U.S. patent application number 13/114733 was filed with the patent office on 2012-11-29 for integrity evaluation system in an implantable hearing prosthesis.
Invention is credited to Paul Carter, Herbert Mauch, Barry Nevison, Peter Seligman.
Application Number | 20120300953 13/114733 |
Document ID | / |
Family ID | 47217825 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120300953 |
Kind Code |
A1 |
Mauch; Herbert ; et
al. |
November 29, 2012 |
INTEGRITY EVALUATION SYSTEM IN AN IMPLANTABLE HEARING
PROSTHESIS
Abstract
An implantable hearing prosthesis, comprising an integrated
integrity system. The integrity system is 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.
Inventors: |
Mauch; Herbert;
(Grenzach-Wyhlen, DE) ; Seligman; Peter;
(Essendon, AU) ; Nevison; Barry; (Tonbridge Kent,
GB) ; Carter; Paul; (West Pennant Hills, AU) |
Family ID: |
47217825 |
Appl. No.: |
13/114733 |
Filed: |
May 24, 2011 |
Current U.S.
Class: |
381/60 |
Current CPC
Class: |
H04R 25/554 20130101;
A61N 1/08 20130101; A61N 1/0541 20130101; H04R 25/305 20130101;
A61N 1/36036 20170801; H04R 2225/67 20130101; A61N 2001/083
20130101 |
Class at
Publication: |
381/60 |
International
Class: |
H04R 29/00 20060101
H04R029/00 |
Claims
1. An implantable hearing prosthesis, comprising: 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.
2. The hearing prosthesis of claim 1, wherein the least one
diagnostic operation performed by the integrity system is a
notification of an error identified during the evaluation.
3. The hearing prosthesis of claim 1, wherein the least one
diagnostic operation performed by the integrity system is an
adjustment of one or more of settings in the device to correct an
error identified during the evaluation.
4. The hearing prosthesis of claim 3, wherein the one or more of
settings adjusted by the integrity system are selected from the
group consisting of: a set of electrodes in use, distribution of
the acoustic sound spectrum across the electrodes in use, acoustic
threshold levels, maximum comfort level, and power supplied for
implant operations.
5. The hearing prosthesis of claim 1, wherein the hearing
prosthesis comprises a power supply and an array of electrodes, and
wherein the integrity system is configured to measure one or more
electrical characteristics selected from the group consisting of:
the power supply voltage over a period of time and under various
load conditions and impedance of one or more electrodes.
6. The hearing prosthesis of claim 1, wherein the hearing
prosthesis comprises a plurality of electrodes, and wherein the
integrity system comprises: an integrity measurement unit
configured to perform bipolar measurements on the plurality of
electrodes; and an evaluator configured to calculate normalized
values for each bipolar pair to evaluate the integrity of the
prosthesis and to perform one or more diagnostic operations based
on the evaluated integrity.
7. The hearing prosthesis of claim 6, wherein the bipolar
measurements are voltage measurements.
8. The hearing prosthesis of claim 7, wherein the bipolar
measurements are variable width bipolar voltage measurements.
9. The hearing prosthesis of claim 6, wherein the bipolar
measurements are impedance measurements.
10. The hearing prosthesis of claim 9, wherein the bipolar
measurements are variable width bipolar impedance measurements.
11. The hearing prosthesis of claim 1, wherein the integrity system
further comprises: a memory for storing pre-determined values; and
a comparator for comparing measurements to the pre-determined
values, wherein the integrity system evaluates the integrity of the
prosthesis based on the comparison
12. The hearing prosthesis of claim 1, wherein the integrity system
measures a plurality of electrical characteristics, and wherein the
integrity system further comprises: a comparator for comparing a
first one of the plurality of measurements to a second one of the
plurality of measurements, wherein the integrity system evaluates
the integrity of the prosthesis based on the comparison.
13. The hearing prosthesis of claim 12, wherein the integrity
system normalizes the first and second measurements prior to
performing the comparison.
14. The hearing prosthesis of claim 1, further comprising external
and implantable components configured to communicate via a radio
frequency (RF) link, and wherein the integrity system is configured
to measure the one or more electrical characteristics during idle
periods in the RF link.
