Signal processing apparatus

• US 8,560,034 B1
• Filed: 07/06/1998
• Issued: 10/15/2013
• Est. Priority Date: 10/06/1993
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel, Elfadel, Ibrahim M., McCarthy, Rex J., Weber, Walter M., Smith, Robert A.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US09/110,542
• Time in Patent Office: 5,580 Days
• Field of Search: 600/310, 600/322, 600/323, 600/330, 600/336, 600/473, 600/476, 356/41, 356/39
• 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 5/14551 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 5/7214 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 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• 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: G06F 2218/04 : Denoising

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 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 for measuring saturation of a blood constituent in a patient comprising the steps of:

irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;

sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals including motion components; and

determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that

i) an amount of motion is the same at the same time for each of said intensity signals, and

ii) the motion components of said intensity signals are proportional to one another.

2. A method for measuring saturation of a blood constituent in a patient comprising the steps of:

irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;

sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals including motion components; and

determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that

i) an amount of motion is the same at the same time for each of said intensity signals, and

ii) the motion components of said intensity signals are proportional to one another,

wherein the step of determining said saturation further comprises

representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion terms being proportional to one another for each of said intensity signals;

taking the logarithm of each representation of said first and second intensity signals;

removing signal portions outside a known band of interest to create first and second filtered signals;

equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;

equating the second filtered signal of the second intensity signal to r_as+r_vn, where r_a is a ratio indicative of saturation;

expressing said representations as a matrix;

using said matrix to determine r_a by assuming s and n are uncorrelated; and

determining said saturation from r_a.

3. The method of claim 2, further comprising the step of displaying said saturation on a monitor.

4. A method for measuring the saturation of a blood constituent in a patient comprising the steps of:

irradiating said patient with electromagnetic radiation of two discrete, different wavelengths;

sensing an intensity of said radiation for each of said wavelengths after it passes through a portion of said patient to produce first and second intensity signals;

representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion terms being proportional to one another for each of said intensity signals;

taking the logarithm of each representation of said first and second intensity signals;

removing signal portions outside a known band of interest to create first and second filtered signals;

equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;

equating the second filtered signal of the second intensity signal to r_as+r_vn, where r_a is a ratio indicative of saturation;

expressing said representations as a matrix;

using said matrix to determine r_a by assuming s and n are uncorrelated; and

determining said saturation from r_a.

5. An apparatus for measuring the saturation of a blood constituent in a patient comprising:

first and second emitters, said emitters emitting radiation of first and second different wavelengths;

a detector for sensing an intensity of said light, said detector being mounted relative to said first and second emitters so that said light is detected after it passes through a portion of said patient;

a controller for alternatively activating said emitters so that said detector detects the different wavelengths at different times to produce first and second intensity signals including motion components; and

control means for determining said saturation by mathematically manipulating said first and second intensity signals without subtracting said motion components and with the assumptions that

i) an amount of motion is the same at the same time for each of said intensity signals, and

ii) the motion components of said intensity signals are proportional to one another.

6. The apparatus of claim 5, further comprising a display, coupled to said control means, for displaying said saturation.

7. A pulse oximeter for measuring the saturation of a blood constituent in a patient comprising:

first and second emitters, said emitters emitting radiation of first and second different wavelengths;

a detector for sensing an intensity of said light, said detector being mounted relative to said first and second emitters so that said light is detected after it passes through a portion of said patient;

a controller for alternatively activating said emitters so that said detector detects the different wavelengths at different times to produce first and second intensity signals including motion components; and

control means for determining said saturation by mathematically manipulating said first and second intensity signals with the assumptions that

i) an amount of motion is the same at the same time for each of said intensity signals, and

ii) the motion components of said intensity signals are proportional to one another,

wherein said control means further comprises

means for representing each of said intensity signals as a function of concentration, the wavelength corresponding to the intensity signal, and a time-variable motion term corresponding to motion noise, said motion term being correlated for each of said intensity signals;

means for taking the logarithm of each representation of said first and second intensity signals;

means for removing signal portions outside a known band of interest to create first and second filtered signals;

means for equating the first filtered signal of the first intensity signal to s+n, where n is the portion of the signal due to motion and s is the portion of the signal not due to motion;

means for equating the second filtered signal of the second intensity signal to r_as+r_vn, where r is a ratio indicative of saturation;

means for expressing said representations as a matrix;

means for using said matrix to determine r_a by assuming s and n are uncorrelated; and

means for determining said saturation from r_a.