Implantable electrochemical measurements

Abstract

Presented herein are techniques for using an implantable medical system to monitor body tissue and / or body fluid of a recipient via an electrochemical measurement, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. In accordance with embodiments presented herein, a reference electrode having a stable electrical potential is provided for use in performing the electrochemical measurement.

Description

IMPLANTABLE ELECTROCHEMICAL MEASUREMENTSBACKGROUNDField of the Invention[oooi] The present invention relates generally to performing electrochemical measurements in a recipient.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, an implantable medical device system is provided. The implantable medical device system includes a reference electrode having a stable electrical potential and being in contact with a recipient. The implantable medical device system also includes at least one processor configured to perform cyclic voltammetry (CV) within the recipient by iteratively sweeping an electrical potential of at least one working electrode in the recipient with respect to the stable electrical potential of the reference electrode back and forth betweena lower limit and an upper limit and analyzing a current flow in the recipient in response to the sweeping of the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode.

[0005] In another aspect, a method for performing a potentiodynamic electrochemical measurement in a recipient is provided. The method includes repeatedly sweeping a first potential of at least one working electrode implanted in a recipient with respect to a second potential of a reference electrode between a lower potential and an upper potential, the reference electrode being in contact with the recipient, and measuring current passing between the at least one working electrode and at least one counter electrode resulting from the sweeping of the first potential of the at least one working electrode with respect to the second potential of the reference electrode.

[0006] In yet another aspect, a method is provided. The method includes directing, via a processor, current flow within a recipient between at least one working electrode to at least one counter electrode, the at least one working electrode and the at least one counter electrode being in contact with the recipient, repeatedly adjusting, via the processor, an electrical potential at the at least one working electrode relative to a stable electrical potential of a reference electrode in contact with the recipient between a first limit and a second limit, and measuring, via the processor, the current flow within the recipient in response to the adjusting of the electrical potential at the at least one working electrode relative to the stable electrical potential.

[0007] In still another aspect, an implantable medical device system is provided. The implantable medical device system includes a working electrode configured to be implanted in a recipient, a counter electrode configured to be implanted in the recipient, circuitry configured to iteratively adjust an electrical potential of the working electrode from a first limit to a second limit and from the second limit to the first limit to result in a flow of current between the working electrode to the counter electrode, and a reference electrode in contact with the recipient and configured such that the flow of current through the reference electrode is impeded.

[0008] In a further aspect, an implantable medical device system, includes a reference electrode having a stable electrical potential and being in contact with a recipient. The implantable medical device system also includes at least one processor configured to perform electrical impedance spectroscopy (EIS) within the recipient by applying a time varying electrical potential or current to at least one working electrode in the recipient with referenceto the stable electrical potential of the reference electrode, resulting in a current flow in the recipient and analyzing a measurement of the current flow in the recipient.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:[ooio] FIG. 1 is a schematic diagram illustrating a medical device system with which aspects of the techniques presented herein can be implemented;[ooii] FIG. 2 is a schematic diagram illustrating another medical device system with which aspects of the techniques presented herein can be implemented;

[0012] FIG. 3 is a schematic diagram illustrating yet another medical device system with which aspects of the techniques presented herein can be implemented;

[0013] FIG. 4 is a schematic diagram illustrating still another medical device system with which aspects of the techniques presented herein can be implemented;

[0014] FIG. 5 is a flowchart of a method for performing operations with which aspects of the techniques presented herein can be implemented;

[0015] FIG. 6A is a schematic diagram illustrating a cochlear implant system with which aspects of the techniques presented herein can be implemented;

[0016] FIG. 6B is a side view of a recipient wearing a sound processing unit of the cochlear implant system of FIG. 6A;

[0017] FIG. 6C is a schematic view of components of the cochlear implant system of FIG. 6A; and

[0018] FIG. 6D is a block diagram of the cochlear implant system of FIG. 6A.DETAILED DESCRIPTION

[0019] Presented herein are techniques for using an implantable medical system to monitor body tissue and / or body fluid of a recipient via an electrochemical measurement, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. In accordance with embodiments presented herein, a reference electrode having a stable electrical potential is provided for use in performing the electrochemical measurement.

[0020] For example, in certain embodiments, a working electrode is positioned within the body tissue and / or body fluid, and a reference electrode is applied to the recipient. CV is performed by iteratively or repeatedly sweeping an electrical potential of the working electrode relative to an electrical potential of the reference electrode from a first limit or value (e.g., a lower limit or a minimum) to a second limit or value (e.g., an upper limit or a maximum) and from the second limit to the first limit. A current flow provided in response to the sweeping of the electrical potential of the working electrode relative to the electrical potential of the reference electrode is then analyzed. The current flow, such as a current measurement, may indicate various parameters of the body tissue and / or body fluid, such as a material composition or structure of the body tissue and / or body fluid. As an example, a current measurement may be used to determine whether a state of the body tissue and / or body fluid is desirable and / or whether undesirable particles (e.g., blood) are in the body tissue and / or body fluid. As such, CV can be used to monitor the body tissue and / or body fluid and to perform a corresponding action in response, such as to mitigate effects of the presence of undesirable particles in the body tissue and / or body fluid.

[0021] To perform CV effectively within the recipient, the reference electrode is arranged to have a stable electrical potential such that the electrical potential of the working electrode relative to the electrical potential of the reference electrode accurately reflects the electrical potential being output at the working electrode. For instance, it is desirable for the structure, composition, position, and / or geometry of the reference electrode to remain relatively constant throughout performance of CV. To this end, in some embodiments, a surface of the reference electrode is treated. As an example, the surface is manufactured and / or cleaned to avoid parasitic capacitance that can affect the electrical potential of the reference electrode. As another example, current flow through the reference electrode is avoided for a target duration of time prior to performance of CV to maintain a constant state of the reference electrode. As a further example, a coating (e.g., gel, such as a hydrogel) is applied to the surface of the reference electrode to hinder changes in chemical composition of the reference electrode. In additional or alternative embodiments, a removable reference electrode (e.g., a patch) having a stable electrical potential is utilized, and a connector may be electrically coupled to the removable reference electrode to enable measurement of the electrical potential of the reference electrode. For example, an integrated conductor of an implantable medical device is used to electrically couple to the reference electrode. Additionally or alternatively, a separate connector is inserted through the recipient and electrically coupled to the reference electrode.The reference electrode may be applied to (e.g., in contact with) the recipient during CV performance and removed after CV performance is completed. In any of such embodiments, the reference electrode provides a stable electrical potential to be used as reference with respect to the electrical potential of the working electrode during CV performance.

