Apparatus for monitoring CHF patients using bio-impedance technique

• US 20050107719A1
• Filed: 12/27/2004
• Published: 05/19/2005
• Est. Priority Date: 07/03/2002
• Status: Active Grant

• Current Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Original Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Inventors: Arad (Abbound), Shimon
• Granted Patent: US 8,131,354 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0044 for the heart
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/7289 Retrospective gating, i.e. associating measured signals or images with a physiological event after the actual measurement or image acquisition, e.g. by simultaneously recording an additional physiological signal during the measurement or image acquisition
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal

Abstract

A method of estimating stroke volume of the heart, comprising: taking a first set of electrical data of the chest at a first phase of the cardiac cycle; estimating a first volume of the heart from the first set of electrical data; taking a second set of electrical data of the chest at a second phase of the cardiac cycle; estimating a second volume of the heart from the second set of electrical data; and using the difference between the first and second volumes of the heart to estimate the stroke volume of the heart.

Claims

1. A method for generating impedance images of the chest, comprising:

acquiring electrical data of the chest;

obtaining electrocardiograph data of a patient;

analyzing the electrocardiograph data to obtain information about breathing parameters at the time the electrical data was acquired; and

reconstructing at least one impedance image of the chest from the electrical data and the information about breathing parameters;

wherein the information about breathing parameters reduces the sensitivity of the at least one impedance image to breathing parameters.

2. A method according to claim 1, wherein reconstructing at least one impedance image comprises:

reconstructing at least one preliminary impedance image of the chest from the electrical data; and

correcting the at least one preliminary impedance images to form the at least one impedance image, taking into account the breathing parameters.

3. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing changes in RR intervals.

4. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing changes in a voltage measured at a same phase in each cardiac cycle.

5. A method according to claim 1, wherein analyzing the electrocardiograph data comprises analyzing the average over one or more cardiac cycles of a voltage measured by the electrocardiograph.

6. A method according to claim 2, wherein reconstructing at least one preliminary image comprises reconstructing a plurality of preliminary images, and correcting the at least one impedance images comprises sorting the preliminary images into a plurality of bins according to the breathing parameters.

7. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the state of expansion of the lungs.

8. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the elapsed time since the last maximum expansion of the lungs.

9. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to the elapsed time since the last minimum expansion of the lungs.

10. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a cardiac volume.

11. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a heart rate.

12. A method according to claim 6, wherein sorting the preliminary images into bins comprises sorting according to a phase of the cardiac cycle.

13. A method according to claim 1, wherein acquiring the electrical data comprises gating by the cardiac cycle.

14. A method according to claim 13, wherein gating by the cardiac cycle comprises using the peak of the R-wave to trigger acquiring the electrical data.

15. A method according to claim 2, wherein correcting the at least one preliminary impedance images comprises averaging the impedance data acquired over one or more breathing cycles.

16. A method according to claim 2, wherein reconstructing at least one preliminary image comprises reconstructing a plurality of preliminary images for which the impedance data was acquired at a plurality of phases in the breathing cycle, and correcting the at least one preliminary impedance images comprises averaging the preliminary impedance images.

17. A method according to claim 1, and including measuring the air flow into the lungs, and calibrating the information about breathing parameters obtained from the electrocardiograph using said measured air flow.

18. A method according to claim 1, and including measuring the air flow out of the lungs, and calibrating the information about breathing parameters obtained from the electrocardiograph using said measured air flow.

19. A method according to claim 1, wherein reconstructing at least one impedance image of the chest comprises using a finite volume method.

20. A method according to claim 1, wherein acquiring electrical data of the chest comprises measuring potentials at a plurality of voltage-measuring locations on the body, while applying known currents at a plurality of current-applying locations on the body.

21. A method for generating an impedance image of the chest, comprising:

acquiring electrical data of the chest; and

using a finite volume method to calculate an impedance image from the electrical data.

22. A method according to claim 21, wherein acquiring electrical data of the chest comprises measuring potential differences between one or more pairs among a plurality of voltage-measuring locations on the body, while applying known currents at a plurality of current-applying locations on the body.

23. A method according to claim 22, wherein applying known currents comprises applying a current between a first pair of current-applying locations at substantially opposite sides of the chest.

24. A method according to claim 23, wherein measuring potentials comprises measuring the potential difference between two voltage-measuring locations at substantially opposite sides of the chest, different from the first pair of current-applying locations.

25. A method according to claim 23, wherein applying known currents is repeated, using a second pair of current-applying locations that are substantially on opposite sides of the chest and differ from the first pair of current-applying locations.

