Electrode monitoring

Abstract

Presented herein are techniques for monitoring a physical state (e.g., surface area) of one or more implantable electrodes of an implantable medical device / implantable component and using the physical state to adjust operation of the implantable component. More specifically, an exemplary implantable medical device includes one or more electrodes that are used to deliver electrical stimulation (current signals) to a recipient.

Description

ELECTRODE MONITORINGBACKGROUNDField of the Invention[oooi] The present invention relates generally to techniques for monitoring the electrodes of implantable medical devices.Related Art

[0002] Medical devices have provided a wide range of therapeutic benefits to recipients over recent decades. Medical devices can include internal or implantable components / devices, external or wearable components / devices, or combinations thereof (e.g., a device having an external component communicating with an implantable component). Medical devices, such as traditional hearing aids, partially or fully-implantable hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc.), pacemakers, defibrillators, functional electrical stimulation devices, and other medical devices, have been successful in performing lifesaving and / or lifestyle enhancement functions and / or recipient monitoring for a number of years.

[0003] The types of medical devices and the ranges of functions performed thereby have increased over the years. For example, many medical devices, sometimes referred to as “implantable medical devices,” now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease / injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and / or data received from external devices that are part of, or operate in conjunction with, implantable components.SUMMARY

[0004] In one aspect, a first method is provided. The first method comprises: performing a plurality of impedance measurements at one or more implantable electrodes over a period of time; tracking the plurality of impedance measurements over the period of time to detect a nonlinear increase in an impedance of at least one implantable electrode of the one or more implantable electrodes; and in response to detecting a non-linear increase in the impedance ofthe at least one implantable electrode, generating an output indicating a reduction in a surface area of the at least one implantable electrode of the one or more implantable electrodes.

[0005] In another aspect, a second method is provided. The second method comprises: delivering, over a period of time, stimulation pulses to a recipient via at least one implantable electrode; monitoring, over the period of time, an impedance of the at least one implantable electrode; based on the monitoring, identifying a non-linear change in the impedance of the at least one implantable electrode indicative of a change in a surface area of the at least one implantable electrode; and initiating one or more remedial actions in response to identifying the change in the surface area of the at least one implantable electrode.

[0006] In another aspect, a system is provided. The system comprises: a display screen; a memory; and at least one processor operably coupled to the display screen and the memory, wherein the at least one processor is configured to: control a plurality of stimulating electrodes of an implantable medical device implanted in a recipient to deliver a plurality of stimulation signals to the recipient; obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes; and analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes.

[0007] In another aspect, one or more non-transitory computer readable storage media comprising instructions are provided. The instructions when executed by a processor, cause the processor to: control a plurality of stimulating electrodes of an implantable medical device implanted in a recipient to deliver a plurality of stimulation signals to the recipient; obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes; and analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:

[0009] FIG. 1A is a schematic diagram illustrating a cochlear implant system with which aspects of the techniques presented herein can be implemented;[ooio] FIG. IB is a side view of a recipient wearing a sound processing unit of the cochlear implant system of FIG. 1A;[ooii] FIG. 1C is a schematic view of components of the cochlear implant system of FIG. 1 A;

[0012] FIG. ID is a block diagram of the cochlear implant system of FIG. 1A;

[0013] FIG. IE is a schematic diagram illustrating a computing device with which aspects of the techniques presented herein can be implemented;

[0014] FIG. 2A is an example of an initial clinical session, in which an external device has a connection to the implant and the stimulating assembly, which has an electrode with an initial surface area;

[0015] FIG. 2B is a top view of the stimulating assembly and the electrode of FIG. 2A at the time of the initial clinical session;

[0016] FIG. 2C is an example of a new clinical session, in which the electrode has corroded (worn, dissolved, eroded, etc.) and has a new surface area, which is a reduced surface area in comparison to the initial surface area;

[0017] FIG. 2D is a top view of the stimulating assembly and the electrode of FIG. 2C at the time of the new clinical session;

[0018] FIG. 2E is an example of electrode “wear,” in which the electrode can have a different amount or slope of wear across its surface;

[0019] FIG. 2F is an example of electrode “dissolution,” in which the electrode can have an uneven surface (e.g., rough, bumps, porosity, etc.);

[0020] FIG. 2G is an example of electrode “corrosion,” in which the electrode can have a thin layer of foreign material at least partially covering the upper surface thereof;

[0021] FIG. 3 is a flowchart of a method for determining a change in surface area based on a change in impedance, according to an example embodiment;

[0022] FIG. 4A is a flowchart of a method according to an example embodiment;

[0023] FIG. 4B is a flowchart of a method according to an example embodiment;

[0024] FIG. 5A is a graph illustrating how the change in impedance is proportional to the change in surface area, and that the rate of change in impedance tends to increase with reduction in surface area;

[0025] FIG. 5B is an example to illustrate how the curve of FIG. 5A would change if the variable M is changed;

[0026] FIG. 5 C is an example to illustrate how the curve of FIG. 5A would change if the variable N is decreased;

[0027] FIG. 5D is an example to illustrate how the curve of FIG. 5A would change if the variable N is increased;

[0028] FIG. 5E is a graph that shows a trend in the average change in impedance over time in a cochlear implant;

[0029] FIG. 6 is a flowchart of a method according to an example embodiment;

[0030] FIG. 7 is a flowchart of a method according to an example embodiment;

[0031] FIG. 8 is a flowchart of a method according to an example embodiment;

[0032] FIG. 9 is a flowchart of another method, which is a variation on the method of FIG. 8, according to another example embodiment;

[0033] FIG. 10 is a schematic diagram illustrating a vestibular stimulator system with which aspects of the techniques presented herein can be implemented; and

[0034] FIG. 11 is a schematic diagram illustrating a retinal prosthesis system with which aspects of the techniques presented herein can be implemented.DETAILED DESCRIPTION

[0035] Presented herein are techniques for monitoring a physical state (e.g., surface area) of one or more implantable electrodes of an implantable medical device / implantable component and using the physical state to adjust operation of the implantable component. More specifically, an exemplary implantable medical device includes one or more electrodes that are used to deliver electrical stimulation (current signals) to a recipient. In accordance withembodiments presented herein, the implantable medical device is configured to obtain / capture data associated with one or more electrode (“electrode data”) and use the electrode data to determine a level of wear, dissolution, or corrosion of at least one of the electrodes. The data is obtained in situ (e.g., in a non-invasive manner while the electrodes are implanted in the recipient). In one non-limiting example embodiment, the implantable medical device is a cochlear implant. In certain example embodiments, the obtained electrode data can include impedance data (impedances), or other electrical data (e.g., voltages, currents, etc.) that can be used to derive (e.g., calculate, estimate, etc.) impedances.

[0036] Electrodes can undergo a loss of material (loss of surface area) as a result of, for example, delivery of stimulation signals. The loss of surface area can, in turn, lead to safety issues (e.g., exceeding the Shannon limit for neurostimulation), or may lead to electrode failure (and the need for explantation of the failed electrode / array). However, this phenomenon is hard to predict and difficult to manage using known controllable parameters (e.g., electrical stimulation settings / parameters), due to large variability in both in vitro and field data, as well as the unknown influence of many other factors. Existing implantable components / devices do not implement a method of detection or monitoring for the loss of electrode material, specifically. In particular, monitoring electrode corrosion in cochlear implants and other neural stimulators is difficult and there are no proven technologies available that can do this. Known techniques, such as cyclic voltammetry and impedance spectroscopy, are relatively untested and unproven in terms of working in situ.

[0037] As such, presented herein are systems and methods for monitoring / detecting the loss of electrode material and initiating one or more remedial actions based herein. As noted, the reduction in surface area of an electrode can be due to various factors, including but not limited to wear, dissolution, and / or corrosion of the material forming the tissue-facing surface of the electrode. The reduction in surface area can linear or non-linear (e.g., the surface area could change in a non-linear way due to increasing stimulation charge densities).

[0038] In certain embodiments, devices / systems (e.g., clinical systems, implantable components, mobile devices, etc.) can be enhanced with the ability to monitor / track a history of impedance data (impedance test results) associated with individual electrodes, and analyze the impedance data to determine whether there is an abnormal change (e.g., unusual rise) in impedance, which is indicative of a reduction in electrode surface area. When an abnormal change in impedance is detected, the device can initiate one or more remedial actions. For example, in certain embodiments, the device can generate a warning or alert regarding theabnormal change in impedance (and / or regarding the reduced surface area of the electrode). In other embodiments, the system can use the analysis of the impedance data in a closed-loop control system to, for example, adjust one or more stimulation parameters of the implantable medical device.

[0039] For example, an implantable medical device could be configured to perform in vivo analysis of data associated with one or more electrodes and, accordingly, determine an “amount” of wear, dissolution, or corrosion, in terms of an amount of electrode material that has been lost, and / or an amount of electrode material that is remaining. In certain embodiments, the amount of electrode material can be represented by a surface area (e.g., based on length, width, depth / thickness, or a combination thereof). Additionally or alternatively, the obtained data can be used to determine a “rate” of wear, dissolution, or corrosion, in terms of how fast the electrode is losing its effective surface area. The electrode data can represent a current physical state of the electrode, a future / predicted physical state of the electrode, a current rate of wear, dissolution, or corrosion, a future / predicted rate of wear, dissolution, or corrosion. The electrode data can represent, or may be used to derive (calculate, estimate), a projected lifespan of the electrode (e.g., in terms of months / years of useful life remaining, and / or a date (e.g., month / year) corresponding to the end of useful life for the electrode.

[0040] Based on the analyzing the obtained electrode data, one or more remedial actions can be taken, as needed or desired. The one or more remedial actions can include, but are not limited to, identifying an adjustment of a stimulation parameter or operational setting of the medical device to change a future rate of wear, dissolution, or corrosion, instructing the recipient to use the medical device in a different manner, etc.

[0041] Thus, the system and techniques described herein provide a method to detect the loss of electrode surface area so that, for example, stimulation parameters or operational settings can be adjusted to minimize further loss due to wear, dissolution, and / or corrosion, effectively avoiding the complete failure of the electrode channel (which may otherwise occur in the absence of any adjustments to stimulation parameters, operational settings, or other preventative actions). In addition to improving overall reliability and lifetime of implantable medical devices, the system and techniques described herein can also provide users (e.g., implant recipients, clinicians, etc.) with a greater degree of assurance that the electrodes will not fail (or at least would not fail without providing any warning to that effect). Further, the system and techniques described herein can enable implant recipients to enjoy the benefits of certain functions without them being limited due to the uncertainty in predicting electrodewear, dissolution, and / or corrosion that results in a reduction of usable electrode surface area, as will be explained in detail below.

[0042] There are a number of different types of devices in / with which embodiments of the present invention may be implemented. Merely for ease of description, the techniques presented herein are primarily described with reference to a specific device in the form of a cochlear implant system. However, it is to be appreciated that the techniques presented herein may also be partially or fully implemented by any of a number of different types of devices, including hearing devices, implantable medical devices, wearable devices (e.g., smartwatches), consumer electronic devices (e.g., mobile phones), etc. As used herein, the term “hearing device” is to be broadly construed as any device that delivers sound signals to a user in any form, including in the form of acoustical stimulation, mechanical stimulation, electrical stimulation, etc. As such, a hearing device can be a device for use by a hearing -impaired person (e.g., hearing aids, middle ear auditory prostheses, bone conduction devices, direct acoustic stimulators, electro-acoustic hearing prostheses, auditory brainstem stimulators, bimodal hearing prostheses, bilateral hearing prostheses, dedicated tinnitus therapy devices, tinnitus therapy device systems, combinations or variations thereof, etc.) or a device for use by a person with normal hearing (e.g., consumer devices that provide audio streaming, consumer headphones, earphones, and other listening devices). In other examples, the techniques presented herein can be implemented by, or used in conjunction with, various implantable medical devices, such as vestibular devices (e.g., vestibular implants), visual devices (i.e., bionic eyes), sensors, pacemakers, drug delivery systems, defibrillators, functional electrical stimulation devices, catheters, seizure devices (e.g., devices for monitoring and / or treating epileptic events), sleep apnea devices, electroporation devices, etc.

[0043] FIGs. 1A-1D illustrates an example cochlear implant system 102 with which aspects of the techniques presented herein can be implemented. The cochlear implant system 102 comprises an external component 104 that is configured to be directly or indirectly attached to the body of the user, and an intemal / implantable component 112 that is configured to be implanted in or worn on the head of the user. In the examples of FIGs. 1A-1D, the implantable component 112 is sometimes referred to as a “cochlear implant.” FIG. 1A illustrates the cochlear implant 112 implanted in the head 154 of a user, while FIG. IB is a schematic drawing of the external component 104 worn on the head 154 of the user. FIG. 1C is another schematic view of the cochlear implant system 102, while FIG. ID illustrates further details of thecochlear implant system 102. For ease of description, FIGs. 1A-1D will generally be described together.

[0044] In the examples of FIGs. 1A-1D, the external component 104 comprises a sound processing unit 106, an external coil 108, and generally, a magnet fixed relative to the external coil 108. The cochlear implant 112 includes an implantable coil 114, an implant body 134, and an elongate stimulating assembly 116 configured to be implanted in the user’s cochlea. In one example, the sound processing unit 106 is an off-the-ear (OTE) sound processing unit, sometimes referred to herein as an OTE component, which is configured to send data and power to the implantable component 112. In general, an OTE sound processing unit is a component having a generally cylindrically shaped housing 111 and which is configured to be magnetically coupled to the user’s head 154 (e.g., includes an integrated external magnet 150 configured to be magnetically coupled to an intemal / implantable magnet 152 in the implantable component 112). The OTE sound processing unit 106 also includes an integrated external (headpiece) coil 108 (the external coil 108) that is configured to be inductively coupled to the implantable coil 114.

[0045] It is to be appreciated that the OTE sound processing unit 106 is merely illustrative of the external devices that could operate with implantable component 112. For example, in alternative examples, the external component 104 may comprise a behind-the-ear (BTE) sound processing unit configured to be attached to, and worn adjacent to, the recipient’s ear. In general, a BTE sound processing unit comprises a housing that is shaped to be worn on the outer ear of the user and is connected to the separate external coil assembly via a cable, where the external coil assembly is configured to be magnetically and inductively coupled to the implantable coil 114. It is also to be appreciated that alternative external components could be located in the user’s ear canal, worn on the body, etc.

