Using related signals to reduce ECG noise

• US 5,704,365 A
• Filed: 11/14/1995
• Issued: 01/06/1998
• Est. Priority Date: 11/14/1994
• Status: Expired due to Term

• Current Assignee: Spacelabs Healthcare, Inc. (OSI Systems Incorporated)
• Original Assignee: Cambridge Heart Inc.
• Inventors: Cohen, Richard J., Judell, Neil, Albrecht, Paul, Arnold, Jeffrey M.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US08/557,883
• Time in Patent Office: 784 Days
• Field of Search: 128/696, 128/698-700, 128/702, 128/704, 128/705, 128/733, 128/734, 128/901
• US Class Current: 600/515
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/222 combined with detection or measurement of physiological parameters, e.g. heart rate
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A method of reducing noise in a signal that represents a physiologic process includes obtaining multiple input signals, measuring a relationship between noise content of the input signals, and combining the input signals in consideration of the measured relationship to produce an output signal having low noise content. The multiple input signals may include, for example, two or more primary physiologic input signals or one or more primary physiologic input signals and two or more secondary input signals that represent noise. The method may further include dividing one or more ECG input signals and secondary input signals into set of segments, where each set of segments represents a beat of the ECG signal, measuring a relationship between noise content of corresponding points from successive sets of segments, and combining the input signals based on the measured relationship.

Claims

1. A method of producing a measurement of alternans, comprising:

obtaining multiple input signals, at least one of which represents activity of a patient'"'"'s heart;

determining a relationship between noise content of the input signals;

combining the input signals in consideration of the measured relationship to reduce effects of the noise content of the input signals and produce a measurement of alternans.

2. The method of claim 1, wherein the signal that represents activity of a patient'"'"'s heart is obtained using an electrode and the multiple input signals include a secondary input signal that represents a property of the electrode.

3. The method of claim 2, wherein the property of the electrode represented by the secondary input signal comprises an impedance of the electrode.

4. The method of claim 1, wherein multiple input signals are obtained using segments of a multi-segment electrode.

5. The method of claim 1, wherein the multiple input signals include a secondary input signal that represents physical activity by a patient.

6. The method of claim 5, wherein the physical activity comprises motion of the patient.

7. The method of claim 6, wherein the secondary input signal is obtained using an electrode applied to the patient'"'"'s skin and represents changes in electrical properties of an electrode-skin interface due to patient motion.

8. The method of claim 1, wherein the multiple input signals include a secondary input signal that is representative of respiratory activity of a patient.

9. A method of creating a noise-reduced result from an ECG signal, comprising:

obtaining multiple input signals that include one or more ECG input signals and one or more secondary input signals that represent noise;

dividing the one or more ECG input signals into sets of one or more points, wherein each set of points is synchronized to a beat of the ECG input signal;

dividing the one or more secondary input signals into sets of one or more points, wherein each set of points of the secondary input signal is synchronized with a corresponding set of points of the ECG input signal;

measuring a relationship between noise content of corresponding points from successive sets of points for the ECG input signal and the secondary input signal; and

combining the input signals in consideration of the measured relationship to produce a result having low noise content.

10. The method of claim 9, further comprising:

defining a desired result as a combination of one or more of the input signals;

modelling a low-noise result that approximates the desired result as a combination of two or more of the input signals, the model of the low-noise result including variable parameters that represent the relative contribution made to the low-noise result by each of the two or more input signals;

based on the relationship between noise content of the input signals, producing an error metric that represents noise content in the low-noise result, wherein the noise content in the low-noise result and a value of the error metric are affected by values assigned to the variable parameters of the model of the low-noise result; and

determining values of the variable parameters that cause the error metric to satisfy a predetermined condition;

wherein the step of combining comprises combining the input signals to produce the low-noise result using the determined values of the variable parameters.

11. The method of claim 10, wherein a first ECG input signal and a first secondary input signal are obtained using segments of a multi-segment electrode that is applied to a patient'"'"'s skin.

12. The method of claim 11, wherein the step of modelling the low-noise result comprises modelling the low-noise result as a combination of at least the first ECG input signal and the first secondary input signal.

13. The method of claim 10, wherein the step of determining comprises determining values of the variable parameters that reduce the value of the error metric.

14. The method of claim 10, wherein the step of determining comprises determining values of the variable parameters that reduce the error metric while satisfying an additional condition.

15. The method of claim 14, wherein:

the combination of input signals that models the low-noise result includes the one or more input signals that define the desired result, and

the additional condition satisfied by the step of determining requires that a sum of the identified variable parameters associated with the one or more input signals that define the desired result equals a sum of parameters associated with the desired result.

16. The method of claim 14, wherein:

the desired result represents a physiologic signal sensed at a first location that is remote from a signal source, the first location being identified relative to the signal source by a first vector;

at least two of the input signals represent the physiologic signal;

each input signal that represents the physiologic signal represents the physiologic signal as sensed at a location corresponding to that input signal, the location being remote from the signal source and identified relative to the signal source by a corresponding vector; and

the additional condition satisfied by the step of determining requires that a sum of the vectors corresponding to the input signals that represent the physiologic signals, with each vector being weighted by the identified variable parameter associated with the corresponding input signal, equals the first vector.

17. The method of claim 10, wherein the step of defining the desired result comprises defining the desired result as a linear combination of two or more of the input signals.

18. The method of claim 10, wherein the desired result and the low-noise result represent an ECG signal.

19. The method of claim 18, further comprising using the low-noise result in producing a measurement of alternans.

20. The method of claim 19, wherein at least a first input signal of the multiple input signals is obtained using an electrode applied to a patient'"'"'s skin, and wherein the multiple input signals include a second input signal that represents an impedance of the electrode.

