Thoracic or intracardiac impedance detection with automatic vector selection

• US 20060241512A1
• Filed: 04/20/2005
• Published: 10/26/2006
• Est. Priority Date: 04/20/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Kwok, Jonathan, Stahmann, Jeffrey E., Hartley, Jesse W., Yu, Yinghong, Lee, Kent, Ding, Jiang
• Granted Patent: US 7,630,763 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• 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: A61N 1/36185 Selection of the electrode configuration
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3686 configured for selecting the electrode configuration on a lead A61N1/3688 takes precedence

Abstract

This document discusses, among other things, a cardiac function management device or other implantable medical device that includes a test mode and a diagnostic mode. During a test mode, the device cycles through various electrode configurations for collecting thoracic impedance data. At least one figure of merit is calculated from the impedance data for each such electrode configuration. In one example, only non-arrhythmic beats are used for computing the figure of merit. A particular electrode configuration is automatically selected using the figure of merit. During a diagnostic mode, the device collects impedance data using the selected electrode configuration. In one example, the figure of merit includes a ratio of a cardiac stroke amplitude and a respiration amplitude. Other examples of the figure of merit are also described.

Claims

1. A method comprising:

measuring a first impedance signal between at least first and second electrodes, which define a first electrode configuration, in a subject'"'"'s thorax;

extracting a first cardiac stroke signal from the first impedance signal;

extracting a first respiration signal from the first impedance signal;

extracting a first cardiac amplitude measurement from the first cardiac stroke signal;

extracting a first respiration amplitude measurement from the first cardiac stroke signal;

computing a first comparative measurement between the first cardiac amplitude measurement and the first respiration amplitude measurement;

measuring a second impedance signal between at least third and fourth electrodes, which define a second electrode configuration, in a subject'"'"'s thorax, wherein at least one of the third and fourth electrodes is a different electrode from at least one of the first and second electrodes;

extracting a second cardiac stroke signal from the second impedance signal;

extracting a second respiration signal from the second impedance signal;

extracting a second cardiac amplitude measurement from the second cardiac stroke signal;

extracting a second respiration amplitude measurement from the second cardiac stroke signal;

computing a second comparative measurement between the second cardiac amplitude measurement and the second respiration amplitude measurement; and

using the first and second comparative measurements as a basis for selecting one of the first and second electrode configurations for subsequent extraction of at least one of the respiration and cardiac stroke signals.

2. The method of claim 1, in which:

the computing the first comparative measurement includes computing a ratio between the first cardiac amplitude measurement and the first respiration amplitude measurement; and

the computing the second comparative measurement includes computing a ratio between the second cardiac amplitude measurement and the second respiration amplitude measurement.

3. The method of claim 1, in which the using the first and second comparative measurements as a basis for selecting one of the first and second electrode configurations includes selecting the first electrode configuration if first comparative measurement exceeds the second comparative measurement.

4. The method of claim 3, in which the respiration signal is of interest and used in a diagnostic algorithm performed by an implantable medical device, and in which the first comparative measurement is one of:

(1) a ratio of the first respiration signal to the first cardiac signal; and

(2) a difference of the first respiration signal less the first cardiac signal; and

in which the second comparative measurement is a comparable one of;

(I) a ratio of the second respiration signal to the second cardiac signal; and

(2) a difference of the second respiration signal less the second cardiac signal.

5. The method of claim 1, further comprising:

comparing the first and second comparative measurements to a threshold value; and

if the first and second comparative measurements are both less than the threshold value, then disabling the subsequent extraction of at least one of the respiration and cardiac stroke signals.

6. The method of claim 1, in which at least one of:

the extracting the first cardiac amplitude measurement includes determining a central tendency of the first cardiac amplitude measurement over a plurality of cardiac cycles;

the extracting the second cardiac amplitude measurement includes determining a central tendency of the second cardiac amplitude measurement over a plurality of cardiac cycles;

the extracting the first respiration amplitude measurement includes determining a central tendency of the first respiration amplitude measurement over a plurality of respiration cycles; and

the extracting the second respiration amplitude measurement includes determining a central tendency of the second respiration amplitude measurement over a plurality of respiration cycles.

7. The method of claim 1, including excluding the first cardiac amplitude measurement from consideration if a corresponding heartbeat is deemed arrhythmic.

8. A method comprising:

measuring a first impedance signal between at least first and second electrodes, which define a first electrode configuration, in a subject'"'"'s thorax;

extracting a first cardiac stroke signal from the first impedance signal;

extracting a first respiration signal from the first impedance signal;

extracting a first cardiac amplitude measurement from the first cardiac stroke signal;

extracting a first respiration amplitude measurement from the first cardiac stroke signal;

computing a first ratio by dividing the first respiration amplitude measurement by the first cardiac amplitude measurement;

measuring a second impedance signal between at least third and fourth electrodes, which define a second electrode configuration, in a subject'"'"'s thorax, wherein at least one of the third and fourth electrodes is a different electrode from at least one of the first and second electrodes;

extracting a second cardiac stroke signal from the second impedance signal;

extracting a second respiration signal from the second impedance signal;

extracting a second cardiac amplitude measurement from the second cardiac stroke signal;

extracting a second respiration amplitude measurement from the second cardiac stroke signal;

computing a second ratio by dividing the second respiration amplitude measurement by the second cardiac amplitude measurement; and

selecting the first electrode configuration for subsequent extraction of the respiration signal if the first ratio exceeds the second ratio.