[0046] Although the cochlear implant system 102 includes the sound processing unit 106 and the cochlear implant 112, as described below, the cochlear implant 112 can operate independently from the sound processing unit 106, for at least a period, to stimulate the user. For example, the cochlear implant 112 can operate in a first general mode, sometimes referred to as an “external hearing mode,” in which the sound processing unit 106 captures sound signals which are then used as the basis for delivering stimulation signals to the user. The cochlear implant 112 can also operate in a second general mode, sometimes referred as an “invisible hearing” mode, in which the sound processing unit 106 is unable to provide sound signals to the cochlear implant 112 (e.g., the sound processing unit 106 is not present, the soundprocessing unit 106 is powered-off, the sound processing unit 106 is malfunctioning, etc.). As such, in the invisible hearing mode, the cochlear implant 112 captures sound signals itself via implantable sound sensors and then uses those sound signals as the basis for delivering stimulation signals to the user. Further details regarding operation of the cochlear implant 112 in the external hearing mode are provided below, followed by details regarding operation of the cochlear implant 112 in the invisible hearing mode. It is to be appreciated that reference to the external hearing mode and the invisible hearing mode is merely illustrative and that the cochlear implant 112 could also operate in alternative modes.

[0047] In FIGs. 1A and 1C, the cochlear implant system 102 is shown with an external device 110, configured to implement aspects of the techniques presented. The external device 110, which is shown in greater detail in FIG. 1 E, is a computing device, such as a personal computer (e.g., laptop, desktop, tablet), a mobile phone (e.g., smartphone), remote control unit, etc. The external device 110 and the cochlear implant system 102 (e.g., sound processing unit 106 or the cochlear implant 112) wirelessly communicate via a bi-directional communication link 126. The bi-directional communication link 126 may comprise, for example, a short-range communication, such as Bluetooth link, Bluetooth Low Energy (BLE) link, a proprietary link, etc.

[0048] Returning to the example of FIGs. 1A-1D, the sound processing unit 106 of the external component 104 also comprises one or more input devices configured to capture and / or receive input signals (e.g., sound or data signals) at the sound processing unit 106. The one or more input devices include, for example, one or more sound input devices 118 (e.g., one or more external microphones, audio input ports, telecoils, etc.), one or more auxiliary input devices 128 (e.g., audio ports, such as a Direct Audio Input (DAI), data ports, such as a Universal Serial Bus (USB) port, cable port, etc.), and a short-range wireless transmitter / receiver (wireless transceiver) 120 (e.g., for communication with the external device 110), each located in, on or near the sound processing unit 106. However, it is to be appreciated that one or more input devices may include additional types of input devices and / or less input devices (e.g., the short- range wireless transceiver 120 and / or one or more auxiliary input devices 128 could be omitted).

[0049] The sound processing unit 106 also comprises the external coil 108, a charging coil 130, a closely-coupled radio frequency transmitter / receiver (RF transceiver) 122, at least one rechargeable battery 132, and an external sound processing module 124. The external sound processing module 124 can be configured to perform a number of operations and can be formedby one or more processors (e.g., one or more Digital Signal Processors (DSPs), one or more uC cores, etc.), firmware, software, etc. arranged to perform operations described herein. That is, external sound processing module 124 can be implemented as firmware elements, partially or fully implemented with digital logic gates in one or more application-specific integrated circuits (ASICs), partially or fully in software, etc. Although certain functional operations may be described as being implemented / performed at the external sound processing module 124, it is to be appreciated that these elements could also or alternatively be implemented / performed as part of the implantable sound processing module 158, as part of the external device 110, etc.

[0050] Returning to the example of FIGs. 1A-1D, the implantable component 112 comprises an implant body (main module) 134, a lead region 136, and the intra-cochlear stimulating assembly 116, all configured to be implanted under the skin (tissue) 115 of the user. The implant body 134 generally comprises a hermetically-sealed housing 138 that includes, in certain examples, at least one power source 125 (e.g., one or more batteries, one or more capacitors, etc.) 125, in which RF interface circuitry 140 and a stimulator unit 142 are disposed. The implant body 134 also includes the intemal / implantable coil 114 that is generally external to the housing 138, but which is connected to the RF interface circuitry 140 via a hermetic feedthrough (not shown in FIG. ID).

[0051] As noted, stimulating assembly 116 is configured to be at least partially implanted in the user’s cochlea. Stimulating assembly 116 includes a plurality of longitudinally spaced intra-cochlear electrical stimulating contacts (electrodes) 144 that collectively form a contact array (electrode array) 146 for delivery of electrical stimulation (current) to the recipient’s cochlea. Stimulating assembly 116 extends through an opening in the recipient’s cochlea (e.g., cochleostomy, the round window, etc.) and has a proximal end connected to stimulator unit 142 via lead region 136 and a hermetic feedthrough (not shown in FIG. ID). Lead region 136 includes a plurality of conductors (wires) that electrically couple the electrodes 144 to the stimulator unit 142. The implantable component 112 also includes an electrode outside of the cochlea, sometimes referred to as the extra-cochlear electrode (ECE) 139.

[0052] As noted, the cochlear implant system 102 includes the external coil 108 and the implantable coil 114. The external magnet 150 is fixed relative to the external coil 108 and the intemal / implantable magnet 152 is fixed relative to the implantable coil 114. The external magnet 150 and the intemal / implantable magnet 152 fixed relative to the external coil 108 and the intemal / implantable coil 114, respectively, facilitate the operational alignment of the external coil 108 with the implantable coil 114. This operational alignment of the coils enablesthe external component 104 to transmit data and power to the implantable component 112 via a closely-coupled wireless link 148 formed between the external coil 108 with the implantable coil 114. In certain examples, the closely-coupled wireless link 148 is a radio frequency (RF) link. However, various other types of energy transfer, such as infrared (IR), electromagnetic, capacitive and inductive transfer, may be used to transfer the power and / or data from an external component to an implantable component and, as such, FIG. ID illustrates only one example arrangement.

[0053] As noted above, sound processing unit 106 includes the external sound processing module 124. The external sound processing module 124 is configured to process the received input audio signals (received at one or more of the input devices, such as sound input devices 118 and / or auxiliary input devices 128), and convert the received input audio signals into output control signals for use in stimulating a first ear of a recipient or user (i.e., the external sound processing module 124 is configured to perform sound processing on input signals received at the sound processing unit 106). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in the external sound processing module 124 are configured to execute sound processing logic in memory to convert the received input audio signals into output control signals (stimulation signals) that represent electrical stimulation for delivery to the recipient.

[0054] As noted, FIG. ID illustrates an embodiment in which the external sound processing module 124 in the sound processing unit 106 generates the output control signals. In an alternative embodiment, the sound processing unit 106 can send less processed information (e.g., audio data) to the implantable component 112 and the sound processing operations (e.g., conversion of input sounds to output control signals 156) can be performed by a processor within the implantable component 112.

[0055] In FIG. ID, according to an example embodiment, output control signals (stimulation signals) are provided to the RF transceiver 122, which transcutaneously transfers the output control signals (e.g., in an encoded manner) to the implantable component 112 via external coil 108 and implantable coil 114. That is, the output control signals (stimulation signals) are received at the RF interface circuitry 140 via implantable coil 114 and provided to the stimulator unit 142. The stimulator unit 142 is configured to utilize the output control signals to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea via one or more of the stimulating contacts (electrodes) 144. In this way, cochlear implant system 102 electrically stimulates the user’s auditory nerve cells, bypassing absent or defectivehair cells that normally transduce acoustic vibrations into neural activity, in a manner that causes the recipient to perceive one or more components of the input audio signals (the received sound signals).

[0056] As detailed above, in the external hearing mode the cochlear implant 112 receives processed sound signals from the sound processing unit 106. However, in the invisible hearing mode, the cochlear implant 112 is configured to capture and process sound signals for use in electrically stimulating the user’s auditory nerve cells. In particular, as shown in FIG. ID, an example embodiment of the cochlear implant 112 can include a plurality of implantable sound sensors 165(1), 165(2) that collectively form a sensor array 160, and an implantable sound processing module 158. Similar to the external sound processing module 124, the implantable sound processing module 158 may comprise, for example, one or more processors and a memory device (memory) that includes sound processing logic. The memory device may comprise any one or more of: Non-Volatile Memory (NVM), Ferroelectric Random Access Memory (FRAM), read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical / tangible memory storage devices. The one or more processors are, for example, microprocessors or microcontrollers that execute instructions for the sound processing logic stored in memory device.

[0057] In the invisible hearing mode, the implantable sound sensors 165(1), 165(2) of the sensor array 160 are configured to detect / capture input sound signals 166 (e.g., acoustic sound signals, vibrations, etc.), which are provided to the implantable sound processing module 158. The implantable sound processing module 158 is configured to convert received input sound signals 166 (received at one or more of the implantable sound sensors 165(1), 165(2)) into output control signals 156 for use in stimulating the first ear of a recipient or user (i.e., the implantable sound processing module 158 is configured to perform sound processing operations). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in implantable sound processing module 158 are configured to execute sound processing logic in memory to convert the received input sound signals 166 into output control signals 156 that are provided to the stimulator unit 142. The stimulator unit 142 is configured to utilize the output control signals 156 to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea, thereby bypassing the absent or defective hair cells that normally transduce acoustic vibrations into neural activity.

[0058] It is to be appreciated that the above description of the so-called external hearing mode and the so-called invisible hearing mode are merely illustrative and that the cochlear implant system 102 could operate differently in different embodiments. For example, in one alternative implementation of the external hearing mode, the cochlear implant 112 could use signals captured by the sound input devices 118 and the implantable sound sensors 165(1), 165(2) of sensor array 160 in generating stimulation signals for delivery to the user.

[0059] Also illustrated in FIG. ID is measurement and control circuitry 170 (also referred to herein simply as control circuitry 170), which in this example is incorporated into the implant body 134 of the cochlear implant 112. The control circuitry 170 is configured to measure impedances of the electrodes. In certain embodiments, the control circuitry 170 is also configured to detect anomalous changes in impedance (e.g., which may be indicative of a reduction in electrode surface area, as described further below), and control one or multiple current sources to correct or compensate the stimulation parameters and thereby reduce an amount and / or a rate of change in impedance (and hence, reduce an amount and / or a rate of reduction in surface area according to the above example).

[0060] The measurement and control circuitry 170 can include, for example, one or more measurement capacitors, one or more differential amplifiers connected with the one or more measurement capacitors, and a controller connected with the one or more differential amplifiers, wherein the controller is further connected with the stimulator unit 142 (which comprises a plurality of current sources and can also be referred to elsewhere herein as a “stimulation module”). Such components can be implemented in, for example, micro electromechanical systems (MEMS) or with other technology suitable for the particular application. As used elsewhere herein, the term “measurement circuitry” can refer to the one or more measurement capacitors, the one or more differential amplifiers, and their corresponding connections to other components, and the term “control circuitry” can refer to the controller and its corresponding connections to other components.

[0061] In alternative embodiments, one or more operations described above with reference to the control circuitry 170, such as the detection of anomalous changes in impedance, can be performed by another device, such as the external component 104, the external device 110, or another device in direct or indirect communication with cochlear implant 112.

[0062] FIG. IE is a block diagram illustrating one example arrangement for an external computing device 110 configured to perform one or more operations in accordance with certainembodiments presented herein. As shown in FIG. IE, in its most basic configuration, the external computing device 110 includes at least one processing unit 183 and a memory 184. The processing unit 183 includes one or more hardware or software processors (e.g., Central Processing Units) that can obtain and execute instructions. The processing unit 183 can communicate with and control the performance of other components of the external computing device 110. The memory 184 is one or more software or hardware-based computer-readable storage media operable to store information accessible by the processing unit 183. The memory 184 can store, among other things, instructions executable by the processing unit 183 to implement applications or cause performance of operations described herein, as well as other data. The memory 184 can be volatile memory (e.g., RAM), non-volatile memory (e.g., ROM), or combinations thereof. The memory 184 can include transitory memory or non-transitory memory. The memory 184 can also include one or more removable or non-removable storage devices. In examples, the memory 184 can include random access memory (RAM), read only memory (ROM), EEPROM (Electronically-Erasable Programmable Read-Only Memory), flash memory, optical disc storage, magnetic storage, solid state storage, or any other memory media usable to store information for later access. By way of example, and not limitation, the memory 184 can include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media or combinations thereof. In certain embodiments, the memory 184 comprises logic 185 that, when executed, enables the processing unit 183 to perform aspects of the techniques presented.

[0063] In the illustrated example of FIG. IE, the external computing device 110 further includes a network adapter 186, one or more input devices 187, and one or more output devices 188. The external computing device 110 can include other components, such as a system bus, component interfaces, a graphics system, a power source (e.g., a battery), among other components. The network adapter 186 is a component of the external computing device 110 that provides network access (e.g., access to at least one network 189). The network adapter 186 can provide wired or wireless network access and can support one or more of a variety of communication technologies and protocols, such as ETHERNET, cellular, BLUETOOTH, near-field communication, and RF (Radiofrequency), among others. The network adapter 186 can include one or more antennas and associated components configured for wireless communication according to one or more wireless communication technologies and protocols. The one or more input devices 187 are devices over which the external computing device 110 receives input from a user. The one or more input devices 187 can include physically-actuatable user-interface elements (e.g., buttons, switches, or dials), a keypad, keyboard, mouse, touchscreen, and voice input devices, among other input devices that can accept user input. The one or more output devices 188 are devices by which the computing device 110 is able to provide output to a user. The output devices 188 can include a display 190 (e.g., a liquid crystal display (LCD)) and one or more speakers 191, among other output devices for presentation of visual or audible information to the recipient, a clinician, an audiologist, or other user.

[0064] It is to be appreciated that the arrangement for the external computing device 110 shown in FIG. IE is merely illustrative and that aspects of the techniques presented herein can be implemented at a number of different types of systems / devices including any combination of hardware, software, and / or firmware configured to perform the functions described herein. For example, the external computing device 110 can be a personal computer (e.g., a desktop or laptop computer), a hand-held device (e.g., a tablet computer), a mobile device (e.g., a smartphone), a surgical system, and / or any other electronic device having the capabilities to perform the associated operations described elsewhere herein.