21. The method of claim 20, wherein the step of modelling the low-noise result comprises modelling the low-noise result as a combination of at least the first and second input signals.

22. The method of claim 20, wherein the first input signal and at least a third input signal are obtained using segments of a multi-segment electrode.

23. The method of claim 22, wherein the step of modelling the low-noise result comprises modelling the low-noise result as a combination of at least the first, second and third input signals.

24. The method of claim 19, wherein at least a first input signal and a second input signal of the multiple input signals are obtained using segments of a multi-segment electrode that is applied to a patient'"'"'s skin.

25. The method of claim 24, wherein the step of modelling the low-noise result comprises modelling the low-noise result as a combination of at least the first and second input signals.

26. The method of claim 9, wherein:

at least a first ECG input signal is obtained using an electrode applied to a patient'"'"'s skin, and

at least a first secondary input signal represents an impedance associated with the electrode, and wherein

the step of combining comprises combining the first ECG input signal and the first secondary input signal.

27. The method of claim 26, wherein the first ECG input signal and at least a third input signal are obtained using segments of a multi-segment electrode.

28. The method of claim 27, wherein the step of combining comprises combining the first ECG input signal, the first secondary input signal, and the third input signal.

29. The method of claim 9, wherein multiple input signals are obtained using segments of a multi-segment electrode.

30. The method of claim 9, wherein a secondary input signal represents physical activity by a patient.

31. The method of claim 30, wherein the physical activity comprises motion of the patient.

32. The method of claim 31, wherein the secondary input signal is obtained using an electrode applied to the patient'"'"'s skin and represents changes in electrical properties of an electrode-skin interface due to patient motion.

33. The method of claim 9, wherein a secondary input signal represents respiratory activity of a patient.

34. The method of claim 9, wherein the step of combining comprises combining the input signals in consideration of the measured relationship to produce a measurement of alternans.

35. A method of creating a noise-reduced result, comprising:

measuring two or more primary input signals, each primary input signal representing activity of a patient'"'"'s heart;

defining a desired result as a combination of the primary input signals;

measuring a secondary input signal that includes information about noise content in the desired result;

combining two or more of the primary input signals and the secondary input signal to produce a result that approximates the desired result and has reduced noise relative to the desired result.

36. The method of claim 35, wherein a primary input signal and the secondary input signal are obtained using segments of a multi-segment electrode.

37. The method of claim 36, wherein a primary input signal is obtained using an electrode and the secondary input signal represents a property of the electrode.

38. The method of claim 37, wherein the property of the electrode represented by the secondary input signal comprises an impedance of the electrode.

39. The method of claim 35, wherein the step of combining comprises combining the input signals to produce a measurement of alternans.

40. A method of creating a noise-reduced result, comprising:

measuring input signals that include primary input signals, each primary input signal representing activity of a patient'"'"'s heart;

defining a desired result as a combination of one or more of the primary input signals;

measuring a relationship between noise content of the primary input signals; and

combining the primary input signals in view of the measured relationship to produce a result that has reduced noise relative to the desired result.

41. The method of claim 40, wherein:

the input signals include a secondary input signal related to noise, and

a primary input signal and the secondary input signal are obtained using segments of a multi-segment electrode.

42. The method of claim 40, wherein a primary input signal is obtained using an electrode and the input signals include a secondary input signal that represents a property of the electrode.

43. The method of claim 42, wherein the property of the electrode represented by the secondary input signal comprises an impedance of the electrode.

44. The method of claim 40, wherein the input signals include a secondary input signal that represents physical activity by the patient.

45. The method of claim 44, wherein the physical activity comprises motion of the patient.

46. The method of claim 45, wherein the secondary input signal is obtained using an electrode applied to the patient'"'"'s skin and represents changes in electrical properties of an electrode-skin interface due to patient motion.

47. The method of claim 44, wherein the physical activity comprises respiratory activity of the patient.

48. The method of claim 44, wherein the primary input signal and the secondary input signal are obtained using segments of a multi-segment electrode.

51. The method of claim 40, wherein the step of combining comprises combining the input signals to produce a measurement of alternans.

49. A method of creating a low-noise result, comprising:

measuring one or more primary input signals that represent an ECG signal;

measuring one or more secondary input signals that represent noise in the ECG signal;

identifying one or more beats of the ECG signal;

determining parameters of the primary input signals and the secondary input signals for each identified beat of the ECG signal;

producing, based on the determined parameters, a noise metric that represents noise content in the low-noise result; and

combining the input signals in consideration of the noise metric to produce a result having low noise content.

50. A method of creating a noise-reduced result, comprising:

measuring input signals that include a primary input signal representing activity of a patient'"'"'s heart and a secondary input signal that represents physical activity by the patient;

determining a relationship between noise content of the primary input signal and noise content of the secondary input signal; and

combining the primary input signal and the secondary input signal in consideration of the determined relationship to produce a noise-reduced result.

52. The method of claim 50, wherein the physical activity comprises motion of the patient.

53. The method of claim 50, wherein the secondary input signal is obtained using an electrode applied to the patient'"'"'s skin and represents changes in electrical properties of an electrode-skin interface due to patient motion.

54. The method of claim 50, wherein the physical activity comprises respiratory activity of the patient.

55. The method of claim 50, wherein the primary input signal and the secondary input signal are obtained using segments of a multi-segment electrode.

56. The method of claim 50, wherein the step of combining comprises combining the input signals to produce a measurement of alternans.

57. The method of claim 50, wherein the primary input signal is obtained using an electrode and wherein a third input signal represents a property of the electrode.

58. The method of claim 57, wherein the property of the electrode represented by the third input signal comprises an impedance of the electrode.