ADAPTIVE FILTERING FOR MORE RELIABLY DETERMINING PHYSIOLOGICAL PARAMETERS

• US 20090216499A1
• Filed: 02/06/2007
• Published: 08/27/2009
• Est. Priority Date: 02/20/2006
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Moersdorf, Hans-Joachim, Tobola, Andreas, Vogl, Ulrich
• Granted Patent: US 8,676,542 B2
• Time in Patent Office: Days
• US Class Current: 702/190
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G06F 2218/04 Denoising

Abstract

Apparatus for reducing an interference portion in a time-discrete signal further including a useful portion, including a first provider for providing the time-discrete signal including the interference portion and the useful portion; a second provider for providing a first time-discrete reference signal including a first interference portion, and a second time-discrete reference signal including a second interference portion, the second interference portion being shifted in phase relative to the first interference portion. The apparatus further includes a subtractor for generating a differential signal from the two reference signals, the differential signal including a frequency component caused by the first and second interference portions; and a manipulator for manipulating the time-discrete signal on the basis of the differential signal such that in a manipulated time-discrete signal the frequency component is reduced.

Claims

1. An apparatus for reducing an interference portion in a time-discrete signal further comprising a useful portion, the apparatus comprising:

a first provider for providing the time-discrete signal comprising the interference portion and the useful portion, the first provider being adapted to sample an iterative optical signal which corresponds to bright periods during which a transmit light source adopts an on state;

a second provider for providing a first time-discrete reference signal comprising a first frequency component of the interference portion, and a second time-discrete signal comprising a second frequency component of the interference portion, the first and second frequency components being shifted in phase, and the second provider for providing the first and second reference signals being adapted to sample two optical signals which correspond to dark periods during which no transmit light source adopts an on state;

a subtractor for generating a differential signal from the two reference signals, the differential signal comprising a third frequency component caused by the first and second frequency components; and

a manipulator for manipulating the time-discrete signal on the basis of the differential signal, such that in a manipulated time-discrete signal the interference portion is reduced.

2. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal and the second provider for providing the first and second time-discrete reference signals are implemented to provide the time-discrete signals by sampling analog signals using a sampler comprising a sampling frequency.

3. The apparatus as claimed in claim 2, wherein the sampler is implemented to generate the time-discrete signal, the first and second time-discrete reference signals in that sampling is sequentially performed at different points in time at regular time intervals.

4. The apparatus as claimed in claim 3, wherein the first provider for providing the time-discrete signal and the second provider for providing the first and second time-discrete reference signals each comprise a low pass whose cutoff frequency corresponds to at least the reciprocal value of half the sampling duration of the sampler.

5. The apparatus as claimed in claim 4, wherein the manipulator for manipulating the time-discrete signal is adapted to manipulate frequency components in the differential signal in terms of their amplitudes and phase positions such that a difference between the differential signal and the time-discrete signal is reduced.

6. The apparatus as claimed in claim 5, wherein the manipulator is implemented to filter the differential signal using a digital filter, the coefficients of the digital filter being set such that the difference between the time-discrete signal and the filtered differential signal is smaller than the difference between the time-discrete signal and the differential signal.

7. The apparatus as claimed in claim 4, wherein the manipulator is adapted to filter the time-discrete signal using a digital filter and to set the coefficients of the digital filter such that frequency components in the time-discrete signal which come up in the differential signal are reduced in terms of their amplitudes.

8. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal and the second provider for providing the time-discrete reference signals are adapted to sample optical signals.

9. The apparatus as claimed in claim 1, further comprising a former for forming a weighted sum of the two time-discrete reference signals, which supplies the weighted sum of the two time-discrete reference signals to the first provider for providing the time-discrete signal, and the first provider for providing the time-discrete signal being implemented to subtract the weighted sum from an original signal and to provide the result as a time-discrete signal.

10. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal is implemented to provide the signal on the basis of an infrared transmit light source or a red transmit light source.

11. The apparatus as claimed in claim 1, wherein the first provider for providing a time-discrete signal is implemented to provide a signal which has passed a tissue of a living being.

12. The apparatus as claimed in claim 1, wherein the apparatus for reducing an interference portion in a time-discrete signal is implemented to provide a signal comprising information on a physiological parameter.

13. The apparatus as claimed in claim 1, wherein the apparatus for reducing an interference portion in a time-discrete signal is implemented to provide a signal comprising information on a heart rate or a blood oxygen saturation value of a living being.

14. The apparatus as claimed in claim 1, wherein the first provider for providing a time-discrete signal is implemented to process an iterative optical signal, the optical signal comprising sequences, and a sequence comprising at least two bright periods during which a transmit light source adopts an ON state and at least one dark period during which no transmit light source adopts the ON state, and the at least two bright periods being irregularly arranged within a sequence, and the first provider for providing the time-discrete signal further being implemented to provide the time-discrete signal in accordance with a bright transmit channel on the basis of the information on the arrangement of the bright periods within the sequence.

15. The apparatus as claimed in claim 1, wherein the second provider for providing the first and second time-discrete reference signals is implemented to receive iterative optical signals, the optical signal comprising sequences, and a sequence comprising at least two dark periods during which no transmit light source adopts an ON state and at least one bright period during which a transmit light source adopts an ON state, and the at least two dark periods being irregularly arranged within the sequence.