[0065] As noted, presented herein are an implant system and methods for the detection of corroding electrodes in implantable medical devices using impedance tests and other data. Neurostimulating electrodes undergo the gradual loss of material as they are used for stimulation. If severe corrosion occurs, a reduced surface area and increased charge density will further accelerate the corrosion process of this electrode. A significant reduction in electrode surface area may lead to stimulation pulses exceeding the Shannon limit, as this safety risk is related to charge density, which can result in damage to nerve cells. The significant loss of electrode material can eventually lead to failure of the stimulation channel and thereby impact the recipient’s hearing performance outcomes. If multiple electrodes fail, the efficacy of the implantable medical devices would be severely impacted and the device may even need to be explanted. In summary, severe corrosion of electrodes can ultimately impact the reliability and longevity of the implantable medical device.

[0066] For example, cochlear implant electrodes are expected to deliver stimulation over the lifetime of the recipient, which can potentially last up to 20 years, 30 years, 50 years or more from initial implantation (depending on the device and its usage). Wear, dissolution, and / or corrosion of one or more of the electrodes can occur over these time periods (or in shorter periods of time in some instances), resulting in the reduction of utility / function of the electrode, and in some cases, resulting in the eventual loss of utility / function. Generally, the smaller thesize of the electrode, and the smaller the surface area exposed to the ambient environment in particular, the higher / faster the rate of wear, dissolution, or corrosion, and the sooner the electrode will experience a level of wear, dissolution, or corrosion that negatively impacts functionality.

[0067] In addition, an increase in charge density of the electrode can result in an increased rate of wear, dissolution, or corrosion, and / or a shortened utilitarian life expectancy of the electrode (i.e., the faster the electrode array reaches the end of its useful life). For example, the implantable portion of the medical device can apply multipolar stimulation from the electrodes, which can result in higher charge levels for a given electrode (e.g., compared to monopolar stimulation). Multipolar stimulation can be used to focus the stimulation and improve hearing performance, and can also improve channel independence, spectral resolution, and speech understanding. However, the use of multipolar stimulation can further add to the statistical likelihood and / or actual occurrence of premature electrode wear, dissolution, or corrosion (e.g., in comparison to monopolar stimulation).

[0068] The rate of wear, dissolution, or corrosion for a particular electrode may depend on various factors, including but not limited to, stimulation waveform amplitude and / or pulse width, the number of pulses delivered per hour / day / week / month, the position of the respective electrodes on the stimulating assembly, the position of the respective electrodes in the body of the recipient (e.g., in the cochlea), a degree of fibrous tissue growth, and / or a chemical composition of the ambient environment of the electrode (e.g., the perilymph inside the cochlea). However, a significant portion of the variance of the rate of wear, dissolution, or corrosion cannot be accounted for by charge density alone. Thus, a generalized prediction for each individual person or electrode is not feasible, and the rate of wear, dissolution, or corrosion cannot be accurately estimated at the time of implantation.

[0069] Currently existing implantable medical devices do not have any detection method for electrode corrosion. One possible technique for managing electrode corrosion may involve limiting certain stimulation parameters, such as the maximum current / charge, but this technique may in turn compromise or negate some of the benefits of certain stimulation strategies. Further, due to large variability in both in vitro and field data, there is a high degree of uncertainty in predicting the effect(s) of electrode corrosion. For these reasons, the risk cannot be fully mitigated, or else a very conservative approach needs to be taken with respect to the stimulation strategy in order to mitigate the risk of electrode corrosion, neither of which is ideal.

[0070] The system and techniques described herein provide a solution to the above-described problems with regard to the monitoring and detection of electrode corrosion, by utilizing the impedance measurement functionality of the implant and / or corresponding clinical software. As used herein, the term “impedances” can refer to one or more of Common Ground Impedances, Monopolar Impedances (e.g., MP1, MP2), Four Point Impedances, or Time Varying Impedances (e.g., Trans Impedance Matrix (TIM)), for example. In general, cochlear implant impedances represent the resistance to flow of current between two electrodes or groups of electrodes. Systems presented herein allow for simultaneous stimulation and recording in various configurations as detailed below. Impedance is derived from the known, applied current (I) and the measured voltage (V) using Ohm’s law (V = I x R).

[0071] “Common Ground Impedance”: In the common ground mode, current is applied and voltage is measured between a single intracochlear electrode and all other intracochlear electrodes shorted together. An increase in common ground impedance averaged across electrodes is coincident with a delayed shift in hearing thresholds, whereas stable averaged common ground impedance is associated with stable hearing thresholds. Common ground impedance can be measured along the electrode array to provide frequency-specific information reflecting tissue growth and health along the cochlea.

[0072] “Monopolar Impedance” (MP1 or MP2): This impedance measurement mode stimulates and records from an individual intracochlear electrode that is grounded to the two extracochlear grounds (i.e., the pin and case grounds). This is measured at one time point at the end of the stimulating pulse, which encapsulates all elements of impedance. It can be measured for each individual electrode which can provide insight into frequency-specific changes in acoustic hearing thresholds.

[0073] “Four Point Impedance”: Four-point impedance is measured by utilizing four adjacent intracochlear electrodes and applying current between the two outer electrodes while measuring the voltage differential between the inner two electrodes. The four adjacent electrodes can run from basal to apical ends of the electrode array to provide frequency-specific electrophysiological information along the cochlea. An increase in total four-point impedances is associated with cochlea bleeding / inflammation and fibrosis development that can lead to delayed increases in hearing thresholds following cochlear implantation. In general, four-point impedances have been found to rise within 24 hours of cochlear implantation and 3 months postoperatively, particularly in the basal region, aligning with the natural timeline of acute and chronic inflammatory responses. Individual inflammatory response times can vary acrossindividual recipients. Thus, an increase in postoperative four-point impedances could be preceding or occurring concurrently with an increase in acoustic hearing thresholds.

[0074] “Time Varying Impedance” / “Trans Impedance Matrix” (TIM): Trans impedance matrices are measured in the same mode as monopolar (MP1+2) described above. It expands the information collected by assessing impedance at numerous time points during the pulse. This allows the impedance measures to be analyzed into sub-components of “access impedance” and “polarization impedance.” Increasing access impedance and stable polarization impedance is associated with hearing threshold changes, which indicates the utility of this measure as a biomarker for acoustic hearing changes.

[0075] FIG. 2A is an example of an initial clinical session 205, in which an external device 210 has a connection 248 to the implant and the stimulating assembly 216. The electrode 244 shown in FIG. 2A may be a new / virgin electrode, or an electrode that is still relatively early in its lifecycle, for example, without any corrosion, wear, dissolution, etc. (or with only a minimal amount thereof). FIG. 2B is a top view of the stimulating assembly 216 and the electrode 244 of FIG. 2A at the time of the initial clinical session 205.

[0076] Referring to FIGs. 2A-2B, the electrode 244 has an initial surface area (Ai) at the time of the initial clinical session 205. The initial surface area (Ai) may be defined by one or more of a first length (LI), a first width (Wl), and / or a first depth (DI) (i.e., first thickness). In certain embodiments, the initial surface area (Ai) can be defined by a combination of LI, Wl, and DI. In other embodiments, Ai can be estimated or derived from only one or two of LI, Wl, and / or DI. Using the clinical software, the external device 210 obtains initial impedance measurements x (Zi) for corresponding electrodes of the stimulating assembly 216 during the initial clinical session 205 of FIGs. 2A and 2B.

[0077] FIG. 2C is an example of a new clinical session 215, in which the electrode 244 has corroded (worn, dissolved, eroded, etc.) and has a new surface area (An), which is a reduced surface area in comparison to the initial surface area (Ai). The electrode 244 shown in FIG. 2C may be an electrode that is somewhere in the middle of its lifecycle, or nearing the end of its lifecycle, for example. FIG. 2D is a top view of the stimulating assembly 216 and the electrode 244 of FIG. 2C at the time of the new clinical session 215.

[0078] Referring to FIGs. 2C-2D, the electrode 244 now has a new surface area (An) at the time of the new clinical session 215. The new surface area (An) may be defined by one or more of a second length (L2), a second width (W2), and / or a second depth (D2) (i.e., secondthickness). In certain embodiments, the new surface area (An) can represent a combination of L2, W2, and D2. In other embodiments, An may represent only one or two of L2, W2, and / or D2. Using the clinical software, the external device 210 obtains new impedance measurements y (Zn) for corresponding electrodes of the stimulating assembly 216 during the new clinical session 215 of FIGs. 2C and 2D.

[0079] A change in impedance y-x (AZ=Zn-Zi) can be determined from the initial impedance x (Zi) and the new impedance y (Zn), and according to an aspect of the techniques described herein, the change in impedance y-x (AZ=Zn-Zi) is converted into a change in surface area (AA=An-Ai). That is, the unknown, new surface area (Ai) can be derived (calculated, estimated) from the known values of the initial surface area (An), the initial impedance x (Zi), and the new impedance y (Zn), according to the techniques described herein.

[0080] The inventors have identified that there is an empirical relationship between changes in impedance (Z) and electrode surface area (A) as follows:

[0081] where Zn is the new impedance (i.e., a current impedance value) of the electrode 244, Zi is the initial impedance (i.e., reference / baseline impedance value), An is the new surface area (i.e., a current surface area) of the electrode, and Ai is the initial surface area (i.e., reference / baseline surface area) of the electrode. In one non-limiting illustrative example, M is an optional scaling value or multiplier (e.g., 1.01, etc.), and N is an exponential value (e.g., -0.74, etc.). It should be appreciated that the specific values of M and N may vary depending on certain factors such as implant type, electrode type, electrode material, stimulation strategy, and the like, such that various different values for M and N may be used according to other example embodiments.

[0082] The initial values for Zi (reference / baseline impedance) and Ai (reference / baseline surface area) are known in advance, and the new value for Zn (current impedance value) can be measured by the external device 210. Then, the new value for An (current surface area), which is an unknown variable, can be derived (i.e., calculated, estimated, solved for, etc.) based on the measured new impedance value Zn and the known initial surface area Ai and the known initial impedance value Zi, according to the empirical relationship defined by the formula above.

[0083] As noted, however, the particular equation and any specific values thereof (e.g., for the variable M and / or the variable N) described in connection with examples embodiments herein are merely intended to be informative in nature, and can change accordingly for each different electrode array, each different type of electrode, etc. The formula was derived from a vast amount of test data, and any specific values (e.g., M=1.01 andN=-0.74) may only be applicable to the specific electrodes or array type tested in that experiment (i.e., different electrodes or array types would likely have different values to some degree). As such, the variables M and N are considered to be adjustable values that can be “tuned” for different electrodes, array types, implantable medical devices, specific stimulation strategies, particular stimulation modes or types, etc., respectively. The purpose of presenting the particular equation above is to demonstrate that the change in impedance (AZ=Zn-Zi) is proportional to the change in surface area (AA=An-Ai), and that the new surface area (An) can be derived (calculated, estimated) from the change in impedance and the initial surface area (Ai), at least assuming that certain other relevant variables remained constant. The specific formula (i.e., the values for the variables M and / or N) for different electrodes, arrays, implantable medical devices, stimulation strategies, etc. would need to be derived, and can then be used to detect a present change or predict a future change in electrode surface area (e.g., due to electrode corrosion, wear, dissolution, etc.) based on the abnormal change in impedance. Thus, it is possible that separate models can be developed for each electrode type and array design, and the relevant model can then be applied in operation depending on the electrode / array being used, for example. Likewise, multiple models could be applied to classify or categorize the reduced surface area (e.g., provide an indication of the type or extent of wear, dissolution, corrosion, etc.).

[0084] Additionally or alternatively, instead of determining discrete values for the variables M and N, a suitable “range” of values can be determined from clinical data, and the range can be further updated, refined, narrowed, and / or otherwise optimized over time as additional clinical data is collected and analyzed and additional feedback is obtained with respect to a given electrode, array, implantable medical device, stimulation strategy, etc. The use of a range technique (defined by upper and lower values) can provide more flexibility and a greater margin of error, for example.

[0085] In some examples, the reduction in usable electrode surface area can be caused by “wear” of the surface material overtime, or by “dissolution” of the surface material overtime, which are both characterized by the actual physical loss of at least some of the electrode surfacematerial. For example, the overall height / thickness of the electrode may decrease over time as it wears (i.e., erodes), and this decrease can be non-uniform across the surface of the electrode (e.g., one side may wear out faster than another side, or the edges can wear out faster than middle region). In another example, the uniformity of the electrode surface may change over time as the electrode surface material dissolves (e.g., uneven surface, or different porosities). The term dissolution as used herein can encompass “passive dissolution” (i.e., the reduction in the amount of material of the electrode resulting from chemical reactions due to the biological environment, without the application of electrical current) and / or “active dissolution” (i.e., the reduction in the amount of material of the electrode resulting from actual use of the electrode to provide electrical current to the environment). More specifically, the removal of material from the electrode occurs due to chemical or electrochemical reactions that occur when an electrode is at rest potential (i.e., not used to pass current to the environment) in an electrolyte. The removal of material also occurs due to electrochemical reactions, and often at a faster rate, when an electrode is used to provide electrical current to the environment (i.e., it is the same electrochemical process, but modified by the changing potential on the electrode that occurs during electrical stimulation). Thus, passive dissolution corresponds to the reduction of material that occurs electrochemically when an electrode sits at rest in an electrolyte, and active dissolution corresponds to the reduction of electrode material that occurs when the electrode is used to pass current. In either case, the terms wear and dissolution refer to a change in the physical state of the electrode itself, relative to that which was the case when the electrode was new.