[0022] For ease of description, the techniques presented herein are primarily described with reference to performing a specific type of electrochemical measurement, namely cyclic voltammetry (CV). However, it is to be appreciated the techniques presented herein could also be used to perform other types of electrochemical measurements in a recipient. For example, aspects of the techniques presented herein could be used to perform electrochemical impedance spectroscopy (EIS).

[0023] 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 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 consumer electronic device (e.g., mobile phones), wearable devices (e.g., smartwatches), hearing devices, implantable medical devices, wearable devices, etc. consumer electronic devices, wearable devices (e.g., smart watches, etc.), 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.

[0024] FIG. 1 is a schematic diagram of an example implantable medical device system 100 with which aspects of the techniques presented herein can be implemented. The implantable medical device system 100 is configured to perform a potentiodynamic electrochemical measurement operation to monitor body tissue and / or body fluid 102 of a recipient. For example, the implantable medical device system 100 includes a monitoring module or system 104 (e.g., circuitry, a control system) configured to perform the potentiodynamic electrochemical measurement operation.

[0025] The monitoring module 104 includes a memory 106 and a processor 108. The processor 108 includes one or more hardware or software processors (e.g., Central Processing Units, microprocessors, microcontrollers) that can obtain and execute instructions. The memory 106 includes one or more software or hardware-based computer-readable storage media operable to store information accessible by the processor 108. The memory 106 can store, among other things, instructions or logic executable by the processor 108 to implement applications or cause performance of operations described herein, as well as other data. The memory 106 can include transitory memory or non-transitory memory, as well as one or more removable or nonremovable storage devices. For example, the memory 106 may comprise any one or more of: Non-Volatile Memory (NVM), Ferroelectric Random Access Memory (FRAM), read only memory (ROM), random access memory (RAM), Electronically-Erasable Programmable Read-Only Memory (EEPROM), magnetic disk storage media devices, solid state storage devices, optical storage media devices, flash memory devices, electrical, optical, or other physical / tangible memory storage devices. By way of example, and not limitation, the memory 106 can include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency (RF), infrared (IR), and other wireless media or combinations thereof. The illustrated monitoring module 104 also includes sensing or measurement circuitry 110. The sensing circuitry 110 may monitor various parameters during operation of the monitoring module 104. By way of example, the sensing circuitry 110 may monitor parameters that result from performance of the potentiodynamic electrochemical measurement operation. Additionally or alternatively, the sensing circuitry 110 may monitor parameters that cause or initiate performance of the potentiodynamic electrochemical measurement operation.

[0026] In some embodiments, the potentiodynamic electrochemical measurement operation performed by the monitoring module 104 includes CV. To this end, the implantable medical device system 100 also includes a working electrode 112, a counter electrode 114, and areference electrode 116. The working electrode 112 and the counter electrode 114 are electrically coupled to one another via the body tissue and / or body fluid 102. For example, the monitoring module 104 outputs an electrical potential that causes a current flow to be directed from the working electrode 112, through the body tissue and / or body fluid 102, and to the counter electrode 114. The monitoring module 104 adjusts the electrical potential being output during performance of CV.

[0027] For example, the monitoring module 104 (e.g., the sensing circuitry 110) references an electrical potential of the reference electrode 116 to measure an electrical potential output at the working electrode 112 relative to the electrical potential of the reference electrode 116 for adjusting the electrical potential output at the working electrode 112. During CV performance, the monitoring module 104 (e.g., the processor 108) sweeps or adjusts the electrical potential output at the working electrode relative to the electrical potential of the reference electrode back and forth between a lower limit and an upper limit. In other words, the monitoring module 104 alternates between increasing the electrical potential of the working electrode relative to the electrical potential of the reference electrode from the lower limit to the upper limit and decreasing the electrical potential of the working electrode relative to the electrical potential of the reference electrode from the upper limit to the lower limit. Graph 118 illustrates an example operation of the monitoring module 104 to output electrical potential at the working electrode 112 over time. In particular, the graph 118 indicates that the electrical potential of the working electrode 112 relative to the electrical potential of the reference electrode 116 increases at a selected rate from a lower electrical potential value 120 to an upper electrical potential value 122 and decreases from the upper electrical potential value 122 to the lower electrical potential value 120 at the selected rate . In this manner, the monitoring module 104 controls the electrical potential output at the working electrode 112 to adjust the electrical potential of the working electrode 112 relative to the electrical potential of the reference electrode 116 between the lower electrical potential value 120 and the upper electrical potential value 122 at a constant rate. The increase and decrease of the electrical potential of the working electrode 112 relative to the electrical potential of the reference electrode 116 is repeated for multiple cycles. By way of example, a target quantity (e.g., five) of cycles of increasing and decreasing the electrical potential of the working electrode 112 relative to the electrical potential of the reference electrode 116 is performed to complete a single CV operation.

[0028] During CV performance, a chemical reaction (e.g., protein oxidation) occurs in the body tissue and / or body fluid 102 and causes a change in a current measurement of the resultingcurrent flow through the recipient. The chemical reaction, and the corresponding change of the current measurement, are based on different parameters, such as a composition and / or structure, of the body tissue and / or body fluid 102. Thus, the monitoring module 104 (e.g., the sensing circuitry 110) monitors the current measurement of the current flow to determine a state of the body tissue and / or body fluid 102 or of the recipient in general. For example, an undesirable current measurement may indicate presence of certain undesirable or unintended particles, such as blood, in the body tissue and / or body fluid 102. An action may then be performed based on the current measurement, such as to remove the particles from or block flow of the particles into the body tissue and / or body fluid 102. Thus, CV performance can help improve or maintain a desirable condition of the recipient (e.g., of the body tissue and / or body fluid 102).

