1. Field of the Invention
The present invention relates to implantable hearing prosthesis, and more particularly, to an integrity testing system in an implantable hearing prosthesis.
2. Related Art
Implantable hearing prostheses include implantable hearing aids, cochlear implants, optically stimulating implants, middle ear stimulators, bone conduction devices, brain stem implants, direct acoustic cochlear stimulators, electro-acoustic devices and other devices providing acoustic, mechanical, optical, and/or electrical stimulation to an element of a recipient's ear. Such devices are subject to failure or malfunctions due to, for example, manufacturing defects, degradation of materials over time or changes in the recipients inner-ear function. If an issue is reported with a conventional implantable hearing prosthesis, an appointment is required with a health care professional, referred to herein as clinician, at a clinic where a number of tests are carried out to test the integrity of the prosthesis, and to determine the source of the failure. These tests are performed using specialist integrity testing equipment, and are performed in a reactive manner. That is, such testing is only performed after a recipient or user has indicated that there may be a problem with the hearing prosthesis, such as a decrease in hearing performance or other non-auditory symptoms that reduce device effectiveness.
The clinician who performs such testing is generally a specialist who is trained to use specialized integrity testing equipment. As such, the testing is generally expensive and time-consuming procedure for all involved. Furthermore, because device problems may be intermittent, the test results may be inconclusive, provide a false positive (false conclusion that the device is working correctly), and/or require subsequent additional follow-up testing to determine the nature of the problem.
In one aspect of the present invention, an implantable hearing prosthesis is provided. The prosthesis comprises: an integrated integrity system configured to measure one or more electrical characteristics of at least one component of the prosthesis, to evaluate the integrity of the prosthesis based on the measurements, and to perform at least one diagnostic operation based on the evaluation.
In another embodiment of the present invention, a method for evaluating the integrity of an implantable hearing prosthesis is provided. The method comprises: measuring one or more electrical characteristics of at least one component of the prosthesis; determining, based on the measurements, if there is error in the operation of the prosthesis; and performing at least one diagnostic operation to determine whether there is an error in the operation of the prosthesis.
In a still other embodiment of the present invention, an implantable hearing prosthesis is provided. The prosthesis comprises: means for measuring one or more electrical characteristics of at least one component of the prosthesis; means for determining, based on the measurements, if there is an error in the operation of the prosthesis; and means for performing at least one diagnostic operation to determine whether there is an error in the operation of the prosthesis.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be described with reference to the drawings in which:
FIG. 1 is a schematic block diagram illustrating an implantable hearing prosthesis having an integrated integrity system therein, in accordance with embodiments of the present invention;
FIG. 2 illustrates a method of assessing the integrity of an implantable hearing prosthesis, in accordance with embodiments of the present invention;
FIG. 3 are graphs of a normalized variable bi-polar impedance measurement matrix, in accordance with embodiments of the present invention;
FIG. 4 are graphs of a representation of a normalized variable bi-polar impedance measurement matrix, by common distance from the active electrode, in accordance with embodiments of the present invention;
FIG. 5 illustrates a portion of an electrode array and a model of the resistance values present when insulation breakdown occurs, in accordance with embodiments of the present invention;
FIG. 6 graphs a normalized representation of a variable bi-polar impedance measurement matrix of a cochlea which is partially ossified, in accordance with embodiments of the present invention; and
FIG. 7 illustrates a method of self-correcting escalation in an integrity system or method, in accordance with embodiments of the present invention.
Embodiments of the present invention are generally directed to an implantable hearing prosthesis comprising an integrated system that is configured to evaluate the integrity or operational performance of the prosthesis. This integrated system, referred to herein as an integrity evaluation system or simply integrity system, is configured to measure one or more electrical characteristics of a component of the prosthesis. The system evaluates the integrity of the prosthesis based on these measurements, and performs at least one diagnostic operation based on the evaluation. In one embodiment, the diagnostic operation is a notification of an error identified during the evaluation. In another embodiment, the diagnostic operation is an adjustment of one or more of settings in the device to correct an error identified during the evaluation.
The integrity system uses one or more of a number of different measurements to evaluate whether the prosthesis is operating as desired. In particular, the voltage of the power supply, the electrode voltage and/or the electrode impedance, is measured and used to evaluate the operational performance.
As noted above, implantable hearing prostheses include implantable hearing aids, cochlear implants, optically stimulating implants, middle ear stimulators, bone conduction devices, brain stem implants, direct acoustic cochlear stimulators, electro-acoustic devices and other devices providing acoustic, mechanical, optical, and/or electrical stimulation to an element of a recipient's ear. Such prostheses may experience a number of failures including, but not limited to, electrode damage, malfunctioning implantable electronics, such as intermittent operation resulting from radio frequency link insufficiencies, or other conditions resulting in an unstable power supply voltage.