[0086] FIG. 2E is an example of electrode “wear,” in which the electrode 244 can have a different amount of wear. In certain examples, the electrode 244 may have a different shape, a different slope, etc. in comparison to the new / virgin electrode of FIGs. 2A-2B. FIG. 2F is an example of electrode “dissolution,” in which the electrode 244 can have an uneven surface (e.g., rough, bumps, porosity, etc.). In certain examples, the electrode 244 may have different porosities (Pl, P2, P3) at different depths. In other examples, the electrode 244 may have different layers or materials (Ml, M2, M3) at different depths. In some examples, a “wear status” or a “dissolution status” can be determined (e.g., to indicate an amount of surface area that has been lost, or an amount of surface area that is remaining) based on analysis of the impedance measurements in relation to reference / baseline impedance measurements. In some other examples, a “wear rate” or a “dissolution rate” can be determined (e.g., to indicate a speed or timing with respect to the reduction in surface area) based on analysis of the impedancemeasurements in relation to reference / baseline impedance measurements. It should also be appreciated that the general term “wear” can cover both the passive dissolution and active dissolution phenomena, as well as erosion and any other phenomenon that may cause the physical reduction in surface area of a given electrode over time.

[0087] In another example, the reduction in usable electrode surface area can be caused by “corrosion” of the surface material of the electrode over time, which is characterized by some other material (e.g., a fdm, rust, foreign substance, etc.) effectively forming on, adhering to, or otherwise covering at least a portion of the tissue-facing surface of the electrode. That is, in the specific example of corrosion, there may or may not be any actual physical loss (i.e., wear or dissolution) of the electrode surface material itself; rather, the lost surface area refers to the portion(s) of the electrode surface that has / have corroded and are no longer usable (or are substantially less effective) for the delivery of stimulation signals as otherwise intended / expected (i.e., under normal operating conditions in the absence of any corrosion). As noted, corrosion of implant electrodes is a relatively new phenomenon that is not widely known or understood in this field of technology. Presumably, the corrosion (e.g., film, rust, foreign substance, etc.) does not have the same electrically conductive properties compared to the electrode surface material in its new / virgin state, and therefore results in degraded operation (e.g., inconsistent stimulation, unintended stimulation, over-stimulation, under-stimulation, etc.).

[0088] FIG. 2G is an example of electrode “corrosion,” in which the electrode 244 can have a thin layer of foreign material at least partially covering the upper surface thereof, such as a film 247a that has formed thereon in one example, or rust 247b in another example, or some other build-up of foreign material. In some examples, a “corrosion status” can be determined (e.g., to indicate an amount of the electrode surface area that is corroded, or an amount of uncorroded electrode surface area that is remaining) based on analysis of the impedance measurements in relation to reference / baseline impedance measurements. In some other examples, a “corrosion rate” can be determined (e.g., to indicate a speed or timing with respect to the corrosion that results in the reduced effective surface area of the electrode) based on analysis of the impedance measurements in relation to reference / baseline impedance measurements.

[0089] In FIGs, 2E, 2F, and 2G, the initial upper surface (Si) is shown with a dashed line, and the new upper surface (Sn) is shown with a solid line. Aremammg denotes an amount of the electrode’s surface area that is still left. Aiost denotes an amount of the electrode’s surface area that has worn, dissolved, corroded, etc. In some example embodiments, one or both of anamount of electrode material remaining (Aremammg) and / or an amount of material lost (Aiost) can be derived (calculated, estimated) according to the techniques described herein, from the initial surface area (Ai), the initial impedance (Zi) and the new impedance (Zn). In some example embodiments, the calculation / estimation can be refined using other clinical data (e.g., stimulation parameters, usage data, implant duration / age, initial impedance, biological data, etc.), and / or other analysis techniques (e.g., electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), etc.) to improve accuracy.

[0090] FIG. 3 is a flowchart of a method 300 for determining a change in surface area based on a change in impedance, according to an example embodiment. At operation 310, the method 300 includes obtaining an initial impedance (Zi) for one or more electrodes implanted in a recipient during an initial clinical session at a first time. At operation 320, the method 300 includes storing the initial impedance (Zi) and an initial surface area (Ai) for the one or more electrodes, as reference / baseline values. At operation 330, the method 300 includes obtaining a new impedance (Zn) for the one or more electrodes implanted in the recipient during a new clinical session at a second time. At operation 340, method 300 includes deriving a new surface area (An) for the one or more electrodes, based on the initial surface area (Ai) and a difference between the initial impedance (Zi) and the new impedance (Zn).

[0091] Thus, a change in impedance (AZ = Zn / Zi) is converted into a change in surface area (AA = An / Ai) according to the techniques described herein. In certain examples, operation 340 may include determining a change in surface area, an amount of surface area lost, and / or an amount of surface area remaining, which can be an indication used to characterize the state of wear, dissolution, and / or corrosion of the electrode. Additionally or alternatively, operation 340 may include determining a rate of the reduction in surface area of the electrode.

[0092] In certain embodiments, a functionality can be added to the clinical software to track the history of impedance measurements, and also to notify a user (e.g., a clinician and / or the recipient) when a change (e.g., an abnormal rise) in impedance over time is detected. The corresponding reduction in electrode surface area can be deduced using the above formula to assess the severity of the wear, dissolution, or corrosion (refer to FIGs. 2C-2G). If needed, a warning can be provided to the user / clinician to prompt a change of stimulation parameters in order to slow, minimize, or prevent further loss of electrode material, as described further below.

[0093] FIG. 4A is a flowchart of a method 400 according to an example embodiment. At operation 410, the method 400 includes obtaining data relating to an impedance of at least one electrode of a stimulating assembly implanted in a recipient. At operation 420, the method 400 includes analyzing the obtained data to determine a wear / dissolution / corrosion status, and / or a rate of wear / dissolution / corrosion, of the at least one electrode of the stimulating assembly.

[0094] The obtained data can correspond to current, voltage, and / or impedance readings. The obtained data may also correspond to cyclic voltammetry (CV) data and / or charge storage capacity (CSC) data in some examples. The obtained data can be obtained using electrochemical impedance spectroscopy (EIS) techniques in some other examples. Baseline data (“standard” impedance data) can be collected, either at the time of implantation or a relatively short time thereafter, for example. During later testing periods, current data is collected for comparison with the baseline data. If there is a change in a variable from the stabilized baseline data, this can be indicative of a change in the wear / dissolution status or the wear / dissolution rate of the electrode. In another variation, the collection of baseline data can also be implemented for devices that have already been implanted in the recipient for a relatively long period of time . In this case, the system can analyze the current data with respect to the baseline data in order to deduce any relative change in the surface area based on a relative change in the impedance.

[0095] The status can correspond to an amount (e.g., a percentage, a ratio) of the electrode that has worn, dissolved, or corroded relative to the new / virgin electrode at the time of implantation. The amount can correspond to a mass, a volume, a thickness, and / or a surface area, and may be an actual dimensional amount (e.g., one or more number values). The analyzing can be executed by the medical device of which the electrode array is a part (e.g., by the implantable portion and / or by the external portion of a cochlear implant).

[0096] In certain examples, a neural network or a trained expert system can be utilized to automatically analyze the obtained data (e.g., impedance readings, etc.). Data from various recipients can be obtained or is otherwise available, and artificial intelligence or machine learning technologies can be utilized to ascertain a pattern or relationship between the various features detailed therein that can be utilized to provide an indicia of the wear / dissolution rate and / or of the wear / dissolution status of an electrode.

[0097] FIG. 4B is a flowchart of a method 450 according to an example embodiment. At operation 460, the method 450 includes obtaining data relating to a wear / dissolution / corrosionstatus and / or a rate of wear / dissolution / corrosion of at least one electrode of a stimulating assembly implanted in a recipient. At operation 470, the method 450 includes analyzing the obtained data to determine one or more remedial actions to reduce a future rate of wear / dissolution / corrosion of the at least one electrode, and / or to compensate for the wear / dissolution / corrosion of the at least one electrode.

[0098] As noted above, in certain examples, a neural network or a trained expert system can be utilized to automatically analyze the obtained data (e.g., impedance readings, etc.). Data from various recipients can be obtained or is otherwise available, and artificial intelligence or machine learning technologies can be utilized to ascertain a pattern or relationship between the various features detailed therein that can be utilized to provide an indicia of the wear / dissolution rate and / or of the wear / dissolution status of an electrode.

[0099] In one example embodiment, the remedial action can be triggered in response to a determination that the wear / dissolution status of the electrode (i.e., the current amount of wear / dissolution that has been experienced by the electrode) has reached a certain threshold percentage of the total value of the new / virgin electrode (i.e., its original mass, volume, thickness, surface area, etc.). Similarly, the remedial action can be triggered in response to a determination that the wear / dissolution rate of the electrode (i.e., how fast the reduction in surface area is occurring) is higher than a certain threshold rate (e.g., the current rate will likely result in the electrode wearing out, dissolving, or corroding before the end of the recipient’s lifetime).[ooioo] In one example embodiment, the remedial action is to identify an adjustment of a stimulation parameter or an operational setting of the medical device of which the electrode is a part. Several illustrative examples of adjustments include, but are not limited to: adjust (reduce / decrease) the current level applied by the electrode, adjust (reduce / decrease) the stimulation pulse rate applied by the electrode, adjust (increase) the stimulation pulse width, adjust (reduce / decrease) the degree of focusing for one or more channels when using multipolar stimulation (i.e., redistribute charge / current to spread out the stimulation to neighboring electrodes), change the stimulation mode / type (from a higher charge mode / type to a lower charge mode / type), change channels (shift sound to another channel), disable one or more channels, or otherwise adjust the makeup of certain channels (e.g., using a different combination of electrodes to provide stimulation, instead of the wom / dissolved electrode).[ooioi] In certain example embodiments, the system can use the techniques described herein to balance the benefit of slowing down the rate of wear / dissolution with resulting loss in hearing performance. Adjusting (e.g., reducing / decreasing) the operational parameter to reduce (slow down) a future rate of wear / dissolution / corrosion can also decrease hearing performance. Conversely, adjusting (e.g., increasing) the operational parameter to increase hearing performance can also increase the rate of wear / dissolution / corrosion. Various kinds of adjustments (e.g., smaller or larger amounts of adjustment, or adjusting different parameters / settings) can be used to achieve this balance. In one example implementation, the recipient or the medical device itself can dynamically switch between a “high-performance mode” and a “reduced-performance mode,” as needed over time (e.g., depending on the recipient’s environment and desired usage). This switching of modes could be performed on- demand (based on manual user input), or automatically (based on detecting changes in the recipient’s environment, identifying that certain sound classes are present, etc.). For example, the high-performance mode (e.g., increased current / charge level, focused multipolar mode, etc.) can be used when there is speech or music present in the recipient’s environment, and the reduced-performance mode (e.g., reduced current / charge level, monopolar or bipolar mode, etc.) can be used when there is quiet or noise present in the recipient’s environment. Generally, the goal is to maintain sufficient longevity of the electrode (e.g., for the lifetime of the recipient) while still ensuring an ideal level of hearing performance as a result of the adjustments of the operational parameter(s) overtime.

[0102] In another example embodiment, the remedial action can be to instruct the recipient to use medical device in a different manner to reduce the rate of wear / dissolution / corrosion, and thereby extend longevity of the electrodes. Several illustrative examples of such instructions include, but are not limited to: limit use of the medical device (e.g., only when engaging in conversations, listening to music, etc.), reduce the proportion of time and / or a number of listening environments in which focused multipolar stimulation is delivered by the implant, reduce the amount of time that the implant is used per day, per week, etc., reduce the volume to a lower level (to the extent possible while maintaining a sufficient level of hearing performance), use monopolar and / or bipolar stimulation modes more often or whenever possible (e.g., rather than focused multipolar), use a stimulation strategy of lower complexity and / or less focus by default and only a stimulation strategy of higher complexity and / or greater focus only for certain situations, as needed.

[0103] In one example, the adjustment is identified and output (displayed) at operation 470. The clinician or the recipient can then decide whether to implement the identified adjustment. In another example, the identified adjustment is automatically applied at operation 470 (i.e., without the need for any user input from the clinician or the recipient to accept / approve the adjustment).

[0104] Thus, iterative techniques can be utilized to determine whether and how to adjust the operation of the medical device (e.g., cochlear implant, etc.) to obtain utility with respect to reducing the rate of wear, dissolution, or corrosion or otherwise extending the longevity of the electrode (e.g., so as to long at least as along as the lifetime of the recipient, or at least as long as possible while maintaining acceptable hearing performance).

[0105] Now referring again to the examples described above with reference to FIGs. 2A-2G and FIG. 3, and referring further to FIG. 5 A which is a graph illustrating how the change in impedance is proportional to the change in surface area, the above equation can also be simplified to an exponential function Y = M(X)'N, where Y represents the change in impedance (Zn / Zi, or AZ) and X represents the change in surface area (An / Ai, or AA), and where M = 1.01 and N = -0.74 in the non-limiting illustrative examples above, as represented by the curve 507 in FIG. 5A. As shown in FIG. 5A, the rate of change in impedance tends to increase with reduction in surface area, and this non-linear relationship can be exploited to implement the techniques described herein.

[0106] FIGs. 5B, 5C, and 5D show various examples merely to illustrate how the curve 507 shown in the graph of FIG. 5A would change if one of the variables (e.g., M or N) is changed. If the variable M is increased (e.g., to 10 as shown in FIG. 5B), the resulting curve 517 in FIG. 5B will have a substantially similar shape and slope as the curve 507 in FIG. 5A, such that changing M can act as a multiplier that magnifies the result (but does not substantially alter the result). For example, the variable M could be set to 1 (or in theory, M could simply be omitted from the equation entirely) without significantly altering the outcome of the analysis. On the other hand, if the variable N is changed (e.g., to -0.1 as shown in FIG. 5C, or to -3 as shown in FIG. 5D), the resulting curve 527 in FIG. 5C and the resulting curve 537 in FIG. 5D will each have a substantially different shape and slope from the curve 507 of FIG. 5 A, such that changing N therefore alters the relationship between the change in impedance (Y) compared to the change in surface area (X) in the simplified equation. The variable N is most likely related to the shape of the electrode (e.g., the edge effect, surface roughness, three-dimensional shape, etc.), and further development can be performed to more accurately know how the initialgeometry of the electrode would drive surface area changes. The point here is that the techniques described herein are much more sensitive to changes in the exponent (N) than to changes in the multiplier (M).