[0029] In certain embodiments, the monitoring module 104 is configured to inform a user of the current measurements. As an example, the monitoring module 104 is configured to output the current measurements to a device of the user. As another example, the monitoring module 104 includes or is communicatively coupled to a display and is configured to cause the display to provide the current measurements. Thus, the user can observe the current measurements monitored by the monitoring module 104 and perform a corresponding action in response. In additional or alternative embodiments, the monitoring module 104 is configured to perform an additional action based on the current measurements. For instance, the monitoring module 104 is configured to compare the current measurements to a threshold or target current measurement (e.g., an expected current value or range of values corresponding to a desirable state of the body tissue and / or body fluid 102) and perform an action based on the comparison. By way of example, the monitoring module 104 is configured to output a notification indicative of whether the state of the body tissue and / or body fluid 102 is desirable based on the current measurement relative to the threshold current measurement. As such, the monitoring module 104 can directly indicate the state of the body tissue and / or body fluid 102 to the user without the user having to analyze raw data related to current measurements.

[0030] It is important for the electrical potential of the reference electrode 116 to remain stable such that the electrical potential being output at the working electrode 112 desirably results in a current flow measurement that accurately indicates the parameters of the body tissue and / or body fluid 102. For example, an unstable electrical potential of the reference electrode 116 may cause unintended adjustments of the electrical potential being output at the working electrode 112 such that the change in current measurements are primarily influenced by theadjustments of the output electrical potential, rather than by the state of the body tissue and / or the body fluid 102. In such cases, the state of the body tissue and / or body fluid 102 may not be accurately determined based on the current measurements, and an appropriate action may not be performed in response. The electrical potential of the reference electrode 116 can be stabilized in different ways described herein, such as by manufacturing and / or treating the reference electrode to reduce current flow therethrough and / or by incorporating a removable reference electrode with a known electrical potential and electrically coupling the reference electrode to the monitoring module 104.

[0031] In some embodiments, each of the working electrode 112, counter electrode 114, and reference electrode 116 is positioned in contact with the same body tissue and / or body fluid 102. Alternatively, at least one of the working electrode 112, counter electrode 114, and reference electrode 116 can be placed in contact with a different body tissue and / or body fluid 102. In an example, the working electrode 112 and the counter electrode 114 are positioned within the recipient and are in contact with the same body tissue and / or body fluid 102, whereas the reference electrode 116 is external to the recipient and is in contact with a different body tissue and / or body fluid 102. In another example, the working electrode 112 and the counter electrode 114 are positioned in contact with different body tissues and / or body fluids 102. The arrangement of the working electrode 112, counter electrode 114, and reference electrode 116 can be based on the body tissue and / or body fluid 102 to be monitored, as well as based on a configuration of the reference electrode 116.

[0032] Moreover, although the illustrated implantable medical device system 100 includes a single working electrode 112, counter electrode 114, and reference electrode 116, it should be noted that multiple working electrodes 112, counter electrodes 114, and / or reference electrodes 116 can be implemented. For example, electrical potentials are separately output to different working electrodes 112 to monitor different body tissues and / or body fluids 102. In certain embodiments, the electrical potential of a single reference electrode 116 can be used to control the respective electrical potential being output at separate working electrodes 112. In other words, a common electrical potential is used as reference for different electrical potentials output at multiple working electrodes 112. In additional or alternative embodiments, electrical potentials of multiple reference electrodes 116 are respectively used for electrical potentials being output at separate working electrodes 112. For example, the electrical potential of each reference electrode 116 is dedicated to adjusting the electrical potential output at a respective, corresponding working electrode 112.

[0033] Furthermore, it should be noted that in some embodiments, at least a portion of the monitoring module 104 is implanted on the recipient. For example, the memory 106, the processor 108, and / or the sensing circuitry 110 may be a part of a medical device configured to be inserted into the recipient. In additional or alternative embodiments, at least a portion of the monitoring module 104 is external to the recipient. For instance, the sensing circuitry 110 is external to the recipient and is electrically coupled to the working electrode 112 and / or to the counter electrode 114 to measure the electrical potential at the working electrode 112, the electrical potential at the reference electrode 116, and / or the current passing between the working electrode 112 and the counter electrode 114.

[0034] FIG. 2 is a schematic diagram of an example implantable medical device system 150 having an implantable housing or enclosure 152 configured to be implanted in a recipient. For instance, the implantable medical device system 150 includes an implantable device with the implantable housing 152. The implantable housing 152 contains a monitoring module 154, which has a memory 156, a processor 158, and sensing or measurement circuitry 160. Additionally, a working electrode 162, a counter electrode 164, and a reference electrode 166 (e.g., composed of a metal, such as platinum) are integrated with the implantable housing 152 and electrically coupled to the monitoring module 154. The working electrode 162, counter electrode 164, and reference electrode 166 extend at least partially external to the implantable housing 152 to enable the working electrode 162, counter electrode 164, and reference electrode 166 to contact body tissue and / or body fluid 168 of the recipient.

[0035] To stabilize the electrical potential of the reference electrode 166, the reference electrode 166 is manufactured and / or treated to resist changes that would affect its electrical potential. For instance, a property or state of a surface 170 of the reference electrode 166 is controlled via uniform manufacturing and / or uniform cleaning techniques to block or interrupt current flow therethrough that would otherwise change the electrical potential of the reference electrode 166 (e.g., by depositing or removing a charge via the interface between the reference electrode 166 and the body tissue and / or body fluid 168 in contact with the reference electrode 166). As an example, the reference electrode 166 is designed to avoid parasitic capacitance from adjacent electrical potentials (e.g., of the working electrode 162, of the counter electrode 164, of a body cell, such as a neuron) that would otherwise induce some current flow through the reference electrode 166. As another example, a coating 172 is applied to the surface 170 of the reference electrode 166, such as at an end 173 of the reference electrode 166 in contact with the body tissue and / or body fluid 168, to block current flow between the referenceelectrode 166 and the body tissue and / or body fluid 168. The coating 172 can include, for example, a gel containing a mixture of biocompatible ions (e.g., sodium, chlorine). In some embodiments, the coating 172 can dissolve overtime (e.g., after CV performance is completed) to enable other usages of the reference electrode 166, such as to enable current flow therethrough, after dissolving of the ions. In additional or alternative embodiments, the ions are resistant to dissolving to enable usage for additional CV operations. Moreover, the sensing circuitry 160 can include a high impedance amplifier (e.g., having 10A12 ohms) to enable measurement of the electrical potential of the reference electrode 166 (e.g., relative to the electrical potential of the working electrode 162) while impeding current flow through the reference electrode 166. Such arrangements of the reference electrode 166 can potentially enable an already existing electrode of the implantable housing 152 to be used for CV. Thus, implementation of a separate reference electrode, along with components used to electrically couple the separate reference electrode to the monitoring module 154, may be avoided.