Embodiments of the present invention are described herein with reference to a specific implantable hearing prosthesis, namely a cochlear implant comprising an implantable component and an external component. It would be appreciated that embodiments of the present invention are not limited to this particular type of prosthesis and may be implemented in other implantable hearing prosthesis.
FIG. 1 is a schematic block diagram of a cochlear implant 100 in accordance with embodiments of the present invention. As shown, cochlear implant 100 comprises an implantable component comprising a main module 102 and an electrode array 122. Main module 102 comprises a transceiver 106, a signal processing unit 108, an integrity measurement unit 109, and a stimulator 120.
Cochlear implant 100 further comprises an external component 104. External component 104 includes a transceiver 124 that transfers power and/or data to transceiver 106 via an inductive radio frequency (RF) link 134, a microphone 126, pre-processing unit 128, and a battery 132. External component 104 also includes an evaluator 130 that, along with measurement unit 109, form an integrity system. Evaluator 130 is configured to process calculations made by measurement unit 109, and/or store the processed values or measurements in memory 131. Evaluator 130 further includes a comparator 133 that compares measured/processed values stored in memory with pre-determined thresholds that are also stored in memory. Such pre-determined thresholds may be being either fixed values or values dependent on results of calculations.
As noted above, external component 104 includes a pre-processing unit 128. Pre-processing unit 128 processes the output of microphone 126 that is positioned on the ear of the implant recipient. The coded signals generated by pre-processing unit 128 are provided to the transceiver 124 for transmission to transceiver 106.
The data signals received by transceiver 106 are processed by signal processing unit 108, then provided to stimulator 120. Stimulator 120 generates electrical stimulation signals for delivery to the receiver via electrodes of electrode array 122. Electrode array 122 may comprises one or more reference electrodes, extra-cochlea electrodes, or electrodes implanted in the recipient's cochlear. As such, the stimulation signals are delivered to the nerve cells in a recipient's cochlea, thereby facilitating perception of sound received by microphone 126.
As noted above, cochlear implant 100 includes an integrity system comprising measurement unit 109 and evaluator 130. The integrity system is configured to perform a number of tests to evaluate the operation of cochlear implant 100. These tests may be initiated manually or automatically. Additionally, the tests may be continuous (i.e. be continually performed during operation of the implant) or may be performed periodically.
In embodiments of the present invention, a test is initiated by evaluator 130 via communication link 134, and is performed by measurement unit 109. The results of the measurement are then sent back to evaluator 130 via communication link 134. Evaluator 130 processes the results of the tests and may then perform one or more diagnostic operations based thereon. The diagnostic operations include, for example, taking action to rectify or mitigate the identified issue, storing the results in memory 131 for later analysis, report or signal the issue in an identifiable manner to the recipient or other user, etc. In one embodiment, evaluator 130 activates an error indicating unit 136 that notifies the recipient of the issue. Error indicating unit 136 notifies the recipient of the error using, for example, a recorded announcement streamed to the recipient from memory 131, or a warning light or LED, or other audible or visual indicator.
FIG. 2 is a flowchart illustrating a method 240 of evaluating or assessing the integrity of an implantable hearing prosthesis, such as cochlear implant 100 of FIG. 1. The method begins at step 242 where bipolar impedance values are obtained from the electrodes of cochlear implant electrode array. As shown, step 242 includes two actions, including measuring the impedance between each of the electrodes, and then performing a common ground measurement. These measurements are described in greater detail below. Generally, the voltage between the relevant electrodes is measured at a known current, and Ohm's law is used to calculate the impedance. If the same stimulation current is used, it is possible to use voltage values instead of impedance values. By way of example, the following description of method 240 will explain the steps involved using impedance values. It should be understood, however, that voltage values can be used in the same manner.
Once the bipolar impedance values have been obtained, a normalized impedance matrix is generated at step 244. One exemplary method for generating a normalized impedance matrix is described in detail below. Next, at step 246, the normalized impedance matrix is compared with expected values to determine whether the integrity of the device is as expected, that is, whether an issue has been detected. It would be appreciated that this comparison step does not necessarily involve a direct comparison of two values, but rather may involve calculations based on the normalized impedance values. For example, comparison of one electrode's impedance or voltage values to the average values for all other electrodes may provide an indication of an issue.
Based on the results of the comparison at step 246, an issue decision is made at step 248. If no issue is indicated, then method 240 returns to step 242 to measure the impedance values, and the method is repeated. If an issue is detected, a diagnostic operations 250 is performed. The type of diagnostic operation 250 provided may depend on different factors, such as what issue is detected. As noted above, one output is to alert the recipient that the integrity system has detected an issue. Alternatively or additionally, other diagnostic operations include alerting a health care provider or storing an alert for an appropriate time, such as at the next visit to the health care provider. Additionally, the diagnostic operation may include taking corrective action to alter settings of the cochlear implant so as to attempt to remedy the issue. Potential corrective actions for a cochlear implant are discussed in detail below.