9. The method of claim 8, in which:

the first and third electrodes are configured as a common electrode that is located on a housing of a pectorally-implanted implantable medical device, and the second electrode is located in association with an atrium of the subject, and the fourth electrode is located in association with a ventricle of the subject.

10. The method of claim 8, further comprising:

comparing the first and second ratios to a threshold value; and

if the first and second ratios are both less than the threshold value, then disabling the subsequent extraction of at least one of the respiration signal over the second period of time.

11. A method comprising:

measuring a first impedance signal between at least first and second electrodes, which define a first electrode configuration, in a subject'"'"'s thorax;

extracting a first cardiac stroke signal from the first impedance signal;

extracting a first respiration signal from the first impedance signal;

extracting a first cardiac amplitude measurement from the first cardiac stroke signal;

extracting a first respiration amplitude measurement from the first cardiac stroke signal;

computing a first ratio by dividing the first cardiac amplitude measurement by the first respiration amplitude measurement;

measuring a second impedance signal between at least third and fourth electrodes, which define a second electrode configuration, in a subject'"'"'s thorax, wherein at least one of the third and fourth electrodes is a different electrode from at least one of the first and second electrodes;

extracting a second cardiac stroke signal from the second impedance signal;

extracting a second respiration signal from the second impedance signal;

extracting a second cardiac amplitude measurement from the second cardiac stroke signal;

extracting a second respiration amplitude measurement from the second cardiac stroke signal;

computing a second ratio by dividing the second cardiac amplitude measurement by the second respiration amplitude measurement; and

selecting the first electrode configuration for subsequent extraction of the cardiac signal if the first ratio exceeds the second ratio.

12. The method of claim 11, in which:

the first and third electrodes are configured as a common electrode that is located on a housing of a pectorally-implanted implantable medical device, and the second electrode is located in association with an atrium of the subject, and the fourth electrode is located in association with a ventricle of the subject.

13. The method of claim 11, further comprising:

comparing the first and second ratios to a threshold value; and

if the first and second ratios are both less than the threshold value, then disabling the subsequent extraction of at least one of the cardiac stroke signal.

14. A method comprising:

measuring impedance signals in a subject'"'"'s thorax using different corresponding electrode configurations;

extracting, from each of the impedance signals, a cardiac stroke signal and a corresponding respiration signal obtained using the same electrode configuration as the corresponding cardiac stroke signal;

computing ratios between amplitudes of each cardiac stroke signal and the corresponding respiration signal; and

selecting a particular one of the electrode configurations for subsequently measuring an impedance signal to obtain at least one of an respiration signal and a cardiac stroke signal impedance-derived respiration, the selecting the particular one of the electrode configurations determined using values of the ratios relative to at least one of each other and a predefined threshold value.

15. The method of claim 14, in which the selecting the particular one of the electrode configurations includes choosing the particular one of the electrode configurations that corresponds to a largest respiration/stroke amplitude ratio among the computed ratios, and further comprising using the selected particular one of the electrode configurations for subsequently obtaining a respiration signal.

16. The method of claim 14, in which the selecting the particular one of the electrode configurations includes choosing the particular one of the electrode configurations that corresponds to a largest stroke/respiration amplitude ratio among the computed ratios, and further comprising using the selected particular one of the electrode configurations for subsequently obtaining a cardiac stroke signal.

17. A system comprising:

an implantable medical device (IMD), the IMD comprising;

an impedance detector circuit, including inputs configured to receive impedance signals from different electrode configurations in a subject'"'"'s thorax;

a cardiac stroke signal filter circuit, coupled to the impedance detector circuit to receive the impedance signals and extract therefrom corresponding cardiac stroke signals;

a respiration signal filter circuit, coupled to the impedance detector circuit to receive the impedance signals and to extract therefrom corresponding respiration signals;

a cardiac stroke amplitude measurement circuit, coupled to the cardiac stroke signal filter circuit to receive the cardiac stroke signals and to extract therefrom corresponding cardiac stroke amplitudes;

a respiration amplitude measurement circuit, coupled to the respiration signal filter circuit to receive the respiration signals and to extract therefrom corresponding respiration amplitudes; and

a processor circuit, including instructions executable or otherwise interpretable to compute comparative measurement between each cardiac stroke amplitude and each corresponding respiration amplitude from the same electrode configuration, and based on relative values of the comparative measurement associated with each electrode configuration to select a particular electrode configuration for use in obtaining at least one of a cardiac stroke signal and a respiration signal for use in a diagnostic or therapeutic algorithm.

18. The system of claim 17, in which the comparative measurement is a ratio between the cardiac stroke amplitude and the respiration amplitude associated with the same electrode configuration as the cardiac stroke amplitude.

