Signal processing apparatus and method

• US 20040204638A1
• Filed: 05/04/2004
• Published: 10/14/2004
• Est. Priority Date: 03/07/1991
• Status: Abandoned Application

• Current Assignee: Esmaiel Kiani-Azarbayjany, Mohamed Kheir Diab
• Original Assignee: Esmaiel Kiani-Azarbayjany, Mohamed Kheir Diab
• Inventors: Diab, Mohamed Kheir, Kiani-Azarbayjany, Esmaiel
• Application Number:
  US10/839,309
• Publication Number:
  US 20040204638A1
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• 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 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• 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

A signal processor which acquires a first signal, including a first desired signal portion and a first undesired signal portion, and a second signal, including a second desired signal portion and a second undesired signal portion, wherein the first and second desired signal portions are correlated. The signals may be acquired by propagating energy through a medium and measuring an attenuated signal after transmission or reflection. Alternatively, the signals may be acquired by measuring energy generated by the medium. A processor of the present invention generates a noise reference signal that is a combination of the undesired signal portions and is correlated to both the first and second undesired signal portions. The noise reference signal is then used to remove the undesired portion of each of the first and second measured signals. The processor of the present invention may be employed in physiological monitors wherein the known properties of energy attenuation through a medium are used to determine physiological characteristics of the medium. Many physiological conditions, such as the pulse of a patient or the concentration of a constituent in a medium, can be determined from the desired portion of the signal after undesired signal portions, such as those caused by erratic motion, are removed.

Claims

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

receiving a plurality of intensity signals from 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

calculating a representative value of blood oxygen saturation based on an assumption that oxygen saturation of pulsing blood remains relatively constant over a predetermined portion of the period of time.

2. The method of claim 1, wherein the plurality of intensity signals include motion induced noise.

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

receiving a plurality of intensity signals from 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

calculating a representative value of blood oxygen saturation based on an assumption that oxygen saturation of pulsing blood changes relatively slowly.

4. The method of claim 3, wherein the calculating comprises use of a self-optimizing filter language.

5. The method of claim 3, wherein the plurality of intensity signals include motion induced noise.

6. A method of determining blood oxygen saturation comprising:

receiving first and second intensity signals from light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood; and

calculating oxygen saturation based upon 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.

7. 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 based on assumptions corresponding to an amount of change in the oxygen saturation of pulsing blood over a predetermined portion of the period of time.

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

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

10. The patient monitoring device of claim 7, wherein the plurality of intensity signals include motion induced noise.

11. The patient monitoring device of claim 7, wherein the signal processing system further performs calculations using a self-optimizing filter language.