15. The hearing prosthesis of claim 1, wherein the integrity system
is configured to continually measure the one or more electrical
characteristics.
16. A method for evaluating the integrity of an implantable hearing
prosthesis, comprising: 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 a determine whether there is an error in the operation
of the prosthesis.
17. The method of claim 16, wherein performing at least one
diagnostic operation comprises: providing a notification of the
identified error.
18. The method of claim 16, wherein performing at least one
diagnostic operation comprises: adjusting of one or more of
settings in the device to correct the error.
19. The method of claim 18, adjusting of one or more of settings in
the device to correct the error comprises: adjusting settings
selected from the group consisting of: a set of electrodes in use,
distribution of the acoustic sound spectrum across the electrodes
in use, acoustic threshold levels, maximum comfort level, and power
supplied for implant operations.
20. The method of claim 16, wherein the hearing prosthesis
comprises a power supply and an array of electrodes, and wherein
measuring one or more electrical characteristics of at least one
component of the prosthesis further comprises: measuring one or
more electrical characteristics selected from the group consisting
of: the power supply voltage over a period of time and under
various load conditions and impedance of one or more
electrodes.
21. The method of claim 16, wherein the hearing prosthesis
comprises a plurality of electrodes, and wherein measuring one or
more electrical characteristics of at least one component of the
prosthesis further comprises: performing bipolar measurements on
the plurality of electrodes.
22. The method of claim 21, wherein the method further comprises:
calculating normalized values for each bipolar pair; and
determining, based on the normalized values, if there is error in
the operation of the prosthesis.
23. The method of claim 16, wherein the hearing prosthesis has a
memory for storing pre-determined values, and wherein the method
further comprises: comparing the measurements of the one or more
electrical characteristics to the pre-determined values; and
determining, based on the comparison, if there is error in the
operation of the prosthesis.
24. The method of claim 16, further comprising: measuring a first
electrical characteristic; measuring a second electrical
characteristic; comparing the measurements of the first and second
electrical characteristics to one another; and determining, based
on the comparison, if there is error in the operation of the
prosthesis.
25. The method of claim 24, further comprising: normalizing the
measurements of the first and second electrical characteristics
prior to performing the comparison.
26. The method of claim 16, wherein the hearing prosthesis
comprises external and implantable components configured to
communicate via a radio frequency (RF) link, and wherein the method
comprises: measuring one or more electrical characteristics during
idle periods in the RF link.
27. The method of claim 16, wherein measuring one or more
electrical characteristics comprises: continually measuring the one
or more electrical characteristics.
28. The method of claim 16, wherein measuring one or more
electrical characteristics comprises: automatically measuring the
one or more electrical characteristics.
29. The method of claim 16, wherein measuring one or more
electrical characteristics comprises: measuring the one or more
electrical characteristics in response to an input signal.
30. An implantable hearing prosthesis, comprising: 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 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.
31. The hearing prosthesis of claim 30, wherein the means for
performing at least one diagnostic operation comprises: means for
providing a notification of the identified error.
32. The hearing prosthesis of claim 30, wherein the means for
performing at least one diagnostic operation comprises: means for
adjusting of one or more of settings in the device to correct the
error.
33. The hearing prosthesis of claim 32, wherein the means for
adjusting of one or more of settings in the device to correct the
error comprises: means for adjusting settings selected from the
group consisting of: a set of electrodes in use, distribution of
the acoustic sound spectrum across the electrodes in use, acoustic
threshold levels, maximum comfort level, and power supplied for
implant operations.
34. The hearing prosthesis of claim 30, wherein the hearing
prosthesis comprises a power supply and an array of electrodes, and
wherein the means for measuring one or more electrical
characteristics of at least one component of the prosthesis further
comprises: means for measuring one or more electrical
characteristics selected from the group consisting of: the power
supply voltage over a period of time and under various load
conditions and impedance of one or more electrodes.
35. The hearing prosthesis of claim 30, wherein the hearing
prosthesis comprises a plurality of electrodes, and wherein the
means for measuring one or more electrical characteristics of at
least one component of the prosthesis further comprises: means for
performing bipolar measurements on the plurality of electrodes.