[0036] In some embodiments, the state of the surface 170 can also be controlled by avoiding current flow through the reference electrode 166 for a target duration of time prior to performance (e.g., a scheduled performance) of CV. Avoiding current flow through the reference electrode 166 for the target duration of time enables the reference electrode 166 to settle and rest such that the reference electrode 166 does not undergo any changes after the target duration of time has elapsed. As such, the reference electrode 166 is at an equilibrium during CV performance to help provide a stable electrical potential.

[0037] FIG. 3 is a schematic diagram of an example implantable medical device system 200 with an implantable housing 202 that contains a monitoring module 204 having a memory 206, a processor 208, and sensing or measurement circuitry 210. A working electrode 212 and a counter electrode 214 are integrated with the implantable housing 202 and in contact with body tissue and / or body fluid 216 of a recipient. However, a reference electrode 218 of the implantable medical device system 200 is separate from the implantable housing 202. For example, the reference electrode 218 is a removable patch (e.g., a silver / silver chloride gel patch) that can be applied to the body tissue and / or body fluid 216 (e.g., the same or different body tissue and / or body fluid 216 monitored by the monitoring module 204), such as skin and / or exposed tissue, during CV performance and removed from the skin and / or exposed tissue after CV performance has been completed. The reference electrode 218 is electrically coupled to the monitoring module 204 to enable the monitoring module 204 to determine and utilize the electrical potential of the reference electrode 218.

[0038] In the illustrated embodiment, the implantable housing 202 includes an integrated connector 220, such as a flying lead (e.g., of an existing electrode). The connector 220 is routed (e.g., through the recipient) to connect to the reference electrode 218 and enable usage of the reference electrode 218 during CV performance. After CV performance has been completed, the connector 220 can be electrically decoupled from the reference electrode 218 to enable removal of the reference electrode 218 from the recipient. In this manner, the reference electrode 218 may be selectively applied to the recipient for CV performance.

[0039] FIG. 4 is a schematic diagram of an example implantable medical device system 250 with an implantable housing 252 containing a monitoring module 254 that includes a memory 256, a processor 258, and sensing or measurement circuitry 260. A working electrode 262 and counter electrode 264 are integrated with the implantable housing 252, and a reference electrode 266 is separate from the implantable housing 252. For example, the reference electrode 266 is a removable patch applied to skin and / or exposed tissue of the recipient. The working electrode 262, the counter electrode 264, and the reference electrode 266 are in contact with body tissue and / or body fluid 268 of the recipient.

[0040] A connector 270 (e.g., a needle, a pin) separate from the implantable housing 252 and separate from the reference electrode 266 is used to electrically couple the monitoring module 254 and the reference electrode 266 to one another. For example, the connector 270 is inserted through the body tissue and / or body fluid 268 to which the reference electrode 266 is applied. The portion of the connector 270 in contact with the body tissue and / or body fluid 268 is insulated to avoid undesirable electrical coupling with the body tissue and / or body fluid 268 and enable desirable measurement of the electrical potential of the reference electrode 266. However, the ends of the connector 270 are conductive to enable electrical coupling to the monitoring module 254 and / or to the reference electrode 266.

[0041] The implantable housing 252 includes a first port 272, such as a feedthrough, configured to receive the connector 270 to enable the connector 270 to electrically couple to the monitoring module 254. Additionally, the reference electrode 266 includes a second port 274 configured to receive the connector 270 to enable the connector 270 to electrically couple to the reference electrode 266. By way of example, the connector 270 is electrically coupled to the monitoring module 254 and to the reference electrode 266 via the ports 272, 274 during CV performance. After completion of CV, the connector 270 can removed from each of the ports 272, 274, thereby electrically decoupling the monitoring module 254 and the reference electrode 266 from one another, and the connector 270 can be removed from the recipient. Thereference electrode 266 can also be removed from the recipient after completion of CV. Thus, the reference electrode 266 and / or the connector 270 can be selectively implemented for CV performance.

[0042] It should be noted that further embodiments that incorporate a reference electrode can be utilized. As an example, a reference electrode separate from an implantable housing can include an integral connector that is used to electrically couple to the monitoring module to enable CV performance utilizing the electrical potential of the reference electrode. As another example, a removable reference electrode can be treated to have a stable electrical potential (e.g., by uniform manufacturing and / or uniform cleaning, by blocking current flow therethrough for a duration of time prior to CV performance, by applying a coating). For any of such embodiments, the electrical potential of the reference electrode is used to adjust the electrical potential output at the working electrode.

[0043] FIG. 5 is a flowchart of an example method 300 for performing CV to monitor body tissue and / or body fluid of a recipient of an implantable medical device. For example, the method 300 may be performed by any of the implantable medical device systems (e.g., the processor of the monitoring module) described herein. At block 302, current flow to a reference electrode, which is applied to the recipient, is initially blocked for a target duration of time. For example, the target duration of time can include 1-5 hours, 5-10 hours, or more than 10 hours. Blocking current flow to the reference electrode for the target duration of time can enable the reference electrode to settle to an equilibrium state in which the electrical potential of the reference electrode is stable. Thus, after the target duration of time has elapsed, the stable electrical potential of the reference electrode can be utilized as an accurate reference point or baseline. In some embodiments, the reference electrode is integrated with (e.g., an existing component of) the implantable medical device. In additional or alternative embodiments, the reference electrode is a removable reference electrode.

[0044] At block 304, an electrical potential of a working electrode, which is in contact with the body tissue and / or body fluid of the recipient, relative to the stable electrical potential of the reference electrode is swept between a first limit and a second limit. In other words, the electrical potential of the working electrode relative to the stable electrical potential is iteratively or repeatedly adjusted back and forth between the first limit and the second limit, such as by increasing the electrical potential of the working electrode relative to the stable electrical potential at a selected rate from the first limit to the second limit and decreasing the electrical potential of the working electrode relative to the stable electrical potential at the sameselected rate from the second limit to the first limit. As a result of the electrical potential output at the working electrode, a current flows from the working electrode, through the body tissue and / or body fluid in contact with the working electrode, and to a counter electrode electrically coupled to the working electrode.