[0107] FIG. 5E is a graph resulting from a data analysis that shows a trend (average change in impedance) over time in a cochlear implant. The x-axis represents a number of years since switching on the implantable medical device, and the y-axis represents an average change in impedance (as a percentage per day). As shown in FIG. 5E, a data analysis of existing cochlear implant electrodes indicates that impedance measurements between 3-17 years after activation (switching on the implantable medical device) are relatively stable with low variability (i.e., the average change in impedance (% / day) shown in FIG. 5E remains substantially steady in a range between approximately -0.01% and approximately +0.01% from year 3 to year 17), which supports the feasibility of detecting electrode corrosion and predicting the onset of electrode corrosion using the system and techniques described herein. By contrast, the impedance measurements between 17-21 years after implant activation are somewhat less stable with more variability (i.e., the average change in impedance (% / day) shown in FIG. 5E is approximately -0.02% at year 19 and -0.04% at year 21).

[0108] The curve in the graph of FIG. 5E (average change in impedance) has a very different shape compared to the curve in the graph of FIG. 5A that is caused by a loss of surface area (e.g., due to corrosion, dissolution, wear, etc.). An analysis on how this might affect the detection or prediction of corrosion or dissolution / wear based on the above equation (or the simplified version thereof) demonstrated that with variability and changes in impedance seen in the field, the detection of a significant loss of surface area is still possible.

[0109] Although it makes sense that the charge density increases as the surface area reduces, and in turn, corrosion / dissolution / wear increases with increasing charge density, the exact nature of the relationship between impedance and surface area was previously unknown in this field of technology. In particular, the inventors have discovered that the rate of change in impedance is “non-linear” in nature, and increases along with the reduction in surface area over time. As corrosion and dissolution / wear occurs over an extended period of time, then it can be said that the amount and / or rate of corrosion / dissolution / wear changes with time. Knowing that the rate of change in impedance increases as surface area decreases, the system is better able to separate out impedance changes based on biological matter or other causes of impedance changes that (presumably) do not track with the smooth curve (e.g., as shown in thegraph of FIG. 5A), and focus the analysis on impedance changes that are based on electrode corrosion or dissolution / wear, specifically.[oono] Thus, the system and techniques described herein can enable the monitoring of impedance changes overtime, the detection of a reduction in electrode surface area (i.e., detect the occurrence of wear, erosion, passive dissolution, active dissolution, or corrosion), and the estimation of the “status” and / or the “rate” of change of one or more implanted electrodes with respect surface area (i.e., estimate the remaining usable lifetime of one or more electrodes that have experienced wear, dissolution, or corrosion). This monitoring, detection, and estimation can be performed in a non-invasive manner with respect to the recipient (i.e., without the need for an invasive surgical explantation procedure to remove or otherwise physically access the electrodes). The system and techniques described herein can help to avoid or prevent a deleterious reduction in surface area of a given electrode over the electrode’s lifetime (i.e., a wear event, a dissolution event, a corrosion event, etc. that results in the electrode no longer being able to stimulate at a utilitarian level), and / or can otherwise extend the useful lifetime of the electrode beyond that which would be the case in the absence of the techniques described herein. Thus, the example embodiments described herein provide for the determination that a deleterious reduction in electrode surface area (e.g., due to wear, dissolution, or corrosion) is currently in progress or will likely occur at some time in the future, so that one or more utilitarian actions can be taken (manually by the clinician or recipient, or automatically by the implant system itself) in order to remediate, prevent, or otherwise avoid that wear / dissolution / corrosion event.[ooni] Generally, the electrode surface area “status” may refer to an amount of usable / effective surface area of an electrode that has been lost and / or that is left remaining (whether the reduction in surface area is due to wear, dissolution, or corrosion). In one example, the electrode surface area status may be expressed as a percentage of the electrode’s surface area that has been lost (due to corrosion, dissolution, or wear). In another example, the electrode surface area status may be expressed as a percentage of the electrode’s surface area that is still remaining (relative to virgin / new / reference / baseline). Generally, the electrode surface area reduction “rate” may refer to a speed or timing of the reduction of the usable / effective surface area of the electrode (whether the reduction is due to wear, dissolution, or corrosion). For example, the electrode surface area reduction rate may be expressed as an estimated usable life expectancy of the electrode (e.g., in terms of estimated time remaining in MM / YY, or predicted expiration date in MM / YY). The electrode surface area “status” and / or the electrode surfacearea reduction “rate” can be re-calculated and updated over time as the electrode has further reduction in surface area (e.g., due to corrosion, dissolution, or wear) and new impedance measurements are captured.

[0112] However, it should be appreciated that the descriptions provided above are merely nonlimiting illustrative examples, and in general various other techniques for rating electrodes or determining electrode status (with respect to reduced surface area, corrosion, dissolution, wear, etc.) could also be used, such as electrode surface area “ratings” (e.g., high / medium / low, good / okay / bad, etc.) or electrode surface area “rankings” (e.g., on a scale of 1-5, or 1-10, etc.) with the highest rating or ranking representing a new / virgin electrode or a reference / baseline impedance, and the lowest rating or ranking representing a substantially reduced surface area or a substantially corroded / dissolved / wom electrode).

[0113] In certain embodiments, additional data such as stimulation parameters (e.g., current level (amplitude), stimulation rate (frequency), pulse width (duration), stimulation mode (type), etc.) and date of implantation (or elapsed time since implantation), can also be analyzed to provide some further input or guidance regarding the likelihood of electrode corrosion occurring. This additional information can be incorporated into the system to enable the system to make a more informed and accurate judgment when a change in impedance is detected. That is, this additional information would help to minimize the uncertainty caused by noise in the data or other factors influencing electrode impedance.

[0114] Further characterization methods, including but not limited to voltage polarization across the electrode interface, electrochemical impedance spectroscopy, and / or cyclic voltammetry data can also be integrated to estimate changes in electrode surface area. For example, unlike regular impedance measurements, these further characterization methods can allow the electrode -electrolyte interface to be characterized independently from other parts of the system, such as the biological environment (e.g., tissue and / or ambient environment within the recipient). This can allow more accurate estimation of the changes in electrode surface area by reducing or eliminating other environmental factors and the effects thereof on impedance measurements. That is, the system can have the ability to separate / distinguish the contribution of reduced electrode surface area to impedance measurements for an electrode from any contribution of tissue and / or ambient environment to the impedance measurements.

[0115] In some examples, the system can provide a recommendation to adjust one or more stimulation parameters with respect to one or more stimulating electrodes, or to adjust one ormore operational settings of the implantable medical device, in response to detecting the abnormal change in impedance (that indicates the reduction in electrode surface area). The recommendation may identify which stimulation parameter(s) or operational setting(s) is / are to be adjusted. The recommendation can be provided to a clinician and / or to the recipient of the implantable medical device, so that the clinician or recipient can manually implement the recommended adjustment.

[0116] In some other examples, the system can automatically determine and apply an adjustment to one or more stimulation parameters or to one or more operational settings in response to detecting the abnormal change in impedance (that indicates the reduction in electrode surface area), with or without the need for any manual user input from a clinician or the recipient. For example, various threshold values can be set (and adjusted) for triggering various actions or adjustments to be performed with respect to the implantable medical device. In some examples, a single threshold value could be used to trigger a particular action or adjustment. In some other examples, multiple threshold values could be used to trigger different actions or adjustments (e.g., to escalate the scale of the adjustments, to try different adjustments over time, etc.).

[0117] In addition to the reference / baseline impedance measurements, comparisons between current impedance measurements could also be made in relation to some previous impedance measurements (i.e., some intermediate measurements over some time period after implantation / fitting and reference / baseline, but before an adjustment to stimulation parameters or operational settings is made), to analyze whether the adjustment has been effective and / or the degree to which the adjustment has compensated for reduced surface area, reduced the rate of reduction in surface area, or minimized future loss of surface area. If these additional results indicate little to no improvement, then further adjustments could be made (reduce a particular parameter / setting even more) and / or different adjustments could be made (try changing some other parameter(s) / setting(s) instead this time, and repeat the impedance measurement and analysis process later to assess whether there are any notable differences), and / or more extreme measures could also be taken if needed (such as disabling electrodes, disabling certain stimulation modes / types, or possibly even electrode replacement / reimplantation if feasible, depending on the type of implantable medical device for which the techniques described herein are being applied).

[0118] The techniques described herein can also be extended to provide a dynamic approach that automatically adjusts projections of electrode corrosion based on the stimulation strategyemployed (e.g., the stimulation mode / type, etc.). In another example, data logging can be used on a contact-by-contact basis to identify when the stimulation strategy should use an “overused electrode” differently (e.g., use an electrode that has experienced wear, dissolution, or corrosion less frequently, or use a lower maximum current / charge for that electrode), so as to preserve remaining surface area of one or more contacts. As noted, the parameters involved are driven in part by the stimulation characteristics, such as the maximum current / charge and how often that current / charge is pushed through the electrode. The frequency of the impedance measurements can also potentially affect the results.

[0119] In certain examples, artificial intelligence (Al) and machine learning (ML) techniques can be used to perform the analysis on results of the impedance tests to determine whether abnormal changes in impedance have occurred, and / or to automatically identify and apply suitable adjustment(s) to stimulation parameter(s) and / or operational setting(s) based on the analysis of the impedance measurements. As such, one or more analysis models (e.g., AI / ML models, neural networks, etc.) can be trained to analyze impedance measurements using training data sets (e.g., a large corpus of clinical data), and the one or more analysis models can be updated over time as new impedance measurements are captured, the analysis is repeated, and relevant feedback is provided in connection with the techniques described herein.

[0120] Now referring to FIGs. 6, 7, 8, and 9, the system and techniques described herein can be used to implement various methods for the monitoring of physical states of stimulating electrodes and the management of stimulation strategies based thereon. These example methods are intended to be non-limiting and illustrative in nature, and many other variations are also possible.

[0121] FIG. 6 is a flowchart of a method 600 according to an example embodiment. At operation 610, the method 600 includes performing a plurality of impedance measurements at one or more implantable electrodes over a period of time. At operation 620, the method 600 includes tracking the plurality of impedance measurements over the period of time to detect a non-linear increase in an impedance of at least one of the one or more implantable electrodes. In response to detecting a non-linear increase in the impedance of at least one of the one or more implantable electrodes, at operation 630, method 600 includes generating an output indicating a reduction in a surface area of the at least one of the one or more implantable electrodes.

[0122] In some example embodiments, operation 610 includes periodically performing one or more impedance measurements at the at least one implantable electrode over the period of time . For example, operation 610 may include one or more of: periodically performing one or more common ground impedance measurements, periodically performing one or more monopolar impedance measurements, periodically performing one or more four-point impedance measurements, or periodically performing one or more time-varying impedance measurements.

[0123] In one example, the method may further include monitoring stimulation parameters of the stimulation pulses over the period of time, and using the stimulation parameters and the impedance of the at least one implantable electrode over the period of time to detect the nonlinear increase in the impedance of the at least one implantable electrode indicative of the change in the surface area of the at least one implantable electrode.

[0124] In one example, the method may further include monitoring a voltage polarization across an interface of the at least one implantable electrode over the period of time, and using the voltage polarization of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time to detect the non-linear increase in the impedance of the at least one implantable electrode indicative of the change in the surface area of the at least one implantable electrode.

[0125] In one example, the method may further include performing impedance spectroscopy of the at least one implantable electrode over the period of time, and using the impedance spectroscopy of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time to detect the non-linear increase in the impedance of the at least one implantable electrode indicative of the change in the surface area of the at least one implantable electrode.

[0126] In one example, the method may further include obtaining cyclic voltammetry data of the at least one implantable electrode over the period of time, and using the cyclic voltammetry data of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time in the identifying of the change in the impedance of the at least one implantable electrode indicative of the change in the surface area of the at least one implantable electrode.

[0127] FIG. 7 is a flowchart of a method 700 according to an example embodiment. At operation 710, method 700 includes delivering, over a period of time, stimulation pulses to a recipient via at least one implantable electrode. At operation 720, method 700 includesmonitoring, over the period of time, an impedance of the at least one implantable electrode. Based on the monitoring, at operation 730, the method includes identifying a non-linear change in the impedance of the at least one implantable electrode indicative of a change in a surface area of the at least one implantable electrode. At operation 740, the method 700 includes initiating one or more remedial actions in response to identifying the change in the surface area of the at least one implantable electrode.

[0128] In one example, initiating one or more remedial actions at operation 740 includes generating an output indicating the change in the surface area. The output quantifies at least one of an amount of the change in the surface area (e.g., percentage lost or percentage remaining) or a rate of the change in the surface area (e.g., a current rate or a future rate).

[0129] In one example, initiating one or more remedial actions at operation 740 includes adjusting one or more parameters of the stimulation pulses delivered via the at least one implantable electrode to reduce a likelihood of additional surface area change of the at least one implantable electrode. For example, the adjustment may include one or more of: reducing a rate at which the stimulation pulses are delivered via the at least one implantable electrode, reducing a stimulation level at which the stimulation pulses are delivered via the at least one implantable electrode, or increasing a pulse width at which the stimulation pulses are delivered via the at least one implantable electrode.

[0130] In one example, the one or more remedial actions are configured to reduce a future rate of change in the surface area of the at least one implantable electrode. In another example, the one or more remedial actions are configured to compensate for the change in the surface area of the at least one implantable electrode.

[0131] FIG. 8 is a flowchart of a method 800 according to an example embodiment. At operation 810, the method 800 includes controlling a plurality of stimulating electrodes of an implantable medical device implanted in a recipient to deliver a plurality of stimulation signals to the recipient. At operation 820, the method 800 includes obtaining results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes. At operation 830, the method 800 includes analyzing the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes.

[0132] If an abnormal change in impedance is not detected (No at decision 835), the method 800 can return to operation 810 (or operation 820) and continue monitoring over time andupdating the analysis. If an abnormal change in impedance is detected (Yes at decision 835), then one or more remedial actions to reduce a future rate of reduction in the surface area of the one or more stimulating electrodes and / or to compensate for reduction in the surface area of the one or more stimulating electrodes is / are initiated, at operation 840.