36. The hearing prosthesis of claim 35, further comprising: means
for calculating normalized values for each bipolar pair; and means
for determining, based on the normalized values, if there is error
in the operation of the prosthesis.
37. The hearing prosthesis of claim 30, further comprising: means
for storing pre-determined values; means for comparing the
measurements of the one or more electrical characteristics to the
pre-determined values; and means for determining, based on the
comparison, if there is error in the operation of the
prosthesis.
38. The hearing prosthesis of claim 30, further comprising: means
for measuring a first electrical characteristic; means for
measuring a second electrical characteristic; means for comparing
the measurements of the first and second electrical characteristics
to one another; and means for determining, based on the comparison,
if there is error in the operation of the prosthesis.
39. The hearing prosthesis of claim 38, further comprising: means
for normalizing the measurements of the first and second electrical
characteristics prior to performing the comparison.
40. The hearing prosthesis of claim 30, wherein the hearing
prosthesis comprises external and implantable components configured
to communicate via a radio frequency (RF) link, and wherein the
method comprises: means for measuring one or more electrical
characteristics during idle periods in the RF link.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to implantable hearing
prosthesis, and more particularly, to an integrity testing system
in an implantable hearing prosthesis.
[0003] 2. Related Art
[0004] 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.
[0005] 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.
SUMMARY
[0006] 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.
[0007] 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.
[0008] 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
[0009] Embodiments of the present invention will be described with
reference to the drawings in which:
[0010] 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;
[0011] FIG. 2 illustrates a method of assessing the integrity of an
implantable hearing prosthesis, in accordance with embodiments of
the present invention;
[0012] FIG. 3 are graphs of a normalized variable bi-polar
impedance measurement matrix, in accordance with embodiments of the
present invention;
[0013] 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;
[0014] 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;
[0015] 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
[0016] FIG. 7 illustrates a method of self-correcting escalation in
an integrity system or method, in accordance with embodiments of
the present invention.
DETAILED DESCRIPTION
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
TABLE-US-00001 TABLE 1 Matrix of variable width bipolar impedance
relationships Indifferent Electrode E1 E2 E3 E4 E5 E6 E7 E8 E9 E10
E11 E12 Active E1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 BP +
7 BP + 8 BP + 9 BP + 10 BP + 11 Electrode E2 BP - 1 CG BP + 1 BP +
2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 BP + 8 BP + 9 BP + 10 E3 BP -
2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 BP + 8
BP + 9 E4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP +
5 BP + 6 BP + 7 BP + 8 E5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP
+ 2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 E6 BP - 5 BP - 4 BP - 3 BP -
2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 E7 BP - 6 BP
- 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP +
5 E8 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP
+ 2 BP + 3 BP + 4 E9 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP -
2 BP - 1 CG BP + 1 BP + 2 BP + 3 E10 BP - 9 BP - 8 BP - 7 BP - 6 BP
- 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2 E11 BP - 10 BP - 9
BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1
E12 BP - 11 BP - 10 BP - 9 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 BP -
