Signal processing apparatus

• US 8,948,834 B2
• Filed: 03/02/2005
• Issued: 02/03/2015
• Est. Priority Date: 03/07/1991
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel, Weber, Walter M.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US11/070,081
• Publication Number:
  US 20050209517A1
• Time in Patent Office: 3,625 Days
• Field of Search: 600/309, 600/310, 600/330, 600/322, 600/323, 600/324, 600/325, 600/326, 600/481, 600/500, 600/501, 600/502
• 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 for measuring a physiological parameter, comprising:

measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said plurality of signals corresponds to sensed optical energies from a plurality of wavelengths.

2. The method of claim 1 wherein said physiological parameter is a function of an oxygen saturation.

3. The method of claim 1 wherein said interference component comprises signal components caused by motion, respiratory artifact, ambient light, optical scattering and other interference between a tissue location being sensed and a sensor.

4. The method of claim 1 wherein said processing said plurality of signals further comprises decorrelating said plurality of signals by minimizing a cross-correlation of said plurality of signals, to obtain a plurality of decorrelated signals;

and

normalizing said plurality of decorrelated signals to obtain the plurality of principal components.

5. The method of claim 1 wherein said processing said plurality of signals comprises decorrelating said plurality of signals by singular-value decomposition of said plurality of signals, to obtain the plurality of principal components.

6. The method of claim 1 wherein said processing said plurality of signals comprises decorrelating said plurality of signals by multiplying said plurality of signals the inverse square root of the covariance matrix of said plurality of signals to obtain the plurality of principal components.

7. The method of claim 1 further comprising obtaining a ratio of mixing coefficients from said matrix of mixing coefficients, wherein said ratio corresponds to a ratio of modulation ratios of red to infrared signals, wherein said plurality of signals comprise modulated optical signals in the red and infrared ranges.

8. The method of claim 7 further comprising extracting a second measure of said physiological parameter from said ratio, wherein said second measure of said physiological parameter corresponds to an oxygen saturation.

9. The method of claim 1 further comprising extracting said interference component from another one of said plurality of independent components.

10. A method for measuring a physiological parameter, comprising:

measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said physiological parameter is a function of a pulse rate.

11. A method for measuring a physiological parameter, comprising:

measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said plurality of signals corresponds to sensed optical energies from a plurality of wavelengths from different times.

12. A method for measuring a physiological parameter, comprising:

measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said first measure of a physiological parameter corresponds to a pulse rate.

13. A pulse oximeter, comprising:

a sensor configured for measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

a computer useable medium having computer readable code embodied therein for measuring a physiological parameter, said computer readable code configured to execute functions comprising;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said physiological parameter is a pulse rate.

14. A pulse oximeter, comprising:

a sensor configured for measuring a plurality of signals, wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

a computer useable medium having computer readable code embodied therein for measuring a physiological parameter, said computer readable code configured to execute functions comprising;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said plurality of signals corresponds to sensed optical energies from a plurality of wavelengths.

15. The pulse oximeter of claim 14 wherein said physiological parameter is an oxygen saturation.

16. The pulse oximeter of claim 14 wherein said interference component comprises signal components caused by motion, respiratory artifact, ambient light, optical scattering and other interference between a tissue location being sensed and a sensor.

17. The pulse oximeter of claim 14 wherein said processing said plurality of signals comprises decorrelating said plurality of signals by minimizing a cross-correlation of said plurality of signals, to obtain a plurality of decorrelated signals;

and

normalizing said plurality of decorrelated signals to obtain the plurality of principal components.

18. The pulse oximeter of claim 14 wherein said processing said plurality of signals comprises decorrelating said plurality of signals by singular-value decomposition of said plurality of signals, to obtain the plurality of principal components.

19. The pulse oximeter of claim 14 wherein said processing said plurality of signals comprises decorrelating said plurality of signals by multiplying said plurality of signals by the inverse square root of the covariance matrix of said plurality of signals to obtain the plurality of principal components.

20. The pulse oximeter of claim 14 wherein said processing said plurality of principal components comprises successive rotations to minimize estimated mutual information among outputs of the invention.

21. The pulse oximeter of claim 14 further comprising obtaining a ratio of mixing coefficients from said matrix of mixing coefficients, wherein said ratio corresponds to a ratio of modulation ratios of red to infrared signals.

22. The pulse oximeter of claim 21 further comprising extracting a second measure of said physiological parameter from said ratio, wherein said second measure of said physiological parameter corresponds to an oxygen saturation.

23. The pulse oximeter of claim 14 wherein said first measure of a physiological parameter corresponds a pulse rate.

24. The pulse oximeter of claim 14 further comprising extracting said interference component from another one of said plurality of independent components.

25. A pulse oximeter, comprising:

a sensor configured for measuring a plurality of signals;

wherein each of said signals comprises a source component corresponding to said physiological parameter and an interference component;

a computer useable medium having computer readable code embodied therein for measuring a physiological parameter, said computer readable code configured to execute functions comprising;

processing said plurality of signals to obtain a plurality of principal components;

processing said plurality of principal components to obtain a plurality of independent components, wherein a matrix of said plurality of signals corresponds to a matrix product of a matrix of said plurality of independent components and a matrix of mixing coefficients; and

extracting a first measure of said physiological parameter corresponding to said source component from one of said plurality of independent components, wherein said plurality of signals corresponds to sensed optical energies from a plurality of wavelengths from different times.