Method and apparatus for a morphology-preserving smoothing filter

US 7,294,109 B2
Filed: 09/16/2003
Issued: 11/13/2007
Est. Priority Date: 07/27/2000
Status: Expired due to Term

First Claim

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1. A method for processing a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the method comprising:

applying a portion of the input signal to a plurality of filters to produce a plurality of filtered signal portions of varying smoothness;

comparing the plurality of filtered signal portions to the portion of the input signal to generate a plurality of deviations;

comparing one or more of the plurality of deviations to a maximum deviation limitation to select one of the plurality of filtered signal portions, the selected one filtered signal portion having a deviation less than the maximum deviation limitation;

generating an output signal representative of a smoothed version of the input signal from a combination of a plurality of successive selected one filtered signal portions which substantially preserve the desired waveform with the spikes while substantially removing the noise component; and

outputting the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.

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Abstract

A method and apparatus for implementing a signal morphology preservation smoothing scheme. The smoothing scheme includes generating an output signal representative of a filtered version of the input signal, wherein the output signal is generated by adaptively removing low amplitude, high frequency noise components while simultaneously preserving signal morphology of the input signal. The smoothing scheme includes comparison of a distance metric against a distance threshold to determine whether an initial smoothed version of the input signal would be oversmoothed or undersmoothed. Then the smoothing scheme appropriately increments, decrements, or maintains the initial level of smoothing to generate an optimal smoothed signal representative of the output signal.

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54 Claims

1. A method for processing a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the method comprising:
- applying a portion of the input signal to a plurality of filters to produce a plurality of filtered signal portions of varying smoothness;
  
  comparing the plurality of filtered signal portions to the portion of the input signal to generate a plurality of deviations;
  
  comparing one or more of the plurality of deviations to a maximum deviation limitation to select one of the plurality of filtered signal portions, the selected one filtered signal portion having a deviation less than the maximum deviation limitation;
  
  generating an output signal representative of a smoothed version of the input signal from a combination of a plurality of successive selected one filtered signal portions which substantially preserve the desired waveform with the spikes while substantially removing the noise component; and
  
  outputting the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
- - 2. The method of claim 1, wherein the input signal is a physiologic signal.
  - 3. The method of claim 2, wherein the input signal is a cardiac signal.
  - 4. The method of claim 1, wherein the portion of the input signal includes at least one discrete sample.
  - 5. The method of claim 4, further comprising selecting a filtered signal portion from the plurality of filtered signal portions that has a largest deviation that remains less than the maximum deviation limitation as the select one of the plurality of filtered signal portions.
  - 6. The method of claim 1, wherein comparing one or more of the plurality of deviations to a maximum deviation limitation to select one of the plurality of filtered signal portions includes determining an initial distance metric corresponding to an initial one of the plurality of filtered signal portions.
  - 7. The method of claim 6, wherein the initial one of the plurality of filtered signal portions is a select one of the plurality of filtered signal portions for an immediately preceding portion of the input signal.
  - 8. The method of claim 6, wherein comparing one or more of the plurality of deviations to a maximum deviation limitation includes comparing the initial distance metric against the maximum deviation limitation.
  - 9. The method of claim 8, wherein the maximum deviation limitation is selected based on the input signal and balances removing noise components with substantially preserving morphology of the input signal.
  - 10. The method of claim 8, further comprising selecting a second one of the plurality of filtered signal portions having a deviation less than the maximum deviation limitation when the initial distance metric corresponding to the initial one of the plurality of filtered signal portions is at least equal to the maximum deviation limitation.
  - 11. The method of claim 8, wherein the plurality of filtered signal portions are indexed according to the plurality of deviations, and comparing one or more of the plurality of deviations to a maximum deviation limitation includes determining another distance metric corresponding to a second filtered signal portion that is adjacently indexed to the initial one of the plurality of filtered signal portions and is associated with an increased deviation from the portion of the input signal.
  - 12. The method of claim 11, wherein at least one of the initial distance metric and the another distance metric is determined by D(i_n)=|y_in(n)−
    - x(n)|.
  - 13. The method of claim 11, wherein at least one of the initial distance metric and the another distance metric is determined by:
    - $D (i_{n}) = \frac{1}{4} \sum_{m = n - 2}^{n + 1} \langle y_{i n} (m) - x (m) \rangle .$
  - 14. The method of claim 11, wherein the second filtered signal portion becomes the selected one of the plurality of filtered signal portions when the another distance metric is smaller than the maximum deviation limitation.
  - 15. The method of claim 1, wherein the plurality of filtered signal portions of varying smoothness is produced using a selection of equations in which n represents the portion of the input signal and m represents an index for the plurality of filtered signal portions that are indexed according to the plurality of deviations, the selection of equations including:
    - $\begin{matrix} y_{o} (n) = x (n), \\ y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), \\ y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), \\ y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and \\ y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m) . \end{matrix}$
  - 16. The method of claim 1, wherein the select one filtered signal portion is associated with a largest deviation from the portion of the input signal that is less than the maximum deviation limitation.

