Medical device temperature estimation

Patent metadata

Field	Value
Publication number	US-10554069-B2
Application number	US-201715843854-A
Country	US
Kind code	B2
Filing date	Dec 15, 2017
Priority date	Dec 15, 2017
Publication date	Feb 4, 2020
Grant date	Feb 4, 2020

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.

First claim

What is claimed is:

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 )− A 0 e −t/τ , 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,
A 0 =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 A 0 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−( C 1 +C 2 *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;
C 1 =a first constant value;
C 2 =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−( C 3 +C 4 *I BATT −C 5 *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
C 3 =a first constant value;
C 4 =a second constant value;
C 5 =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−( C 6 +C 7 *I BATT +C 8 *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;
C 6 =a first constant value;
C 7 =a second constant value;
C 8 =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 in

Assignees

• Medtronic Inc

Inventors

• Paralikar Kunal
• Fehrmann Elizabeth A
• Gaddam Venkat R
• Morgan Boysie
• Olson David P
• Jackson Jadin C

Classifications

• H02J7/971

  the charge cycle being controlled or terminated in response to non-electric parameters · CPC title

• H02J7/975 Primary

  in response to temperature · CPC title

• A61N1/36071

  Pain · CPC title

• G01K13/00

  Thermometers specially adapted for specific purposes · CPC title

• H02J50/10

  using inductive coupling · CPC title