3 BP - 2 BP - 1 CG E13 BP - 12 BP - 11 BP - 10 BP - 9 BP - 8 BP - 7
BP - 6 BP - 5 BP - 4 BP - 3 BP - 2 BP - 1 E14 BP - 13 BP - 12 BP -
11 BP - 10 BP - 9 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP - 2
E15 BP - 14 BP - 13 BP - 12 BP - 11 BP - 10 BP - 9 BP - 8 BP - 7 BP
- 6 BP - 5 BP - 4 BP - 3 E16 BP - 15 BP - 14 BP - 13 BP - 12 BP -
11 BP - 10 BP - 9 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 E17 BP - 16 BP
- 15 BP - 14 BP - 13 BP - 12 BP - 11 BP - 10 BP - 9 BP - 8 BP - 7
BP - 6 BP - 5 E18 BP - 17 BP - 16 BP - 15 BP - 14 BP - 13 BP - 12
BP - 11 BP - 10 BP - 9 BP - 8 BP - 7 BP - 6 E19 BP - 18 BP - 17 BP
- 16 BP - 15 BP - 14 BP - 13 BP - 12 BP - 11 BP - 10 BP - 9 BP - 8
BP - 7 E20 BP - 19 BP - 18 BP - 17 BP - 16 BP - 15 BP - 14 BP - 13
BP - 12 BP - 11 BP - 10 BP - 9 BP - 8 E21 BP - 20 BP - 19 BP - 18
BP - 17 BP - 16 BP - 15 BP - 14 BP - 13 BP - 12 BP - 11 BP - 10 BP
- 9 E22 BP - 21 BP - 20 BP - 19 BP - 18 BP - 17 BP - 16 BP - 15 BP
- 14 BP - 13 BP - 12 BP - 11 BP - 10 Indifferent Electrode E13 E14
E15 E16 E17 E18 E19 E20 E21 E22 Active E1 BP + 12 BP + 13 BP + 14
BP + 15 BP + 16 BP + 17 BP + 18 BP + 19 BP + 20 BP + 21 Electrode
E2 BP + 11 BP + 12 BP + 13 BP + 14 BP + 15 BP + 16 BP + 17 BP + 18
BP + 19 BP + 20 E3 BP + 10 BP + 11 BP + 12 BP + 13 BP + 14 BP + 15
BP + 16 BP + 17 BP + 18 BP + 19 E4 BP + 9 BP + 10 BP + 11 BP + 12
BP + 13 BP + 14 BP + 15 BP + 16 BP + 17 BP + 18 E5 BP + 8 BP + 9 BP
+ 10 BP + 11 BP + 12 BP + 13 BP + 14 BP + 15 BP + 16 BP + 17 E6 BP
+ 7 BP + 8 BP + 9 BP + 10 BP + 11 BP + 12 BP + 13 BP + 14 BP + 15
BP + 16 E7 BP + 6 BP + 7 BP + 8 BP + 9 BP + 10 BP + 11 BP + 12 BP +
13 BP + 14 BP + 15 E8 BP + 5 BP + 6 BP + 7 BP + 8 BP + 9 BP + 10 BP
+ 11 BP + 12 BP + 13 BP + 14 E9 BP + 4 BP + 5 BP + 6 BP + 7 BP + 8
BP + 9 BP + 10 BP + 11 BP + 12 BP + 13 E10 BP + 3 BP + 4 BP + 5 BP
+ 6 BP + 7 BP + 8 BP + 9 BP + 10 BP + 11 BP + 12 E11 BP + 2 BP + 3
BP + 4 BP + 5 BP + 6 BP + 7 BP + 8 BP + 9 BP + 10 BP + 11 E12 BP +
1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 BP + 8 BP + 9 BP + 10
E13 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 BP + 8 BP +
9 E14 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6 BP + 7 BP
+ 8 E15 BP - 2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP + 5 BP + 6
BP + 7 E16 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP + 4 BP +
5 BP + 6 E17 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2 BP + 3 BP
+ 4 BP + 5 E18 BP - 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP + 1 BP + 2
BP + 3 BP + 4 E19 BP - 6 BP - 5 BP - 4 BP - 3 BP - 2 BP - 1 CG BP +
1 BP + 2 BP + 3 E20 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP - 2 BP -
1 CG BP + 1 BP + 2 E21 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4 BP - 3 BP
- 2 BP - 1 CG BP + 1 E22 BP - 9 BP - 8 BP - 7 BP - 6 BP - 5 BP - 4
BP - 3 BP - 2 BP - 1 CG
[0040] The diagonal of the matrix is populated with common ground
measurements for the respective electrode. Common Ground (CG)
measurements measure an intra-cochlear electrode as an active
electrode against all the other intra-cochlear electrodes connected
together via a temporary short circuit so as to function as a
collective indifferent electrode.
[0041] After acquisition and storage of the impedance measurements,
the variable bipolar measurements are normalized by the use of the
respective common ground impedance value for both the active and
indifferent electrode of the bipolar pair. The normalized impedance
Z.sub.norm for each Bipolar pair can calculated by the use of
Equation 1:
Normalized impedance Z norm = Z BP - Z CG ( indifferent ) Z CG (
acive ) Equation 1 ##EQU00001##
[0042] The resulting normalized impedance matrix can then be
stored, in memory 131, and compared, using comparator 133, with
past impedance measurements. An issue is identified if the
comparison determines that the measurement deviates from the stored
value by a predetermined threshold. This results in a diagnostic
operation as described above.