[0045] At block 306, the current flow is analyzed. For example, a current measurement is monitored as the electrical potential of the working electrode relative to the stable electrical potential is swept. In particular, the current measurement may change as the electrical potential of the working electrode relative to the stable electrical potential is adjusted between the first limit and the second limit, and the current measurement (e.g., change in current measurement) is indicative of a state (e.g., composition, structure) of the body tissue and / or body fluid of the recipient. Thus, the current flow is measured in response to the sweeping of the electrical potential of the working electrode relative to the stable electrical potential. In certain embodiments, information related to the current measurement is output to a user. As an example, the current measurement is directly provided. As another example, the current measurement is compared to a threshold or target current measurement value, and an output is provided based on the comparison. For instance, in response to the current measurement being different than the threshold current measurement value (e.g., by greater than a threshold amount), an output is provided to indicate a potentially undesirable state of the body tissue and / or body fluid. In either case, the information output to the user can prompt the user to perform an appropriate action in response.

[0046] In some embodiments, the method 300 can be performed during performance of another operation, such as implantation of the implantable medical device. For instance, performance of the method 300 (e.g., to acquire current flow measurements for determining a condition of the recipient) can help performance of the other operation (e.g., to adjust implantation of the implantable medical device based on the condition of the recipient indicated by the current flow measurements).

[0047] In additional or alternative embodiments, the reference electrode is removed (e.g., detached from the recipient) after CV performance, such as after the current flow is analyzed at block 306. By way of example, the reference electrode and a connector that enables utilization of the electrical potential of the reference electrode are decoupled form one another to enable removal of the reference electrode. In such embodiments, another reference electrode and / or connector can be implemented to enable a subsequent CV performance via the method 300.

[0048] FIGs. 6A-6D illustrate an example cochlear implant system 402 with which aspects of the techniques presented herein can be implemented to enable the cochlear implant system 402 to monitor body tissue and / or body fluid. The cochlear implant system 402 comprises an external component 404 that is configured to be directly or indirectly attached to the body of the user, and an intemal / implantable component 412 that is configured to be implanted in or worn on the head of the user. In the examples of FIGs. 6A-6D, the implantable component 412 is sometimes referred to as a “cochlear implant.” FIG. 6A illustrates the cochlear implant 412 implanted in the head 454 of a user, while FIG. 6B is a schematic drawing of the external component 404 worn on the head 454 of the user. FIG. 6C is another schematic view of the cochlear implant system 402, while FIG. 6D illustrates further details of the cochlear implant system 402. For ease of description, FIGs. 6A-6D will generally be described together.

[0049] In the examples of FIGs. 6A-6D, the external component 404 comprises a sound processing unit 406, an external coil 408, and generally, a magnet fixed relative to the external coil 408. The cochlear implant 412 includes an implantable coil 414, an implant body 434, and an elongate stimulating assembly 416 configured to be implanted in the user’s cochlea. In one example, the sound processing unit 406 is an off-the-ear (OTE) sound processing unit, sometimes referred to herein as an OTE component, that is configured to send data and power to the implantable component 412. In general, an OTE sound processing unit is a component having a generally cylindrically shaped housing 411 and which is configured to be magnetically coupled to the user’s head 454 (e.g., includes an integrated external magnet 450 configured to be magnetically coupled to an intemal / implantable magnet 452 in the implantable component 412). The OTE sound processing unit 406 also includes an integrated external (headpiece) coil 408 (the external coil 408) that is configured to be inductively coupled to the implantable coil 414.

[0050] It is to be appreciated that the OTE sound processing unit 406 is merely illustrative of the external devices that could operate with implantable component 412. For example, in alternative examples, the external component 404 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 414. It is also to be appreciated that alternative external components could be located in the user’s ear canal, worn on the body, etc.

[0051] Although the cochlear implant system 402 includes the sound processing unit 406 and the cochlear implant 412, as described below, the cochlear implant 412 can operate independently from the sound processing unit 406, for at least a period, to stimulate the user. For example, the cochlear implant 412 can operate in a first general mode, sometimes referred to as an “external hearing mode,” in which the sound processing unit 406 captures sound signals which are then used as the basis for delivering stimulation signals to the user. The cochlear implant 412 can also operate in a second general mode, sometimes referred as an “invisible hearing” mode, in which the sound processing unit 406 is unable to provide sound signals to the cochlear implant 412 (e.g., the sound processing unit 406 is not present, the sound processing unit 406 is powered-off, the sound processing unit 406 is malfunctioning, etc.). As such, in the invisible hearing mode, the cochlear implant 412 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 412 in the external hearing mode are provided below, followed by details regarding operation of the cochlear implant 412 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 412 could also operate in alternative modes.

[0052] In FIGs. 6A and 6C, the cochlear implant system 402 is shown with an external device 410, configured to implement aspects of the techniques presented. The external device 410 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 410 and the cochlear implant system 402 (e.g., sound processing unit 406 or the cochlear implant 412) wirelessly communicate via a bi-directional communication link 426. The bi-directional communication link 426 may comprise, for example, a short-range communication, such as Bluetooth link, Bluetooth Low Energy (BLE) link, a proprietary link, etc.

[0053] Returning to the example of FIGs. 6A-6D, the sound processing unit 406 of the external component 404 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 406. The one or more input devices include, for example, one or more sound input devices 418 (e.g., one or more external microphones, audio input ports, telecoils, etc.), one or more auxiliary input devices 428 (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) 420 (e.g., for communication with the external device 410), each located in, on, ornear the sound processing unit 406. 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 420 and / or one or more auxiliary input devices 428 could be omitted).

[0054] The sound processing unit 406 also comprises the external coil 408, a charging coil 430, a closely-coupled radio frequency transmitter / receiver (RF transceiver) 422, at least one rechargeable battery 432, and an external sound processing module 424. The external sound processing module 424 can be configured to perform a number of operations which are represented in FIG. 6D by a sound processor 433. The sound processor 433 can be formed by 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, the sound processor 433 can each be implemented as a firmware element, partially or fully implemented with digital logic gates in one or more application-specific integrated circuits (ASICs), partially or fully in software, etc. Although FIG. 6D illustrates the sound processor 433 as being implemented / performed at the external sound processing module 424, it is to be appreciated that the sound processor 433 (e.g., functional operations) could also or alternatively be implemented / performed as part of the implantable sound processing module 458, as part of the external device 410, etc.

