Medical device temperature estimation

• US 10,554,069 B2
• Filed: 12/15/2017
• Issued: 02/04/2020
• Est. Priority Date: 12/15/2017
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Paralikar, Kunal, Fehrmann, Elizabeth A., Gaddam, Venkat R., Morgan, Boysie, Olson, David P., Jackson, Jadin C.
• Primary Examiner(s): Diao, M Baye
• Application Number:
  US15/843,854
• Publication Number:
  US 20190190296A1
• Time in Patent Office: 781 Days
• Field of Search: 320137
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61M 2205/3368 Temperature
• CPC Class Codes: A61M 2205/3538 using electrical conduction through the body of the patient
• CPC Class Codes: A61M 2205/8243 by induction
• CPC Class Codes: A61M 25/00 Catheters; Hollow probes dilators A61M29/00; peritoneal catheters A61M1/285; tracheal tubes A61M16/04; for drainage A61M27/00; for uterus, vagina or rectum A61M31/00 ; for measuring or testing A61B; materials for catheters A61L29/00
• CPC Class Codes: A61N 1/36007 of urogenital or gastrointestinal organs, e.g. for incontinence control
• CPC Class Codes: A61N 1/36062 Spinal stimulation
• CPC Class Codes: A61N 1/36071 Pain
• CPC Class Codes: A61N 1/37223 Circuits for electromagnetic coupling
• CPC Class Codes: A61N 1/3787 from an external energy source
• CPC Class Codes: G01K 13/00 Thermometers specially adapted for specific purposes
• CPC Class Codes: G01K 7/00 Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat giving results other than momentary value of temperature G01K3/00 ; Power supply therefor, e.g. using thermoelectric elements
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 7/007188 the charge cycle being controlled or terminated in response to non-electric parameters
• CPC Class Codes: H02J 7/007192 in response to temperature

Abstract

Devices, systems, and techniques for monitoring the temperature of a device used to charge a rechargeable power source are disclosed. Implantable medical devices may include a rechargeable power source that can be transcutaneously charged. The temperature of an external charging device and/or an implantable medical device may be monitored to control the temperature exposure to patient tissue during a charging session used to recharge the rechargeable power source. In one example, a temperature sensor may sense a temperature of an internal portion of a device, wherein the housing of the device is not directly thermally coupled to the temperature sensor. A temperature for the housing of the device may then be estimated based on the sensed temperature provided by the non-thermally coupled temperature sensor. A processor may then control charging of the rechargeable power source based on the determined temperature for the housing.

Claims

1. A method comprising:

sensing, by a temperature sensor, a temperature of an internal portion of an implantable medical device during a charging process;

determining, by processing circuitry and based on the sensed temperature of the internal portion of the implantable medical device and an algorithm, a temperature of a housing of the implantable medical device, the temperature sensor sensing the temperature of the internal portion of the medical device without being thermally coupled to the housing of the medical device,

wherein the algorithm is representative of an estimated temperature differential between the internal portion and the housing, the estimated temperature differential determined based on a transfer function, wherein the transfer function is based on a temperature decay curve of the housing; and

controlling, by the processing circuitry, charging of a rechargeable power source of the medical device based on the determined temperature of the housing.

2. The method of claim 1, wherein the temperature decay curve is derived using a first constant based on the temperature difference between the internal portion and the housing, and a second constant based on a time constant for the temperature decay curve.

3. The method of claim 1, wherein determining the temperature of the housing comprises determining the temperature of the housing based on the transfer function of the temperature decay curve defined as:

T_f(t)=T_H(t)−

A₀e<sup>−

t/τ</sup>

, wherein;

T_H(t)=the temperature of the internal portion of the implantable medical device,

T_f(t)=temperature of the housing,

t=0 is taken as the time at which a charging process is shut off,

A₀=temperature difference between T_H and T_f at the time the charging process is shut off, and

τ

=a time constant.

4. The method of claim 3, wherein the time constant τ

is a time required for a temperature difference between the temperature T_H and the temperature T_f of a front face of the implantable medical device to achieve a value of thirty-seven percent of the initial values for A₀ when T_f is held constant.

5. The method of claim 1, wherein the transfer function based on the temperature decay curve of the housing is further based at least in part on a measured electrical parameter associated with the charging process.

6. The method of claim 5, wherein the measured electrical parameter is a charging current applied to a battery within the implantable medical device during the charging process.

