Devices, systems, and methods that take an action when an external recharger is not positioned over an intended implantable medical device during recharge

Abstract

An external recharger that provides recharge power to an implantable medical device may be mispositioned during recharge, such as being placed over another metal object or another implantable medical device. A parameter that correlates with the external recharger being placed over the intended implantable medical device during recharge is obtained and compared to a threshold. The parameter meeting the threshold indicates that the external recharger is positioned over the intended implantable medical device. When the parameter does not meet the threshold, thus indicating that the external recharger is not positioned over the intended implantable medical device, then a corrective action is taken.

Description

DEVICES, SYSTEMS, AND METHODS THAT TAKE AN ACTION WHEN AN EXTERNALRECHARGER IS NOT POSITIONED OVER AN INTENDED IMPLANTABLE MEDICALDEVICE DURING RECHARGECROSS-RELATED CLAIM

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 675,806 filed July 26, 2024, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] Embodiments relate to the recharging of an implantable medical device. More particularly, embodiments relate to taking an action to address situations where an external recharger is not positioned over an intended implantable medical device during an attempt to recharge the intended implantable medical device.BACKGROUND

[0003] Implantable medical devices may provide medical therapy such as electrical stimulation, electrical sensing, and / or other tasks related to medical care of patients. The implantable medical device contains a battery to provide the electrical power necessary for the operation of the implantable medical device. To address the electrical needs of the implantable medical device over a period of time, the battery may be rechargeable. The battery is recharged via an external recharger that inductively couples to a recharging circuit of the implantable medical device. The external recharger may also communicate with the implantable medical device to exchange information including information relevant to the recharge.

[0004] During the recharge, the recharge power being output by the external recharger must be controlled to avoid overheating. One manner of controlling the recharge power involves monitoring the heating at the implantable medical device to prevent the heating from becoming too high. An added benefit of heat-based control is that should the external recharger be positioned incorrectly, the heat-based control will fail-safe. One example where this may occur is a patient with bilaterally positioned implantable medical devices. Thepatient may inadvertently position the recharger over a different device than the recharger is currently communicating with about the recharge, which presents a potentially troublesome scenario that the heat-based control handles via the failsafe.

[0005] However, heat-based control of the recharge may cause the recharge efficiency to be less than desired, thereby prolonging the recharge. Therefore, other manners of controlling recharge that allow for a greater efficiency may be of interest. Yet, other types of recharge control may not operate in such a way as to benefit from the failsafe provided by the heat-based control.SUMMARY

[0006] Embodiments address issues such as these and others by providing a system where the external recharger may employ a more efficient recharge control such as a temperature-based control while providing a failsafe for situations where the external recharger is not positioned over the intended implantable medical device during recharge. For instance, the system may monitor a parameter that correlates with the external device being positioned over the implantable medical device. Examples include such parameters as the temperature at the implantable medical device in relation to the recharge time that has elapsed, an integral of charge current reported by the implantable medical device, and / or a proximity signal strength between the implantable medical device and external device. The parameter can then be compared to a parameter value threshold to determine if any action should be taken, where the result of the comparison is indicative of whether the external recharge is positioned over the intended implantable medical device.

[0007] Embodiments provide a method of recharging an implantable medical device. The method involves outputting recharging power from an external recharger. The method involves obtaining a first parameter based on a temperature measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device. The method involves determining whether the first parameter meets a first threshold, wherein the first threshold is independent of the temperature measurement at the implantable medical device and indicates a position of the externalrecharger relative to the implantable medical device. The method also involves taking an action based on whether the first parameter is above or below the first threshold.

[0008] Embodiments provide a system that includes an external recharger configured to output recharging power. The system includes an implantable medical device configured to receive the recharging power. At least one of the external recharger or the implantable medical device is further configured to obtain a first parameter based on a temperature measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device. At least one of the external recharger or the implantable medical device is further configured to determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device. At least one of the external recharger or the implantable medical device is further configured take an action based on whether the first parameter is above or below the first threshold.

[0009] Embodiments provide an implantable medical device that includes a processor and a recharge circuit that is coupled to the processor and that is for receiving recharging power from an external recharger. The processor is configured to obtain a first parameter that is based on a temperature measurement at the implantable medical device and that correlates with the external recharger being positioned over the implantable medical device. The processor is further configured to determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device. The processor is further configured to take an action based on whether the first parameter is above or below the first threshold.

[0010] Embodiments provide an external recharger that includes a processor and a recharge circuit coupled to the processor. The processor is configured to cause the recharge circuit to begin outputting recharging power. The processor is configured to obtain a first parameter that is based on a temperature measurement at the implantable medical device and that correlates with the external recharger being positioned over an implantable medical device. The processor is configured to determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medicaldevice and that indicates the external recharger is positioned over the implantable medical device. The processor is configured to take an action based on whether the first parameter is above or below the first threshold.

[0011] Embodiments provide a system that includes an external recharger configured to output recharging power and an implantable medical device configured to receive the recharging power. While the external recharger is outputting the recharging power, at least one of the external recharger or the implantable medical device is further configured to obtain a proximity signal strength between the external recharger and the implantable medical device wherein the proximity signal strength correlates with the external recharger being positioned over the implantable medical device. Also while the external recharger is outputting the recharging power, at least one of the external recharger or the implantable medical device is further configured to determine whether the proximity signal strength meets a threshold based on an expected proximity signal strength that indicates that the external recharger is positioned over the implantable medical device. Additionally while the external recharger is outputting the recharging power, at least one of the external recharger or the implantable medical device is further configured to take an action based on whether the proximity signal strength is above or below the threshold.

[0012] Embodiments provide a system that includes an external recharger configured to output recharging power according to a time sequence and an implantable medical device configured to receive the recharging power. At least one of the external recharger or the implantable medical device is further configured to obtain a parameter based on a charge current measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device. At least one of the external recharger or the implantable medical device is further configured to determine whether the charge current parameter that correlates with external recharger being positioned over the implantable medical device meets a threshold that is independent of the charge current measurement at the implantable medical device and that is based on the time sequence of the recharging power that indicates the external recharger is positioned over the implantable medical device. At least one of the external recharger or the implantable medical device is also further configured to take an action based on whether the parameter is above or below the thresholdDESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows an example of an operating environment for embodiments that take action when an external recharger is not positioned over an intended implantable medical device during recharge.

[0014] FIG. 2 shows a block diagram illustrating a bilateral implantable medical device scenario where the external recharger is positioned over the intended implantable medical device.

[0015] FIG. 3 shows a block diagram illustrating a bilateral implantable medical device scenario where the external recharger is positioned over an unintended implantable medical device.

[0016] FIG. 4 shows an example of an external recharger and an implantable medical device to be recharged where one or both may take action when the external recharger is not positioned over the implantable medical device during recharge.

[0017] FIG. 5 shows an example of operations that may be performed to take action when a consideration of a parameter that correlates with the external recharger being positioned over the intended implantable medical device indicates the external recharger is not positioned over the intended implantable medical device during recharge.

