LOCATING FIDUCIAL POINTS IN A PHYSIOLOGICAL SIGNAL

• US 20100204599A1
• Filed: 02/10/2009
• Published: 08/12/2010
• Est. Priority Date: 02/10/2009
• Status: Active Grant

• Current Assignee: Braemar Incorporated
• Original Assignee: Cardionet Incorporated
• Inventors: Pu, Yachuan, Gropper, Charles, Lin, Dongping
• Granted Patent: US 8,200,319 B2
• Time in Patent Office: Days
• US Class Current: 600/523
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/327 Generation of artificial ECG signals based on measured signals, e.g. to compensate for missing leads
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Systems, devices, methods, and techniques relating to the identification of fiducial points. In one aspect, a machine implemented method includes obtaining a first time varying physiological signal and a second time varying physiological signal that relate to biological activity of an organism, the first time varying physiological signal and the second time varying physiological signal forming an analytic pair wherein the analytic pair has a time varying phase angle, defining a reference line by a lower boundary of a representation of the time varying phase angle with respect to a time period, and identifying a fiducial point based on the reference line.

Claims

1. A machine implemented method comprising:

obtaining a first time varying physiological signal and a second time varying physiological signal that relate to biological activity of an organism, the first time varying physiological signal and the second time varying physiological signal forming an analytic pair wherein the analytic pair has a time varying phase angle;

defining a reference line by a boundary of a representation of the time varying phase angle with respect to a time period; and

identifying a fiducial point based on the reference line.

2. The machine implemented method of claim 1, further comprising approximating the time varying phase angle, wherein the approximation of the varying phase angle φ

<sub>Δ

{right arrow over (A)}(ti+K)</sub> is defined by the function;

${\mathrm{\varphi <br><br>}}_{\mathrm{\Delta <br><br>}<br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)}\approx <br><br>\frac{\mathrm{imag}\left[\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)\right]}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)<br><br>}=\frac{\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)}{\sqrt{{\left(x<br><br>\left(t_{i+K}\right)-x<br><br>\left(t_i\right)\right)}^2+{\left(\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)\right)}^2}}$

where x(t) comprises the first time varying physiological signal and {circumflex over (x)}(t) comprises the second time varying physiological signal, x(t) and {circumflex over (x)}(t) forming the analytic pair {right arrow over (A)}(t);

where i is a current sample;

where K is K samples away; and

where Δ

{right arrow over (A)}(t_i+k) is the change of the two vectors ((x(t_i), {circumflex over (x)}(t_i)) and (x(t_i+K), {circumflex over (x)}(t_i+K)).

3. The machine implemented method of claim 1, wherein the reference line comprises an isoelectric line defined by a lower boundary of the representation of the time varying phase angle.

4. The machine implemented method of claim 1, further comprising:

calculating a corresponding function to a downslope or an upslope of the representation of the time varying phase angle within the time period; and

wherein identifying a fiducial point based on the reference line comprises identifying a fiducial point based on an intersection of the corresponding function and the reference line.

5. The machine implemented method of claim 4, wherein calculating a corresponding function to a downslope of the representation of the time varying phase angle comprises calculating a tangent line where the downslope has a minimum slope.

6. The machine implemented method of claim 4, wherein calculating a corresponding function to an upslope of the representation of the time varying phase angle comprises calculating a tangent line where the upslope has a maximum slope.

7. The machine implemented method of claim 4, wherein identifying a fiducial point based on an intersection of the corresponding function and the reference line comprises offsetting the intersection by a constant.

8. The machine implemented method of claim 4, wherein calculating a corresponding function to a downslope or an upslope of the representation of the time varying phase angle comprises calculating the regression line of the downslope or the upslope of the representation of the time varying phase angle within the time period.

9. The machine implemented method of claim 1, comprising applying a trigonometric function to the time varying phase angle to create the representation.

10. The machine implemented method of claim 1,

wherein obtaining a first time varying physiological signal comprises obtaining a sensed signal x(t);

and

wherein obtaining a second time varying physiological signal {circumflex over (x)}(t) comprises obtaining a transformation of x(t) to form the analytic pair {right arrow over (A)}(t).

