Device for reducing signal noise in a fetal ECG signal

• US 6,658,284 B1
• Filed: 04/26/2000
• Issued: 12/02/2003
• Est. Priority Date: 12/22/1998
• Status: Expired due to Term

• Current Assignee: Neoventa Medical AB
• Original Assignee: Neoventa Medical AB
• Inventors: Rosén, Karl G., Samuelsson, Arne
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Assistant Examiner(s): Oropeza, Frances P.
• Application Number:
  US09/530,207
• Time in Patent Office: 1,315 Days
• Field of Search: 600/373, 600/376, 600/377, 600/383, 600/509, 600/511, 600/515, 600/516, 600/517, 600/519, 607/116, 607/139
• US Class Current: 600/511
• CPC Class Codes: A61B 5/344 Foetal cardiography
• CPC Class Codes: A61B 5/4362 Assessing foetal parameters

Abstract

Apparatus for reducing signal noise in a fetal ECG signal obtained by using a unipolar ECG lead configuration 1, 3 thereby detecting a predominant T wave vector and avoiding changes in ECG waveform shape due to fetal rotation through the birth canal. The ECG signal is transmitted by means of a first signalling link 5 to the signal noise reducing components which include a conventional analogue filter 7, a digital high pass filter 9 for attenuating low frequencies and with a predetermined cut-off frequency, the cut-off frequency being essentially between 0.2 and 1.7 Hz, and a further digital filter 11. The filtered ECT signal is arranged as output signal from the electrical arrangement by means of a second signalling link 13.

Claims

1. A method of reducing noise in a fetal ECG signal, said method comprising the steps of:

connecting electrodes to a fetus and maternal skin in a unipolar configuration; and

feeding the signal detected by said electrodes through a first high pass filter, cut-off frequency of the first high pass filter being between 0.2 and 2.7 Hz.

2. A method as claimed in claim 1, wherein the cut-off frequency is less than 1.7 Hz.

3. A method as claimed in claim 1, wherein the signal is also fed through a notch filter, the notch filter being arranged to attenuate mains frequency contents of the signal.

4. A method as claimed in claim 3, wherein the notch filter attenuates signal components having frequencies of 50 Hz or 60 Hz.

5. A method as claimed in claim 1, wherein the signal is digitised before being passed through a second high pass filter.

6. A method as claimed in claim 5, wherein the signal comprises a sequence of ECG complexes in a form of uncompensated samples, each ECG complex including a QRS complex and the method further comprises the steps of:

identifying ECG complexes of an ECG signal and their P-Q points;

obtaining an approximating function to a curve between one P-Q point and a proceeding or a succeeding P-Q points by using a number of proceeding and succeeding P-Q points, the number being at least one; and

using compensated samples to derive an output signal.

7. A method as claimed in claim 6, wherein the step of obtaining an approximating function to the curve comprises determination of slopes of lines between P-Q points and proceeding or succeeding P-Q points;

and compensated values y[i] are obtained according to;

y[i]=x[i]−

m−

k (i−

ipq), where i, x[i], m, k and ipq denote index for each sample, uncompensated sample with index i, level of the P-Q point for the present complex, slope for the present complex, index for the P-Q point sample, respectively.

8. A method as claimed in claim 6, wherein the step of obtaining an approximating function to the curve comprises determination of polynomials of higher degree than one, the polynomials being based on a P-Q point and proceeding and/or succeeding P-Q points.

9. A method as claimed in claim 6, further comprising the step of passing the signal through an averaging filter associated with second high pass filter.

10. A method as claimed in claim 1, further comprising the step of displaying at least part of the filtered signal.

20. An apparatus as claimed in claim 1, further comprising means for displaying at least part of a noise-reduced signal.

11. Apparatus for obtaining a fetal ECG signal comprising exploring electrodes for connection to the fetus and the maternal skin in a unipolar configuration in order to detect an ECG signal and a signal noise reducing device linked to the electrodes by means of a first signalling link, wherein the signal noise reducing device comprises a first high pass filter, cut-off frequency of the first filter being between 0.2 and 2.7 Hz.

12. An apparatus as claimed in claim 11, wherein the cut-off frequency is less than 1.7 Hz.

13. An apparatus as claimed in claim 11, wherein the signal is also fed through a notch filter, the notch filter being arranged to attenuate mains frequency contents of the signal.

14. An apparatus as claimed in claim 13, wherein the notch filter attenuates signal components having frequencies of 50 Hz or 60 Hz.

15. An apparatus as claimed in claim 13, wherein the signal is subsequently digitised before being passed through a second high pass filter.

16. An apparatus as claimed in claim 15, wherein the second high pass filter comprises:

means for identifying ECG complexes of the ECG signal and their P-Q points;

means for obtaining an approximating function to a curve between one P-Q point and a proceeding or a succeeding P-Q points by using a number of proceeding and succeeding P-Q points, the number being at least one; and

means for using compensated samples to derive an output signal.

17. An apparatus as claimed in claim 16, wherein the means for obtaining an approximating function to the curve is arranged for determination of slopes of lines between P-Q points and proceeding or succeeding P-Q points;

and compensated values y[i] are obtained according to;

y[i]=x[i]−

m−

k(i−

ipq), where i, x[i], m, k and ipq denote index for each sample, uncompensated sample with index i, level of the P-Q point for the present complex, slope for the present complex, index for the P-Q point sample, respectively.

18. An apparatus as claimed in claim 16, wherein the means for obtaining an approximating function to the curve is arranged for determination of polynomials of higher degree than one, the polynomials being based on a P-Q point and proceeding and/or succeeding P-Q points.

19. An apparatus as claimed in claim 16, further comprising an averaging filter associated with the second high pass filter.

21. An apparatus for reducing noise in a fetal ECG signal comprising a first high pass filter having a cut-off frequency between 0.2 and 2.7 Hz and a second high pass filter comprising

means for identifying ECG complexes of an ECG signal and their P-Q points;

means for obtaining an approximating function to a curve between one P-Q point and a proceeding or a succeeding P-Q points by using a number of proceeding and succeeding P-Q points, the number being at least one; and

means for using compensated samples to derive an output signal.