[0018] FIG. 6 shows an example of operations where proximity signal strength between the external recharger and intended implantable medical device is considered relative to a threshold based on an expected signal strength when determining whether to take action during recharge.

[0019] FIG. 7 shows an example of operations where intended implantable medical device measured temperature is considered relative to a threshold based on a minimum temperature from a look-up for elapsed recharge time when determining whether to take action during recharge.

[0020] FIG. 8 shows an example of operations where an integral of charge current over time detected at the intended implantable medical device is considered relative to a threshold based on charge current when determining whether to take action during recharge.

[0021] FIG. 9 shows an example of operations where a measured temperature of the intended implantable medical device is considered relative to a threshold translated frommetal loading and corresponding recharge heating when determining whether to take action during recharge.

[0022] FIG. 10 shows an example of operations where an implantable medical device recharge related signal such as a measured temperature profile is considered relative to a threshold such as a pre-defined step response curve based on a time sequencing of recharge power when determining whether to take action during recharge.DETAILED DESCRIPTION

[0023] Embodiments provide for determining whether to take action during recharge, such as stopping or lowering the recharge power while temperature-based control of the recharge power is being implemented. The determination may be based on considering a parameter that correlates with an external recharge being positioned over an implantable medical device versus being positioned elsewhere, such as being positioned over an intended implantable medical device rather than over an unintended implantable medical device in a bilateral implantable medical device scenario.

[0024] FIG. 1 shows a typical environment for various embodiments of a medical system 100. In this example, medical system 100 may include an external recharger 110 and at least one implantable medical system 130 that is present within a patient body 120. In this particular example, there is a bilateral configuration where a second implantable medical system 160 is also present. The implantable medical system 130 may include an implantable medical device 132 connected to an implantable medical lead 134. Likewise, the implantable medical system 160 may include an implantable medical device 162 that may be connected to an implantable medical lead. External recharger 110 provides recharging of a rechargeable power source such as a battery present in the implantable medical device 132 and / or the implantable medical device 162.

[0025] The external recharger 110 may be placed on or near the patient body 120, such as on the chest of the patient body 120 or another location that is in proximity to the implantable medical device 132 and / or implantable medical device 162. External recharger 110 may be placed on the bare skin of the patient body 120, over clothes on the patient body 120, over medical bandages on the patient body 120, combinations thereof, or any other material thatmay be between the patient body 120 and external medical device 110 that would allow implantable medical device 132 and / or implantable medical device 162 to be recharged.

[0026] The implantable medical device 132 has been implanted into a subcutaneous pocket 140, although other implantation locales may be used depending on the procedure. Likewise, the implantable medical device 162 has been implanted into a subcutaneous pocket 164, although other implantation locales may be used. The at least one implantable medical lead 134, or lead and extension combination, of the implantable medical system 130 is routed between a therapy delivery target 142 and the implantable medical device 132. Likewise, at least one implantable medical lead 166, or lead and extension combination, of the implantable medical system 160 may be routed between another therapy delivery target within the body 120 and the implantable medical device 162. As an alternative, one or both implantable medical systems 130, 160 may be leadless designs and not include the implantable medical lead.

[0027] In this example of FIG. 1, the implantable medical device 132 is an implantable neurostimulator (INS) configured for adaptive deep brain stimulation, as the implantable medical lead 134 has a distal end 136 and distal electrodes 138 positioned within the brain at the target location 142 for the stimulation to be applied. Other examples of implantable medical devices include but are not limited to neurostimulators for spinal cord stimulation where the implantable medical lead 134 is directed to the spinal cord, peripheral nerve stimulation where the implantable medical lead 134 is directed to a peripheral nerve, sacral nerve stimulation where the implantable medical lead 134 is directed to a sacral nerve, cardiac stimulation where the implantable medical lead 134 is directed to cardiac tissue, tibial neuromodulation where there may be no implantable medical lead 134, and the like.

[0028] An issue may arise with recharging where the external recharger 110 intends to recharge a particular implantable medical device, such as implantable medical device 132 of FIG. 1, and begins communicating with the implantable medical device 132 for purposes of controlling the recharge. However, the external recharger 110 may be mispositioned. For instance, the external recharger 110 may be placed somewhere else either initially or at some point during the recharge process. For instance, the external recharger 110 may be positioned near some other metal object that creates an inductive load similar to the implantable medical device. As another example, in the bilateral configuration example shown in FIG. 1 , a usermay inadvertently position the external recharger 110 over the unintended implantable medical device, such as implantable medical device 162 which may also provide an inductive load. Thus, the intended implantable medical device is not receiving the recharge power being output by the external recharger 110. When temperature-based control is being used by the external recharger 110, detecting that the intended implantable medical device is not being recharged may not be readily determined, especially early in the recharging process.

[0029] This issue is further illustrated in FIGS. 2 and 3. In FIG. 2, the external recharger 110 has been positioned over the implantable medical device 132 that is intended to be recharged. Wireless recharge power 210 in the form of a particular rate of transmission of electromagnetic energy is being output by the external recharger 110 which couples to a recharge unit of the implantable medical device 132. According to one or more embodiments disclosed herein, the external recharger 110 has established communications with the implantable medical device 132 to exchange information 220 such as a temperature being sensed at the implantable medical device by a temperature sensor of the implantable medical device 132, charge current being provided to the battery of the implantable medical device 132, and the like. Additionally, a reflected impedance 221 resulting from a metal loading on the recharge circuit of the external recharger 110 by the recharge circuit and other metal of the implantable medical device 132 is detectable by the external recharger 110. Meanwhile, the other implantable medical device 162 is far enough from the implantable medical device 132 and the external recharger 110 that is positioned over the implantable medical device 132 that recharge power reaching the implantable medical device 162 is negligible.

[0030] Thus, recharge is proceeding as expected in FIG. 2. According to embodiments disclosed herein, this is confirmed by at least one of the implantable medical device 132 and / or the external recharger 110 performing an analysis involving the information 220 and in some cases the reflected impedance 221. Embodiments performing one or more types of this analysis are discussed in more detail below in relation to FIGS. 5-10.

[0031] Placing the external recharger 110 over an object other than the intended implantable medical device 132 can lead to many safety issues, especially if the other object is a life sustaining device and / or is not designed to receive recharge energy. For example, recharging energy could couple onto deep brain stimulation or cardiac device leads and cause issues at the therapy target. The recharging energy could cause a malfunction of theelectronics within an unintended implantable medical device 162. Furthermore, the existence of orthopedic metal implants or other metal objects near the intended implantable medical device 132 could be a factor. Therefore, it is important to detect the positioning of the external recharger 110 relative to the intended implantable medical device 132 and take a corrective action when the external recharge 110 is not positioned over the implantable medical device 132.

