Fluid status detection from a cardiac electrical signal and impedance signal

Patent metadata

Field	Value
Publication number	US-11298547-B2
Application number	US-201916521963-A
Country	US
Kind code	B2
Filing date	Jul 25, 2019
Priority date	Jul 27, 2018
Publication date	Apr 12, 2022
Grant date	Apr 12, 2022

Abstract

A medical device is configured to generate fluid status signal data of a patient by determining impedance metrics from an impedance signal, determining cardiac electrical signal amplitudes from a cardiac electrical signal and determining a calibration relationship between the impedance metrics and cardiac electrical signal amplitudes. The medical device generates a fluid status signal data by adjusting cardiac electrical signal amplitudes according to the determined calibration relationship. The fluid status signal data may be displayed or monitored for detecting a change in the patient's fluid status.

First claim

The invention claimed is:

1. A medical device, comprising:
a sensing circuit configured to receive a cardiac electrical signal via electrodes coupled to the medical device;
an impedance sensing circuit configured to apply a drive signal to electrodes coupled to the medical device and sense a resultant impedance signal;
a telemetry circuit configured to transmit fluid status data to another medical device; and
a control circuit coupled to the sensing circuit, the impedance sensing circuit and the telemetry circuit, the control circuit configured to:
determine a plurality of impedance metrics from the impedance signal;
determine a first plurality of amplitudes from the cardiac electrical signal;
determine a first calibration relationship between the plurality of impedance metrics and the first plurality of amplitudes;
determine a second plurality of amplitudes from the cardiac electrical signal; and
generate fluid status signal data by adjusting the second plurality of amplitudes according to the determined first calibration relationship.

2. The device of claim 1 , further comprising a power source coupled to the control circuit and the impedance sensing circuit for generating the drive signal, wherein the power source life is conserved by using the first calibration relationship compared to implantable medical devices that solely use the impedance signal to acquire fluid status signal data.

3. The device of claim 2 , wherein the power source is a battery.

4. The device of claim 1 , wherein the control circuit is further configured to control the telemetry circuit to transmit the fluid status signal data to another medical device for generating a display of the fluid status signal data.

5. The device of claim 1 , wherein the control circuit is configured to determine each of the first plurality of amplitudes and each of the second plurality of amplitudes by determining an R-wave amplitude of the cardiac electrical signal.

6. The device of claim 1 , wherein the control circuit is configured to determine each one of the first plurality of amplitudes by determining a cardiac event amplitude of the cardiac electrical signal during each one of a plurality of cardiac cycles.

7. The device of claim 1 , wherein determining the first calibration relationship comprises determining at least one of a coefficient or a constant used for adjusting each of the second plurality of amplitudes.

8. The device of claim 1 , wherein determining the first calibration relationship comprises generating a look-up table of calibrated cardiac electrical signal amplitudes.

9. The device of claim 1 , wherein the control circuit is further configured to determine the calibration relationship by:
determining the plurality of impedance metrics over a calibration time interval;
determining the first plurality of cardiac electrical signal amplitudes during the calibration time interval;
determining a range of the plurality of impedance metrics;
extending the calibration time interval in response to the range of the plurality of impedance metrics being less than a minimum range; and
determining the calibration relationship using the plurality of impedance metrics and the plurality of cardiac electrical signal amplitudes determined over the extended calibration time interval.

10. The device of claim 1 , wherein the control circuit is further configured to generate a fluid status signal by:
determining at least two impedance metrics from the impedance signal and spaced apart by a time interval;
determining the second plurality of amplitudes of the cardiac electrical signal during the time interval; and
generating a fluid status signal comprising at least one of the two impedance metrics and the adjusted second plurality of amplitudes of the cardiac electrical signal.

11. The device of claim 1 , wherein the control circuit is further configured to:
determine a verification impedance metric from the impedance signal after determining the second plurality of amplitudes from the cardiac electrical signal;
determine a verification amplitude of the cardiac electrical signal corresponding in time to the verification impedance metric;
adjust the verification amplitude of the cardiac electrical according to the first calibration relationship;
compare the adjusted verification amplitude to the verification impedance metric; and
re-determine the first calibration relationship in response to the adjusted verification amplitude being greater than a threshold difference from the verification impedance metric.

12. The device of claim 1 , wherein the control circuit is further configured to:
detect a threshold change in the adjusted second plurality of amplitudes; and
re-determine the first calibration relationship in response to detecting the threshold change.

13. The device of claim 1 , further comprising a posture sensor configured to produce a signal correlated to patient body posture and coupled to the control circuit;
wherein the control circuit is further configured to:
detect a change in patient body posture from the posture sensor signal, the change in patient body posture being from a first patient body posture corresponding to the first calibration relationship to a second patient body posture different than the first patient body posture;
determine a second calibration relationship between the impedance signal and the cardiac electrical signal, the second calibration relationship corresponding to the second patient body posture;
determine a third plurality of amplitudes of the cardiac electrical signal after the detected change in patient body posture; and
generate the fluid status signal data by adjusting the third plurality of amplitudes according to the second calibration relationship.

14. The device of claim 13 , wherein the control circuit is configured to determine the first calibration relationship using at least one impedance metric determined from the impedance signal after the detected change in patient body posture and an impedance metric determined from the impedance signal before the detected change in patient body posture.

15. The device of claim 13 , wherein determining the first calibration relationship and the second calibration relationship by the control circuit comprises generating a look-up table comprising a first calibration parameter corresponding to the first patient body posture and a second calibration parameter corresponding to the second patient body posture.

16. The device of claim 13 , wherein the control circuit is further configured to:
generate a first fluid status signal comprising the adjusted second plurality of amplitudes corresponding to the first patient body posture; and
generate a second fluid status signal comprising the adjusted third plurality of cardiac electrical signal amplitudes corresponding to the second patient body posture.

17. The device of claim 13 , wherein the control circuit is further configured to generate the fluid status signal data by:
updating the first calibration relationship each time the first patient body posture is detected;
adjusting cardiac electrical signal amplitudes that are acquired while the first patient body posture is being detected according to the first calibration relationship;
updating the second calibration relationship each time the second patient body posture is detected;
adjusting cardiac electrical signal amplitudes that are acquired while the second patient body posture is being detected according to the second calibration relationship;
generating a first fluid status signal by appe

Assignees

• Medtronic Inc

Inventors

• Song Zhendong
• Zielinski Todd M
• Lee Brian B

Classifications

• A61B2560/0223

  of calibration, e.g. protocols for calibrating sensors · CPC title

• A61N1/36585 Primary

  controlled by two or more physical parameters · CPC title

• A61N1/36535

  controlled by body position or posture · CPC title

• A61N1/37211

  Means for communicating with stimulators · CPC title

• A61N1/3627

  for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy · CPC title