[0043] An exemplary output response of an electrode array is shown
in FIG. 3. More specifically, FIG. 3 illustrates that the
normalized impedances have a value of zero when the indifferent and
active electrodes are the same, increase to a value of around 0.7
to 0.8 at the direct neighboring electrode, and asymptotically
reach a value of around 1 for electrode numbers more distant on
either side of the active electrode.
[0044] Comparison of the normalized impedance of the electrodes can
be further simplified by comparing electrodes at a common distance
from other electrodes. As noted above, for a typical electrode
array, the normalized impedances have a value of zero when the
indifferent and active electrodes are the same. By comparing
indifferent electrodes at the same distance in the array from the
active electrode, a response function can be determined that again
can be bounded by a pre-determined threshold to indicate whether
function is within an acceptable tolerance.
[0045] FIG. 4 is a plot of normalized impedance measurements
grouped by distance from the active electrode. FIG. 4 shows that,
in this example, when electrodes are compared by their distance
from the active electrode, the normalized impedance measurements
vary by, at most, 0.1. In this manner, evaluator 130 could, for
example, determine that a normalized impedance measurement greater
than 0.15 from the other normalized impedance measurements, at the
same distance from the active electrode, identifies an impedance
issue that requires a diagnostic operation, such as reporting to
the recipient or healthcare professional in an identifiable
manner.
[0046] FIG. 5 illustrates a model showing that the electrode
profiles in the normalized impedance matrix will change based on
the presence of a shunt impedance between two electrodes, or due to
changes in the perilymph properties in the cochlea. FIG. 5 shows
only a portion of an electrode array 122 containing electrodes E1
to E5. The model divides the intracochlear impedance, which is seen
by the stimulation current driven over the electrodes, into the
electrode tissue impedance component (Z.sub.e1 to Z.sub.e5) and the
perilymph impedance component (Z.sub.p12 to Z.sub.p45) between each
electrode. In this example, a shunt impedance (Z.sub.s) is present
between electrodes E2 and E4. A shunt impedance, in this context,
is an unintended electrical path with a particular impedance value.
This could be due to, for example, the breakdown on an insulating
barrier between electrodes that creates at least a partial
unintended electrical path.
[0047] If the normalized impedance for an electrode pair is
affected by a shunt impedance (Z.sub.norm(shunt)), the shunt
impedance Z.sub.s will be in parallel to the electrode tissue
impedance between the electrode pair. This will influence both the
bipolar impedance measurements between the two electrodes affected,
and the common ground impedance measurement for both the active and
indifferent electrode of the pair. The resulting influence on the
normalized impedance can be described by
[0048] Equation 2.
Normalized impedance involving shunt Z norm ( shunt ) = Z BP Z s -
Z CG ( indifferent ) Z s Z CG ( active ) Z s Equation 2
##EQU00002##
[0049] If the electrode pair in an implantable hearing device is
affected by a weak shunt impedance, the shunt impedance will be
large compared to the bipolar impedance over the affected electrode
pair. The normalized impedance will not be affected as shown in
[0050] Equation 3 and will give an expected value of 0.7 to 1,
depending on the width of the bipolar mode (that is, the distance
from the active electrode) for this electrode pair.
Normalized impedance involving weak shunt Z norm ( shun ) = Z norm
1 with Z s .gtoreq. Z BP Equation 3 ##EQU00003##
[0051] If the electrode pair in an implantable hearing device is
affected by a strong shunt impedance, the shunt impedance will be
equal or smaller compared to the bipolar impedance over the
affected electrode pair. The normalized impedance will be affected
by the shunt as shown in
[0052] Equation 4 and depending on the magnitude of the shunt will
tend towards a value of 0.
Normalized impedance involving strong shunt Z norm ( shunt ) = Z s
- Z s Z s 0 with Z s .ltoreq. Z BP Equation 4 ##EQU00004##
[0053] Accordingly, shunt impedances, which are representative of
unintended electrical paths between electrodes, can be detected by
comparison of the impedance values against expected values, as well
as against corresponding values at the same distance from the
active electrode.
