Signal processing apparatus

• US 20040068164A1
• Filed: 09/30/2003
• Published: 04/08/2004
• Est. Priority Date: 03/07/1991
• Status: Active Grant

• Current Assignee: Esmaiel Kiani-Azarbayjany, Ibrahim M. Elfadel, Mohamed K. Diab, Rex J. Mccarthy, Robert A. Smith, Walter M. Weber
• Original Assignee: Esmaiel Kiani-Azarbayjany, Ibrahim M. Elfadel, Mohamed K. Diab, Rex J. Mccarthy, Robert A. Smith, Walter M. Weber
• Inventors: Elfadel, Ibrahim M., Weber, Walter M., Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel, Smith, Robert A., McCarthy, Rex J.
• Granted Patent: US 7,496,393 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02154 by optical transmission
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 6/00 : Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment instruments measuring radiation intensity for application in the field of nuclear medicine, e.g. in vivo counting, G01T1/161; apparatus for taking X-ray photographs G03B42/02
• CPC Class Codes: A61B 8/00 : Diagnosis using ultrasonic, sonic or infrasonic waves imaging of objects using sonar G01S15/00
• CPC Class Codes: A61B 8/5276 : due to motion
• CPC Class Codes: G01N 2021/3144 : for oxymetry
• CPC Class Codes: G06F 2218/04 : Denoising
• CPC Class Codes: H04B 1/123 : using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

The present invention involves a method and an apparatus for analyzing measured signals, including the determination of a measurement of correlation in the measured signals during a calculation of a physiological parameter of a monitored patient. Use of this invention is described in particular detail with respect to blood oximetry measurements.

Claims

1. A method of determining whether a signal is reliable enough for use in a determination of a physiological characteristic of pulsing blood, the m 2. The method of claim 1, further comprising indicating when the indication of correlation is below a threshold.

3. The method of claim 2, wherein the threshold comprises about 0.75.

4. The method of claim 2, wherein the indicating comprises disqualifying the at least two intensity signals.

5. The method of claim 2, wherein the indicating comprises generating an indication that the light-sensitive detector is defective.

6. The method of claim 2, wherein the indicating comprises generating an indication that the light-sensitive detector is malfunctioning.

7. The method of claim 2, wherein the indicating comprises generating an indication that the at least two intensity signals do not satisfy an expected signal model.

8. The method of claim 2, wherein the indicating comprises generating an audio warning.

9. The method of claim 2, wherein the indicating comprises generating a visual warning.

10. The method of claim 2, wherein at least some of the plurality of intensity signals include motion induced noise.

11. The method of claim 10, further comprising indicating when the indication of correlation is below a threshold.

12. The method of claim 11, wherein the threshold comprises about 0.75.

13. The method of claim 11, wherein the indicating comprises disqualifying the at least two intensity signals.

14. The method of claim 11, wherein the indicating comprises at least one of generating an indication that the light-sensitive detector is defective and generating an indication that the light-sensitive detector is malfunctioning.

15. The method of claim 11, wherein the indicating comprises at least one of generating an indication that the at least two intensity signals do not satisfy an expected signal model, generating an audio warning, and generating a visual warning.

16. In a system that calculates a physiological characteristic, a method of determining a measure of confidence that one or more intensity signals will result in an accurate determination of a physiological characteristic of pulsing blood, the method comprising:

receiving a plurality of intensity signals from light-sensitive detector which detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood;

determining an indication of correlation between at least two of the plurality of intensity signals; and

based on the indication of correlation, conducting an evaluation of whether one or more intensity signals will result in an accurate determination of a physiological characteristic.

17. The method of claim 16, further comprising:

providing at least first and second calculation techniques, wherein each calculation technique is capable of generating at least one value representative of the physiological characteristic; and

based on the evaluation, utilizing at least one of the first and second calculation techniques to determine a resulting value indicative of the physiological characteristic.

18. The method of claim 16, wherein the determining an indication of correlation further comprises determining a plurality of indications of correlation.

19. The method of claim 16, further comprising determining a malfunction of the system based on the evaluation.

20. The method of claim 19, wherein the malfunction corresponds to the light-sensitive detector.

21. The method of claim 16, further comprising determining the system is malfunctioning based on the evaluation.

22. The method of claim 16, further comprising determining whether one of the plurality of intensity signals satisfies a signal model based on the evaluation.

23. The method of claim 16, further comprising indicating when the indication of correlation is below a threshold.

24. The method of claim 23, wherein the threshold comprises about 0.75.

25. The method of claim 16, wherein at least some of the plurality of intensity signals include motion induced noise.

26. A method of determining oxygen saturation of pulsing blood, the method comprising:

receiving a plurality of signals from a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood;

determining representative values of oxygen saturation based on the plurality of intensity signals; and

averaging the representative values over time to determine a resulting value of the oxygen saturation of the pulsing blood, wherein the averaging is varied depending upon a level of motion noise in at least one of the plurality of intensity signals.

27. A patient monitor capable of determining one or more physiological characteristics of pulsing blood using intensity signals from an optical probe, the patient monitor comprising:

at least one conductive element which receives a plurality of intensity signals from light-sensitive detector which detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood; and

a processor which determines an indication of correlation between at least two of the plurality of intensity signals and, based on the indication of correlation, determines whether to include one or more of the plurality of intensity signals in a determination of a physiological characteristic of pulsing blood.

28. The patient monitor of claim 27, wherein the processor also indicates when the indication of correlation is below a threshold.

29. The patient monitor of claim 28, wherein the threshold comprises about 0.75.

30. The patient monitor of claim 28, wherein the processor disqualifies the at least two intensity signals when the indication of correlation is below the threshold.

31. The patient monitor of claim 28, wherein the processor generates an indication that the light-sensitive detector is defective when the indication of correlation is below the threshold.

32. The patient monitor of claim 28, wherein the processor generates an indication that the light-sensitive detector is malfunctioning when the indication of correlation is below the threshold.

33. The patient monitor of claim 28, wherein the processor generates an indication that the at least two intensity signals do not satisfy an expected signal model when the indication of correlation is below the threshold.

34. The patient monitor of claim 28, wherein the processor generates an audio warning when the indication of correlation is below the threshold.

35. The patient monitor of claim 28, wherein the processor generates a visual warning when the indication of correlation is below the threshold.

36. The patient monitor of claim 28, wherein at least some of the plurality of intensity signals include motion induced noise.

37. The patient monitor of claim 36, wherein the processor also indicates when the indication of correlation is below a threshold.

38. The patient monitor of claim 37, wherein the threshold comprises about 0.75.

39. The patient monitor of claim 37, wherein the processor disqualifies the at least two intensity signals when the indication of correlation is below the threshold.

40. The patient monitor of claim 37, wherein the processor generates at least one of an indication that the light-sensitive detector is defective and an indication that the light-sensitive detector is malfunctioning when the indication of correlation is below the threshold.

41. The patient monitor of claim 37, wherein the processor generates at least one of an indication that the at least two intensity signals do not satisfy an expected signal model, an audio warning, and a visual warning when the indication of correlation is below the threshold.