[0133] FIG. 9 is a flowchart of a method 900 according to another example embodiment. The method 900 is a variation of the method 800 of FIG. 8, and operations 910, 920, and 930 are the same or similar to operations 810, 820, and 830. As such, a description of these operations will not be repeated again. In the variation of FIG. 9, however, there is a further determination made regarding whether the surface area of the one or more electrodes is below a predetermined threshold. If the surface area is still above the predetermined threshold (No at decision 945), then a first remedial action to reduce a future rate of reduction in the surface area of the one or more stimulating electrodes is initiated, at operation 940. If the surface area of the one or more electrodes is below the predetermined threshold (Y es at decision 945), then a second remedial action to compensate for further reduction in the surface area of the one or more stimulating electrodes is initiated, at operation 950. Thus, FIG. 9 is an example in which different remedial actions can be taken, depending on whether the surface area of the electrode is above or below the predetermined threshold.

[0134] The example embodiments described above provide systems, devices, and / or methods that can enable the detection of wear, dissolution (passive or active), or corrosion, and provide an estimation of the status of one or more implanted electrodes with respect to wear, dissolution, or corrosion. The techniques can also provide an estimation of the remaining lifetime of the one or more implanted electrodes based on the status of the respective electrodes. Some example embodiments can help to prevent, avoid, inhibit, or limit the occurrence of deleterious wear events of a given electrode (i.e., that would otherwise result in the electrode no longer being able to stimulate at a utilitarian level) over the lifetime of the electrode, or otherwise extend the lifetime of the electrode beyond that which would be the case in the absence of the techniques described herein. Thus, the techniques described herein provide for the detection of a deleterious electrode wear event that is currently in progress or that will likely occur in the future, so that certain remedial actions can be taken to address the current or future occurrence of wear, dissolution, or corrosion of the electrode.

[0135] For example, a utilitarian result of the teachings described herein is that one or more stimulation channels of a cochlear implant can continue to be utilized (i.e., for a period of time beyond that which would otherwise be the case if the deleterious wear event were to occur).In addition, the teachings detailed herein can be utilized to determine that certain channels are no longer providing utilitarian stimulation (and / or why certain channels will no longer provide utilitarian stimulation, thus enabling workaround channels to be developed by adjusting the electrodes that are utilized to provide stimulation, where electrodes that still have structural effectiveness for stimulation can be utilized to a greater degree so as to compensate for the failed electrode(s) of the underlying initial channels.

[0136] As noted, the implantable portion of the medical device is configured to, while implanted in a human, obtain data indicative of wear, dissolution (passive or active), or corrosion of at least one of the plurality of electrodes of the stimulating assembly. In one example embodiment, the implantable portion can correspond to a receiver-stimulator of a cochlear implant, and can have a logic circuit (e.g., control circuitry 170 of FIG. ID) that can be configured to control the application of electrical signals to the various pertinent electrode(s) so as to provide voltage differentials in a controlled manner between electrodes. According to other examples, the logic circuit could be in the external component of the cochlear implant (e.g., sound processing unit). Further, the implantable component can be configured to provide a telemetry signal to the external device that is indicative of voltage readings or current readings (and / or impedance readings that are based on the voltage / current readings). The telemetry signal can include raw data (for analysis by the external device), or can include the results of an analysis executed by the implantable component itself. Thus, the existing electrodes of a cochlear implant electrode array can be utilized in combination with the electrodes of the implantable component (and / or the external component, such as a sound processor, or other external device) to obtain electrical measurements relating to the electrodes. The signals applied to the electrodes can be modified to provide the stimulus that results in enablement of a phenomenon that can be read by read electrodes that corresponds to the obtained data.

[0137] In an example embodiment, the implantable portion (receiver-stimulator) is configured to transcutaneously communicate the obtained data (raw electrical measurement data) and / or data based thereon (e.g., impedance measurement data, or results of analyzing the electrical measurement data) to an external device located outside the human via an inductance coil of the implantable portion. The transceiver of the implantable portion is configured to provide a telemetric signal from the implantable portion, through the skin of the human, to the external portion (e.g., sound processor) or an external device (e.g., a computer or smartphone).

[0138] In some example embodiments, the medical device is configured to analyze the obtained data to determine an electrode status (e.g., wear status, dissolution status, corrosionstatus) of one or more electrodes of the stimulating assembly, and communicate an indication of the electrode status. In some example embodiments, the analysis is executed by the external component (e.g., sound processing unit), which can be in the form of a microprocessor or electronic circuitry with logic circuits configured to analyze the data and extract certain indicators (i.e., which correspond to latent variables) that can be used to determine the status of the electrode (and its physical state). The communication of the electrode status can be by way of a port (e.g., USB) on the external component, a wireless link (e.g., Bluetooth) with a remote device, or other telemetric communication arrangement. The electrode status can be stored in a memory, which can be accessed and updated at various times (e.g., periodically, on- demand, responsive to a detection event, responsive to an adjustment to an operational parameter of the device, etc.).

[0139] In some other example embodiments, it is the implantable portion of the medical device that is configured to analyze the obtained data and determine the electrode status of the one or more electrodes of the stimulating assembly, and communicate an indication of the wear status (e.g., to the external portion of the medical device, or to another external device such as a computer or smartphone in communication with the implantable portion). The pertinent microprocessors and / or other electronics can be located in the receiver-stimulator of the implant, and the data signal can be sent with the telemetry link noted above.

[0140] In one example embodiment, the electrode status can be a “general electrode status” that simply provide a warning or indication that the one or more electrode(s) of the stimulating assembly is / are experiencing a deleterious wear event (e.g., an erosion phenomenon, a passive dissolution phenomenon, an active dissolution phenomenon, or a corrosion phenomenon), or will likely experience such a deleterious wear event in the future, that could potentially be problematic in the short term and / or in the long term. In another example embodiment, the electrode status can be a “specific electrode status” that indicates an amount (e.g., a particular percentage, range, ranking, rating, etc.) of the electrode material that still remains. A specific wear status can be used to deduce an approximate physical state of the electrode, and / or to estimate the remaining life of the electrode. In one non-limiting illustrative example, the implantable portion can determine a general electrode status, and the external portion (or an external device) can determine a specific electrode status based on further analysis of the obtained data (and / or possibly other clinical data associated with the recipient).

[0141] In some example embodiments, the medical device is configured to enable an adjustment of an operation of the implantable component (e.g., cochlear implant) so as toreduce a future rate of wear, dissolution, or corrosion of the one or more electrodes of the stimulating assembly from which the data was obtained. For example, the medical device can be configured to enable reduction of a pulse rate and / or reduction of a degree of focusing for some or all stimulation channels to reduce a stimulation amplitude associated with a given electrode. Further, this adjustment technique can also be used to extend the longevity or otherwise reduce the future rate of wear, dissolution, or corrosion of one or more other electrodes of the stimulating assembly (i.e., other than the given electrode from which the data was obtained). Thus, the medical device is configured to automatically adjust an operation of the implantable portion in order to compensate for the wear, dissolution, or corrosion of the one or more electrodes of the stimulating assembly. In some other example embodiments, the implantable portion of the medical device is configured to adjust its own operation (e.g., reduce pulse rate, reduce degree of focusing, reduce amplitude, etc.) so as to reduce the future rate of wear, dissolution, or corrosion for the one or more electrodes of the stimulating assembly.

[0142] At some point, a determination can be made that the electrode is no longer effective for stimulation, and efforts can be made to preserve the other remaining electrodes. For example, the surface area of a given electrode may be reduced to a level that is below a threshold value, and then a remedial action (e.g., shifting channels, or implementing a constructive and / or destructive interference regime) can be taken to compensate for the wear of the given electrode. Another possibility at the end of life of the electrode is that the electrode and its corresponding stimulation parameter are no longer under a safety limit (e.g., Shannon limit). In this example, the stimulation parameter can be changed to comply with the safety limit, or else the electrode can be disabled altogether at the end of its life.

[0143] Some example embodiments described herein contemplate an automatic adjustment by the medical device and / or its implantable portion. However, a manual adjustment is also possible according to other example embodiments. For example, the medical device and / or its implantable portion can be configured to automatically recommend a particular remedial action to reduce the future rate of wear, dissolution, or corrosion of the given electrode and / or one or more other electrodes of the stimulating assembly. Likewise, the medical device and / or its implantable portion can be configured to automatically recommend a particular adjustment to a stimulation parameter or an operation of the implantable portion to compensate for the wear, dissolution, or corrosion of the given electrode (as noted above). In these examples, the device simply generates and outputs the recommendation, without actively implementing the adjustment in an automated manner, and then a user (e.g.., a clinician or the recipient) candecide whether to accept or otherwise manually implement the recommended adjustment, if desired.

[0144] The various measurements and other data collection techniques described herein can be made on an individual electrode, a selected subset of electrodes, a representative test electrode, or all of the electrodes of an array at regular intervals (e.g., daily, weekly, monthly, yearly, etc.) and / or at irregular intervals (e.g., on-demand, responsive to a detection event, responsive to an adjustment to a stimulation parameter or operational setting of the implant, etc.), and can be logged (i.e., collected and stored) by one or more components of the system, such as the implantable portion, the external portion (e.g., sound processor), or an external device (e.g., computer or smartphone) or other remote server in communication with the implantable portion or the external portion. Changes in one or more of these measurements over time in a way that is known to be characteristic of wear, dissolution, or corrosion of electrodes can be detected (e.g., via a software algorithm running in the implantable portion and / or the external portion of the medical device, or the external device or other remote server). The algorithm may also consider data that is logged relating to the usage of the medical device (e.g., cochlear implant), such as the number of stimulation pulses, the current amplitude, the phase duration of pulses delivered, etc. over the life of the device through one or multiple or all of the electrodes. Generally, any stimulation parameter or other operational setting that can be logged can be further utilized to derive (calculate, estimate) or otherwise deduce the current electrode status (e.g., an amount of wear, dissolution, or corrosion, and / or a current or future rate of wear, dissolution, or corrosion) according to the techniques described herein.

[0145] The algorithm may also take into account the position of the electrode in the array, the position of the electrode array within the human recipient, and / or the status of neighboring electrodes, which are spatial variables that can potentially impact the various measurements described herein. By taking into account these spatial variables, the accuracy of the data analysis can be further improved, so as to further increase the accuracy of the analysis relating to the electrode status and / or the rate of wear, dissolution, or corrosion. The algorithm can then calculate an estimate of the wear status and / or the wear rate of one or multiple or all of the electrodes in the array, and this information can be delivered to a clinician or the human recipient, who can then decide whether any changes to stimulation parameters or other operational settings are warranted in order to reduce the risk of premature wear, dissolution, or corrosion, and / or to otherwise determine how to accommodate or compensate for the fact that an electrode has effectively worn out, dissolved, or corroded to a significant degree thatultimately affects operation of the device (i.e., substantially reduces the efficacy of stimulation).

[0146] As noted above, one or more latent variables can be utilized to ascertain or otherwise estimate an electrode state (e.g., a state of wear, a state of dissolution, a state of corrosion, etc.) of an electrode. In particular, certain electrical properties such as voltage, current, and / or impedance that can be measured by the implantable portion of the medical device can be impacted by properties of an electrode at different points during its lifetime. These properties can be measured by passing a measurement current between two electrodes (e.g., using one out of a plurality of intra-cochlear electrodes (ICEs) of an array as a “source,” and using either an extra-cochlear electrode (ECE) or another one of the intra-cochlear electrodes of the array as a “sink”), and measuring a voltage between the same two electrodes at a time while the current is being passed. The impedance can then be calculated or otherwise derived by dividing the voltage by the current (i.e., Z = V / 1). Upon the occurrence of a given electrode wear event, dissolution event, or corrosion event, there is a relatively distinct change in the aforementioned electrical properties. For example, a relatively distinct change in impedance (Z) can be detected by the analysis, and used to generate the electrode status that is indicative of the amount and / or the rate of wear, dissolution, or corrosion of the electrode. Stated another way, the implantable electrode array is configured to provide an abrupt change in an electrical phenomenon (e.g., at least a certain minimum / threshold percentage difference in the values of current, voltage, and / or impedance) upon one or more electrodes reaching a certain wear status, dissolution status (passive or active), or corrosion status.

[0147] It is noted that the electrodes can have different sizes and shapes, and hence, can have different exposed surfaces areas. In one non-limiting illustrative example, a given electrode can have a number of layers, and one or more of the layers can have different structural properties (e.g., different materials, different porosities, etc.) that can affect the measurement of the electrical properties (e.g., current, voltage, and / or impedance) in various ways. For example, an electrode can have an upper layer (top layer) that is exposed to the ambient environment (e.g., the cochlea region within the body of the recipient), with a surface area that is rectangular in shape, or a surface area that is circular or oblong in shape, etc., a lower layer that is not exposed, and one or more intermediate layers disposed between the upper layer and the lower layer. One or more of these layers can be formed from different materials (e.g., platinum, iridium, gold, silver, etc., or alloys of two or more of such materials) and / or can have different thicknesses, such that they each have a different electrical property in relation to oneanother. The electrical properties can be monitored (e.g., daily, weekly, monthly, yearly), and upon detecting a change of the electrical properties or otherwise detecting that the electrical property is indicative of the lower layer or one of the intermediate layers, rather than the upper layer, certain features regarding the wear, dissolution, or corrosion of the electrode can be determined. In such examples, a different material / layer can be incorporated into the electrode at a certain depth to establish the point at which the electrode has worn, dissolved, or corroded to that point.

[0148] In some examples, the different materials that are utilized for the lower layer (and / or any intermediate layers) of an electrode can have different cyclic voltammetry (CV) spectrum relative to the material(s) that is / are utilized for the upper layer. Cyclic voltammetry measurements can be performed periodically or irregularly using the implantable portion of the medical device. If one of the CV readings indicates a difference, such as a change in shape from a first shape representing a first material (e.g., platinum) to a second shape that is more representative of a second material (e.g., iridium), then that can serve as an indication that the electrode has worn, dissolved, or corroded to the depth where the second material was deposited. Such techniques involving the use of materials with different electrical properties to identify wear, dissolution, or corrosion can be used in conjunction with the above-described techniques that use a distinct change in impedance over time to identify a change in surface area in order to provide more accurate and reliable estimations of the electrode status.

