Impedance monitoring for detecting pulmonary edema and thoracic congestion

• US 20040102712A1
• Filed: 11/25/2002
• Published: 05/27/2004
• Est. Priority Date: 11/25/2002
• Status: Active Grant

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Shult, Rebecca, Belalcazar, Andres, Patterson, Robert
• Granted Patent: US 7,313,434 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/4878 Evaluating oedema

Abstract

An implantable medical device includes a housing for the implantable device that is sized for implantation in a chest region of a patient and includes a housing electrode. A left ventricular lead port is connectable to a proximal end of a lead having first and second insulated conductors that extend from the proximal end of the lead to corresponding first and second electrodes near a distal end of the lead. An electrical impedance measurement circuit is electrically connected to the left ventricular lead port and the housing electrode. The circuit may inject current between the first lead electrode and the housing electrode, and measure a voltage potential, created by the current injection, between the second lead electrode and the housing electrode. The ratio of the measured voltage to injected current may be used for assessing pulmonary edema. The lead electrodes may be located in a left ventricular coronary vein.

Claims

1. An implantable medical device comprising:

a housing for the implantable device sized for implantation in a chest region of a patient and comprising a housing electrode;

a left ventricular lead port into which a proximal end of a lead is connectable, the lead having first and second conductors that are insulated from one another and that extend from the proximal end of the lead to corresponding first and second electrodes positioned near a distal end of the lead; and

an electrical impedance measurement circuit electrically connected to the left ventricular lead port and to the housing electrode, the circuit to inject current between the first lead electrode and the housing electrode, and to measure a voltage potential between the second lead electrode and the housing electrode, the voltage potential created by the current injection.

2. The device of claim 1 further comprising a lead having first and second conductors that are insulated from one another and that extend from the proximal end of the lead to corresponding first and second electrodes positioned near a distal end of the lead.

3. The device of claim 2 wherein the first and second electrodes are configured for positioning within a left ventricular coronary vein.

4. The device of claim 2 wherein the first and second electrodes are, respectively, first and second epicardial electrodes.

5. The device of claim 4 wherein the electrical impedance measurement circuit injects electrical current between the first epicardial lead electrode and the housing electrode, and measures a voltage potential created thereby between the second epicardial lead electrode and the housing electrode to make an electrical impedance measurement.

6. The device of claim 4 wherein the epicardial electrodes are configured to be sutured to a wall of a left ventricle.

7. The device of claim 1 wherein the electrical impedance measurement circuit injects electrical current between the first electrode and the housing electrode, and measures a voltage potential created thereby between the second electrode and the housing electrode to make an electrical impedance measurement.

8. The device of claim 7 wherein the electrical impedance measurement is used to assess pulmonary edema.

9. The device of claim 7 further comprising a telemetry circuit for transmitting electrical impedance measurements to a receiving station.

10. The device of claim 7 wherein the impedance measurement circuit measures electrical impedance at a moment of end-systole and end-expiration.

11. The device of claim 7 wherein the impedance measurement circuit measures electrical impedance at a specified heart rate range.

12. The device of claim 7 wherein the impedance measurement circuit measures electrical impedance at a specified posture.

13. The device of claim 1 wherein the housing electrode is a can electrode.

14. The device of claim 1 wherein the housing electrode is a header electrode.

15. An implantable medical device, comprising:

a housing for the implantable device sized for implantation in a chest region of a patient and comprising a housing electrode;

a left ventricular lead port into which a proximal end of a first lead is connectable, the first lead having first and second conductors that are insulated from one another and that extend from the proximal end of the first lead to corresponding first and second electrodes positioned near a distal end of the first lead;

a right atrial lead port into which a proximal end of a second lead is connectable, the second lead having first and second conductors that are insulated from one another and that extend from the proximal end of the second lead to corresponding third and fourth electrodes positioned near a distal end of the second lead; and

an electrical impedance measurement circuit electrically connected to the left ventricular lead port, the housing electrode, and the right atrial lead port, the circuit to inject a first current between the first electrode and the housing electrode, and to measure a first voltage potential between the second electrode and the housing electrode, the first voltage potential created by the first current injection, the circuit to further inject a second current between the third electrode and the housing electrode, and to measure a second voltage potential between the fourth electrode and the housing electrode, the second voltage potential created by the second current injection.

16. The device of claim 15 further comprising first and second leads, wherein:

the first lead has first and second conductors that are insulated from one another and that extend from the proximal end of the first lead to corresponding first and second electrodes positioned near a distal end of the first lead; and

the second lead has third and fourth conductors that are insulated from one another and that extend from the proximal end of the second lead to corresponding third and fourth electrodes positioned near a distal end of the second lead.

17. The device of claim 15, wherein:

the electrical impedance measurement circuit injects a first electrical current between the first electrode and the housing electrode, and measures a first voltage potential created thereby between the second electrode and the housing electrode to make a first electrical impedance measurement; and

the electrical impedance measurement circuit injects a second electrical current between the third electrode and the housing electrode, and measures a second voltage potential created thereby between the fourth electrode and the housing electrode to make a second electrical impedance measurement.

18. The device of claim 17 wherein the impedance measurement circuit measures the second electrical impedance at a moment of end-diastole and end-expiration.

19. The device of claim 17 wherein the device further comprises a circuit that calculates a weighted combination of the first and second electrical impedances.

20. A method of monitoring pulmonary edema in a human being, the method comprising:

injecting an electrical current between a first electrode located in a coronary vein of a left ventricle and a housing of a medical device implanted in a chest region; and

measuring a voltage potential between a second electrode located in the coronary vein of the left ventricle and the medical device housing.

21. The method of claim 20 further comprising calculating an impedance value by taking a ratio of the measured voltage potential to the injected current.

22. The method of claim 21 wherein the impedance value is used to assess pulmonary edema.

23. A method of monitoring pulmonary edema in a human being, the method comprising:

injecting a first electrical current between a first electrode located in a coronary vein of a left ventricle and a housing of a medical device implanted in a chest region;

measuring a first voltage potential between a second electrode located in the coronary vein of the left ventricle and the medical device housing, the first voltage potential created by the first current injection;

injecting a second electrical current between a third electrode located in a right atrium and the medical device housing; and

measuring a second voltage potential between a fourth electrode located in the right atrium and the medical device housing, the second voltage potential created by the second current injection.

24. The method of claim 23 further comprising:

calculating a first impedance value by taking a first ratio of the measured first voltage potential to the injected first current; and

calculating a second impedance value by taking a second ratio of the measured second voltage potential to the injected second current.

25. The method of claim 24 wherein a weighted combination of the first and second impedance values is used to assess pulmonary edema.

26. A method of measuring electrical impedance in a human being, the method comprising measuring an electrical impedance at a moment of end-systole and end-expiration, the electrical impedance measured between a housing of a medical device implanted in a chest region and electrodes located in a coronary vein of a left ventricle.

27. The method of claim 26 wherein the measured electrical impedance is used to assess pulmonary edema.

28. A method of determining electrical impedance in a human being, the method comprising:

measuring an electrical impedance between a housing of a medical device implanted in a chest region and electrodes located in a coronary vein of a left ventricle;

determining a degree of pulmonary edema in the human being, the determination based on the measured electrical impedance;

receiving orientation information from a posture sensor, the orientation information indicating a position of the human being; and

adjusting a relationship between the electrical impedance and the degree of pulmonary edema based on the orientation information.