Power supply monitoring for an implantable device

Abstract

A method and an apparatus for determining a time period remaining in a useful life of an energy storage device in an implantable medical device. The method may include measuring a voltage of the energy storage device to produce a measured voltage, and comparing the measured voltage to a transition voltage. While the measured voltage is greater than or equal to the transition voltage, the time period remaining in the energy storage device's useful life is approximated based upon a function of charge depleted. While the measured voltage is less than the transition voltage, the time period remaining in the energy storage device's useful life is approximated based upon a higher order polynomial function of the measured voltage. The transition voltage corresponds to a predetermined point on a energy storage device voltage depletion curve representing the voltage across the energy storage device over time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIG. 1 is a stylized diagram of an implantable medical device suitable for use in the present disclosure implanted into a patient's body and an external programmer;

FIG. 2 is a block diagram of an implantable medical device and an external unit that communicates with the implantable medical device, in accordance with one illustrative embodiment of the present disclosure;

FIGS. 3A and 3B are graphical representations of a battery voltage depletion curve typical of an energy storage device or battery, in accordance with illustrative embodiments of the present disclosure;

FIG. 4 is a flowchart representation of a method of providing a warning signal relating to a power supply of the implantable medical device, in accordance with one illustrative embodiment of the present disclosure;

FIG. 5 is a flowchart representation of a method of performing a calibration of a charge depletion tabulation, in accordance with one illustrative embodiment of the present disclosure;

FIG. 6 is a more detailed flowchart illustrating a method of performing the charge depletion calculation indicated in FIG. 4, in accordance with one illustrative embodiment of the present disclosure;

FIG. 7 is a more detailed flowchart illustrating a method of performing an end-of-service (EOS) and/or an elective replacement indication (ERI) determination, as indicated in FIG. 4, in accordance with one illustrative embodiment of the present disclosure;

FIG. 8 is an illustrative graphical representation of battery capacity estimation for a battery having a voltage depletion curve described by a polynomial equation in the region after the transition voltage V_knee;

FIG. 9 is an illustrative graphical representation comparison of low load and high load coefficients for the polynomial equation of FIG. 8, including an intermediate polynomial that represents intermediate coefficients achieved with rounded averages;

FIG. 10 is an illustrative graphical representation of how V_knee varies as a function of I_avg and program settings in accordance with one embodiment of the present disclosure;

FIG. 11 is a graphical representation of the approximately linear relationship between the temperature and the number of volts necessary to correct V_bat for temperature in accordance with one illustrative embodiment of the present disclosure; and

FIG. 12 is a detailed flowchart illustrating an alternative method of performing an end-of-service (EOS) and/or an elective replacement indication (ERI) determination, as indicated in FIG. 4, in accordance with one illustrative embodiment of the present disclosure.

Claims

1. A method for determining a time period remaining in a useful life of an energy storage device in an implantable medical device, the method comprising: measuring a voltage of the energy storage device to produce a measured voltage;comparing the measured voltage to a transition voltage;while the measured voltage is greater than or equal to the transition voltage, determining a time period remaining in the energy storage device's useful life based upon a function of charge depleted; andwhile the measured voltage is less than the transition voltage, determining a time period remaining in the energy storage device's useful life based upon a higher order polynomial function of the measured voltage;wherein the transition voltage corresponds to a predetermined point on an energy storage device voltage depletion curve representing the voltage across the energy storage device over time.

2. The method of claim 1, wherein while the measured voltage is less than the transition voltage, the time remaining in the energy storage device's useful life is approximated according to the higher order polynomial function of the measured voltage: Time remaining=% remaining×[Cinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vmeasured)))/2a;

3. The method of claim 1, wherein the transition voltage is approximately 2.6 volts.

4. The method of claim 1, wherein the transition voltage comprises a variable value based upon the average current consumption rate.

5. The method of claim 4, wherein the transition voltage comprises a variable value based upon the consumption rate according to the following equation: Transition Voltage=the maximum of W volts or (X volts−(LOG(Iavg/Y))/Z);

6. The method of claim 1, wherein the measured voltage is corrected with an impedance correction factor for use in determining the time period remaining in the energy storage device's useful life.

7. The method of claim 6, wherein the impedance correction factor is a constant.

8. The method of claim 6, wherein the measured voltage is corrected by the impedance correction factor according to the following equation: Voltage used to calculate time remaining=Vmeasured+[Rconst×Iavg];

9. The method of claim 1, wherein while the measured voltage is greater than or equal to the transition voltage, determining a time period remaining in the energy storage device's useful life further comprises calculating the time period based upon the total charge depleted, and at least one of the total available electrical charge and a consumption rate.

10. The method of claim 2, further comprising: measuring the temperature of the energy storage device;calculating a Vcompensated by compensating the value for Vmeasured for temperature; andreplacing Vmeasured with Vcompensated to calculate Time remaining.

11. The method of claim 10, further comprising: measuring the temperature of the energy storage device;compensating the value for Vmeasured for temperature according to the following algorithm: Vcompensated=Vmeasured+(K×(Tbaseline−Tmeasurement));wherein Vmeasured is the measured voltage, Tmeasured is the measured temperature, Tbaseline is a base temperature, and K is a temperature compensation constant; andreplacing Vmeasured with Vcompensated in the calculation of Time remaining such that: Time remaining=% remaining×[Cinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vcompensated)))/2a;

12. An implantable medical device, comprising: an energy storage device powering the implantable medical device;a stimulation unit operatively coupled to the energy storage device that provides an electrical signal; anda controller operatively coupled to the stimulation unit and the energy storage device, the controller comprising: a charge depletion determination unit that determines an electrical charge depleted by the energy storage device during operation of the implantable medical device;a voltage determination unit that determines whether a measured voltage across the energy storage device is greater than or equal to a transition voltage; anda useful life determination unit that determines a time period remaining in the energy storage device's useful life based upon 1) a function of the electrical charge depleted while the measured voltage is greater than or equal to the transition voltage, and 2) a higher order polynomial function of the measured voltage while the measured voltage is less than the transition voltage;wherein the transition voltage corresponds to a predetermined point on the energy storage device voltage depletion curve.