A number of different types of integrity tests may be implemented by an integrity system in accordance with embodiments of the present invention. A first such test is referred to herein as a supply voltage test. The supply voltage test is used to evaluate the stability of the implant's power supply voltage (Vdd) over a period of time and under various load conditions. The load condition of the supply voltage may depend on, for example, the effective total stimulation rate, the electrode impedances, the loudness of the overall sound environment, etc. Additionally, because in certain implants the RF link 134 (FIG. 1) is used to transfer power and data from the external component 104, the main module 102 has supply voltage (Vdd) dependent on the stability of the RF link. One test involves measuring the value of Vdd over time while varying the RF power level (energy level) of the RF link, and tracking the stability of Vdd. Alternatively or additionally, the supply voltage test may measure the effective current drawn from battery 132.
As noted above, certain tests in accordance with embodiments of the present invention may be performed continuously or periodically. In one embodiment, the Vdd stability is continually or periodically tracked and stored by evaluator 130 in memory 131. This allows for monitoring of daily real life conditions, as compared with laboratory or clinic conditions. That is, the supply voltage can be monitored during stimulation as well as in specific test conditions.
In certain embodiments of the present invention, cochlear implant 100 has an alternative external or internal power source. In such embodiments, the RF link 134 may not be used for transmission of power, but monitoring of Vdd may be still be performed using other methods to determine, for example, if battery is defective or there is some other electrical fault.
Another test that may be used in embodiments of the present invention is the bipolar impedance electrode array test. In this test, measurement unit 109 measures the electrode potentials generated as a result of electrical stimulation so as to determine the impedance of the electrodes in the array. That is, the measured voltage between two or more electrodes, along with the knowledge of the current that was supplied, allows impedance to be calculated using Ohm's law.
The electrode array test detects and measures anomalous and unwanted stimulation current flow between individual electrodes of an electrode array through the use of variable bipolar impedance measurements, and a normalization calculation on the resulting impedance matrix. Alternatively, the variable bipolar voltage measurements and a normalization calculation of the resulting voltage matrix is used. The normalization allows a clear distinction of electrodes showing anomalies, as compared to electrodes that are operating according to specification. Furthermore, the normalization shows characteristic signatures for physiological/anatomical properties in the cochlea, such as ossification and scar tissue growth around the in-situ electrode array.
The exemplary electrode array test described herein refers to calculating impedance values, creating an impedance matrix and creating a normalized impedance matrix. However, it would be appreciated that voltage, current and impedance have a fixed relationship and, therefore, it is possible to generate a voltage matrix which can be used in the same manner as an impedance matrix and create a normalized voltage matrix. Therefore, the same principles as described herein may be used to create and use a normalized voltage matrix.
The creation and use of an intra-cochlear impedance matrix is described in detail below. The matrix that is created can be used to provide information on the insulation properties between the physical electrode contacts and can detect conductive bridges between individual electrodes.
In an exemplary electrode array test, evaluator 130 instructs stimulator 120 to deliver a pre-determined stimulation current over each electrode pair of electrode array 122. Measurement unit 109 performs voltage measurements for the relevant electrode pair when a stimulation current is applied. By measuring the resulting electrode voltage and the known stimulation current, the impedance for the respective electrode pair is calculated. The voltage measurements are returned to evaluator 130 via transceivers 106 and 124.
The measurement sequence contains a series of variable bipolar impedance measurements, covering all electrodes in electrode array 122. A bipolar (BP) impedance measurement measures the impedance between a pair of the electrodes.
In one illustrative implementation, electrode array 122 comprises twenty two electrodes in a line (a one dimensional array). The electrodes may be conveniently referred to as electrodes E1 to E22. The first impedance measurement is made between a first electrode E1, which acts as an active electrode, and a second electrode E2, immediately beside the first electrode, that acts as an indifferent electrode. This is known as a BP+1 measurement it measures the impedance between an indifferent electrode (E2) that is one higher (numerically and physically), in the array than the active electrode (E1). If E2 is the active electrode and E1 the indifferent electrode, then the impedance measurement is known as a BP−1. By further increasing the distance from the first electrode, the bipolar mode widens to BP+2, BP+3, and so forth up to the number of electrodes available on the array. Each electrode is operated as active electrode and the impedance measured against each of the other electrodes in the array, giving a matrix of measurements 22 by 22 in size, as shown below in Table 1.
Matrix of variable width bipolar impedance relationships