[0032] In FIG. 3, it can be seen that the external recharger 110 is now positioned over the implantable medical device 162 which is not intended to be receiving the recharge power, as the external recharger 110 is communicating with the implantable medical device 132. The user may have been confused as to which implantable medical device is intended to be recharged and positioned the external recharger 110 over the unintended implantable medical device 162 or may have inadvertently moved the external recharger 110 from being positioned over the intended implantable medical device 132 to being positioned over the unintended implantable medical device 162. Thus, the recharge power is being provided to the unintended implantable medical device 162. Meanwhile, the intended implantable medical device 132 is far enough from the unintended implantable medical device 162 and the external recharger 110 that is positioned over the unintended implantable medical device 162 that recharge power reaching the intended implantable medical device 132 is negligible. However, according to one or more embodiments disclosed herein, the external recharger 110 has established communications with the intended implantable medical device 132 to exchange information 220 such as a temperature being sensed at the implantable medical device 132 by a temperature sensor of the implantable medical device 132, charge current being provided to the battery of the implantable medical device 132, and the like. Yet, reflected impedance 221 resulting from the metal loading on the recharge circuit of the external device 110 by the recharge circuit and other metal of the unintended implantable medical device 162 is detected by the external device 110.

[0033] Thus, recharge of the intended implantable medical device 132 is not proceeding as expected in FIG. 3. According to embodiments disclosed herein, this situation is discovered by at least one of the implantable medical device 132 and / or the external recharger 110 performing the analysis involving the information 220, and in some cases thereflected impedance 221. As noted above, embodiments performing one or more types of this analysis are discussed in more detail below in relation to FIGS. 5-10.

[0034] Upon determining that the intended implantable medical device 132 is not being recharged due to the external recharger 110 not being positioned over the intended implantable medical device 132, a corrective action may be taken by at least one of the external recharger 110 and / or the intended implantable medical device 132. For instance, the external recharger 110 may stop the recharge, lower the recharge power being output, or switch to an exclusively heat-based control of the level of recharge power being output. Additionally or alternatively, the external recharger 110 may provide a notification to the user that the external recharger 110 is not positioned over the intended implantable medical device 110. This notification may be visual, audible and / or haptic and may include a countdown timer such as via a user interface display to indicated when the recharge will terminate if the recharger remains positioned away from the intended implantable medical device 110. Furthermore, the feedback may also be used to indicate when the recharger 110 is correctly positioned over the intended implantable medical device 110, such as by providing an audible and / or haptic feedback to allow the user to recognize when the correct position has been achieved. For embodiments where the implantable medical device 132 performs the analysis or otherwise is made aware of the result of the analysis, the implantable medical device 132 may generate a flag that is transmitted to the external recharger 110 or other external device to provide a notification about the situation to the external recharger 110 and / or to the user of the external recharger 110.

[0035] FIG. 4 shows a block diagram of an example of the medical system 100. The block diagram includes the external recharger 110, implantable medical device 132, and implantable medical lead 134, where the implantable medical lead 134 extends to the therapy delivery target 142 of the patient 120.

[0036] External recharger 110 may include various components. For instance, the external recharger may include at least one processor 230, memory 232 coupled to the processor, and a recharging unit 234 coupled to the processor. Memory 232 may store instructions executed by processor 230, where the processor 230 may be a general purpose programmable processor, a dedicated purpose processor, hardwired logic, and the like. Additionally, the external recharger may include communication circuitry, such as a transmitcircuit 236 and a receive circuit 238. In at least some embodiments, these communication circuits 236, 238 may operate via far field electromagnetic signals. In at least some embodiments, these communication circuits 236, 238 may include an additional unidirectional or bidirectional proximity circuit configuration to transmit a proximity signal 222 that requires the implantable medical device 132 to be in close proximity to exchange the proximity signal 222 with the external recharger 110. While shown as distinct components, the transmit and receive circuits 236, 238 may be implemented as a transceiver.

[0037] Implantable medical device 132 may also include various components. For instance, the implantable medical device may include a recharging unit 240, a processor 246, and memory 248 where the recharging unit and memory 248 are coupled to the processor 246. Memory 248 may store instructions executed by processor 246, where the processor 246 may also be a general purpose programmable processor, a dedicated purpose processor, hardwired logic, and the like. Additionally, the implantable medical device may include communication circuitry, such as a transmit circuit 250 and a receive circuit 252. In at least some embodiments, these communication circuits 250, 252 may operate by exchanging far field electromagnetic signals. In at least some embodiments, these communication circuits 250, 252 may include an additional unidirectional or bidirectional proximity circuit configuration to transmit and receive the proximity signal 222 that requires the implantable medical device 132 to be in close proximity to the external recharger to exchange the proximity signal 222 with the external recharger 110. While shown as distinct components, the transmit and receive circuits 250, 252 may be implemented as a transceiver.

[0038] Implantable medical device 132 may additionally include a temperature sensor 242 and / or a recharge current sensor 244. Temperature sensor 242 may measure the temperature of implantable medical device 132 and / or the temperature of the patient body surrounding implantable medical device 132 which may be used for temperature-based control of recharging as well as to provide temperature readings for the analysis discussed below in relation to FIGS. 5-10. One or more temperature sensors 242 may measure one or more portions of implantable medical device 132 and / or the surrounding patient tissue of implantable medical device 132. Additionally or alternatively, temperature-based control of the recharging may be based in whole or in part on temperature sensing occurring via one or more temperature sensors that may be included at the external medical device 110.

[0039] Recharging unit 234 of the external recharger 110 may generate recharge energy at a given rate as recharging power 210. Recharging power 210 may be coupled from the external medical device 110 to implantable medical device 132 via the recharging unit 240. Recharge current sensor 244 may sense the electrical current going into the battery of the implantable medical device 132 from the recharge unit 240 as a result of receiving the recharge power 210 from the external recharger 110.

[0040] FIG. 5 shows an example 300 of operations that may be performed to provide the analysis of whether the external recharger 110 is positioned over the implantable medical device 132 that is intended to be receiving the recharge energy during recharge by the external recharger 110. Initially, the external recharger 110 begins the recharge process by establishing communications with the implantable medical device 132 that is intended to be recharged and by outputting recharge power at an operation 302. A parameter that correlates with the external recharger 110 being positioned over the intended implantable medical device 132 is then obtained at an operation 304.

[0041] As discussed below with respect to the types of analysis in FIGS. 6-10, there are multiple types of parameters that correlate with the external recharger 110 being positioned over the intended implantable medical device 132. In one instance, a proximity signal strength between the external recharger 110 and the implantable medical device 132 serves as the parameter. In other instances, the measured temperature of the implantable medical device 132 serves as the parameter. In another instance, an integral of the charge current or other charge current based value received by the implantable medical device 132 over time may serve as the parameter. In yet another instance, a measured profile of temperature of the implantable medical device 132 may serve as the parameter. Where the external recharger 110 is performing the analysis, the implantable medical device communicates this parameter value as the data 220 discussed above in relation to FIGS. 2-4.