[0055] Returning to the example of FIGs. 6A-6D, the implantable component 412 comprises an implant body (main module) 434, a lead region 436, and the intra-cochlear stimulating assembly 416, all configured to be implanted under the skin (tissue) 415 of the user. The implant body 434 generally comprises a hermetically-sealed housing 438 that includes, in certain examples, at least one power source 425 (e.g., one or more batteries, one or more capacitors, etc.), in which RF interface circuitry 440 and a stimulator unit 442 are disposed. The implant body 434 also includes the intemal / implantable coil 414 that is generally external to the housing 438, but which is connected to the RF interface circuitry 440 via a hermetic feedthrough (not shown in FIG. 6D).

[0056] As noted, stimulating assembly 416 is configured to be at least partially implanted in the user’s cochlea. Stimulating assembly 416 includes a plurality of longitudinally spaced intra-cochlear electrical stimulating contacts (electrodes) 444 that collectively form a contact array (electrode array) 446 for delivery of electrical stimulation (current) to the recipient’s cochlea. Stimulating assembly 416 extends through an opening in the recipient’s cochlea (e.g., cochleostomy, the round window, etc.) and has a proximal end connected to stimulator unit442 via lead region 436 and a hermetic feedthrough (not shown in FIG. 6D). Lead region 436 includes a plurality of conductors (wires) that electrically couple the electrodes 444 to the stimulator unit 442. The implantable component 412 also includes an electrode outside of the cochlea, sometimes referred to as the extra-cochlear electrode (ECE) 439.

[0057] As noted, the cochlear implant system 402 includes the external coil 408 and the implantable coil 414. The external magnet 450 is fixed relative to the external coil 408 and the intemal / implantable magnet 452 is fixed relative to the implantable coil 414. The external magnet 450 and the intemal / implantable magnet 452 fixed relative to the external coil 408 and the intemal / implantable coil 414, respectively, facilitate the operational alignment of the external coil 408 with the implantable coil 414. This operational alignment of the coils enables the external component 404 to transmit data and power to the implantable component 412 via a closely-coupled wireless link 448 formed between the external coil 408 with the implantable coil 414. In certain examples, the closely-coupled wireless link 448 is a RF link. However, various other types of energy transfer, such as 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. 6D illustrates only one example arrangement.

[0058] As noted above, sound processing unit 406 includes the external sound processing module 424. The external sound processing module 424 is configured to process the received input audio signals (received at one or more of the input devices, such as sound input devices 418 and / or auxiliary input devices 428), 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 424 is configured to perform sound processing on input signals received at the sound processing unit 406). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in the external sound processing module 424 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.

[0059] As noted, FIG. 6D illustrates an embodiment in which the external sound processing module 424 in the sound processing unit 406 generates the output control signals. In an alternative embodiment, the sound processing unit 406 can send less processed information (e.g., audio data) to the implantable component 412, and the sound processing operations (e.g., conversion of input sounds to output control signals 456) can be performed by a processor within the implantable component 412.

[0060] In FIG. 6D, according to an example embodiment, output control signals (stimulation signals) are provided to the RF transceiver 422, which transcutaneously transfers the output control signals (e.g., in an encoded manner) to the implantable component 412 via external coil 408 and implantable coil 414. That is, the output control signals (stimulation signals) are received at the RF interface circuitry 440 via implantable coil 414 and provided to the stimulator unit 442. The stimulator unit 442 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) 444. In this way, cochlear implant system 402 electrically stimulates the user’s auditory nerve cells, bypassing absent or defective hair 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).

[0061] As detailed above, in the external hearing mode the cochlear implant 412 receives processed sound signals from the sound processing unit 406. However, in the invisible hearing mode, the cochlear implant 412 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. 6D, an example embodiment of the cochlear implant 412 can include a plurality of implantable sound sensors 465(1), 465(2) that collectively form a sensor array 460, and an implantable sound processing module 458. Similar to the external sound processing module 424, the implantable sound processing module 458 may comprise, for example, one or more processors and a memory device (memory) that includes sound processing logic.

[0062] In the invisible hearing mode, the implantable sound sensors 465(1), 465(2) of the sensor array 460 are configured to detect / capture input sound signals 466 (e.g., acoustic sound signals, vibrations, etc.), which are provided to the implantable sound processing module 458. The implantable sound processing module 458 is configured to convert received input sound signals 466 (received at one or more of the implantable sound sensors 465(1), 465(2)) into output control signals 456 for use in stimulating the first ear of a recipient or user (i.e., the implantable sound processing module 458 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 458 are configured to execute sound processing logic in memory to convert the received input sound signals 466 into output control signals 456 that are provided to the stimulator unit 442. The stimulator unit 442 is configured to utilize the output control signals 456 to generate electricalstimulation 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.

[0063] 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 402 could operate differently in different embodiments. For example, in one alternative implementation of the external hearing mode, the cochlear implant 412 could use signals captured by the sound input devices 418 and the implantable sound sensors 465(1), 465(2) of sensor array 460 in generating stimulation signals for delivery to the user.

[0064] According to the techniques of the present disclosure, external sound processing module 424 may also include an inertial measurement unit (IMU) 470. The IMU 470 is configured to measure the inertia of the user's head, that is, motion of the user's head. As such, IMU 470 comprises one or more sensors 475 each configured to sense one or more of rectilinear or rotatory motion in the same or different axes. Examples of sensors 475 that may be used as part of IMU 470 include accelerometers, gyroscopes, inclinometers, compasses, and the like. Such sensors may be implemented in, for example, micro electromechanical systems (MEMS) or with other technology suitable for the particular application.

[0065] As also illustrated in FIG. 6D, in certain examples, a second IMU 480 including one or more sensors 485 is incorporated into implantable sound processing module 458 of implant body 434. Second IMU 480 may serve as an additional or alternative IMU to IMU 470 of external sound processing module 424. Like sensors 475, sensors 485 may each be configured to sense one or more of rectilinear or rotatory motion in the same or different axes. Examples of sensors 485 that may be used as part of IMU 480 include accelerometers, gyroscopes, inclinometers, compasses, and the like. Such sensors may be implemented in, for example, micro MEMS or with other technology suitable for the particular application. For hearing devices that include an implantable sound processing module, such as implantable sound processing module 458, that includes an IMU, such as IMU 480, the techniques presented herein may be implemented without an external processor. Accordingly, a hearing device that includes an implant body 434 and lacks an external component 404 may be configured to implement the techniques presented herein.