17. A method for processing a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the method comprising:
- generating an output signal representative of a filtered version of the input signal by adaptively removing noise components from the input signal, wherein each of the input signal and the output signal includes discrete samples;
  
  determining a desired filtering level from a number of filtering levels for each of the discrete samples of the input signal;
  
  determining a desired smoothed signal representative of the desired waveform from a number of smoothed signals corresponding to the desired filtering level, wherein the desired smoothed signal is calculated from a selection of equations including;
  
  $y_{0} (n) = x (n), y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and$ $y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m); and$ analyzing the desired smoothed signal representative of the desired waveform to identify or monitor the physiological state or event.
- View Dependent Claims (18, 19)
- - 18. The method of claim 17, further comprising diagnosing a condition using an analysis of the desired smoothed signal representative of the desired waveform.
  - 19. The method of claim 17, further comprising configuring a therapy using an analysis of the desired smoothed signal representative of the desired waveform.

20. A system for filtering a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the system comprising a processor to:
- receive a portion of the input signal;
  
  produce a plurality of filtered signal portions of varying smoothness from the portion of the input signal;
  
  determine a plurality of deviations between the plurality of filtered signal portions and the portion of the input signal;
  
  compare one or more of the plurality of deviations to a maximum deviation limitation to select one of the plurality of filtered signal portions, the selected one filtered signal portion having a deviation less than the maximum deviation limitation; and
  
  generate an output signal representative of a smoothed version of the input signal from a combination of a plurality of successive selected one filtered signal portions which substantially preserve the desired waveform with the spikes while substantially removing the noise component; and
  