19. The system of claim 18, in which at least one of the cardiac stroke signal and the respiration signal for use in the diagnostic or therapeutic algorithm is a cardiac stroke signal, and the ratio is the cardiac stroke amplitude divided by the respiration amplitude, and the processor circuit operates to select the particular electrode configuration that is associated with the largest value of the corresponding ratio relative to the value of ratios corresponding to another at least one electrode configuration.

20. The system of claim 18, in which at least one of the cardiac stroke signal and the respiration signal for use in the diagnostic or therapeutic algorithm is a respiration signal, and the ratio is the respiration amplitude divided by the cardiac stroke amplitude, and the processor circuit operates to select the particular electrode configuration that is associated with the largest value of the corresponding ratio relative to the value of another one or more ratios corresponding to another one or more electrode configurations.

21. The system of claim 18, in which the processor operates to compare a value of at least one ratio associated with an electrode configuration to a predefined threshold value, and to disable the obtaining at least one of a cardiac stroke signal and a respiration signal for use in a diagnostic or therapeutic algorithm if the value of at least one ratio does not exceed the threshold value.

22. A method comprising:

measuring a first impedance signal between at least first and second electrodes, which define a first electrode configuration, in a subject'"'"'s thorax;

calculating a first figure of merit using the first impedance signal;

measuring a second impedance signal between at least third and fourth electrodes, which define a second electrode configuration, in a subject'"'"'s thorax, wherein at least one of the third and fourth electrodes is a different electrode from at least one of the first and second electrodes;

calculating a second figure of merit using the second impedance signal; and

using values of the first and second figures of merit as a basis for automatically selecting one of the first and second electrode configurations for subsequent diagnostic extraction of one of the first and second impedance signals.

23. The method of claim 22, further comprising:

placing an implantable medical device in a test mode for performing the acts of measuring the first and second impedance signals, calculating the first and second figures of merit, and automatically selecting one of the first and second electrode configurations;

exiting the test mode and placing an implantable medical device in a diagnostic mode; and

extracting diagnostic impedance data, in the diagnostic mode, using the selected one of the first and second electrode configurations.

24. The method of claim 23, further comprising repeatedly placing the implantable medical device in a test mode for performing the acts of measuring the first and second impedance signals, calculating the first and second figures of merit, and automatically selecting one of the first and second electrode configurations.

25. The method of claim 23, further comprising triggering the test mode upon detecting at least one of a change in heart rate and a change in posture.

26. The method of claim 22, in which the first and second figures of merit comprise an amplitude measurement of a respiration component of the first and second impedance signals, respectively.

27. The method of claim 22, in which the first and second figures of merit comprise an amplitude measurement of a cardiac stroke component of the first and second impedance signals, respectively.

28. The method of claim 22, in which the first and second figures of merit comprise an amplitude measurement of a near-DC fluid status component of the first and second impedance signals, respectively.

29. The method of claim 22, in which the first and second figures of merit comprise a noise measurement of a respiration component of the first and second impedance signals, respectively.

30. The method of claim 29, in which the noise measurement of the respiration component of the respective first and second impedance signals comprises a cardiac stroke component of the respective first and second impedance signals.

31. The method of claim 22, in which the first and second figures of merit comprise a noise measurement of a cardiac stroke component of the first and second impedance signals, respectively.

32. The method of claim 31, in which the noise measurement of the cardiac stroke component of the respective first and second impedance signals comprises a respiration component of the respective first and second impedance signals.

33. A system comprising:

an implantable medical device (IMD), the IMD comprising;

an impedance detector circuit, including inputs configured to receive impedance signals from different electrode configurations in a subject'"'"'s thorax; and

a processor circuit, including instructions executable or otherwise interpretable to a compute at least one figure of merit from each of the different electrode configurations, and using values of the figure of merit from the different electrode configurations for automatically selecting a particular electrode configuration for use in subsequently obtaining diagnostic impedance data.

34. The system of claim 33, in which the processor includes:

a test mode for performing the acts of measuring the first and second impedance signals, calculating the first and second figures of merit, and automatically selecting one of the first and second electrode configurations; and

a diagnostic mode to extract diagnostic impedance data using the selected one of the first and second electrode configurations.

35. The system of claim 33, further including a clock circuit to schedule repeated execution of the test mode.

36. The system of claim 33, in which the first and second figures of merit comprise an amplitude measurement of a respiration component of the first and second impedance signals, respectively.

37. The system of claim 36, in which the first and second figures of merit comprise an amplitude measurement of a cardiac stroke component of the first and second impedance signals, respectively.

38. The system of claim 33, in which the first and second figures of merit comprise a noise measurement of a respiration component of the first and second impedance signals, respectively.

39. The system of claim 38, in which the noise measurement of the respiration component of the respective first and second impedance signals comprises a cardiac stroke component of the respective first and second impedance signals.

40. The system of claim 33, in which the first and second figures of merit comprise a noise measurement of a cardiac stroke component of the first and second impedance signals, respectively.

41. The system of claim 40, in which the noise measurement of the cardiac stroke component of the respective first and second impedance signals comprises a respiration component of the respective first and second impedance signals.