[0149] Values for a new (pristine, virgin) electrode at the time of implantation can be known. For example, values for initial thicknesses, initial exposed surface areas, and initial impedances can be stored as baseline / reference values for the electrodes. As the electrodes are utilized over an extended period of time (e.g., several years), and the longer that the electrode array is exposed to the ambient environment within the human body (e.g., the perilymph within the cochlea), the upper layer of the electrode that is exposed to the ambient environment will eventually wear out, dissolve, and / or corrode over time. Although the precise thickness and exposed surface area is not directly measurable after the time of implantation (e.g., several years later), an indication or representation of the thickness or the exposed surface area can be derived (calculated, estimated) from the known baseline / reference values and through measurements of the current impedances, according to the techniques described herein.

[0150] A minimal degree of wear, dissolution, or corrosion may not result in a substantial change in the electrical properties of the electrode. However, as the electrode continues to wear, dissolve, or corrode over time (due to use and / or exposure to the ambient environment),there will eventually come a point where the thickness and / or the surface area decreases to such an extent that the electrical properties and / or the performance of the implantable portion of the medical device will change in a noticeable and measurable manner. It is also noted that the amount of wear, dissolution, or corrosion can be distributed evenly or unevenly across the exposed upper surface of the electrode (e.g., one side can wear out faster than another side, or the edges can wear out faster than the middle region), such that different layers can be partially exposed and partially covered at different times during the usable life of the electrode. Further, the amount (e.g., percentage) of the surface area of a particular layer that is exposed to the ambient environment can be variable and may be different for different recipients, for different stimulation parameters, and / or for different operational settings of the implant.

[0151] Taking into account the fact that the surface area will be reduced with wear, dissolution, or corrosion, there eventually comes a point that the electrode becomes ineffective (even if there is some material of the underlying electrode remaining), or otherwise the minimal thickness of the remaining electrode material will result in a quickening of the rate of wear, dissolution, or corrosion. Different layers / materials can also have different levels or degrees of inherent resistance to wear, dissolution, or corrosion, such that certain layers / materials may take longer to wear out, dissolve, or corrode than other layers / materials. Thus, it can be said that the rate of wear, dissolution, or corrosion at different times during the usable life of the electrode is “non-linear” in nature (i.e., a reduction in surface area can result in an increase in the wear rate over time). Accordingly, the analysis can be repeated over time and the electrode status (e.g., an amount of wear, dissolution, or corrosion; or a rate of wear, dissolution, or corrosion) can be dynamically updated throughout the lifetime of the electrode, taking into account these variance s / differences in electrode materials. Likewise, any projections regarding the remaining usable life or the expected wear-out date can be recalculated and updated as well to account for these variances / differences.

[0152] Additionally or alternatively, the electrode can have different layers with different “structure” (as distinguished from different materials) or varying degrees of “porosity” at different depths, and the different structure or varying porosity enables the in vivo analysis. As the electrode wears down, erodes, dissolves, corrodes, etc., the lower layers of the electrode become exposed over time. When the region of different structure or varying porosity is exposed, the electrochemical behavior of the surface changes. For example, a lower layer with a greater porosity exposes a different surface area of the electrode to the ambient environment in relation the upper layer (which has a relatively lesser porosity in this example). Conversely,a lower layer with a lesser porosity exposes a different surface area of the electrode to the ambient environment in relation to the upper layer (which has a relatively greater porosity in this example). In either case, at least a distinct change in the surface area (i.e., relative to the upper layer that has worn down to expose the lower layer) can be detected or otherwise deduced from the different electrochemical behavior of the exposed surface of the electrode, and the distinct change in surface area can be utilized as an indicator of the electrode status. Electrochemical measurements can be used to detect the exposure of the change (e.g., decrease or increase) in surface area, and thus determine that the region is exposed (and hence, that the overlying layer has worn away, dissolved, etc.). In some example embodiments, the stimulation history of that electrode (e.g., from device records / logs) can be used in combination with the electrode status to predict the expected remaining lifetime of the electrode (and / or other electrodes of the array).

[0153] One electrochemical measurement technique involves the use of the charge storage capacity (CSC) to provide a measure of the electrochemical reactions that occur at the surface of an electrode (and thereby provide a measure of the porosity of the material at that time in the electrode’s lifespan). The CSC is proportional to the “real” surface area of an electrode (i.e., its “effective” surface area, as distinguished from its “geometric” surface area), and can therefore be used as a measure of the real / effective surface area of the electrode. For example, acyclic voltammogram (CV) method can be performed at different times during the electrode’s lifetime. Since the implant is configured to obtain the current, voltage, and / or impedance data related to the electrodes, the data can be plotted and evaluated (e.g., compared to each other) in order to enable a determination regarding the electrode status (e.g., amount of wear, and / or rate of wear) to be made. That is, the electrode can be configured to trigger a measurable change in a charge storage capacity (CSC) of the electrode, and / or a measurable change in a cyclic voltammetry (CV) spectrum of the electrode, upon experiencing a certain amount of wear, dissolution, or corrosion. Another technique that can be utilized to register the porosity of the electrode (at least the portion of the electrode that is exposed to the ambient environment) is to measure the impedance of the electrode at various times during the electrode’s lifespan. When an area of different porosity is uncovered, the impedance will also change (increase or decrease) in relation to the porosity of the overlying layer that has worn away, dissolved, or corroded.

[0154] Additionally or alternatively, an electrochemical impedance spectroscopy (EIS) technique can be used to separate the contribution of the electrode surface from the contributionof the tissue / ambient environment towards the impedance associated with the electrode. The EIS technique applies voltages and measures currents (or vice versa) over a range of frequencies. For example, low frequency techniques such as cyclic voltammetry (CV) can be utilized to extract information about the electrode surface, since the impedance of the electrode interface becomes dominant at low frequencies. In a simplified example, a pseudo-EIS technique can be performed by taking impedance measurements at different pulse widths, and long duration pulses (e.g., up to 1ms) will give a representation of the real / effective surface area (or porosity) of the electrode interface.

[0155] In summary, the system and techniques described herein can improve the long-term reliability and safety of implantable medical devices. Generally, the example embodiments described herein provide a recipient-specific way to minimize or reduce the risk of premature electrode degradation (rather than relying on estimates of population average wear-out rates, for example). An undesirable situation where high current / charge is passed through a relatively small surface area can be reduced, eliminated, or avoided. The system and techniques can avoid or prevent the complete failure of electrode channels, thereby improving hearing performance outcomes and reliability of implanted electrodes. The system and techniques can provide assurance to clinicians and implant recipients that the electrodes will not fail from severe corrosion without warning. The system and techniques can be used to estimate remaining life of electrodes, and / or to predict future onset of electrode corrosion, for example. In addition, the system and techniques can be used to recommend adjustments to stimulation parameters or other operational settings, and / or to automatically determine and apply such adjustments.

[0156] A non-linear relationship between the rate of change in impedance values and the rate of change in electrode surface area overtime has not been recognized previously in the relevant field of technology. With these additional insights, the system and techniques described herein can also be used to better differentiate impedance changes due to electrode corrosion (or wear / dissolution) from other biological sources of impedance changes (e.g., adjacent tissue or surrounding ambient environment within the recipient).

[0157] Furthermore, the system and techniques permit less conservative limits to be placed on stimulation parameters (such as current / charge, among various others described herein), thereby allowing implant recipients to enjoy more benefits from the implantable medical devices and available stimulation strategies (e.g., stimulation modes / types). For example, the system and techniques are particularly useful for implantable medical devices that implementa “high-charge” stimulation strategy (e.g., a “focused multipolar” stimulation mode / type), for which electrode surface corrosion and monitoring for the same are especially important considerations. Similarly, the system and techniques would be advantageous to integrate into existing and future implantable medical devices that use a large number of relatively small and / or thin contacts, which may be even more susceptible to performance degradation caused by electrode corrosion (or wear / dissolution).

[0158] As previously described, the technology disclosed herein can be applied in any of a variety of circumstances and with a variety of different devices. Example devices that can benefit from technology disclosed herein are described in more detail in FIGS. 10 and 11. The techniques of the present disclosure can be applied to other devices, such as neurostimulators, cardiac pacemakers, cardiac defibrillators, sleep apnea management stimulators, seizure therapy stimulators, tinnitus management stimulators, and vestibular stimulation devices, as well as other medical devices that deliver stimulation to tissue. Further, technology described herein can also be applied to consumer devices. These different systems and devices can benefit from the technology described herein.

[0159] FIG. 10 illustrates an example vestibular stimulator system 1002, with which embodiments presented herein can be implemented. As shown, the vestibular stimulator system 1002 comprises an implantable component (vestibular stimulator) 1012 and an external device / component 1004 (e.g., external processing device, battery charger, remote control, etc.). The external device 1004 comprises a transceiver unit 1060. As such, the external device 1004 is configured to transfer data (and potentially power) to the vestibular stimulator 1012.

[0160] The vestibular stimulator 1012 comprises an implant body (main module) 1034, a lead region 1036, and a stimulating assembly 1016, all configured to be implanted under the skin / tissue (tissue) 1015 of the recipient. The implant body 1034 generally comprises a hermetically-sealed housing 1038 in which RF interface circuitry, one or more rechargeable batteries, one or more processors, and a stimulator unit are disposed. The implant body 134 also includes an intemal / implantable coil 1014 that is generally external to the housing 1038, but which is connected to the transceiver via a hermetic feedthrough (not shown).

[0161] The stimulating assembly 1016 comprises a plurality of electrodes 1044( l)-(3) disposed in a carrier member (e.g., a flexible silicone body). In this specific example, the stimulating assembly 1016 comprises three (3) stimulation electrodes, referred to as stimulation electrodes 1044(1), 1044(2), and 1044(3). The stimulation electrodes 1044(1), 1044(2), and 1044(3)function as an electrical interface for delivery of electrical stimulation signals to the recipient’s vestibular system.

[0162] The stimulating assembly 1016 is configured such that a surgeon can implant the stimulating assembly adjacent the recipient’s otolith organs via, for example, the recipient’s oval window. It is to be appreciated that this specific embodiment with three stimulation electrodes is merely illustrative and that the techniques presented herein may be used with stimulating assemblies having different numbers of stimulation electrodes, stimulating assemblies having different lengths, etc.

[0163] In operation, the vestibular stimulator 1012, the external device 1004, and / or another external device, can be configured to implement the techniques presented herein. That is, the vestibular stimulator 1012, possibly in combination with the external device 1004 and / or another external device, can include an evoked biological response analysis system, as described elsewhere herein.

[0164] FIG. 11 illustrates a retinal prosthesis system 1101 that comprises an external device 1110 (which can correspond to the wearable device 100) configured to communicate with an implantable retinal prosthesis 1100 via signals 1151. The retinal prosthesis 1100 comprises an implanted processing module 1125 and a retinal prosthesis sensor-stimulator 1190 is positioned proximate the retina of a recipient. The external device 1110 and the processing module 1125 can communicate via coils 1108, 1114.

[0165] In an example, sensory inputs (e.g., photons entering the eye) are absorbed by a microelectronic array of the sensor-stimulator 1190 that is hybridized to a glass piece 1192 including, for example, an embedded array of microwires. The glass can have a curved surface that conforms to the inner radius of the retina. The sensor-stimulator 1190 can include a microelectronic imaging device that can be made of thin silicon containing integrated circuitry that convert the incident photons to an electronic charge.

[0166] The processing module 1125 includes an image processor 1123 that is in signal communication with the sensor-stimulator 1190 via, for example, a lead 1188 which extends through surgical incision 1189 formed in the eye wall. In other examples, processing module 1125 is in wireless communication with the sensor-stimulator 1190. The image processor 1123 processes the input into the sensor-stimulator 1190, and provides control signals back to the sensor-stimulator 1190 so the device can provide an output to the optic nerve. That said, in an alternate example, the processing is executed by a component proximate to, or integrated with,the sensor-stimulator 1190. The electric charge resulting from the conversion of the incident photons is converted to a proportional amount of electronic current which is input to a nearby retinal cell layer. The cells fire and a signal is sent to the optic nerve, thus inducing a sight perception.

[0167] The processing module 1125 can be implanted in the recipient and function by communicating with the external device 1110, such as a behind-the-ear unit, a pair of eyeglasses, etc. The external device 1110 can include an external light / image capture device (e.g., located in / on a behind-the-ear device or a pair of glasses, etc.), while, as noted above, in some examples, the sensor-stimulator 1190 captures light / images, which sensor-stimulator is implanted in the recipient.

[0168] As should be appreciated, while particular uses of the technology have been illustrated and discussed above, the disclosed technology can be used with a variety of devices in accordance with many examples of the technology. The above discussion is not meant to suggest that the disclosed technology is only suitable for implementation within systems akin to that illustrated in the figures. In general, additional configurations can be used to practice the processes and systems herein and / or some aspects described can be excluded without departing from the processes and systems disclosed herein.

[0169] This disclosure described some aspects of the present technology with reference to the accompanying drawings, in which only some of the possible aspects were shown. Other aspects can, however, be embodied in many different forms and should not be construed as limited to the aspects set forth herein. Rather, these aspects were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible aspects to those skilled in the art.

[0170] As should be appreciated, the various aspects (e.g., portions, components, etc.) described with respect to the figures herein are not intended to limit the systems and processes to the particular aspects described. Accordingly, additional configurations can be used to practice the methods and systems herein and / or some aspects described can be excluded without departing from the methods and systems disclosed herein.

[0171] According to certain aspects, systems and non-transitory computer readable storage media are provided. The systems are configured with hardware configured to execute operations analogous to the methods of the present disclosure. The one or more non-transitory computer readable storage media comprise instructions that, when executed by one or moreprocessors, cause the one or more processors to execute operations analogous to the methods of the present disclosure.

[0172] Similarly, where steps of a process are disclosed, those steps are described for purposes of illustrating the present methods and systems and are not intended to limit the disclosure to a particular sequence of steps. For example, the steps can be performed in differing order, two or more steps can be performed concurrently, additional steps can be performed, and disclosed steps can be excluded without departing from the present disclosure. Further, the disclosed processes can be repeated.

[0173] Although specific aspects were described herein, the scope of the technology is not limited to those specific aspects. One skilled in the art will recognize other aspects or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative aspects. The scope of the technology is defined by the following claims and any equivalents therein.

