Signal processing apparatus

• US 7,328,053 B1
• Filed: 11/17/1998
• Issued: 02/05/2008
• Est. Priority Date: 10/06/1993
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Elfadel, Ibrahim M., Weber, Walter M., Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel, Smith, Robert A., McCarthy, Rex J.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US09/195,791
• Time in Patent Office: 3,367 Days
• Field of Search: 600/310, 600/322, 600/323, 600/330, 600/336, 600/473, 600/476, 356/41
• US Class Current: 600/336
• 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 system for the enhancement of physiological signals for the measurement of blood oxygen in a subject,

the system comprising:

first and second light sources to direct light toward the subject, said first and second light sources producing light of first and second wavelengths, respectively;

a light detector positioned to detect said first and second light signals after interaction with the subject and to generate first and second signals indicative of an intensity of said first and second detected light signals, respectively, said first generated signal having a first portion arising from light transmitted from said first source and a second portion arising from a first interference source, said second generated signal having a first portion arising from light transmitted from said second source and a second portion arising from a second interference source;

a packet generator to generate a plurality of data packets derived from data comprising said first and second generated signals;

wherein said first and second portions of said first and second generated signals and a ratio of said first portion of said first generated signal to said first portion of said second generated signal have a mathematical relationship; and

a calculator using said mathematical relationship to generate at least first and second functions from said plurality of data packets, said at least first and second functions having a final solution value indicative of said ratio.

2. The system of claim 1 wherein said ratio is indicative of blood oxygen saturation in the subject, the system further including a look-up table containing data relating said ratio to said blood oxygen saturation.

3. The system of claim 1 wherein at least one of said data packets comprises filtered data from at least one of said first and second generated signals.

4. The system of claim 1 wherein at least one of said data packets comprises a component of at least one of said first and second generated signals with the DC removed.

5. The system of claim 1 wherein at least one of said data packets is derived from a group of signals comprising said first generated signal, filtered data from said first generated signal, said second generated signal, filtered data from said second generated signal, and filtered data from a combination of said first and second generated signals.

6. The system of claim 1 wherein said mathematical relationship has the following form:

−

R₁(t_i)+(r_a+r_v)R₁₂(t_i)−

r_ar_vR₂(t_i)=0

where r_a is said ratio, i=1 to 2 for said first and second data packets, respectively, R₁(t_i) is the energy of said first generated signal in the i^th data packet, R₂(t_i) is the energy of said second generated signal in the i^th data packet, R₁₂(t_i) is the correlation between said first and second generated signals in the i^th data packet, and r_v represents a ratio variable of a portion of said first generated signal to a corresponding portion of said second generated signal.

7. The system of claim 6 wherein said calculator is configured to solve for a pair of values, r_a and r_v, by solving linear functions in x and y having the following form:

R₁₂(t₁)x−

R₂(t₁)y=R₁(t₁)

R₁₂(t₂)x−

R₂(t₂)y=R₁(t₂)

where x=r_a+r_v;

y=r_ar_v.

8. A method using a computer for the enhancement of physiological signals for the measurement of blood oxygen in a subject, the method comprising the steps of:

directing first and second light sources toward the subject, said first and second light sources producing light of first and second wavelength, respectively;

detecting first and second light signals after interaction with the subject and generating signals indicative of an intensity of said first and second detected light signals, said first generated signals having a first portion arising from light transmitted from said first source and a second portion arising from a first interference source, said second generated signal having a first portion arising from light transmitted from said second source and a second portion arising from a second interference source;

generating a plurality of data packets derived from data comprising said first and second generated signals, and

using a mathematical relationship of said first and second portions of said first and second generated signals and a ratio of said first portion of said first generated signal to said first portion of said second generated signal to generate at least first and second functions from said plurality of data packets, said at least first and second functions having a solution value indicative of said ratio.

9. The method of claim 8 wherein said ratio is indicative of blood oxygen saturation in the subject, the method further including the step of using a look-up table containing data relating said ratio to said blood oxygen saturation to determine the blood oxygen level in the subject.

10. The method of claim 8 wherein at least one of said plurality of data packets comprises filtered data from said first generated signal.

11. The method of claim 8 wherein is at least one of said plurality of data packets comprises a component of said first generated signal with the DC removed.

12. The method of claim 8 wherein at least one of said plurality of data packets is derived from a group of signals comprising said first generated signal, filtered data from said first generated signal, said second generated signal, filtered data from said second generated signal, a combination of said first and second generated signals, and filtered data from said combination of said first and second generated signals.