[0042] Upon obtaining the parameter, it is then detected whether the parameter meets a threshold at an operation 306. This threshold is chosen so as to be indicative of whether the external recharger 110 is properly positioned over the intended implantable medical device 132 for purposes of delivering the recharge power to the intended implantable medical device 132. The threshold may be found via a look-up or computation or may be a pre-definedvalue, where this determination of the threshold may be performed by the external recharger 110 and / or the intended implantable medical device 132.

[0043] As discussed below with respect to the types of analysis in FIGS. 6-10, there are multiple types of thresholds that may be applied depending on the type of parameters that are obtained. In the instance where a proximity signal strength between the external recharger 110 and the implantable medical device 132 serves as the parameter, the threshold is an expected minimum proximity signal strength where exceeding that threshold indicates the external recharger 110 is positioned over the implantable medical device 132. In one instance where the measured temperature of the implantable medical device 132 serves as the parameter, the threshold is found by looking up in a table the elapsed recharge time. In another instance where the measured temperature of the implantable medical device 132 serves as the parameter, the threshold found by a translation of heat resulting from a metal loading on the recharger. In both cases, exceeding the threshold indicates the external recharger 110 is positioned over the implantable medical device 132. In the instance where the integral of charge current is the parameter, the threshold is based on an expected minimum charge current where exceeding the threshold indicates that the external recharger is positioned over the implantable medical device 132. Alternatively, the parameter may be a measured current amplitude that is compared to a current amplitude threshold. In the instance, where a measured profile of temperature of the implantable medical device 132 serves as the parameter, the threshold is a pre-defined step response curve based on a time sequence of the recharge signal being output by the external recharger 110 where the measured temperature profile exceeding the pre-defined step response curve indicates that the external recharger is positioned over the implantable medical device 132.

[0044] Upon the detection occurring at operation 306, a corrective action is then taken at operation 308 based on whether the parameter is above or below the threshold. For instance, when the detection at operation 306 is that the parameter value does not meet the threshold because the parameter is below the threshold, thereby indicating that the external recharger 110 is not positioned over the implantable medical device 132, the corrective action may be performed. As previously discussed above, the corrective action may be taken by at least one of the external recharger 110 and / or the intended implantable medical device 132 at operation 308. For instance, the external recharger 110 may stop the recharge or lower the rechargepower being output. Additionally or alternatively, the external recharger 110 may provide a visual, audible, and / or haptic notification to the user that the external recharger 110 is not positioned over the intended implantable medical device 110 with the indication of a countdown timer for the termination of the recharge. As also discussed above, the notification may provide visual, audible, and / or haptic feedback to assist the user in repositioning the external recharger 110. For embodiments where the implantable medical device 132 performs the analysis of operation 306 of FIG. 5 or otherwise is made aware of the result of the analysis, the implantable medical device 132 may generate a flag that is transmitted to the external recharger 110 or other external device to provide a notification about the situation to the external recharger 110 and / or to the user of the external recharger 110. The flag may cause the external recharger 110 to then take the corrective action such as stopping the recharge, lowering the recharge power, and / or providing the notification to the user.

[0045] FIG. 6 shows a more detailed view of an example 400 of operations for controlling recharge that uses both heat-based control and temperature-based control while also utilizing the operations of FIG. 5 for purposes of confirming whether the external recharger 110 is positioned over the intended implantable medical device 132 and taking corrective action when that is not the case. In the embodiment of FIG. 6, proximity signal strength between the external recharger 110 and the implantable medical device 132 is the parameter to be used that correlates with the external recharger 110 being positioned over the intended implantable medical device 132.

[0046] Regarding the heat-based and temperature-based control of the recharge process in the example of FIG. 6, there is a control loop for both heat-based and temperature-based control methods operating in parallel. The temperate-based control determines a maximum recharge power to be output by the external recharger at an operation 402. This temperaturebased control of recommended power is provided to an operation 406. The heat-based control also determines a maximum recharge power to be output by the external recharger at an operation 404. The heat-based control of recommended power is also provided to the operation 406. The operation 406 then sets a target recharge power based on the minimum of the temperature-based control recommended recharge power and the heat-based control recommended recharge power so as not to exceed any heat-based or temperature-basedlimits. The target recharge power is then output from the external recharger 110, which then triggers the implementation of operations 408, 410, and 412.

[0047] At operation 408, the measured temperatures of the intended implantable medical device 132 are read where the target recharge power is being provided by the external recharger 110. These measured temperatures are being provided by the temperature sensor 242 of the implantable medical device 132. Where the external recharger 110 is implementing the recharge controls, the temperature reading may be transmitted from the implantable medical device 132 to the external recharger as the data 220 discussed above. Then, at an operation 414, an estimate of the recharger position and maximum applied temperature to the implantable medical device 132 can be made based on the raw temperature readings from the temperature sensor 242 as well as electrical aspects of recharge information, discussed below, that are communicated by the intended implantable medical device and captured in operation 412. This estimate of the maximum applied temperature, which is based on the temperature measurement made by temperature sensor 242 at the intended implantable medical device 132 and that may be communicated back to the external recharger 110, is then fed back to the operation 402 for purposes of determining the maximum recharge power. If the estimated maximum applied temperature-based on measured temperature is too high, then the temperature-based control of operation 402 may recommend a lower recharge power than the present recharge power to operation 406. Reference is made to U.S. Prov. App. No. 63 / 636,005, filed 18 Apr 2024, and to U.S. Pat. No. 11,705,763, assigned to Medtronic, Inc., in relation to the temperature and position estimation at operation 414 and related temperature-based control at operation 402.

[0048] At operation 410, the loading of the actual object receiving the recharge energy 210, such as the intended implantable medical device 132, or any other metal device such as the unintended implantable medical device 162, is detected by the external recharger 110. The raw loading information of operation 410 as well as electrical aspects of recharge information such as charge current and voltage at the implantable medical device that are communicated by the intended implantable medical device and captured in operation 412 are provided to operation 416 where the amount of heat being delivered to the actual object receiving the recharge power is estimated. Equation (1) below shows how a total power, PINS_BATT, is determined for use in the heat estimation at operation 416 while equation (2)below shows a calculation of the estimated heat, QINS, at the implantable medical device as estimated at operation 416. Regarding equation (1), IINS_BAT represents the current entering the battery of the implantable medical device, VINS_BATT represents the voltage of the implantable medical device, and RINS_BATT represents the internal resistance of the battery of the implantable medical device. This information is communicated to the external recharger 110 for embodiments where the external recharger 110 performs the heat estimation according to equations (1) and (2). Regarding equation (2), PTANK is the power output of the external recharger 110, QPRIM is the heat being generated in the recharging circuit coil of the external recharger 110, and PINS_BATT is again the amount of power going to the battery of the object providing the metal loading.(1 ) PlNS_BATT = IlNS_BATT * VlNS_BAT - IlNS_BAT2* RlNS_BAT(2) QINS = PTANK-QPRIM - PINS_BAT

[0049] This estimate of the amount of heat being delivered is then fed back to the operation 404 for purposes of determining the maximum recharge power. If the estimated delivered heat is too high, then the heat-based control of operation 404 may recommend a lower recharge power than the present recharge power to operation 406. Reference is made to U.S. Pat. No. 11,896,838, assigned to Medtronic, Inc., in relation to the heat estimation at operation 416 and related energy control at operation 404.