  output the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.
- View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
- - 21. The system of claim 20, wherein the portion of the input signal includes at least one discrete sample.
  - 22. The system of claim 20, further comprising an implanted medical device that includes the processor.
  - 23. The system of claim 22, wherein the portion of the input signal includes a portion of a cardiac signal and the implanted medical device is configured to receive the portion of the cardiac signal.
  - 24. The system of claim 20, further comprising an implanted medical device and an external programmer that includes the processor in communication with the implanted medical device.
  - 25. The system of claim 20, wherein the processor is configured to select a filtered signal portion from the plurality of filtered signal portions that has a largest deviation that remains less than the maximum deviation limitation as the select one of the plurality of filtered signal portions.
  - 26. The system of claim 25, wherein the processor is configured to determine an initial distance metric corresponding to an initial one of the plurality of filtered signal portions.
  - 27. The system of claim 26, wherein the processor is configured to compare the initial distance metric against the maximum deviation limitation.
  - 28. The system of claim 27, wherein the maximum deviation threshold is selected based on the input signal and balances removing noise components with substantially preserving a morphological representation of the input signal.
  - 29. The system of claim 27, wherein the processor is configured to select a second one of the plurality of filtered signal portions having a deviation less than the maximum deviation limitation when the initial distance metric is at least equal to the maximum deviation limitation.
  - 30. The system of claim 27, wherein the plurality of filtered signal portions are indexed according to the plurality of deviations, and the processor is configured to determine another distance metric corresponding to a second filtered signal portion that is adjacently indexed to the initial one of the plurality of filtered signal portions and is associated with an increased deviation from the portion of the input signal.
  - 31. The system of claim 30, wherein at least one of the initial distance metric and the another distance metric is determined by D(i_n)=|y_in(n)−
    - x(n)|.
  - 32. The system of claim 30, wherein at least one of the initial distance metric and the another distance metric is determined by:
    - $D (i_{n}) = \frac{1}{4} \sum_{m = n - 2}^{n + 1} \langle y_{i n} (m) - x (m) \rangle .$
  - 33. The system of claim 30, wherein the processor is configured to select the second filtered signal portion as the selected one of the plurality of filtered signal portions when the another distance metric is smaller than the maximum deviation limitation.
  - 34. The system of claim 20, wherein the plurality of filtered signal portions of varying smoothness is produced using a selection of equations in which n represents the portion of the input signal and m represents an index for the plurality of filtered signal portions that are indexed according to the plurality of deviations, the selection of equations including:
    - $\begin{matrix} y_{o} (n) = x (n), \\ y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), \\ y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), \\ y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and \\ y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m) . \end{matrix}$
  - 35. The system of claim 20, wherein the selected one filtered signal portion is associated with a largest deviation from the portion of the input signal that is less than the maximum deviation limitation.

36. A system for processing a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the system comprising:
- means for producing a plurality of filtered signal portions of varying smoothness from a portion of the input signal;
  
  means for generating a plurality of deviations between the plurality of signal portions and the portion of the input signal;
  
  means for comparing the plurality of deviations to a maximum deviation limitation to select one of the plurality of filtered signal portions that has a deviation less than the maximum deviation limitation; and
  
  means for generating an output signal representative of a smoothed version of the input signal from a combination of a plurality of successive selected one filtered signal portions which substantially preserve the desired waveform with the spikes while substantially removing the noise component; and
  
  means for outputting the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.
- View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52)
- - 37. The system of claim 36, wherein the portion of the input signal includes at least one discrete sample.
  - 38. The system of claim 36, further comprising an implanted medical device that includes the processor.
  - 39. The system of claim 38, wherein the implant signal includes a cardiac signal, and the implanted medical device is configured to receive the cardiac signal.
  - 40. The system of claim 36, further comprising an implanted medical device and an external programmer that includes the processor in communication with the implanted medical device.
  - 41. The system of claim 36, further comprising means for selecting a filtered signal portion from the plurality of filtered signal portions that has a largest deviation that remains less than the maximum deviation limitation as the select one of the plurality of filtered signal portions.
  - 42. The system of claim 41, wherein the means for comparing the plurality of deviations to a maximum deviation limitation includes means for calculating an initial distance metric corresponding to an initial one of the plurality of filtered signal portions.
  - 43. The system of claim 42, wherein the initial one of the plurality of filtered signal portions is a select one of the plurality of filtered signal portions for an immediately preceding portion of the input signal.
  - 44. The system of claim 42, wherein the means for comparing the plurality of deviations to a maximum deviation limitation includes means for comparing the initial distance metric against the maximum deviation limitation.
  - 45. The system of claim 44, wherein the maximum deviation limitation is selected based on the input signal and balances removing noise components with substantially preserving morphology of the input signal.
  - 46. The system of claim 44, further comprising means to index the plurality of filtered signal portions according to the plurality of deviations, and means to select a second one of the plurality of filtered signal portions having a deviation less than the maximum deviation limitation when the initial distance metric corresponding to the initial one of the plurality of filtered signal portions is at least equal to the maximum deviation limitation.
  - 47. The system of claim 44, further comprising means to index the plurality of filtered signal portions according to the plurality of deviations, and means for determining another distance metric corresponding to a second filtered signal portion that is adjacently indexed to the initial one of the plurality of filtered signal portions and is associated with an increased deviation from the portion of the input signal.
  - 48. The system of claim 47, wherein at least one of the initial distance metric and the another distance metric is determined by D(i_n)=|y_in(n)−
    - x(n)|.
  - 49. The system of claim 47, wherein at least one of the initial distance metric and the another distance metric is determined by:
    - $D (i_{n}) = \frac{1}{4} \sum_{m = n - 2}^{n + 1} \langle y_{i n} (m) - x (m) \rangle .$
  - 50. The system of claim 47, further comprising selecting the second filtered signal portion as the selected one of the plurality of filtered signal portions when the another distance metric is smaller than the maximum deviation limitation.
  - 51. The system of claim 36, wherein the plurality of filtered signal portions of varying smoothness is produced using a selection of equations in which n represents the portion of the input signal and m represents and index for the plurality of filtered signal portions that are indexed according to the plurality of deviations, the selection of equations including:
    - $\begin{matrix} y_{o} (n) = x (n), \\ y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), \\ y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), \\ y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and \\ y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m) . \end{matrix}$
  - 52. The system of claim 36, wherein the selected one filtered signal portion is associated with a largest deviation from the portion of the input signal that is less than the maximum deviation limitation.