[0054] In addition, the normalized impedance matrix can be used to
identify changes in the properties of the perilymph in the cochlea,
such as scar tissue growth or ossification, which would increase
the perilymph impedance. This influence of the perilymph impedance
on the normalized impedance can be shown in Equation 5, where the
variable bipolar and common ground impedance components of the
normalized impedance matrix are replaced with their
electrode-tissue (Z.sub.e) and perilymph impedance (Z.sub.p)
components. Z.sub.p(n,m) in Equation 5 is the perilymph impedance
between a bipolar electrode pair and Z.sub.p(n,x) the perilymph
impedance seen by a common ground measurement.
Normalized impedance based on electrode - tissue and perilymph
impedance Z norm = ( Z e ( n ) + Z p ( n , m ) + Z e ( m ) ) - ( Z
e ( m ) + Z p ( n , x ) ) Z e ( n ) + Z p ( n , x ) Equation 5
##EQU00005##
[0055] Rearranging the equation yields
[0056] Equation 6.
impedance based on electrode - tissue and perilymph impedance (
simplified ) Z norm = Z e ( n ) + Z p ( n , m ) - Z p ( n , x ) Z e
( n ) + Z p ( n , x ) Equation 6 ##EQU00006##
[0057] Changes in the perilymph properties of the cochlea will not
generally affect the whole area of the electrode array equally.
Rather, the changes will affect local areas around a group of
electrodes, for example, a group of electrodes comprising the
electrodes on the basal and apical sides of the electrode. The
perilymph component of the bipolar electrode pair is more affected
by such changes and the perilymph component seen by the common
ground impedance measurement is only significantly affected if most
of the indifferent electrodes would be affected. Using this
simplification it can be assumed that changes in the perilymph
property will increase the bipolar component as shown in
[0058] Equation 7. Local increases in perilymph impedances due to,
for example, scar tissue growth or ossification will yield a value
for the normalized impedance of larger than one.
Influence of increased perilymph impedance Z norm = Z e ( n ) + Z p
( n , m ) .uparw. - Z p ( n , x ) Z e ( n ) + Z p ( n , x )
.gtoreq. 1 Equation 7 ##EQU00007##
[0059] FIG. 6 is a graph showing a plot of an example of a
normalized impedance matrix of an electrode array in a partially
ossified cochlea. Electrodes E1 to around E12 show an increased
perilymph impedance, which is caused by, for example, scar tissue
growth or ossification in this area.
Self-Correcting
[0060] Following implantation, and at subsequent times,
physiological changes occur within the recipient. As such, there is
a need to determine the actual performance of an electrode array
and the response to stimulation provided by the array. For example,
in an implantable hearing device, the response of the auditory
nerve to stimulation by the electrode array is determined. Data
collection for this purpose enables detection and confirmation of
the normal operation of the device, and allows stimulation
parameters to be optimized to suit the characteristics of the
recipient. In the case of an implantable hearing device, this
procedure can include determination of recipient specific
parameters such as threshold levels (T levels) and maximum comfort
levels (C levels) for each stimulation channel. Such data
collection can be performed manually in a clinical setting by
relying on subjective recipient responses, or by taking
measurements directly from the cochlea such as by recording a
neural response to stimulation. A recipient's T and C levels vary
over time as result of tissue degradation (permanent change in
levels), or as a result of a short term condition or illness
(temporary change).
[0061] T and C levels are, generally, stored in an external
component of an implantable hearing prosthesis, but may also be
stored in an internal component, or within a fully implantable
prosthesis with no external components. Because the T and C levels
are stored values, an implantable hearing prosthesis, such as
cochlear implant 100, may operate as a self-correcting device. That
is, the integrity system comprising evaluator 130 and measurement
unit 109, may perform diagnostic operations that correct issues
with the device. The integrity system may, for example, perform
self-correcting by modifying the T and C levels in response to
detection of issues, such as increased perilymph impedance. For
example, the integrity system may increase stimulation levels, that
is, the amount of charge delivered, for stimulation channels which
appear to have high perilymph impedance, in an attempt to improve
hearing at that stimulation channel. As this is a modification
which could potentially provide discomfort to the recipient,
evaluator 130 may provide an indication to the recipient of the
potential fault and ask for confirmation that the T or C level
should be altered. If discomfort or no improvement is registered in
response to the change, then the levels can be reset to the
original values and the issue passed to a clinic for further
analysis.