7. The method of claim 1, wherein determining the temperature of the housing comprises determining the temperature of the housing based on the transfer function defined as:

Avg. Front=Avg. IC−

(C₁+C₂*I_BATT), wherein;

Avg. Front=an estimated temperature at an exterior surface of the implantable medical device;

Avg. IC=an average sensed temperature at the internal portion of the implantable medical device;

C₁=a first constant value;

C₂=a second constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device that is being recharged, and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

8. The method of claim 1, wherein determining the temperature of the housing comprises determining the temperature of the housing based on the transfer function defined as:

Avg. Front=Avg. IC−

(C₃+C₄*I_BATT−

C₅*Q_IMD), wherein;

Avg. Front=an estimated temperature at an exterior surface of the implantable medical device;

Avg. IC=an average sensed temperature at the internal portion of the implantable medical device

C₃=a first constant value;

C₄=a second constant value;

C₅=a third constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device that is being recharged; and

Q_IMD=a heat-loss value (in watts) for the implantable medical device, and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

9. The method of claim 1, wherein determining the temperature of the housing comprises determining the temperature of the housing based on the transfer function defined as:

Avg. Front=Avg. IC−

(C₆+C₇*I_BATT+C₈*I_BATT*I_BATT),

wherein;

Avg. Front=an estimated temperature an at exterior surface of the implantable medical device;

Avg. IC=an average sensed temperature at the internal portion of the implantable medical device;

C₆=a first constant value;

C₇=a second constant value;

C₈=a third constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device that is being recharged; and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

10. The method of claim 1, wherein the temperature sensor comprises a single temperature sensor incorporated into an integrated circuit located within the internal portion of the implantable medical device.

11. The method of claim 1, wherein the temperature sensor comprises a plurality of temperature sensors, and wherein determining the temperature of the housing of the implantable medical device based on the sensed temperature further comprises calculating, by the processing circuitry, a sensed temperature based on an average of the sensed temperatures provided by the plurality of temperature sensors.

12. The method of claim 1, wherein determining the temperature of a housing of the implantable medical device based on the sensed temperature of the internal portion of the medical device further comprises:

retrieving, by the processing circuitry, a value for each of a plurality of constants stored in a memory within the implantable medical device, wherein the value for each of the constants is related to one or more thermal properties of the implantable medical device; and

calculating, by the processing circuitry, the temperature of the housing using the values for the plurality of constants and the sensed temperature as input parameters for the algorithm.

13. The method of claim 12, wherein the one or more values for the plurality of constants stored in memory were stored into the memory prior to implantation of the implantable medical device into a patient.

14. The method of claim 1, wherein controlling charging of the rechargeable power source of the implantable medical device based on the determined temperature of the housing further comprises:

determining, by the processing circuitry, that the determined temperature has exceeded a threshold temperature, and

in response to the determination that the determined temperature has exceeded the threshold temperature, transmitting, by communication circuitry, instructions to an external charging device to further regulate or to terminate the charging of a rechargeable power source.

15. A system comprising:

an implantable medical device comprising a housing enclosing an internal portion;

a temperature sensor disposed within the housing and configured to sense a temperature of the internal portion of the implantable medical device without being directly thermally coupled to the housing and without being configured to sense a temperature of the housing; and

processing circuitry configured to determine a temperature of the housing based on the sensed temperature of the internal portion and an algorithm, and to control charging of a rechargeable power source of the implanted medical device based on the determined temperature of the housing,

wherein the algorithm is representative of an estimated temperature differential between the internal portion and the housing determined based on a transfer function, and

wherein the transfer function is based on a temperature decay curve of the housing.

16. The system of claim 15, wherein the temperature decay curve is derived using a first constant based on the temperature difference between the internal portion and the housing, and a second constant based on a time constant for the temperature decay curve.

17. The system of claim 15, wherein the transfer function of the decay curve is defined as

T_f(t)=T_H(t)−

A₀e<sup>−

t/τ</sup>

, wherein;

T_H(t)=the temperature of the internal portion of the implantable medical device,

T_f(t)=temperature of the housing,

t=0 is taken as the time at which the charging process is shut off,

A₀=temperature difference between T_H and T_f at the time the charging process is shut off, and

τ

=a time constant.

18. The system of claim 17, wherein the time constant τ

is the time required for a temperature difference between the temperature T_H and the temperature T_f of the front face of the implantable medical device to achieve a value of thirty-seven percent of the initial values for A₀ if T_f were held constant.

