Device for reducing signal noise in a fetal ECG signal
First Claim
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.
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Accused Products
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.
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Citations
21 Claims
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1. A method of reducing noise in a fetal ECG signal, said method comprising the steps of:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 20)
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.
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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.
- and compensated values y[i] are obtained according to;
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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.
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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.
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10. A method as claimed in claim 1, further comprising the step of displaying at least part of the filtered signal.
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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.
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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.
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Specification