full capacity.

23. The method of any one of claims 21-22, further comprising: determining, by the processing circuitry, that the state of charge of the first rechargeable power source is greater than the state of charge of the second rechargeable power source; as well as In response to the determination, the processing circuitry controls a reduction in charging current to the first rechargeable power source by at least one of tuning a rectifier circuit of the charging circuitry to a frequency different from a frequency of recharging energy delivered by an external charging device, controlling an oscillator to generate a frequency different from the frequency of the recharging energy, or shunting the recharging energy through a resistive load.

24. The method of any one of claims 21-22, further comprising: opening a circuit of the secondary coil of the first implantable medical device to prevent current from being induced in the secondary coil; When the circuit of the secondary coil is opened, a countdown is initiated by a timer circuit system, and in response to completion of the countdown, the circuit of the secondary coil is closed.

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