19. The system of claim 15, wherein the transfer function based on the temperature decay curve of the housing is further based at least in part on a measured electrical parameter associated with the charging process.

20. The system of claim 19, wherein the measured electrical parameter is a charging current applied to a battery within the implantable medical device during the charging process.

21. The system of claim 15, wherein the transfer function is defined as:

Avg. Front=Avg. IC−

(C₁+C₂*I_BATT), wherein;

Avg. Front=estimated temperature at an exterior surface of the implantable medical device;

Avg. IC=average sensed temperature at the internal portion of the implantable medical device;

C₁=a first constant value;

C₂=a second constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device while the rechargeable power source is being recharged, and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

22. The system of claim 15, wherein the processing circuitry is configured to determine the temperature of the housing based on the transfer function defined as:

Avg. Front=Avg. IC−

(C₃+C₄*I_BATT−

C₅*Q_IMD), wherein;

Avg. Front=estimated temperature at an exterior surface of the implantable medical device;

Avg. IC=average sensed temperature at the internal portion of the implantable medical device

C₃=a first constant value;

C₄=a second constant value;

C₅=is a third constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device while the rechargeable power source is being recharged, and

Q_IMD=heat-loss value (in watts) for the implantable medical device, and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

23. The system of claim 15, wherein the temperature of the housing based on the transfer function defined as:

Avg. Front=Avg. IC−

(C₆+C₇*I_BATT+C₈*I_BATT*I_BATT),

wherein;

Avg. Front=estimated temperature an at exterior surface of the implantable medical device;

Avg. IC=average sensed temperature at the internal portion of the implantable medical device;

C₆=a first constant value;

C₇=a second constant value;

C₈=a third constant value;

I_BATT=a charging current (in amps) that is applied to the rechargeable power source of the implantable medical device while the rechargeable power source is being recharged, and

wherein the estimated temperature at the exterior surface of the implantable medical device is the determined temperature of the housing.

24. The system of claim 15, wherein the processing circuitry is configured to determine that the determined temperature has increased to a threshold temperature, and

in response to the making of the determination that the determined temperature has increased to the threshold temperature, issue instructions to an external charging device to further regulate or to terminate the charging of the rechargeable power source.

25. The system of claim 15, wherein the processing circuitry is configured to determine, based on the determined temperature, that a cumulative thermal dose threshold has been reached, and

in response to the making the determination that the cumulative thermal dose threshold has been reached, issue instructions to an external charging device to terminate the charging of the rechargeable power source.

26. The system of claim 15, wherein the temperature sensor comprises a single temperature sensor incorporated into an integrated circuit located within the internal portion of the implantable medical device.

27. The system of claim 15, further comprising:

a memory coupled to the processing circuitry, the memory configured to store a value for each of one or more constants, the value of the one or more constants determined by one or more thermal properties of the implantable medical device, and the one or more constants configured to be used in the calibration algorithm to determine the temperature of the housing based on the sensed temperature of the internal portion.

28. A system comprising:

means for sensing a temperature of an internal portion of an implantable medical device during a charging process without being directly thermally coupled to a housing of the implantable medical device and without being configured to sense a temperature of the housing;

means for determining a temperature of the housing of the implantable medical device based on the sensed temperature of the internal portion of the medical device and an algorithm, wherein the algorithm is representative of a temperature differential between the internal portion and the housing determined based on a transfer function, wherein the transfer function is based on a temperature decay curve of the housing; and

means for controlling charging of a rechargeable power source of the implantable medical device based on the determined temperature of the housing.

29. The system of claim 28, wherein the temperature decay curve of the housing is derived using a first constant based on the temperature difference between the internal portion and the housing, and a second constant based on a time constant for the temperature decay curve.

30. The system of claim 29, wherein the transfer function of the temperature decay curve is defined as

T_f(t)=T_H(t)−

A₀e<sup>−

t/τ</sup>

, wherein;

T_H(t)=the temperature of the internal portion of the implantable medical device,

T_f(t)=temperature of the housing,

t=0 is taken as the time at which the charging process is shut off,

A₀=temperature difference between T_H and T_f at the time the charging process is shut off, and

τ

=a time constant.

31. The system of claim 28, wherein the transfer function is based at least in part on a measured electrical parameter associated with the charging process.

32. The system of claim 31, wherein the measured electrical parameter is a charging current applied to a battery within the implantable medical device during the charging process.