Signal processing apparatus

• US 7,454,240 B2
• Filed: 05/11/2006
• Issued: 11/18/2008
• Est. Priority Date: 03/07/1991
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Elfadel, Ibrahim M., Weber, Walter M., Diab, Mohamed K., Smith, Robert A., McCarthy, Rex J., Kiani-Azarbayjany, Esmaiel
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US11/432,278
• Publication Number:
  US 20060217609A1
• Time in Patent Office: 922 Days
• Field of Search: 600/310, 600/322, 600/323, 600/330, 600/336
• 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 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 of determining blood oxygen saturation of pulsing blood, the method comprising:

receiving a plurality of intensity signals from a light-sensitive detector over a period of time, wherein the light-sensitive detector detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood, and wherein the plurality of intensity signals include motion induced noise; and

calculating a representative value of blood oxygen saturation by processing the plurality of intensity signals based on at least one equation incorporating an assumption that oxygen saturation of pulsing blood remains relatively constant over a predetermined portion of the period of time.

2. A method of determining blood oxygen saturation of pulsing blood, the method comprising:

receiving a plurality of intensity signals from a light-sensitive detector over a period of time, wherein the light-sensitive detector detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood, and wherein the plurality of intensity signals include motion induced noise; and

calculating a representative value of blood oxygen saturation by processing the plurality of intensity signals based on at least one equation incorporating an assumption that oxygen saturation of pulsing blood changes relatively slowly.

3. The method of claim 2, wherein the calculating comprises:

processing the plurality of intensity signals to produce processed signals responsive to the plurality of intensity signals;

monitoring the processed signals; and

adjusting the processing of the plurality of intensity signals to optimize at least one of the processed signals, wherein said at least one optimized processed signal is used in said calculation of said representative value of said saturation.

4. A method of determining blood oxygen saturation comprising:

receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood, wherein the first and second intensity signals include motion induced noise; and

calculating oxygen saturation by processing the first and second intensity signals based on at least one equation incorporating a principle that the oxygen saturation changes relatively slowly over short periods of time, wherein the calculation occurs during the presence of motion induced noise in the first and second intensity signals.

5. A patient monitoring device which determines an indication of oxygen saturation of pulsing blood, the patient monitoring device comprising:

a light sensitive detector which detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood and outputs a plurality of intensity signals over a period of time based on the detected light; and

a signal processing system which calculates a representative value of blood oxygen saturation by processing the plurality of intensity signals based on at least one equation incorporating assumptions corresponding to an amount of change in the oxygen saturation of pulsing blood over a predetermined portion of the period of time.

6. The patient monitoring device of claim 5, wherein the assumptions include an assumption that the oxygen saturation remains relatively constant over the predetermined portion.

7. The patient monitoring device of claim 5, wherein the assumptions include an assumption that the oxygen saturation remains changes relatively slowly over the predetermined portion.

8. The patient monitoring device of claim 5, wherein

the plurality of intensity signals include motion induced noise and wherein the signal processing system is programmed to be responsive to at least one of the plurality of intensity signals to calculate the representative value without significant interference in the calculation from the motion induced noise.

9. The patient monitoring device of claim 5, wherein the signal processing system is programmed to adjust itself to optimize signals responsive to the plurality of intensity signals, said signals used in the calculation of the representative value.

10. A method of determining blood oxygen saturation of pulsing blood, the method comprising:

receiving a plurality of intensity signals from a light-sensitive detector over a first period of time, wherein the light-sensitive detector detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood, and wherein the plurality of intensity signals include motion induced noise; and

reducing an impact of the intensity signals over the first period of time on a calculation of saturation by processing the plurality of intensity signals based on at least one equation incorporating an assumption that oxygen saturation of pulsing blood remains relatively constant over a predetermined portion of the first period of time.

11. The method of claim 10, comprising limiting the calculation when the saturation varies beyond a predetermined threshold, the predetermined threshold based, at least in part, on physiological limits of the body tissue.

12. A method of determining blood oxygen saturation of pulsing blood, the method comprising:

receiving a plurality of intensity signals from a light-sensitive detector over a period of time, wherein the light-sensitive detector detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood, and wherein the plurality of intensity signals include motion induced noise; and

calculating a first indication of blood oxygen saturation for a first portion of the period of time;

calculating a second indication of blood oxygen saturation for a second portion of the period of time; and

reducing an effect of the intensity signals during the second portion of the period of time on a final indication of oxygen saturation depending upon the amount of variation between the first indication and the second indication.

13. The method of claim 12, comprising clipping the final indication of oxygen saturation to a physiologically limited variation from the first indication, when the second indication varies beyond a predetermined threshold.