26. A method according to claim 25, wherein one of the pairs of current-applying locations comprise a location on the left side of the front of the chest and a location on the right side of the back, and the other pair of current-applying locations comprise a location on the right side of the front of the chest and a location on the left side of the back.

27. A method of estimating stroke volume of the heart, comprising:

generating a first impedance image of the chest according to claim 21, at a first phase of the cardiac cycle;

estimating a first volume of the heart from the first impedance image;

generating a second impedance image of the chest according to claim 21, at a second phase of the cardiac cycle;

estimating a second volume of the heart from the second impedance image; and

using the difference between the first and second volumes of the heart to estimate the stroke volume of the heart.

28. A method of estimating stroke volume of the heart, comprising:

taking a first set of electrical data of the chest at a first phase of the cardiac cycle;

estimating a first volume of the heart from the first set of electrical data;

taking a second set of electrical data of the chest at a second phase of the cardiac cycle;

estimating a second volume of the heart from the second set of electrical data; and

using the difference between the first and second volumes of the heart to estimate the stroke volume of the heart.

29. A method according to any claim 28, wherein one of the first and second phases of the cardiac cycle comprises an end-systole phase.

30. A method according to claim 28, wherein one of the first and second phases of the cardiac cycle comprises an end-diastole phase.

31. A method according to claim 28, wherein estimating at least one of the volumes of the heart from the corresponding set of electrical data comprises generating an impedance image of the chest from said set of electrical data.

32. A method according to claim 31, wherein, for each of said phases of the cardiac cycle, generating the impedance image comprises generating a two-dimensional impedance image of a slice of the chest, and estimating the volume of the heart comprises estimating a cross-sectional area of the interior of the heart.

33. A method according to claim 32, wherein generating the impedance image comprises modeling the cross-sectional area of the interior of the heart as an ellipse.

34. A method according to claim 32, wherein estimating the volume of the heart comprises modeling the cross-sectional area of the interior of the heart as an ellipse.

35. A method according to claim 32, wherein estimating the volume of the heart comprising using a formula which gives the volume of the heart as a function of the cross-sectional area.

36. A method according to claim 35, wherein the volume is proportional to the square of the cross-sectional area.

37. A method according to claim 28, wherein estimating the first volume of the heart comprises generating a first impedance image of the chest, and estimating the second volume of the heart comprises generating a second impedance image of the chest putting constraints on differences between the second impedance image and the first impedance image, but not constraining the volume of the heart to be the same in the first and second impedance images.

38. A method according to claim 37, wherein the second impedance image, aside from the heart, is constrained to be the same as the first impedance image.

39. A method according to claim 28, wherein acquiring electrical data of the chest comprises measuring potential differences between one or more pairs among a plurality of voltage-measuring locations on the body, while applying known currents at a plurality of current-applying locations on the body.

40. A method according to claim 39, wherein applying known currents comprises applying a current between a first pair of current-applying locations at substantially opposite sides of the chest.

41. A method according to claim 40, wherein applying known currents is done a second time, using a second pair of current-applying locations that are substantially on opposite sides of the chest and differ from the first pair of current-applying locations.

42. A method according to claim 41, wherein each of the pairs of current-applying locations comprises a location on the left side of the front of the chest, and a location on the right side of the back.

43. A method according to claim 41, wherein, for each time the known currents are applied, the plurality of voltage-measuring locations comprises three different locations, at least two of them on the front of the chest, and all three of them different from either of the pair of current-carrying locations at which the known currents are being applied at that time.

44. An apparatus for estimating the stroke volume of the heart, comprising:

an electrocardiograph;

an impedance data acquisition system which acquires impedance data of the chest;

a controller which uses data from the electrocardiograph to trigger the data acquisition system to acquire the data at each of a first phase and a second phase of the cardiac cycle; and

a data analyzer which estimates the volume of the heart at the first phase and the second phase from the data acquired at the first phase and the second phase, thereby allowing the stroke volume to be estimated from the difference between the volume of the heart at the first phase and the second phase.

45. An apparatus according to claim 44, wherein the data analyzer is configured to analyze the electrocardiograph data to obtain information about breathing parameters at the time the impedance imaging data was acquired, and is configured to use the information about breathing parameters in estimating the volume of the heart at the first phase and the second phase, thereby making the estimate of the stroke volume more accurate.

46. An apparatus according to claim 44, wherein the electrocardiograph, impedance data acquisition system, and controller comprise a self-contained portable system weighing less than 5 kilograms.

47. An apparatus according to claim 44, including a user interface to the controller whereby the user initiates a pre-set sequence of acquisition of the impedance data, the time of the acquisition being triggered by data from the electrocardiograph.