[0062] As mentioned above, the detection of shunt impedances,
perilymph impedances and the changes of these impedances over time
by evaluator 130 allows automatic detection and reporting of actual
or potential fault conditions in the electrode array of the
implantable hearing device. Also as noted, these detections may be
performed through comparison either to earlier values, other
electrode pairs or to threshold levels.
[0063] Both the supply voltage tests and the electrode array tests
are examples of tests which can be conducted by the integrity
system in accordance with embodiments of the present invention.
These tests may be performed while the recipient is wearing the
prosthesis for daily listening. That is, the tests are real-time
tests performed during normal operation of the prosthesis.
[0064] Sound coding strategies generally use power-up frames to
fill up idle periods, where no, or only low sound, input exists. In
embodiments of the present invention, a power-up frame is replaced
or supplemented with a measurement frame and can, for example,
acquire one measurement point of the impedance matrix. The
measurements are performed with sub-threshold stimulation currents
and, therefore, the recipient would not "hear" any of the test
stimulations. Alternatively, measurement frames could be introduced
at controlled intervals into the stimulation frames, for example,
every few seconds. Since a measurement frame only lasts a few
tenths of micro seconds, equally, the recipient would not notice
them. Where the implantable hearing device has a different power
source, such as in a fully implantable system where all components
are implanted and a battery is used for power, the tests could be
run at night, while the implant is not being used for hearing. The
integrity system could automatically execute the measurements at
regular intervals such as, for example, once a day, week or
month.
[0065] As mentioned above, the integrity system would be tasked
with monitoring the operation of cochlear implant 100, and ensuring
that operation is within pre-defined parameters. A further
improvement is the automatic modification of the operation of
cochlear implant 100. For example, if a shunt, open circuit or
short circuit occurs at a particular electrode due to, for example,
a deterioration of the insulation around the electrode, these
deviations from expectations can be used to automatically
deactivate affected electrodes. For example, if the normalized
impedance matrix has values outside tolerances, then the integrity
system may alter which electrodes are to be used, deactivating
electrodes, if required.
Self-Correcting Escalation
[0066] An integrity system adapted to perform self-correcting
diagnostic operations is sometimes referred to herein as a
self-correcting integrity system. Such systems may also be
implemented as a staged self-correcting escalation integrity
system. In such embodiments, an escalation algorithm as part of the
self-correcting integrity system ensures that recipients receive
the correct level of care and/or choice in the modification of the
function of their medical device.
For example, an escalation algorithm for an implantable hearing
device is implemented as follows: (1) receive error indication that
operation is not as desired, (2) determine appropriate adjustments
based on the error indication, (3) determine whether adjustments to
be made require recipient and/or health care provider approval, (4)
if recipient and/or health care provider approval required: alert
recipient to error condition, (5) if recipient and/or health care
provider approval not required: make self-correcting adjustments,
(6) alert recipient to action taken due to error condition.
[0067] In this manner, the escalation algorithm assesses at what
point self-correcting should take place. If the error condition is
above a pre-defined threshold or is pre-defined as requiring
external approval, the integrity system will report the issue to
the recipient or healthcare professional in an identifiable manner.
Further analysis of the data can then be carried out in a clinical
follow-up session, if necessary, to assess whether any other
alterations can be made or whether explanation is required.
Depending on the severity of the error condition, integrity system
may temporarily deactivate an electrode or make other setting
changes pending confirmation from the recipient of healthcare
professional that an improvement in hearing due to the changes has
occurred. If the integrity system detects issues, but is not able
to clearly determine which electrodes are affected, or too many
electrodes are affected such that automatic correction would cause
a large decrement in performance, the system performs a diagnostic
operation that instructs the recipient to visit a healthcare
provider. The healthcare provider can perform advanced
troubleshooting, such as additional testing using surface potential
electrode measurements.
[0068] If the integrity system deactivates electrodes after an
analysis has been performed, the operation of the implant may be
altered based on the new configuration. For example, the sound
spectrum would be redistributed to the unaffected electrodes. As
such, this is another form of corrective diagnostic operations that
adjust the functionality of the implant to compensate for defective
electrodes caused by current shunts, open and short circuit
electrodes. As such, the recipient's hearing performance would be
restored from the effects of these damaged electrodes without
requiring a visit to a clinic.
