Signal processing apparatus

• US 20020128544A1
• Filed: 01/30/2002
• Published: 09/12/2002
• Est. Priority Date: 03/07/1991
• Status: Abandoned Application

• 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.
• Application Number:
  US10/062,859
• Publication Number:
  US 20020128544A1
• 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 method and apparatus for analyzing two measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, the present invention involves utilizing a transformation which evaluates a plurality of possible signal coefficients in order to find appropriate coefficients. Alternatively, the present invention involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to two measured signals. Use of this invention is described in particular detail with respect to blood oximetry measurements.

Claims

1. A method of determining blood oxygen saturation comprising:

sensing physiological signals resulting from the attenuation of light of at least first and second wavelengths by body tissue carrying pulsing blood;

determining at least two values corresponding to oxygen saturation based upon at least two alternative methods of using the physiological signals; and

determining a resulting value for oxygen saturation from the at least two values corresponding to oxygen saturation.

2. The method of claim 1, wherein the step of determining a resulting value comprises selecting from the at least two values at least one value that is a maximum among the at least two values.

3. The method of claim 1, wherein the step of determining a resulting value comprises averaging at least some of the at least two values.

4. The method of claim 1, wherein one of the alternative methods comprises at least one calculation in the frequency domain.

5. The method of claim 4, wherein the calculation in the frequency domain comprises performing a Fourier Transform on the physiological signals.

6. The method of claim 1, wherein at least one of the at least two alternative methods comprises a calculation based on a ratio of a normalized representation of the physiological signal resulting from the first wavelength to a normalized representation of the physiological signal resulting from the second wavelength.

7. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by a recursive polyphase bandpass filter.

8. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by an adaptive implementation of a recursive polyphase bandpass filter.

9. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by a bank of filters.

10. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by a sum of squares analysis.

11. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on a scan of possible saturation values.

12. The method of claim 11, wherein the calculation based on a scan of possible saturation values comprises a discrete saturation transform.

13. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on determining values for saturation that minimize the correlation between a signal portion and a noise portion of at least one of the physiological signals.

14. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by a Kalman filter.

15. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by a neural network.

16. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected with spectral estimation techniques.

17. The method of claim 6, wherein at least one of the at least two alternative methods comprises selecting at least one of the at least two values based on characteristics of the physiological signals indicative of the quality of the physiological signals.

18. The method of claim 6, wherein step of determining comprises averaging the resulting value over time, said averaging dependent upon characteristics of the physiological signals indicative of the quality of the physiological signal.

19. The method of claim 18, wherein the averaging is based on confidence in the quality of the physiological signals.

20. The method of claim 19, wherein the confidence is determined by analyzing whether there is significant motion noise present in the physiological signals.

21. The method of claim 6, wherein at least one of the at least two alternative methods comprises a calculation based on the physiological signals after they have been effected by an adaptive algorithm.

22. The method of claim 21, wherein at least one of the at least two alternative methods comprises a calculation based upon a scan of values potentially indicative of said physiological parameter.

24. The method of claim 23, wherein the step of determining comprises selecting at least one of the at least two values based on a determination of confidence in the accuracy of physiological signals.

25. The method of claim 23, wherein determining a resulting value comprises averaging the at least two values.

26. The method of claim 25, wherein said step of averaging comprises averaging over a time window, wherein said window is increased for potential of said physiological parameter having a lower confidence of accuracy and decreased for potential values of said physiological parameter having a higher confidence of accuracy.

23. A method of determining pulse rate comprising:

sensing physiological signals resulting from the attenuation of light of at least first and second wavelengths by body tissue carrying pulsing blood;

determining at least two values corresponding to pulse rate based upon at least two alternative methods of processing the physiological signals; and

determining a resulting value for pulse rate from the at least two values corresponding to pulse rate.