Signal processing apparatus

• US 20030036689A1
• Filed: 12/04/2001
• Published: 02/20/2003
• 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 6,650,917 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. In a signal processor that receives at least first and second intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, each intensity signal containing a primary signal portion and a noise portion, said first and second signals substantially adhering to a predefined signal model, a method comprising:

sampling said first and second intensity signals over a period of time;

performing a Fourier transform on the intensity signals; and

determining a least two oxygen saturation values from at least a plurality of magnitudes of the Fourier transformed intensity signals for non-zero frequencies;

determining oxygen saturation from at least one of said at least two values consistent with the predefined signal model.

2. A physiological monitor comprising:

a detector to provide intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, each intensity signal containing a primary signal portion and a secondary signal portion, said intensity signals adhering to a predefined signal model; and

a signal processor coupled to said detector, said signal processor receiving said intensity signals, Fourier transforming said signals, identifying a plurality of peaks of magnitudes from the Fourier transformed signals, and applying a plurality of rules to the peaks of magnitudes in order to determine an estimate for said oxygen saturation.

3. The physiological monitor of claim 2, wherein said signal processor comprises a neural network.

4. The physiological monitor of claim 2, wherein the plurality of rules comprises analysis of a phase from the fourier transformed signals.

5. The physiological monitor of claim 2, wherein the plurality of rules comprises applying a threshold operation to the peaks.

6. A method of determining oxygen saturation comprising:

detecting intensity signals resulting from light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood, each intensity signal containing a primary signal portion and a secondary signal portion;

transforming the intensity signals into the frequency domain such that the signals have a plurality of magnitude and frequency components;

identifying a plurality of peaks of magnitudes in the transformed signals; and

determining at least one of the peaks that represents oxygen saturation.

7. The physiological monitor of claim 31, wherein the transform is a Chirp-Z transform.

8. The physiological monitor of claim 31, wherein the transform is a Fourier transforms.