13. The implantable medical device of claim 12, wherein while the measured voltage is greater than or equal to the transition voltage, the useful life determination unit calculates a time period remaining in the energy storage device's useful life based upon the total charge depleted, and at least one of the total available electrical charge and an average current consumption rate.

14. The implantable medical device of claim 12, wherein while the measured voltage is less than the transition voltage, the useful life determination unit approximates the time remaining in the energy storage device's useful life according to the higher order polynomial function of the measured voltage: Time remaining=% remaining×[Chargeinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vmeasured)))/2a;

15. The implantable medical device of claim 12, wherein the transition voltage is approximately 2.6 volts.

16. The implantable medical device of claim 12, wherein the transition voltage comprises a variable value based upon an average current consumption rate Iavg.

17. The implantable medical device of claim 16, wherein the transition voltage comprises a variable value based upon an average current consumption rate according to the following equation: Transition Voltage=maximum of (W volts or X volts−(LOG(Iavg/Y))/Z);

18. The implantable medical device of claim 12, wherein the measured voltage used to calculate the time period remaining in the energy storage device's useful life is corrected by an impedance correction factor prior to the determination of the time period remaining.

19. The implantable medical device of claim 18, wherein the impedance correction factor is a constant.

20. The implantable medical device of claim 18, wherein the measured voltage is corrected by the impedance correction factor according to the following equation: Voltage used to calculate time remaining=Vmeasured+[Rconst×Iavg];

21. The implantable medical device of claim 21, further comprising a temperature determination unit measures the temperature of the energy storage device;wherein the useful life determination unit compensates the value for Vmeasured for temperature; andwherein the useful life determination unit replaces Vmeasured with Vcompensated to calculate Time remaining.

22. The implantable medical device of claim 21, further comprising a temperature determination unit measures the temperature of the energy storage device;wherein the useful life determination unit compensates the value for Vmeasured for temperature according to the following algorithm: Vcompensated=Vmeasured+(K×(Tbaseline−Tmeasurement));wherein Vmeasured is the measured voltage, Tmeasured is the measured temperature, Tbaseline is a base temperature, and K is a temperature compensation constant; andwherein the useful life determination unit approximates the time remaining in the energy storage device's useful life according to the higher order polynomial function of the measured voltage: Time remaining=% remaining×[Cinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vcompensated)))/2a;

23. A system for determining remaining useful life of a energy storage device in an implantable medical device, comprising: an implantable medical device that delivers an electrical signal to a patient and communicates with an external monitoring device, the implantable medical device comprising: a energy storage device that powers the implantable medical device;a controller operatively coupled to the energy storage device that determines an electrical charge depleted by the energy storage device and a voltage across the energy storage device;wherein: the external monitoring device determines a remaining useful life of the energy storage device based upon (1) the electrical charge depleted if the voltage across the energy storage device is greater than or equal to a transition voltage and (2) a higher order polynomial function of the voltage across the energy storage device if the voltage across the energy storage device is less than the transition voltage; andthe external monitoring device displays an indication of the remaining useful life of a energy storage device of the implantable medical device.

24. The system of claim 23, wherein the transition voltage comprises a variable value based upon an average current consumption rate.

25. The system of claim 23, wherein for a measured voltage less than the transition voltage, the external monitoring device calculates the time remaining in the energy storage device's useful life as: Time remaining=% remaining×[Cinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vmeasured)))/2a;

26. The system of claim 23, wherein the transition voltage comprises a variable value based upon the consumption rate according to the following equation: Transition Voltage=maximum of W volts or (X volts−(LOG(Iavg/Y))/Z);

27. The system of claim 23, wherein the measured voltage used to calculate the time period remaining in the energy storage device's useful life is corrected by an impedance correction factor prior to the determination of the time period remaining.

28. The system of claim 27, wherein the impedance correction factor is a constant.

29. The system of claim 27, wherein the measured voltage is corrected by the impedance correction factor according to the following equation: Voltage used to calculate time remaining=Vmeasured+[Rconst×Iavg];

30. The system of claim 23, wherein the controller measures a temperature of the energy storage device; a temperature determination unit measures the temperature of the energy storage device;wherein the value for Vmeasured is compensated for temperature; andwherein the external monitoring device replaces Vmeasured with Vcompensated to calculate Time remaining.

31. The system of claim 30, wherein the controller measures a temperature of the energy storage device; wherein the measured voltage is compensated for temperature according to the following algorithm: Vcompensated=Vmeasured+(K×(Tbaseline−Tmeasurement)); andwherein Vmeasured is the measured voltage, Tmeasured is the measured temperature, Tbaseline is a base temperature, and K is a temperature compensation constant; andthe external monitoring device calculates the time remaining in the energy storage device's useful life as: Time remaining=% remaining×[Cinitial/Iavg]; and% remaining=(−b+SQRT(b2−4a(c−Vcompensated)))/2a;