16. The apparatus as claimed in claim 1, wherein a sequence of an optical signal is based on a clock in accordance with which the bright and dark periods occur.

17. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal and the second provider for providing the first and second time-discrete reference signals are implemented to operate at a clock higher than 800 Hz.

18. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal and the second provider for providing the first and second time-discrete reference signals are implemented to receive, to store or to generate a binary code word comprising a length and indicating the arrangement of the bright and dark periods, and to link the binary code word with an original signal in a block-by-block manner so as to acquire a digital signal of a transmit channel, the transmit channel being determined by the binary code word, and the block length being defined by the length of the code word, and a value of the transmit channel being extracted per block-by-block linking.

19. The apparatus as claimed in claim 18, wherein the first provider for providing the time-discrete signal and the second provider for providing the first and second time-discrete reference signals are implemented to form a scalar product between the binary code word and a block of the original signal of the length of the binary code word, to weight the result, to link it with other results and to associate an overall result with a transmit channel.

20. The apparatus as claimed in claim 1, wherein the sequence of the optical signal comprises at least two further bright periods originating from a second transmit light source, the first provider for providing the time-discrete signal being implemented to extract a further bright transmit channel using a further binary code word.

21. The apparatus as claimed in claim 1, wherein the manipulator for manipulating the time-discrete signal is implemented to form columns of a matrix from the differential signal in a block-by-block manner, to regard these as coefficients of a linear over-determined equation system, and to solve same by an optimization criterion, as well as to adaptively track the coefficients.

22. The apparatus as claimed in claim 1, wherein the first provider for providing the time-discrete signal is implemented to subdivide the time-discrete signal into blocks, multiply it by a window function, normalize it and/or determine its spectrum.

23. The apparatus as claimed in claim 1, wherein the manipulated time-discrete signal is supplied to a processor implemented to determine a straight regression line in a large group of dots using the CTLSF method (complex total least squares fit) by means of a singular value decomposition.

24. The apparatus as claimed in claim 23, wherein the processor is implemented to determine the linear coefficient using the CTLSF method (complex total least squares fit) for two linearly dependent spectra comprising independent interferences.

25. The apparatus as claimed in claim 24, wherein the processor is implemented to determine the linear coefficient using a singular value decomposition.

26. The apparatus as claimed in claim 1, implemented to determine, from the ratio of two spectral values of two bright transmit channels, blood oxygen saturation or an SpO2 value of an artery which has been radiated.

27. The apparatus as claimed in claim 1, implemented to determine heart rate signals using a spectral analysis of bright transmit channels.

28. The apparatus as claimed in claim 27, implemented to determine a spectral mask which insulates, in the frequency range, those signal portions from the spectrum which comprise the same spectral characteristic as a signal sought for.

29. The apparatus as claimed in claim 28, implemented to determine a spectral mask for pulse signals of a living being with regard to a potential fundamental wave frequency and potential harmonic frequencies, as well as their relations to each other, from the spectra of the bright transmit channels.

30. The apparatus as claimed in claim 29, implemented to infer a subject'"'"'s heart rate from the relation of fundamental wave components and harmonic components within the spectrum of the bright transmit channels.

31. The apparatus as claimed in claim 21, implemented to utilize, for spectral analysis, only such frequency portions of a spectrum which are relevant to a pulse portion.

32. The apparatus as claimed in claim 1, wherein the processor is implemented to receive, to store or to generate a table which associates blood saturation values (SpO2) with quotients of spectral values.

33. The apparatus as claimed in claim 1, wherein the processor is implemented to output a reliability measure of a physiological parameter determined.

34. The apparatus as claimed in claim 23, wherein the processor is implemented to determine the reliability measure from the singular values of a matrix composed of two spectra of two bright transmit channels, a spectrum of the bright transmit channel representing a column of the matrix.

35. The apparatus as claimed in claim 34, wherein the processor is to adapted to derive the reliability measure from the Frobenius norm of the matrix.

36. The apparatus as claimed in claim 33, wherein the processor is implemented to determine a variance of the difference between two bright transmit channels or their spectra and to derive the reliability measure therefrom.

37. The apparatus as claimed in claim 33, wherein the processor is implemented to determine a variance from the difference between bright transmit channels comprising reduced interference, or their spectra, and to derive a reliability measure therefrom.

38. A method of reducing an interference portion in a time-discrete signal further comprising a useful portion, the method comprising:

providing a time-discrete signal comprising the interference portion and the useful portion, comprising sampling an iterative optical signal which corresponds to bright periods during which a transmit light source adopts an on state;

providing a first time-discrete reference signal comprising a first frequency component of the interference portion;

providing a second time-discrete reference signal comprising a second frequency component of the interference portion, the first and second frequency components being shifted in phase, and providing the first and second reference signals comprising sampling optical signals which correspond to dark periods during which no transmit light source adopts an on state;

subtracting the two reference signals and providing a differential signal comprising a third frequency component caused by the first and second frequency components; and

manipulating the time-discrete signal on the basis of the differential signal such that in a manipulated time-discrete signal the interference portion is reduced.