[0050] At operation 412, additional measurements and factors may be considered for control of the recharge including those previously mentioned. For instance, the charge current being sensed by the charge current sensor 244 of the implantable medical device 132 may be obtained and passed along to operation 418 for consideration against a termination criteria reflecting a completed charging process or charging complication. Likewise, voltage limiting and any faults may be determined and passed along to operation 416 to check against termination criteria. If the termination criteria are met, operation 418 may stop the recharge.

[0051] In addition to these operations above, the example 400 also performs operations in parallel to those above to check to see if the external recharger 100 is positioned over the intended implantable medical device 132 to determine if a corrective action is needed. These operations include sending periodic proximity telemetry signals via inductive telemetry from one device to the other, such as from the external recharger 110 to the implantable medical device 132 or vice versa at an operation 420. In either case, whichever of the two is performing the analysis obtains the proximity signal strength that has been received by the receiving device such as by communicating the signal strength as part of the information 220 discussed above over the wireless communication channel between the intended implantable device 132 and the external recharger 110. This proximity signal strength is then passed along to the operation 422 to compare the proximity signal strength to a threshold based on an expected proximity signal strength for an appropriately positioned external recharger 110 where a proximity signal strength greater than the threshold is indicative of the external recharger 110 being positioned over the intended implantable medical device 132. A proximity signal strength below the threshold, or a lack of any response to the proximity signal, indicates the external recharger 110 is not positioned over the intended implantable medical device 132. The estimation of the proximity of the external recharger 110 to the implantable medical device 132 is then passed to operation 424 so that a corrective action is taken when the threshold based on expected proximity signal strength has not been met or no response indicating the proximity signal strength has been received, thereby indicating the external recharger 110 is not positioned over the intended implantable medical device 132.

[0052] FIG. 7 shows a more detailed view of another example 500 of operations for controlling recharge that uses both heat-based control and temperature-based control while also utilizing the operations of FIG. 5 for purposes of confirming whether the external recharger 110 is positioned over the intended implantable medical device 132 and taking corrective action when that is not the case. In the embodiment of FIG. 7, measured temperature or an estimate of the maximum applied temperature-based on measured temperature of the intended implantable medical device 132 is the parameter to be used that correlates with the external recharger 110 being positioned over the intended implantable medical device 132.

[0053] Regarding the heat-based and temperature-based control of the recharge process in the example of FIG. 7, the same operations 402 through 418 are being used here.However, the estimated maximum applied temperature-based on the measured temperature of operation 414, or alternatively the raw temperature of operation 408, is also provided to an operation 502. An expected minimum temperature for the elapsed recharge time, which is a threshold that is independent of the temperature being measured at the implantable medical device, is found by a look-up within a look-up table of temperature versus time stored in local memory or elsewhere. This expected minimum temperature based on the look-up table is then used as a threshold to compare to the estimated maximum temperature based on the temperature measurement from operation 414. If the maximum estimated temperature does not exceed the threshold found in the look-up table, then a corrective action is taken at operation 504.

[0054] FIG. 8 shows a more detailed view of another example 600 of operations for controlling recharge that uses both heat-based control and temperature-based control while also utilizing the operations of FIG. 5 for purposes of confirming whether the external recharger 110 is positioned over the intended implantable medical device 132 and taking corrective action when that is not the case. In the embodiment of FIG. 8, an integral of the charge current sensed at the intended implantable medical device 132 at operation 412 is the parameter to be used that correlates with the external recharger 110 being positioned over the intended implantable medical device 132.

[0055] Regarding the heat-based and temperature-based control of the recharge process in the example of FIG. 8, the same operations 402 through 418 are being used here. However, the sensed charge current of operation 412 is also provided to an operation 602. The parameter that correlates with the external recharged 110 being positioned over the implantable medical device 132 may be based on the charge current to the battery of the implantable medical device 132. This charge current may be integrated in relation to recharge time at operation 602. For instance, this integration may provide a value for the total amount of charge the battery has received during the attempted recharge up to the present time. This result of the integration of charge current is then compared to a threshold for the integration of charge current, such as a threshold based on a total charge current for the recharge time at an operation 604. This threshold may be found in various ways, such asby integrating the amount of heat expected to be delivered to the implantable medical device ( e.g., QINS as indicated in equation (2) shown above or equation (3) as shown and discussed below) for the recharge time multiplied by a lower bound on efficiency, by integrating the metal loading on the external recharger 110 from operation 410 over the recharge time and multiplied by a lower bound on efficiency, by a look-up within a look-up table relating charge amount to recharge time, and the like. If the integral of sensed charge current of the implantable medical device 132 with respect to recharge time does not exceed the threshold, then a corrective action is taken at operation 604.

[0056] FIG. 9 shows a more detailed view of another example 700 of operations for controlling recharge that uses both heat-based control and temperature-based control while also utilizing the operations of FIG. 5 for purposes of confirming whether the external recharger 110 is positioned over the intended implantable medical device 132 and taking corrective action when that is not the case. In the embodiment of FIG. 9, estimated maximum temperature-based on measured temperature of the intended implantable medical device 132 is the parameter to be used that correlates with the external recharger 110 being positioned over the intended implantable medical device 132.

[0057] Regarding the heat-based and temperature-based control of the recharge process in the example of FIG. 9, the same operations 402 through 418 are being used here.However, the parameter that correlates with the external recharger 110 being positioned over the implantable medical device 132 is again based on a temperature measurement at the implantable medical device. The parameter may be the estimated maximum applied temperature- based on measured temperature of operation 414 that is provided to an operation 704. The threshold which is independent of the temperature measurement at the implantable medical device 132 may then be based on metal loading of the external recharger 110. The metal loading of the object receiving the recharge power on the external recharger 110 is provided from operation 410 to an operation 702. The metal loading on the external recharger 110 as a representation of heat that is expected to be input to the implantable medical device 132 during recharge that is then translated into an estimate of expected temperature output at the operation 702. This translation may be done by using a 1-pole or 2- pole transfer function discussed below.