[0069] FIG. 7 is a flowchart of a self-correcting escalation method
760 that may be implemented in embodiments of the present
invention. Method 760 begins at step 762 when an error or issue is
identified by, for example, one of the methods described above. At
step 764, a check is performed to determine whether the error
condition has a pre-defined response. If a pre-defined response is
not available, at step 766 the recipient is alerted that an error
or issue has been detected and, preferably, stores the error
condition for later recall at step 766. The recipient alert can
take a number of different forms, as described above, and can have
a number of different severity levels. For example, a minor loss in
hearing resolution for a cochlear implant may simply alert the
recipient to address the issue at the next health care professional
appointment. A major error may alert the recipient that immediate
attention by a health care professional is required.
[0070] If a pre-defined response is defined for the error or issue
condition, then a further recipient effect determination is
performed at step 768. This step will check what the pre-defined
response requires based on the particulars of the error condition.
For example, in a cochlear implant, an error condition can require
that certain electrodes of the electrode array should no longer be
used and the hearing range should be redistributed over the
remaining functional electrodes. However, if too many electrodes
require to be no longer used, then it would not be possible to
redistribute the sound spectrum. In this instant, the effect
determination step 768 would not allow the settings of the device
to be changed and would revert to step 766 in which the recipient
is alerted of the error condition.
[0071] If the effect determination step 768 determines that the
setting changes are within pre-defined limits, the method continues
to step 770 where setting of the implant are adjusted. At this
stage a "change ok" step 772 alerts the recipient to the changes
and asks to confirm that the settings changes are acceptable. If
the settings are not acceptable to the recipient, then a "revert
changes" step 774 reapplies the original settings and step 766 of
alerting the recipient and storing the error condition is applied.
If the recipient accepts the settings changes, then the method
confirms the settings change at step 776 and stores the error
condition at step 778 so that a health care professional can be
alerted to the error condition and settings change at the next
health care professional meeting.
[0072] Whereas impact resistance has greatly improved in
implantable hearing design, the most fragile component remains the
electrode array and associated lead wires. The most frequently
observed electrode array faults are open or short circuits or
breakdowns of the insulation properties between the electrodes.
Faults on the electrode array and associated lead wires can cause a
significant decrement in hearing performance for the recipient,
especially if undetected due to non-availability or lack of access
to respective test methods. Breakdowns in the insulation properties
between electrodes can cause a significant redistribution of the
stimulation current to other electrodes and by that can reduce
speech intelligibility and cause distorted sound quality.
[0073] In addition, information on perilymph properties in the
cochlea can detect changes caused by, for example, scar tissue
growth or ossification. Such information can be useful in the
troubleshooting process for recipients. Examples are reports of
facial nerve simulation, which are more likely seen with an
ossified cochlea.
[0074] Having information on the perilymph status at hand allows a
more holistic assessment of the case and potentially a better
targeted recommendation for mapping changes, which hopefully will
alleviate the report. Another example is the absence of Neural
Response Telemetry (NRT) recordings, which is often seen with an
ossified cochlea. Traditionally, similar information is only
available by radiography and often difficult to obtain due to
imaging resolution or quality.
[0075] The normalization matrix addresses the current need for
better differential diagnostics for implantable hearing devices
affected by shunting currents in the field. Taking only impedance
measurements is less sensitive than the normalization procedure
described above.
[0076] Implantable hearing prostheses are becoming more common in
markets which currently have poorer service levels either due to
lower education or poorer accessibility of the service providers.
In such markets electrode damage caused by, for example, breaches
in the insulation do not get readily detected. As a result, the
affected recipients may experience a decreased performance. An
implantable hearing prosthesis having an integrated integrity
system to evaluate and repair certain issues (self-correcting)
allows the recipient to maintain the maximum benefit of the device
at all times, even when access to a service provider or clinic is
limited.
[0077] The invention is not limited to the embodiments illustrated
in the drawings but can be varied within the scope of the
accompanying claims.
* * * * *