11. The machine implemented method of claim 10, wherein obtaining a transformation of x(t) comprises obtaining a Hilbert Transformation H(x(t)) of the first time varying physiological signal.

12. The machine implemented method of claim 10, wherein obtaining a transformation of x(t) comprises obtaining a derivative of x(t).

13. The machine implemented method of claim 1,

wherein obtaining a first time varying physiological signal comprises obtaining a first sensed signal based on a first lead configuration;

wherein obtaining a second time varying physiological signal comprises obtaining a second sensed signal based on a second lead configuration wherein the second sensed signal is orthogonal to the first; and

wherein obtaining the first and second time varying physiological signals comprises obtaining the signals from a data storage device.

14. The machine implemented method of claim 1, wherein identifying a fiducial point comprises identifying one of a T-wave offset, T-wave onset, P-wave offset, P-wave onset, Q-point, R-point, and S-point.

15. A system comprising:

one or more computers; and

a computer-readable storage device having a computer program product encoded therein, the computer program product operable to cause the one or more computers to perform operations comprising;

obtaining a first time varying physiological signal and a second time varying physiological signal that relate to biological activity of an organism, the first time varying physiological signal and the second time varying physiological signal forming an analytic pair wherein the analytic pair has a time varying phase angle;

defining a reference line by a boundary of a representation of the time varying phase angle with respect to a time period; and

identifying a fiducial point based on the reference line.

16. The system of claim 15, wherein the computer-readable storage device is further operable to cause the one or more computers to perform operations comprising:

calculating a corresponding function to a downslope or an upslope of the representation of the time varying phase angle within the time period; and

wherein identifying a fiducial point based on the reference line comprises identifying a fiducial point based on an intersection of the corresponding function and the reference line.

17. The system of claim 16, wherein calculating a corresponding function to a downslope or an upslope of the representation of the time varying phase angle comprises calculating one of a tangent line, a regression line, and a least square approximation to the downslope or the upslope.

19. The system of claim 15, wherein the computer-readable storage device is further operable to cause the one or more computers to perform operations comprising:

applying a trigonometric function to the time varying phase angle to create the representation.

20. The system of claim 15, wherein the computer-readable storage device is further operable to cause the one or more computers to perform operations comprising:

approximating the time varying phase angle, wherein the approximation of the varying phase angle φ

<sub>Δ

{right arrow over (A)}(ti+K)</sub> is defined by the function;

${\mathrm{\varphi <br><br>}}_{\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{.}{A}<br><br>\left(t_{i+K}\right)}\approx <br><br>\frac{\mathrm{imag}\left[\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)\right]}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)<br><br>}=\frac{\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)}{\sqrt{{\left(x<br><br>\left(t_{i+K}\right)-x<br><br>\left(t_i\right)\right)}^2+{\left(\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)\right)}^2}}$

where x(t) comprises the first time varying physiological signal and {circumflex over (x)}(t) comprises the second time varying physiological signal, x(t) and {circumflex over (x)}(t) forming the analytic pair {right arrow over (A)}(t);

where i is a current sample;

where K is K samples away; and

where Δ

{right arrow over (A)}(t_i+k) is the change of the two vectors ((x(t_i),{circumflex over (x)}(t_i)), and (x(t_i+K),{circumflex over (x)}(t_i+K)).

21. The system of claim 15,

wherein obtaining a first time varying physiological signal comprises obtaining a sensed signal x(t);

and

wherein obtaining a second time varying physiological signal {circumflex over (x)}(t) comprises obtaining a transformation of x(t) to form the analytic pair {right arrow over (A)}(t).

22. The system of claim 21, wherein obtaining a transformation of x(t) comprises obtaining a Hilbert Transformation H(x(t)) of the first time varying physiological signal.

23. The system of claim 21, wherein obtaining a transformation of x(t) comprises obtaining a derivative of x(t).

24. The system of claim 15, wherein obtaining a first time varying physiological 11 signal comprises obtaining a first sensed signal based on a first lead configuration;

wherein obtaining a second time varying physiological signal comprises obtaining a second sensed signal based on a second lead configuration wherein the second sensed signal is orthogonal to the first; and

wherein obtaining the first and second time varying physiological signals comprises obtaining the signals from a data storage device.