[0058] To find the estimate of expected temperature-based on metal loading, the metal loading detected at the external recharger 110 is converted to an estimate of heat being applied to the object presenting the metal loading. The estimate of heat from metal loading at the external recharger 110 is given by equation (2) presented above, where QINS is again the estimate of heat at the object presenting the metal loading, PTANK is again the power output of the external recharger 110 and QPRIM is again the heat being generated in the recharging circuit coil of the external recharger 110. However, because the external recharger 110 may not be positioned over the intended implantable medical device 132 such that some other object is presenting the metal loading, the power to the battery may be assumed to be zero or some small percentage of total power being delivered to the object for purposes of finding the estimated heat from metal loading. For instance, the power to the battery may be assumed to be 0-10% of total power being provided for an implantable medical device with a metal enclosure or higher, such as up to 30%, for an implantable medical device with a non- metal enclosure. Thus, in equation (2), when the assumption is 0%, this results in the estimated heat being equal to the entire power being provided by the external recharger 110 to the object which maximizes the estimate of expected heat at the object, as shown in equation (3), where PINS is the total power being provided to the object presenting the metal loading.(3) QINS = PTANK-QPRIM = PINS

[0059] The estimate of expected heat from equation (2) or equation (3) may then be applied to the 1-pole or 2-pole transfer function at operation 702 to find the estimate of expected temperature-based on metal loading. The transfer functions represent a mathematical fit to experimentally collected data for a given implantable medical device regarding heat and temperature during recharge at a given implantation location within a patient and with a given external recharger. For instance, one example of a transfer function is a 1-pole transfer function expressed in a transform domain s, which takes the form shown in equation (4) , where dT(s) represents the estimated change in temperature resulting from the metal loading. Kp is based on the thermal coupling to the body of the implantable medical device, and rp which is the coefficient for the one pole is based on a combination ofthe thermal coupling to the body and the heat capacity of the implantable medical device. Likewise, the 2-pole transfer function takes the form shown in equation (5), where Kp is based on a combination of the thermal coupling to the body as well as relative position of the external recharger to the implantable medical device. The zero coefficient TZ, the first pole coefficient TPI, and the second pole coefficient TP2 are based on a combination of the thermal coupling to the body, the heat capacity of the implantable medical device, and a coefficient representing the position of the external recharger relative to the implantable medical device. Through the experimental data collection and mathematical fitting of the transfer functions, these transfer function variables are known for the implantable medical device 132 of interest. Therefore, applying the expected QINS from equation (2) or (3) to the transfer function of either equation (4) or (5) allows computation of the expected temperature from metal loading.(4) dT(s) / QiNs(s) = KP*1 / (1+TP*S)(5) dT(s) / QiNs(s) = Kp*(l+ TZ*S) / ((1+TPI*S) (1+TP2*S))

[0060] The transfer functions represented as equations (4) and (5) above could be trained to always under predict the expected temperature to ensure that the expected temperature which is being used as a threshold indicates a significant problem when the estimated temperature based on the temperature measurement at the implantable medical device at operation 414 is lower than the threshold. If the maximum estimated temperature based on temperature measurement of the implantable medical device 132 does not exceed the expected temperature based on metal loading found in operation 702, then a corrective action is taken at operation 704.

[0061] In the scenario where the implantable medical device 132 is performing the analysis of whether the external recharger 110 is properly positioned, the external recharger 110 may provide its heat level information to the implantable medical device 132. The implantable medical device may then apply the dynamic transfer function to produce the expected temperature based on metal loading at operation 702 that is then compared to theestimated temperature based on measurement at operation 704 to determine whether to take a corrective action.

[0062] FIG. 10 shows a more detailed view of another example 800 of operations for controlling recharge that uses both heat-based control and temperature-based control while also utilizing the operations of FIG. 5 for purposes of confirming whether the external recharger 110 is positioned over the intended implantable medical device 132 and taking corrective action when that is not the case. In the embodiment of FIG. 10, temperature profile measured at the intended implantable medical device 132 is the parameter to be used. The temperature profile is based on temperature measured at the implantable medical device and correlates with the external recharger 110 being positioned over the intended implantable medical device 132.

[0063] Regarding the heat-based and temperature-based control of the recharge process in the example of FIG. 10, the same operations 402 through 418 are being used here except operation 406 is replaced with operation 804. Additionally, operations 408 and 412 provide output to an operation 806. Looking to an operation 802, here a time sequencing of recharge energy algorithm produces a time sequence that is provided to operation 804 where it is applied to the output of the recharge power 210 by the external recharger 110. Thus, the recharge power 210 has a temporal aspect not otherwise present due to the time sequencing which results in a particular heat profile. For example, a time sequencing of the recharge power could produce 500 milliwatts of heat at the object receiving the recharge energy for two minutes followed by 30 seconds of zero milliwatts of heat at the object. As another example of time sequencing, recharge power could be duty cycled periodically. This time sequencing of the recharge power has a corresponding pre-defined step response curve which serves as a threshold that is independent of the temperature measurement at the implantable medical device. The temperature profile of the implantable medical device 132 that is measured during the recharge is then compared to the pre-defined step response acting as the threshold. If the measured temperature profile does not exceed, i.e., is below, the pre-defined step response curve found in operation 806 for at least a minimum number of samples, then a corrective action is taken at operation 808.

[0064] As an alternative, the parameter that correlates with the external recharger being positioned over the implantable medical device may be based on charge current or another 1signal at operation 806 which has been provided by operation 412 in the case of charge current. The threshold may then be a pre-defined step response for charge current that is independent of the measured charge current at operation 412 and that corresponds to the sequencing of power at operation 804 based on the time sequencing algorithm of operation 802. Thus, operation 806 may determine whether the parameter based on the measured charge current meets the threshold that is independent of the measured charge current and if not, then a corrective action is taken at operation 808.

[0065] Determining whether the external recharger 110 is positioned over the implantable medical device 132 that is intended to be recharged even while also relying at least in part on temperature-based control of the recharge allows for the mispositioning of the external recharger 110 to be detected and corrective action to be taken. Therefore, the temperaturebased control of recharge remains compatible with situations where the external recharger 110 may be mispositioned including scenarios with there is a bilateral configuration of implantable medical devices that may give rise to the external recharger 110 being mistakenly placed over the unintended implantable medical device 162.

[0066] Each of the examples of detecting whether a corrective action is needed as provided in FIGS. 6-10 may be used as the sole manner of determining whether to take a corrective action. However, in other embodiments, any combination of two or more of these examples from FIGS. 6-10 may be combined to ultimately determine whether to take a corrective action. As one example of the combination, a corrective action may not be taken until all of the examples shown in FIGS. 6-10 for determining if a corrective action should be taken are performed and all indicate that the corrective action should be taken. As another example of the combination, one example from FIGS. 6-10 that uses a parameter based on measured temperature at the implantable medical device may be combined with another example that does not use a parameter based on a temperature measurement, such as combining the comparison of estimated maximum temperature with the temperature from the look-up table from the example of FIG. 7 being combined with the proximity signal strength being compared to the threshold base on the expected proximity signal strength from the example of FIG. 6, where both must indicate a need for a corrective action in order to take the corrective action. As another example of the combination, one example from FIGS. 6-10 that uses parameter value based on measured temperature at the implantable medical devicemay be combined with another example that does not use a parameter based on a temperature measurement, such as combining the comparison of estimated maximum temperature with the estimated temperature based on metal loading from the example of FIG. 9 being combined with the parameter based on a measurement of charge current compared to the charge current-based threshold from the example of FIG. 8, where both must indicate a need for a corrective action in order to take the corrective action.

