MULTI-FREQUENCY IMPEDANCE MONITORING SYSTEM

• US 20090275855A1
• Filed: 04/30/2008
• Published: 11/05/2009
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: ZIELINSKI, TODD M., Sarkar, Shantanu, Hettrick, Douglas A.
• Granted Patent: US 8,744,565 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 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

A system and method is provided to measure intrathoracic complex impedance and to identify and indicate disease conditions based on the impedance measurements. Multiple impedance vectors may betaken into account, and an optimal vector may be selected to provide the most useful impedance measurement for the identification and indication of disease conditions.

Claims

1. A method of determining and indicating a disease condition, the method comprising:

injecting a first current having a first frequency between a pair of electrodes having a tissue segment therebetween;

measuring a first magnitude of impedance in the tissue segment at the first frequency;

injecting a second current having a second frequency greater than the first frequency between the pair of electrodes having the tissue segment therebetween;

measuring a second magnitude of impedance in the tissue segment at the second frequency;

evaluating a difference between the first magnitude of impedance at the first frequency and the second magnitude of impedance at the second frequency to determine whether the tissue is in a diseased condition; and

providing an indicator of disease based on the determination of whether the tissue segment is in a diseased condition.

2. A method according to claim 1, wherein the pair of electrodes is positioned for intrathoracic impedance measurement.

3. A method according to claim 2, wherein evaluating the difference between the first magnitude of impedance at the first frequency and the second magnitude of impedance at the second frequency to determine whether the tissue is in a diseased condition comprises determining whether the difference between the first magnitude of impedance at the first frequency and the second magnitude of impedance at the second frequency has decreased in order to determine that the tissue is in a state of pulmonary edema

4. A method of determining and indicating a disease condition, the method comprising:

injecting a first current having a first frequency between a pair of electrodes having a tissue segment therebetween;

measuring a magnitude and a phase angle of impedance in the tissue segment at the first frequency;

comparing at least one of the measured magnitude of impedance and the measured phase angle of impedance at the first frequency to a reference value of impedance magnitude and a reference value of impedance phase angle, respectively, established at the first frequency;

evaluating at least one of a difference between the measured magnitude of impedance and the reference value of impedance magnitude, and a difference between the measured phase angle of impedance and the reference value of impedance phase angle, to determine whether the tissue segment is in a diseased condition; and

providing an indicator of disease based oh the determination of whether the tissue is in a diseased condition.

5. A method according to claim 4, wherein the pair of electrodes is positioned for intrathoracic impedance measurement.

6. A method according to claim 5, wherein the first frequency is a low frequency no greater than about 10 kiloHertz, and an indicator of pulmonary edema is provided based on a decrease in the measured magnitude of impedance from the reference value of impedance magnitude.

7. A method according to claim 5, wherein the first frequency is a low frequency no greater than about 10 kiloHertz, and an indicator of pulmonary edema is provided based on an increase in the measured phase angle of impedance from the reference value of impedance phase angle.

8. A method according to claim 5, wherein the first frequency is a low frequency no greater than about 10 kiloHertz, and an indicator of pulmonary edema is provided based on both a decrease in the measured magnitude of impedance from the reference value of impedance magnitude, and an increase in the measured phase angle of impedance from the reference value of impedance phase angle.

9. A method according to claim 5, wherein the first frequency is a high frequency between about 50 kiloHertz and about 100 kiloHertz, and an indicator of myocardial ischemia is provided based on an increase in the measured magnitude of impedance from the reference value of impedance magnitude.

10. A method according to claim 5, wherein the first frequency is a high frequency between about 50 kiloHertz and about 100 kiloHertz, and an indicator of myocardial ischemia is provided based on a decrease in the measured phase angle of impedance from the reference value of impedance phase angle.

11. A method according to claim 5, wherein the first frequency is a high frequency between about 50 kiloHertz and about 100 kiloHertz, and an indicator of myocardial ischemia is provided based on both an increase in the measured magnitude of impedance from the reference value of impedance magnitude, and a decrease in the measured phase angle of impedance from the reference value of impedance phase angle.

12. A method according to claim 5, wherein an indicator of necrotic myocardia is provided based on an increase in the measured magnitude of impedance from the reference value of impedance magnitude.

13. A system for measuring intrathoracic impedance across a plurality of selected tissue segments, comprising:

at least one lead carrying a plurality of electrodes, the electrodes being positioned so that selected pairs of electrodes span selected ones of the plurality of selected tissue segments;

impedance measurement circuitry for measuring an impedance between the selected pairs of electrodes; and

,

processing circuitry for evaluating the measured impedance between at least one of the selected pairs of electrodes to determine whether the tissue segment is in a diseased condition, and for providing an indicator of disease based on the determination of whether the tissue segment is in a diseased condition.

14. A system according to claim 13, wherein the at least one lead is connected to an implantable medical device (IMD) that houses the impedance measurement circuitry and the processing circuitry.

15. A system according to claim 14, wherein the IMD comprises at least one electrode.

16. A system according to claim 15, wherein at least a portion of the at least one lead is positioned over a left ventricle via a cardiac vein or epicardially, and the electrodes carried by the at least one lead are positioned in at least one of the cardiac vein over the left ventricle, epicardially over the left ventricle, a right atrium, and a subclavian vein.

17. A system according to claim 13, wherein at least a portion of the at least one lead is positioned in a right ventricle and the electrodes carried by the at least one lead are positioned in at least one of the right ventricle, a right atrium, a superior vena cava and a subclavian vein.

18. A system according to claim 13, wherein at least a portion of the at least one lead is positioned over a left ventricle via a cardiac vein, and the electrodes carried by the at least one lead are positioned in at least one of the cardiac vein over the left ventricle, a right atrium, and a subclavian vein.

19. A system according to claim 13, wherein at least a portion of the at least one lead is positioned in an inferior vena cava, and the electrodes carried by the at least one lead are positioned in at least one of the inferior vena cava, a right atrium, a superior vena cava and a subclavian vein.

20. A system according to claim 13, wherein the at least one lead includes a first lead positioned in a left lateral thorax, and electrodes carried by the first lead are positioned in the left lateral thorax.

21. A system according to claim 20, wherein the at least one lead further includes a second lead at least partially positioned in a right ventricle, and electrodes carried by the second lead are positioned in at least one of the right ventricle, a right atrium, a superior vena cava and a subclavian vein.

22. A system according to claim 20, wherein the at least one lead further includes a second lead at least partially positioned over a left ventricle via a cardiac vein, and electrodes carried by the second lead are positioned in at least one of the cardiac vein over the left ventricle, epicardially over the left ventricle, a right atrium, and a subclavian vein.

23. A system according to claim 13, wherein a pair of the selected pairs of electrodes is selected for measurement of impedance therebetween based on a determination that a ratio between a cardiac component of impedance and a respiratory component of impedance is greatest among the selected pairs of electrodes.