[0174] It is also to be appreciated that the embodiments presented herein are not mutually exclusive and that the various embodiments may be combined with another in any of a number of different manners.

Claims

CLAIMSWhat is claimed is:

1. A method comprising : performing a plurality of impedance measurements at one or more implantable electrodes over a period of time; tracking the plurality of impedance measurements over the period of time to detect a non-linear increase in an impedance of at least one implantable electrode of the one or more implantable electrodes; and in response to detecting a non-linear increase in the impedance of the at least one implantable electrode, generating an output indicating a reduction in a surface area of the at least one implantable electrode of the one or more implantable electrodes.

2. The method of claim 1, further comprising: periodically performing one or more impedance measurements at the at least one implantable electrode of the one or more implantable electrodes over the period of time.

3. The method of claim 2, wherein periodically performing one or more impedance measurements includes: periodically performing one or more common ground impedance measurements.

4. The method of claim 2, wherein periodically performing one or more impedance measurements includes: periodically performing one or more monopolar impedance measurements.

5. The method of claim 2, wherein periodically performing one or more impedance measurements includes: periodically performing one or more four-point impedance measurements.

6. The method of claim 2, wherein periodically performing one or more impedance measurements includes: periodically performing one or more time-varying impedance measurements.

7. The method of claim 1, 2, 3, 4, 5, or 6, further comprising:monitoring stimulation parameters of stimulation pulses delivered via the at least one implantable electrode over the period of time; and using the stimulation parameters and the impedance of the at least one implantable electrode over the period of time to detect the non-linear increase in the impedance of the at least one implantable electrode indicative of the reduction in the surface area of the at least one implantable electrode.

8. The method of claim 1, 2, 3, 4, 5, or 6, further comprising: monitoring a voltage polarization across an interface of the at least one implantable electrode over the period of time; and using the voltage polarization of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time to detect the nonlinear increase in the impedance of the at least one implantable electrode indicative of the reduction in the surface area of the at least one implantable electrode.

9. The method of claim 1, 2, 3, 4, 5, or 6, further comprising: performing impedance spectroscopy of the at least one implantable electrode over the period of time; and using the impedance spectroscopy of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time to detect the nonlinear increase in the impedance of the at least one implantable electrode indicative of the reduction in the surface area of the at least one implantable electrode.

10. The method of claim 1, 2, 3, 4, 5, or 6, further comprising: obtaining cyclic voltammetry data of the at least one implantable electrode over the period of time; and using the cyclic voltammetry data of the at least one implantable electrode and the impedance of the at least one implantable electrode over the period of time to detect the nonlinear increase in the impedance of the at least one implantable electrode indicative of the reduction in the surface area of the at least one implantable electrode.

11. A method, comprising:delivering, over a period of time, stimulation pulses to a recipient via at least one implantable electrode; monitoring, over the period of time, an impedance of the at least one implantable electrode; based on the monitoring, identifying a non-linear change in the impedance of the at least one implantable electrode indicative of a change in a surface area of the at least one implantable electrode; and initiating one or more remedial actions in response to identifying the change in the surface area of the at least one implantable electrode.

12. The method of claim 11, further comprising: periodically performing one or more impedance measurements at the at least one implantable electrode over the period of time.

13. The method of claim 11, wherein initiating one or more remedial actions comprises: generating an output indicating the change in the surface area.

14. The method of claim 13, wherein the output quantifies at least one of an amount of the change in the surface area or a rate of the change in the surface area.

15. The method of claim 11, 12, 13, or 14, wherein initiating one or more remedial actions comprises: adjusting one or more parameters of the stimulation pulses delivered via the at least one implantable electrode to reduce a likelihood of additional surface area change of the at least one implantable electrode.

16. The method of claim 15, wherein adjusting one or more parameters of the stimulation pulses delivered via the at least one implantable electrode to reduce a likelihood of additional surface area change of the at least one implantable electrode comprises: reducing a rate at which the stimulation pulses are delivered via the at least one implantable electrode.

17. The method of claim 15, wherein adjusting one or more parameters of the stimulation pulses delivered via the at least one implantable electrode to reduce a likelihood of additional surface area change of the at least one implantable electrode comprises: reducing a current level at which the stimulation pulses are delivered via the at least one implantable electrode.

18. The method of claim 15, wherein adjusting one or more parameters of the stimulation pulses delivered via the at least one implantable electrode to reduce a likelihood of additional surface area change of the at least one implantable electrode comprises: increasing a pulse width at which the stimulation pulses are delivered via the at least one implantable electrode.

19. The method of claim 11, 12, 13, or 14, wherein the one or more remedial actions are configured to reduce a future rate of change in the surface area of the at least one implantable electrode.

20. The method of claim 11, 12, 13, or 14, wherein the one or more remedial actions are configured to compensate for the change in the surface area of the at least one implantable electrode.

21. A system comprising : a display screen; a memory; and at least one processor operably coupled to the display screen and the memory, wherein the at least one processor is configured to: control a plurality of stimulating electrodes of an implantable medical device implanted in a recipient to deliver a plurality of stimulation signals to the recipient; obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes; and analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes.

22. The system of claim 21, wherein, to obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes, the at least one processor is configured to: obtain baseline results of a baseline impedance test for each individual stimulating electrode of the plurality of stimulating electrodes, and store the baseline results in the memory; obtain current results of a current impedance test for each individual stimulating electrode of the plurality of stimulating electrodes; and track a history of the current results of the current impedance test with respect to the baseline results of the baseline impedance test for each individual stimulating electrode of the plurality of stimulating electrodes.

23. The system of claim 22, wherein, to analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred, the at least one processor is configured to: analyze the current results of the current impedance test in relation to the baseline results of the baseline impedance test for each individual stimulating electrode of the plurality of stimulating electrodes to determine whether an abnormal rise in impedance has occurred with respect to the one or more stimulating electrodes.

24. The system of claim 21, wherein, to analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred, the at least one processor is configured to: identify that a non-linear change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes, wherein the non-linear change in impedance is an abnormal rise in impedance that is indicative of wear, dissolution, or corrosion of a material forming a tissue-facing surface of the one or more stimulating electrodes.

25. The system of claim 21, 22, 23, or 24, wherein the at least one processor is configured to: generate a warning indicating that a reduced surface area of one or more stimulating electrodes of the plurality of stimulating electrodes has been detected in response todetermining that an abnormal change in impedance has occurred with respect to the one or more stimulating electrodes; and output the warning via the display screen.

26. The system of claim 25, wherein, to generate and output a warning, the at least one processor is configured to: generate a recommendation to adjust one or more stimulation parameters with respect to the one or more stimulating electrodes for which the abnormal change in impedance is detected, in order to compensate for the reduced surface area of the one or more stimulating electrodes; and output the recommendation via the display screen.

27. The system of claim 25, wherein, to generate and output a warning, the at least one processor is configured to: generate a recommendation to adjust one or more stimulation parameters with respect to the one or more stimulating electrodes for which the abnormal change in impedance is detected, in order to minimize further loss of surface area of the one or more stimulating electrodes; and output the recommendation via the display screen.

28. The system of claim 25, wherein, to generate and output a warning, the at least one processor is configured to: generate a recommendation to change a stimulation mode or to limit or avoid using a particular stimulation mode of the implantable medical device; and output the recommendation via the display screen.

29. The system of claim 25, wherein, to generate and output a warning, the at least one processor is configured to: generate a recommendation to discontinue use of the one or more stimulating electrodes for which the abnormal change in impedance is detected in response to determining that the reduced surface area of the one or more stimulating electrodes is below a threshold surface area based on the results of the plurality of impedance tests; and output the recommendation via the display screen.

30. The system of claim 21, 22, 23, or 24, wherein the at least one processor is configured to: automatically adjust one or more stimulation parameters of the implantable medical device in response to determining that an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes based on analyzing the results of the plurality of impedance tests.

31. The system of claim 30, wherein, to automatically adjust one or more stimulation parameters of the implantable medical device, the at least one processor is configured to: automatically decrease a current level of subsequent stimulation signals delivered to the recipient via the one or more stimulating electrodes for which the abnormal change in impedance is detected.

32. The system of claim 30, wherein, to automatically adjust one or more stimulation parameters of the implantable medical device, the at least one processor is configured to: automatically reduce a rate of subsequent stimulation signals delivered to the recipient via the one or more stimulating electrodes for which the abnormal change in impedance is detected.

33. The system of claim 30, wherein, to automatically adjust one or more stimulation parameters of the implantable medical device, the at least one processor is configured to: automatically increase a pulse width of subsequent stimulation signals delivered to the recipient via the one or more stimulating electrodes for which the abnormal change in impedance is detected.

34. The system of claim 21, 22, 23, or 24, wherein the at least one processor is configured to: automatically adjust one or more operational settings of the implantable medical device in response to determining that an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes based on analyzing the results of the plurality of impedance tests.

35. The system of claim 34, wherein, to automatically adjust one or more operational settings of the implantable medical device, the at least one processor is configured to:automatically change a stimulation mode from a first stimulation mode to a second stimulation mode that is different from the first stimulation mode in response to determining that the abnormal change in impedance has occurred; and control one or more of the plurality of stimulating electrodes to deliver subsequent stimulation signals to the recipient using the second stimulation mode.

36. The system of claim 34, wherein, to automatically adjust one or more operational settings of the implantable medical device, the at least one processor is configured to: automatically use one or more alternative stimulating electrodes of the plurality of stimulating electrodes, as a substitute for the one or more stimulating electrodes for which the abnormal change in impedance is detected, to deliver subsequent stimulation signals to the recipient.

37. The system of claim 34, wherein, to automatically adjust one or more operational settings of the implantable medical device, the at least one processor is configured to: automatically disable the one or more stimulating electrodes for which the abnormal change in impedance is detected in response to determining that a current estimated surface area of the one or more stimulating electrodes is below a threshold surface area based on the results of the plurality of impedance tests.

38. The system of claim 21, 22, 23, or 24, wherein the at least one processor is configured to: identify at least one adjustment to at least one stimulation parameter associated with at least one stimulating electrode of the plurality of stimulating electrodes in response to determining that the abnormal change in impedance has occurred with respect to the one or more stimulating electrodes based on analyzing the results of the plurality of impedance tests.

39. The system of claim 38, wherein the at least one processor is configured to: output the at least one adjustment to the at least one stimulation parameter associated with the at least one stimulating electrode.

40. The system of claim 38, wherein the at least one processor is configured to: automatically apply the at least one adjustment to the at least one stimulation parameter associated with the at least one stimulating electrode.

41. The system of claim 38, wherein the at least one adjustment to the at least one stimulation parameter associated with the at least one stimulating electrode is configured to compensate for a reduced surface area of the one or more stimulating electrodes for which the abnormal change in impedance is detected, to reduce a rate at which future reduction in surface area of the one or more stimulating electrodes occurs, or to minimize further loss of surface area of the one or more stimulating electrodes.

42. The system of claim 21, 22, 23, or 24, wherein the at least one processor is configured to: identify at least one adjustment to at least one operational setting of the implantable medical device in response to determining that the abnormal change in impedance has occurred with respect to the one or more stimulating electrodes based on analyzing the results of the plurality of impedance tests.

43. The system of claim 42, wherein the at least one processor is configured to: output the at least one adjustment to the at least one operational setting of the implantable medical device via the display screen.

44. The system of claim 42, wherein the at least one processor is configured to: automatically apply the at least one adjustment to the at least one operational setting of the implantable medical device.

45. The system of claim 42, wherein the at least one adjustment to the at least one operational setting of the implantable medical device is configured to compensate for a reduced surface area of the one or more stimulating electrodes for which the abnormal change in impedance is detected, reduce a rate at which future reduction in surface area of the one or more stimulating electrodes occurs, or minimize further loss of surface area of the one or more stimulating electrodes.

46. The system of claim 21, 22, 23, or 24, wherein, to obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes, the at least one processor is configured to:use an electrochemical impedance spectroscopy (EIS) technique to distinguish a contribution of electrode surface area to the impedance associated with a respective stimulating electrode of the plurality of stimulating electrodes from a contribution of tissue and / or ambient environment to the impedance associated with the respective stimulating electrode.

47. The system of claim 21, 22, 23, or 24, wherein, to obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes, the at least one processor is configured to: capture sets of impedance measurements while using different current levels, different stimulation rates, different pulse widths, or different stimulation modes.

48. The system of claim 47, wherein, to analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred, the at least one processor is configured to: separate a contribution of electrode surface area to the impedance associated with a respective stimulating electrode of the plurality of stimulating electrodes from a contribution of tissue and / or ambient environment to the impedance associated with the respective stimulating electrode based on the sets of impedance measurements captured while using the different current levels, the different stimulation rates, the different pulse widths, or the different stimulation modes.

49. One or more non-transitory computer readable storage media comprising instructions that, when executed by a processor, cause the processor to: control a plurality of stimulating electrodes of an implantable medical device implanted in a recipient to deliver a plurality of stimulation signals to the recipient; obtain results of a plurality of impedance tests over a period of time for each of the plurality of stimulating electrodes; and analyze the results of the plurality of impedance tests to determine whether an abnormal change in impedance has occurred with respect to one or more stimulating electrodes of the plurality of stimulating electrodes.

50. The one or more non-transitory computer readable storage media of claim 49, wherein the instructions when executed further cause the processor to:initiate one or more remedial actions to reduce a future rate of reduction in a surface area of the one or more stimulating electrodes in response to detecting the abnormal change in impedance.

51. The one or more non-transitory computer readable storage media of claim 49, wherein the instructions when executed further cause the processor to: initiate one or more remedial actions to compensate for a reduction in a surface area of the one or more stimulating electrodes in response to detecting the abnormal change in impedance.

52. The one or more non-transitory computer readable storage media of claims 49, 50, or 51, wherein the instructions when executed cause the processor to: analyze the results of the plurality of impedance tests to determine whether the surface area of the one or more stimulating electrodes is below a predetermined threshold; and initiate the one or more remedial actions to compensate for the reduction in the surface area of the one or more stimulating electrodes in response to the surface area being below the predetermined threshold.

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