[0067] The invention may further be described by reference to the following numbered paragraphs:

[0068] Example 1. A method of recharging an implantable medical device, comprising: outputting recharging power from an external recharger; obtaining a first parameter based on a temperature measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device; determining whether the first parameter meets a first threshold, wherein the first threshold is independent of the temperature measurement at the implantable medical device and indicates a position of the external recharger relative to the implantable medical device; and taking an action based on whether the first parameter is above or below the first threshold.

[0068] Example 2. The method of example 1 , wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device at an elapsed recharge time, wherein the first threshold is based on a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0069] Example 3. The method of any of examples 1 or 2, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises a proximity signal strength between the external recharger and the implantable medical device,wherein a second threshold that indicates that the external recharger is positioned over the implantable medical device is based on an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

[0070] Example 4. The method of any of examples 1 or 2, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises an integral of a sensed charge current with respect to elapsed recharge time at the implantable medical device, wherein a second threshold is based on an integral of an expected heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

[0071] Example 5. The method of any of examples 1, 3, or 4, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device, wherein the first threshold is based on metal loading on the external recharger, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0072] Example 6. The method of any of examples 1, 3, or 4, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device, wherein the first threshold comprises a pre-defined step response curve based on a time sequencing of recharge power by the external recharger, and wherein the action is taken when the temperature profile is below the pre-defined step response curve.

[0073] Example 7. The method of any of examples 1-6, wherein the action comprises the external recharger stopping the outputting of recharge power.

[0074] Example 8. The method of any of examples 1-6, wherein the action comprises the external recharger reducing the recharge power being output.

[0075] Example 9. The method of any of examples 1-6, wherein the external recharger is using temperature-based control of a level of recharge power being output and wherein theaction comprises switching to a heat-based control of the level of recharge power being output.

[0076] Example 10. The method of any of examples 1-9, wherein the action comprises a notification that provides feedback regarding the position of the external recharger relative to the implantable medical device.

[0077] Example 11. The method of examples 1-10, wherein the action comprises a notification including a countdown timer until the recharge terminates if the external recharger is not positioned over the implantable medical device.

[0078] Example 12. The method of any of examples 7-9, wherein the action further comprises transmitting, by the implantable medical device, a flag to the external recharger to cause the external recharger to take action.

[0079] Example 13. The method of any of examples 1-12, wherein the external recharger determines the first threshold.

[0080] Example 14. The method of any of examples 1-12, wherein the implantable medical device determines the first threshold.

[0081] Example 15. A system, comprising: an external recharger configured to output recharging power; and an implantable medical device configured to receive the recharging power; wherein at least one of the external recharger or the implantable medical device is further configured to: obtain a first parameter based on a temperature measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the first threshold.

[0082] Example 16. The system of example 15, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device at an elapsed recharge time, wherein the first threshold is obtained from a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0083] Example 17. The system of any of examples 15 or 16, wherein the external recharger further comprises a first proximity communication circuit, wherein the implantable medical device further comprises a second proximity circuit, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises a proximity signal strength between the first proximity circuit of the external recharger and the second proximity circuit of the implantable medical device, and wherein a second threshold that indicates the external recharger is positioned over the implantable medical device is based on an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

[0084] Examplel8. The system of any of examplesl5 or 16, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises an integral of a sensed charge current with respect to elapsed recharge time at the implantable medical device, wherein a second threshold that indicates the external recharger is positioned over the implantable medical device is based on an integral of heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

[0085] Example 19. The system of any of examples 15, 17, or 18, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device, wherein the first threshold is based on ametal loading on the external recharger, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0086] Example 20. The system of any of examples 15, 17, or 18, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device, wherein the first threshold comprises a pre-defined step response curve based on a time sequencing of recharge power by the external recharger, and wherein the action is taken when the temperature profile is below the pre-defined step response curve.

[0087] Example 21. An implantable medical device, comprising: a processor, a recharge circuit that is coupled to the processor and that is for receiving recharging power from an external recharger, wherein the processor is configured to: obtain a first parameter that is based on a temperature measurement at the implantable medical device and that correlates with the external recharger being positioned over the implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the first threshold.

[0088] Example 22. The implantable medical device of example 21, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device at an elapsed recharge time, wherein the first threshold is obtained from a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0089] Example 23. The implantable medical device of any of examples 21 or 22, wherein the implantable medical device further comprises a proximity circuit, wherein a second parameter that correlates with the external recharger being positioned over theimplantable medical device comprises a proximity signal strength between a proximity circuit of the external recharger and the proximity circuit of the implantable medical device, wherein a second threshold that indicates the external recharger is positioned over the implantable medical device comprises an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

[0090] Example 24. The implantable medical device of any of example 21 or 22, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises an integral of a sensed charge current with respect to elapsed recharge time at the implantable medical device, wherein a second threshold that indicates that the external recharger is positioned over the implantable medical device is based on an integral of heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

[0091] Example 25. The implantable medical device of any of example 21, 23, or 24, wherein the first parameter comprises an estimated maximum temperature that is based on the temperature measurement at the implantable medical device, wherein the first threshold is based on a metal loading on the external recharger, and wherein the action is taken when the implantable medical device estimated maximum temperature is below the first threshold.

[0092] Example 26. The implantable medical device of any of examle 21, 23, or 24, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device, wherein the first threshold comprises a predefined step response curve based on a time sequencing of recharge power by the external recharger, and wherein the action is taken when the temperature profile is below the predefined step response curve.

[0093] Example 27. An external recharger, comprisinga processor, a recharge circuit coupled to the processor, wherein the processor is configured to: cause the recharge circuit to begin outputting recharging power;obtain a first parameter that is based on a temperature measurement at the implantable medical device and that correlates with the external recharger being positioned over an implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the threshold.

[0094] Example 28. The external recharger of example 27, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device at an elapsed recharge time, wherein the first threshold is obtained from a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

[0095] Example 29. The external recharger of any of examples 27 or 28, further comprising: a proximity circuit, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises a proximity signal strength between the proximity circuit of the external recharger and a proximity circuit of the implantable medical device, wherein a second threshold that indicates the external recharger is positioned over the implantable medical device comprises an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

[0096] Example 30. The external recharger of any of examples 27 or 28, wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises an integral of a sensed charge current with respect toelapsed recharge time at the implantable medical device, wherein a second threshold that indicates the external recharger is positioned over the implantable medical device is based on an integral of heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

[0097] Example 31. The external recharger of any of examples 27, 29, or 30, wherein the first parameter comprises an estimated maximum temperature that is based on the temperature measurement at the implantable medical device, wherein the first threshold is based on a metal loading on the external recharger, and wherein the action is taken when the estimated maximum temperature is below the first threshold examples 27, 29, or 30, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device , wherein the first threshold comprises a pre-defined step response curve based on a time sequencing of recharge power by the external recharger, and wherein the action is taken when the temperature profile is below the pre-defined step response curve.