53. A system for processing a physiologically sensed input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, comprising:
- a processor to receive the input signal and generate an output signal representative of a filtered version of the input signal by adaptively removing noise components from the input signal, wherein;
  
  the input signal includes a number of discrete samples;
  
  the processor is configured to determine a desired filtering level for each of the discrete samples of the input signal;
  
  the processor is configured to determine a desired smoothed signal from a number of smoothed signals corresponding to the desired filtering level; and
  
  the desired smoothed signal is calculated from a selection of equations including;
  
  $y_{0} (n) = x (n), y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and$ $y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m); and$ the processor is configured to present the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.

54. A system for processing a physiologically sensed input signal detected by at least one detector, the input signal representative of a desired waveform for analysis to identify or monitor a physiologic state or event, the input signal including a noise component, the desired waveform having spikes with a larger amplitude than an amplitude of the noise component, the system comprising:
- means for receiving the input signal;
  
  means for generating an output signal representative of a filtered version of the input signal by adaptively removing noise components from the input signal;
  
  means for determining a desired filtering level from a number of filtering levels for each discrete sample of the input signal; and
  
  means for determining a desired smoothed signal from a number of smooth signals corresponding to the desired filtering level, wherein the desired smoothed signal is calculated from a selection of equations including;
  
  $y_{0} (n) = x (n), y_{1} (n) = \frac{1}{2} \sum_{m = - 1}^{0} x (n + m), y_{2} (n) = \frac{1}{4} \sum_{m = - 2}^{1} x (n + m), y_{3} (n) = \frac{1}{8} \sum_{m = - 4}^{3} x (n + m), and$ $y_{4} (n) = \frac{1}{16} \sum_{m = - 8}^{7} x (n + m); and$ means for outputting the substantially-preserved desired waveform with the spikes indicating the physiologic state or event.

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Current Assignee
Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
Original Assignee
Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
Inventors
Lovett, Eric G., Sweeney, Robert J.
Primary Examiner(s)
MANUEL, GEORGE C

Application Number

US10/663,920
Publication Number

US 20040073125A1
Time in Patent Office

1,519 Days
Field of Search

600/508, 600/509, 600/520, 600/301, 327/551, 327/552, 333/181, 607/9, 607/18, 844/54
US Class Current

600/508
CPC Class Codes

A61B 5/30   Input circuits therefor

A61B 5/316   Modalities, i.e. specific d...

A61B 5/7203   for noise prevention, reduc...

A61N 1/3956   Implantable devices for app...

H03H 17/026   Averaging filters

H03H 21/0043   Adaptive algorithms

Method and apparatus for a morphology-preserving smoothing filter

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Method and apparatus for a morphology-preserving smoothing filter

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