[0066] The implant body 434 also includes a monitoring module 500 in the illustrated embodiment. The monitoring module 500 is configured to perform a potentiodynamicelectrochemical measurement, such as CV, using the techniques discussed herein. For example, the monitoring module 500 is configured to utilize at least some of the electrodes 444 and / or the ECE 439 (e.g., as the working electrode, counter electrode, and / or reference electrode) to perform CV, such as to monitor the cochlea and / or perilymph. Thus, at least some of the electrodes 44 and / or the ECE 439 can have multiple functionalities for stimulating hearing and performing CV. Additionally or alternatively, the monitoring module 500 is configured to utilize a separate electrode (e.g., a removable patch), such as a dedicated electrode, to perform CV. For this reason, a connector 502 is configured to electrically couple the monitoring module 500 and the separate electrode to one another. The connector 502 can be integrated with the implant body 434 (e.g., with the hermetically-sealed housing 438) and / or separate from the implant body 434 and configured to couple to the implant body 434, such as via a port of the hermetically-sealed housing 438, to electrically couple to the monitoring module 500.

[0067] In some embodiments, the monitoring module 500 is configured to perform the potentiodynamic electrochemical measurement during operation to implant the implant body 434 within the recipient. Data (e.g., current measurements) obtained during performance of the potentiodynamic electrochemical measurement can be used to facilitate implantation of the implant body 434 within the recipient. By way of example, in response to receiving undesirable or unexpected results, implantation of the implant body 434 can be adjusted to address or mitigate the undesirable or unexpected results.

[0068] Although the monitoring module 500 is incorporated in the implant body 434 in the illustrated embodiment, the monitoring module 500 can be incorporated in the external component 404 in additional or alternative embodiments to enable the external component 404 to perform a potentiodynamic electrochemical measurement. In either embodiment, the cochlear implant system 402 is configured to perform the potentiodynamic electrochemical measurement, and the cochlear system 402 can transmit data acquired during performance of the potentiodynamic electrochemical measurement to the external device 410 to provide information to a user of the external device 410.

[0069] As noted above, for ease of description, the techniques presented herein have been primarily described with reference to performing a specific type of electrochemical measurement, namely cyclic voltammetry (CV). However, also as noted above, the techniques presented herein could also be used to perform other types of electrochemical measurements in a recipient. In particular, any of the aspects described above could be used to perform othertypes of electrochemical measurements in the recipient. For example, one or more of the above aspects of the techniques presented herein could be used to perform electrochemical impedance spectroscopy (EIS).

[0070] Electrochemical impedance spectroscopy (EIS) can be for the analysis of interfacial properties related to an electrode surface, such as for sensing protein and tissue extent (e.g., protein coverage and fibrous tissue and possibly other types of tissue near an electrode). EIS can be a “non-invasive” technique, causing only minimal change to the electrode condition during sensing. Proteins and soft tissue cannot be imaged by conventional means, increase impedance and power consumption, and may be implicated in loss of residual hearing. In one example, an EIS technique includes applying time varying electrical potentials or currents, such as a sinusoidal wave signal, a non-sinusoidal wave signal, or a pulse signal to the working electrode with respect to the reference electrode to induce a current flow from the working electrode, through the tissue, and to the counter electrode. A current measurement, a voltage measurement, an impedance measurement, and / or any other suitable measurement of the induced current flow is then be monitored and analyzed. Characteristics of the measurements, such as an amplitude, a phase, or other characteristic, can be used to determine a condition of the recipient (e.g., tissue composition). For example, the measurement and / or a characteristic of the measurements is compared with a target value or an expected value. In some embodiments, time varying electrical potential or currents having different frequency components are be applied to the working electrode. For instance, a frequency of a sinusoidal wave signal or a shape / width of a pulse signal related to the time varying electrical potential or currents are adjusted. In additional or alternative embodiments, multiple signals are applied simultaneously or concurrently with one another. For instance, sinusoidal wave signals having different frequencies between a range of values are simultaneously applied to provide respective measurements. The measurements can be separated from one another, such as in the frequency domain via filtering, to enable the measurements to be individually analyzed.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 more processors, cause the one or more processors to execute operations analogous to the methods of the present disclosure.

[0075] 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.

[0076] 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.

[0077] 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. An implantable medical device system, comprising: a reference electrode having a stable electrical potential, wherein the reference electrode is in contact with a recipient; and at least one processor configured to perform cyclic voltammetry (CV) within the recipient by: iteratively sweeping an electrical potential of at least one working electrode in the recipient with respect to the stable electrical potential of the reference electrode back and forth between a lower limit and an upper limit; and analyzing a current flow in the recipient in response to the sweeping of the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode.

2. The implantable medical device system of claim 1, wherein the at least one processor is configured to: measure the electrical potential of the at least one working electrode with respect to the reference electrode during the sweeping of the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode; and analyze the current flow in the recipient by measuring a current passing between the at least one working electrode and at least one counter electrode during the sweeping of the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode.

3. The implantable medical device system of claim 2, comprising the at least one counter electrode, wherein the at least one counter electrode is positioned such that the current flow is directed from the at least one working electrode to the at least one counter electrode through at least one of body tissue or body fluid of the recipient.

4. The implantable medical device system of claim 1, 2, or 3, wherein, to iteratively sweep the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode back and forth between the lower limit and the upper limit, the at least one processor is configured to iteratively:increase the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode at a selected rate from the lower limit to the upper limit; and decrease the electrical potential of the at least one working electrode with respect to the stable electrical potential of the reference electrode at the selected rate from the upper limit to the lower limit.

5. The implantable medical device system of claim 1, 2, or 3, wherein the reference electrode comprises a metallic material having a surface treatment.

6. The implantable medical device system of claim 5, wherein the reference electrode comprises an end that is in contact with at least one of body tissue or body fluid of the recipient, and wherein the surface treatment comprises a gel with a mixture of ions applied to the end of the reference electrode.

