Signal processing apparatus

• US 20020077536A1
• Filed: 12/03/2001
• Published: 06/20/2002
• 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 6,745,060 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 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 calculating oxygen saturation from intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, comprising:

sampling the intensity signals over time;

performing a fourier transform on the intensity signals; and

determining oxygen saturation from at least a plurality of magnitudes of the fourier transformed intensity signals for non-zero frequencies.

2. The method of claim 1, wherein the step of determining comprises generating a ratio of the fourier transformed intensity signals and selecting at least one peak of ratios.

3. The method of claim 2, wherein the selected at least one peak corresponds to the highest oxygen saturation value.

4. The method of claim 3, further comprising the step of determining pulse rate from the frequency of the selected at least one peak.

5. The method of claim 2, wherein selecting at least one peak comprises evaluating the cross correlation between the intensity signals from the first wavelength and the second wavelength.

6. The method of claim 1, wherein the step of determining comprises averaging the oxygen saturation over time.

7. The method of claim 6, wherein the step of averaging comprises altering the averaging depending upon the level of motion noise in the intensity signals.

8. The method of claim 1, wherein the step of determining comprises selecting and averaging a plurality of peaks of ratios of the fourier transformed intensity signals.

14. The pulse oximeter of claim 1, wherein the processor averages oxygen saturation over time.

9. A pulse oximeter comprising:

a detector that generates intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood; and

a processor that executes a fourier transform on the intensity signals, and determines oxygen saturation from at least a plurality of magnitudes of the fourier transformed intensity signals for non-zero frequencies.

10. The pulse oximeter of claim 9, wherein the processor determines oxygen saturation by selecting at least one peak of ratios of the fourier transformed intensity signals.

11. The pulse oximeter of claim 10, wherein the selected at least one peak corresponds to a peak having the highest oxygen saturation value.

12. The pulse oximeter of claim 11, wherein the processor further determines pulse rate from the frequency of the selected at least one peak.

13. The pulse oximeter of claim 10, wherein the processor selects at least one peak by evaluating the cross correlation between the intensity signals from the first wavelength and the second wavelength.

15. The pulse oximeter of claim 14, wherein the processor varies its averaging depending upon the level of motion noise in the intensity signals.

16. The pulse oximeter of claim 9, wherein the processor determines oxygen saturation by selecting and averaging a plurality of peaks of ratios of the fourier transformed intensity signals.

18. The pulse oximeter of claim 17, wherein saturation is determined by selecting at least one peak of ratios of the fourier transformed intensity signals.

19. The pulse oximeter of claim 18, wherein the selected at least one peak corresponds to a peak having the highest oxygen saturation value.

20. The pulse oximeter of claim 19, wherein the frequency of the selected at least one peak provides an indication of pulse rate.

21. The pulse oximeter of claim 18, the at least one peak is selected by evaluating a cross correlation between the intensity signals from the first wavelength and the second wavelength.

22. The pulse oximeter of claim 17, wherein the oxygen saturation is averaged over time.

23. The pulse oximeter of claim 22, wherein the averaging is varied depending upon the level of motion noise in the intensity signals.

24. The pulse oximeter of claim 17, wherein the oxygen saturation is determined by selecting and averaging a plurality of peaks of ratios of the fourier transformed intensity signals.

17. A pulse oximeter wherein intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood are fourier transformed, and once transformed, a plurality of magnitudes of the fourier transformed intensity signals for non-zero frequencies are used to determine oxygen saturation.