[0098] Example 33. A system, comprising:an external recharger configured to output recharging power; and an implantable medical device configured to receive the recharging power;wherein, while the external recharger is outputting the recharging power, at least one of the external recharger or the implantable medical device is further configured to: obtain a proximity signal strength value between the external recharger and the implantable medical device wherein the proximity signal strength correlates with the external recharger being positioned over the implantable medical device; determine whether the proximity signal strength meets a threshold based on an expected proximity signal strength that indicates that the external recharger is positioned over the implantable medical device; and take an action based on whether the proximity signal strength is above or below the threshold.

[0099] Example34. A system, comprising: an external recharger configured to output recharging power according to a time sequence; and an implantable medical device configured to receive the recharging power; wherein at least one of the external recharger or the implantable medical device is further configured to: obtain a parameter based on a chargecurrent measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device;determine whether the charge current parameter that correlates with external recharger being positioned over the implantable medical device meets a threshold that is independent of the charge current measurement at the implantable medical device and that is based on the time sequence of the recharging power that indicates the external recharger is positioned over the implantable medical device; andtake an action based on whether the parameter is above or below the threshold.

[0100] While embodiments have been particularly shown and described, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A system ( 100), comprising : an external recharger (110) configured to output recharging power (210); and an implantable medical device (132) configured to receive the recharging power; wherein at least one of the external recharger or the implantable medical device is further configured to: obtain a first parameter based on a temperature measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the first threshold.

2. The system of claim 1, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device (132) at an elapsed recharge time, wherein the first threshold is obtained from a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

3. The system of any of claims 1 or 2, wherein the external recharger (110) further comprises a first proximity circuit (236, 238), wherein the implantable medical device (132) further comprises a second proximity circuit (250, 252), wherein a second parameter that correlates with the external recharger being positioned over the implantable medical device comprises a proximity signal strength between the firstproximity circuit of the external recharger and the second proximity circuit of the implantable medical device, and wherein a second threshold that indicates the external recharger is positioned over the implantable medical device is based on an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

4. The system of any of claims 1 or 2, wherein a second parameter that correlates with the external recharger (110) being positioned over the implantable medical device (132) comprises an integral of a sensed charge current with respect to elapsed recharge time at the implantable medical device, wherein a second threshold that indicates the external recharger is positioned over the implantable medical device is based on an integral of heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

5. The system of any of claims 1, 3, or 4, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device (132), wherein the first threshold is based on a metal loading on the external recharger (110), and wherein the action is taken when the estimated maximum temperature is below the first threshold.

6. The system of any of claims 1, 3, or 4, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device (132), wherein the first threshold comprises a pre-defined step response curve based on a time sequencing of recharge power (210) by the external recharger (110), andwherein the action is taken when the temperature profile is below the pre-defined step response curve.

7. An implantable medical device (132), comprising: a processor (246), a recharge circuit (240) that is coupled to the processor and that is for receiving recharging power (210) from an external recharger (110), wherein the processor is configured to: obtain a first parameter that is based on a temperature measurement at the implantable medical device and that correlates with the external recharger being positioned over the implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the first threshold.

8. The implantable medical device of claim 7, wherein the first parameter comprises an estimated maximum temperature based on the temperature measurement at the implantable medical device (132) at an elapsed recharge time, wherein the first threshold is obtained from a look-up table of temperature versus time for the elapsed recharge time, and wherein the action is taken when the estimated maximum temperature is below the first threshold.

9. The implantable medical device of any of claims 7 or 8, wherein the implantable medical device (132) further comprises a proximity circuit (250, 252), wherein a second parameter that correlates with the external recharger (110) being positioned over the implantable medical device comprises a proximity signal strength between a proximity circuit (236, 238) of the external recharger and the proximity circuit of the implantable medical device,wherein a second threshold that indicates the external recharger is positioned over the implantable medical device comprises an expected proximity signal strength, and wherein the action is taken when the proximity signal strength is below the second threshold in addition to the first parameter being below the first threshold.

10. The implantable medical device of any of claims 7 or 8, wherein a second parameter that correlates with the external recharger (110) being positioned over the implantable medical device (132) comprises an integral of a sensed charge current with respect to elapsed recharge time at the implantable medical device, wherein a second threshold that indicates that the external recharger is positioned over the implantable medical device is based on an integral of heat at the implantable medical device multiplied by a lower bound on efficiency, and wherein the action is taken when the integrated charge current is below the second threshold in addition to the first parameter being below the first threshold.

11. An external recharger (110), comprising: a processor (230), a recharge circuit (234) coupled to the processor, wherein the processor is configured to: cause the recharge circuit to begin outputting recharging power (210); obtain a first parameter that is based on a temperature measurement at an implantable medical device (132) and that correlates with the external recharger being positioned over the implantable medical device; determine whether the first parameter meets a first threshold that is independent of the temperature measurement at the implantable medical device and that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the first parameter is above or below the threshold.

12. The external recharger of claim 11, wherein the first parameter comprises an estimated maximum temperature that is based on the temperature measurement at the implantable medical device (132), wherein the first threshold is based on a metal loading on the external recharger (110), and wherein the action is taken when the estimated maximum temperature is below the first threshold.

13. The external recharger of claim 11, wherein the first parameter comprises a temperature profile based on the temperature measurement at the implantable medical device (132), wherein the first threshold comprises a pre-defined step response curve based on a time sequencing of recharge power (210) by the external recharger (110), and wherein the action is taken when the temperature profile is below the pre-defined step response curve.

14. A system ( 100), comprising : an external recharger (110) configured to output recharging power (210); and an implantable medical device (132) configured to receive the recharging power; wherein, while the external recharger is outputting the recharging power, at least one of the external recharger or the implantable medical device is further configured to: obtain a proximity signal strength value between the external recharger and the implantable medical device wherein the proximity signal strength correlates with the external recharger being positioned over the implantable medical device; determine whether the proximity signal strength meets a threshold based on an expected proximity signal strength that indicates that the external recharger is positioned over the implantable medical device; and take an action based on whether the proximity signal strength is above or below the threshold.

15. A system ( 100), comprising :31an external recharger (110) configured to output recharging power (210) according to a time sequence; and an implantable medical device (132) configured to receive the recharging power; wherein at least one of the external recharger or the implantable medical device is further configured to: obtain a parameter based on a charge current measurement at the implantable medical device that correlates with the external recharger being positioned over the implantable medical device; determine whether the charge current parameter that correlates with external recharger being positioned over the implantable medical device meets a threshold that is independent of the charge current measurement at the implantable medical device and that is based on the time sequence of the recharging power that indicates the external recharger is positioned over the implantable medical device; and take an action based on whether the parameter is above or below the threshold.

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