25. The system of claim 15, wherein identifying a fiducial point comprises identifying one of a T-wave offset, T-wave onset, P-wave offset, P-wave onset, Q-point, R-point, and S-point.

18. The system of 16, wherein identifying a fiducial point based on an intersection of the corresponding function and the reference line comprises offsetting the intersection by a constant.

26. An apparatus comprising:

circuitry operable to obtain a first time varying physiological signal and a second time varying physiological signal that relate to biological activity of an organism, the first time varying physiological signal and the second time varying physiological signal forming an analytic pair wherein the analytic pair has a time varying phase angle;

circuitry operable to define a reference line by a boundary of a representation of the time varying phase angle with respect to a time period; and

circuitry operable to identify a fiducial point based on the reference line

27. The apparatus of claim 26, further comprising

circuitry operable to transmit the identified fiducial points.

28. The apparatus of claim 26, further comprising

circuitry operable to calculate a corresponding function to a downslope or an upslope of the representation of the time varying phase angle within the time period;

and

wherein the circuitry operable to identify a fiducial point is further operable to identify a fiducial point based on an intersection of the corresponding function and the reference line.

29. The apparatus of claim 28, wherein the circuitry operable to calculate a corresponding function to a downslope or an upslope of the representation of the time varying phase angle is further operable to calculate one of a tangent line, a regression line, and a least square approximation to the downslope or the upslope.

30. The apparatus of claim 28, wherein the circuitry operable to identify a fiducial point based on an intersection of the corresponding function and the reference line is further operable to offset the intersection by a constant.

31. The apparatus of claim 26,

further comprising circuitry operable to approximate the time varying phase angle, wherein the approximation of the varying phase angle φ

<sub>Δ

{right arrow over (A)}(ti+K)</sub> is defined by the function;

${\mathrm{\varphi <br><br>}}_{\mathrm{\Delta <br><br>}<br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)}\approx <br><br>\frac{\mathrm{imag}\left[\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)\right]}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>\stackrel{-><br><br>}{A}<br><br>\left(t_{i+K}\right)<br><br>}=\frac{\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)}{\sqrt{{\left(x<br><br>\left(t_{i+K}\right)-x<br><br>\left(t_i\right)\right)}^2+{\left(\hat{x}<br><br>\left(t_{i+K}\right)-\hat{x}<br><br>\left(t_i\right)\right)}^2}}$

where x(t) comprises the first time varying physiological signal and {circumflex over (x)}(t) comprises the second time varying physiological signal, x(t) and {circumflex over (x)}(t) forming the analytic pair {right arrow over (A)}(t);

where i is a current sample;

where K is K samples away; and

where Δ

{right arrow over (A)}(t_i+k) is the change of the two vectors ((x(t_i),{circumflex over (x)}(t_i)) and (x(t_i+K),{circumflex over (x)}(t_i+K)).

32. The apparatus of claim 26, further comprising circuitry operable to apply a trigonometric function to the time varying phase angle to create the representation.

33. The apparatus of claim 26,

wherein the circuitry operable to obtain a first time varying physiological signal is further operable to obtain a sensed signal x(t);

and

wherein the circuitry operable to obtain a second time varying physiological signal {circumflex over (x)}(t) is further operable to obtain a transformation of x(t) to form the analytic pair {right arrow over (A)}(t).

34. The apparatus of claim 33, wherein the circuitry operable to obtain a transformation of x(t) is further operable to obtain a Hilbert Transformation H(x(t)) of the first time varying physiological signal.

35. The apparatus of claim 33, wherein the circuitry operable to obtain a transformation of x(t) comprises obtaining a derivative of x(t).

36. The apparatus of claim 26,

wherein the circuitry operable to obtain a first time varying physiological signal is further operable to obtain a first sensed signal based on a first lead configuration;

wherein the circuitry operable to obtain a second time varying physiological signal is further operable to obtain a second sensed signal based on a second lead configuration wherein the second sensed signal is orthogonal to the first; and

wherein the circuitry operable to obtain the first and second time varying physiological signals is further operable to obtain the signals from a data storage device.

37. The apparatus of claim 26, wherein the circuitry operable to identify a fiducial point is further operable to identify one of a T-wave offset, T-wave onset, P-wave offset, P-wave onset, Q-point, R-point, and S-point.