7. The implantable medical device system of claim 1, 2, or 3, further comprising: a high impedance amplifier that impedes current flow through the reference electrode, and wherein the at least one processor is configured to determine the stable electrical potential of the reference electrode via the high impedance amplifier.

8. The implantable medical device system of claim 1, 2, or 3, wherein the reference electrode comprises a removable patch applied to exposed tissue of the recipient.

9. The implantable medical device system of claim 8, wherein the at least one processor is disposed in an implantable housing with measurement circuitry, and wherein the implantable housing comprises a feedthrough configured to receive a needle that electrically connects the removable patch to the measurement circuitry.

10. A method for performing a potentiodynamic electrochemical measurement in a recipient, comprising: repeatedly sweeping a first potential of at least one working electrode implanted in a recipient with respect to a second potential of a reference electrode in contact with the recipient between a lower potential and an upper potential; andmeasuring current passing between the at least one working electrode and at least one counter electrode resulting from the sweeping of the first potential of the at least one working electrode with respect to the second potential of the reference electrode.

11. The method of claim 10, comprising blocking current flow between the at least one working electrode and the at least one counter electrode for a target duration of time prior to repeatedly sweeping the first potential of the at least one working electrode with respect to the second potential of the reference electrode.

12. The method of claim 10, comprising removing the reference electrode from contact with the recipient after measuring the current passing between the at least one working electrode and the at least one counter electrode.

13. The method of claim 10, 11, or 12, wherein the at least one working electrode and the at least one counter electrode are of an implantable medical device, and repeated sweeping of the first potential of the at least one working electrode with respect to the second potential of the reference electrode is performed during implantation of the implantable medical device in the recipient.

14. A method, comprising: directing, via a processor, current flow within a recipient between at least one working electrode to at least one counter electrode, wherein the at least one working electrode and the at least one counter electrode are in contact with the recipient; repeatedly adjusting, via the processor, an electrical potential at the at least one working electrode relative to a stable electrical potential of a reference electrode in contact with the recipient between a first limit and a second limit; and measuring, via the processor, the current flow within the recipient in response to the adjusting of the electrical potential at the at least one working electrode relative to the stable electrical potential.

15. The method of claim 14, comprising: blocking, via the processor, the current flow to the reference electrode for a target duration of time prior to repeatedly adjusting the electrical potential at the at least one working electrode relative to the stable electrical potential.

16. The method of claim 14 or claim 15, wherein repeatedly adjusting, via the processor, the electrical potential at the at least one working electrode relative to the stable electrical potential between the first limit and the second limit comprises alternating between: increasing, via the processor, the electrical potential at the at least one working electrode relative to the stable electrical potential from the first limit to the second limit at a selected rate; and decreasing, via the processor, the electrical potential at the at least one working electrode relative to the stable electrical potential from the second limit to the first limit at the selected rate.

17. The method of claim 14 or claim 15, comprising: outputting information related to measurement of the current flow within the recipient.

18. The method of claim 17, comprising: comparing, via the processor, the measurement of the current flow with a target measurement; and outputting, via the processor, the information based on the comparing of the measurement of the current flow with the target measurement.

19. An implantable medical device system, comprising: a working electrode configured to be implanted in a recipient; a counter electrode configured to be implanted in the recipient; circuitry configured to iteratively adjust an electrical potential of the working electrode from a first limit to a second limit and from the second limit to the first limit, resulting in a flow of current between the working electrode and the counter electrode; and a reference electrode in contact with the recipient and configured such that the flow of current through the reference electrode is impeded.

20. The implantable medical device system of claim 19, wherein the reference electrode comprises a gel applied to a surface of the reference electrode to impede the flow of current through the reference electrode.

21. The implantable medical device system of claim 19, wherein the reference electrode comprises a removable patch configured to impede the flow of current therethrough, and the implantable medical device system comprises a connector electrically coupling the circuitry and the reference electrode to one another.

22. The implantable medical device system of claim 21, comprising: an implantable housing containing the circuitry, wherein the connector is integral with the implantable housing.

23. The implantable medical device system of claim 19, 20, 21 , or 22, wherein the circuitry comprises: a high impedance amplifier configured to impede the flow of current through the reference electrode; and a processor configured to determine the electrical potential of the working electrode relative to an electrical potential of the reference electrode via the high impedance amplifier.

24. An implantable medical device system, comprising: a reference electrode having a stable electrical potential, wherein the reference electrode is in contact with a recipient; and at least one processor configured to perform electrical impedance spectroscopy (EIS) within the recipient by: applying a time varying electrical potential or current to at least one working electrode in the recipient with reference to the stable electrical potential of the reference electrode, resulting in a current flow in the recipient; and analyzing a measurement of the current flow in the recipient.

25. The implantable medical device system of claim 24, wherein the at least one processor is configured to perform EIS within the recipient by: applying an additional time varying electrical potential or current to the at least one working electrode in the recipient with reference to the stable electrical potential of the reference electrode, resulting in the current flow in the recipient, wherein the time varyingelectrical potential or current and the additional time varying electrical potential or current include different frequency components.

26. The implantable medical device system of claim 25, wherein the time varying electrical potential or current and the additional time varying electrical potential or current are applied concurrently to the at least one working electrode, and wherein the at least one processor is configured to perform EIS within the recipient by: analyzing respective measurements of the current flow that result from simultaneous application of the time varying electrical potential or current and the additional time varying electrical potential or current to the at least one working electrode.

27. The implantable medical device system of claim 26, wherein the at least one processor is configured to perform EIS within the recipient by: filtering the respective measurements of the current flow to separate the respective measurements in a frequency domain; and analyzing the respective measurements of the current flow separated in the frequency domain.

28. The implantable medical device system of claim 24, 25, 26, or 27, wherein the at least one processor is configured to analyze the current flow in the recipient by: analyzing at least one of an amplitude or phase of a resulting electrical potential or current measurement of the current flow.

29. The implantable medical device system of claim 24, 25, 26, or 27, wherein the reference electrode comprises a metallic material having a surface treatment comprising a gel with a mixture of ions applied to an end of the reference electrode, the end being in contact with at least one of body tissue or body fluid of the recipient.

30. The implantable medical device system of claim 24, 25, 26, or 27, wherein the reference electrode comprises a removable patch applied to exposed tissue of the recipient.

31. The implantable medical device system of claim 30, comprising a connector electrically coupling the at least one processor and the reference electrode to one another.

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