Systems and methods for determining blood oxygen saturation values using complex number encoding

• US 7,440,787 B2
• Filed: 11/28/2005
• Issued: 10/21/2008
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Laboratories, Inc. (Masimo Corporation)
• Inventors: Diab, Mohamed K.
• Primary Examiner(s): Winakur; Eric F
• Assistant Examiner(s): Berhanu; Etsub D
• Application Number:
  US11/288,812
• Publication Number:
  US 20060080047A1
• Time in Patent Office: 1,058 Days
• Field of Search: 600/322, 600/323, 600/324
• US Class Current: 600/323
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• 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 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: A61B 5/743 Displaying an image simultaneously with additional graphical information, e.g. symbols, charts, function plots

Abstract

The disclosure includes pulse oximetry systems and methods for determining point-by-point saturation values by encoding photoplethysmographs in the complex domain and processing the complex signals. The systems filter motion artifacts and other noise using a variety of techniques, including statistical analysis such as correlation, or phase filtering.

Claims

1. An oximeter system comprising:

a noninvasive optical sensor including a detector capable of outputting an output signal indicative of light of at least two wavelengths attenuated by body tissue; and

a processor configured to transform processed signals, each transformed signal responsive to said output signal while remaining in the time domain, said processor also configured to determine point-by-point ratios of values of a first transformed signal responsive to attenuation of a first one of said at least two wavelengths of light to values of a second transformed signal responsive to attenuation of a second one of said at least two wavelengths of light, said ratio taken without concern for zero crossing, and to determine values responsive to said ratios for the physiological parameters of the body tissue.

2. The oximeter system of claim 1, wherein the transformed is configured to transform the first and second processed signals into complex signals, is configured to calculate said point-by-point ratios, each ratio comprising a complex ratio of the values of the first and second processed signals, and is configured to determine from said complex ratios the values of said physiological parameters.

3. The oximeter system of claim 2, further comprising a phase filter configured to pass ones of said point-by-point complex ratios that correspond to a predetermined range of phases.

4. The oximeter system of claim 1, wherein the transform comprises a Hilbert Transform.

5. A method of determining values of physiological parameters from an output signal of a noninvasive optical sensor, the method comprising:

receiving first and second intensity signals from a detector capable of detecting light attenuated by tissue of a patient;

when appropriate, processing said first and second intensity signals in a complex time domain; and

using results of said processing to determine values of one or more physiological parameters of the tissue of the patient.

6. The method of claim 5, further comprising filtering the first and second intensity signals in a complex time domain based on a measurement of confidence.

7. The method of claim 6, wherein the measurement of confidence comprises a correlation value.

8. The method of claim 6 wherein the measurement of confidence comprises one or more values of an associated phase.

9. The method of claim 8, further comprising applying statistical analysis to the results of said processing to determine said values.

10. A method of processing input signals indicative of physiological parameters to determine measurements for said physiological parameters, the method comprising:

receiving a sensor signal from an optical sensor, said sensor signal indicative of a physiological parameter of a patient;

demodulating said sensor signal into first and second intensity signals, each or said first and second intensity signals responsive to attenuation by body tissue of a patient of a different wavelength of said light;

transforming said first and second intensity signals while remaining in the time domain;

calculating a point-by-point ratio of a value of said time domain transformed first intensity signal and a value of said time domain transformed second intensity signal, each point-by-point ratio corresponding to a sampling point; and

determining a measurement for said physiological parameter.

11. The method of claim 10, wherein said determining said measurement comprises:

determining a confidence measure in said first and second intensity signals;

when said confidence measure is high, said determining said measurement comprises determining an output value of said measurement for said point-by-point ratio; and

when said confidence is not high, said determining said measurement comprises one or more of filtering, discarding, or correcting said output value of said measurement for said point-by-point ratio.

12. The method of claim 11, wherein said determining said confidence measure comprises determining a correlation.

13. The method of claim 12, wherein said determining said correlation comprises determining a complex correlation.

14. The method of claim 10, wherein said transforming comprises Hubert transforming.

15. The method of claim 10, wherein said ratio comprises a complex ratio.

18. The method of claim 11, wherein said means for determining said confidence measure comprises means for determining a correlation.

19. The method of claim 12, wherein said means for determining said correlation comprises means for determining a complex correlation.

20. The method of claim 10, wherein said ratio comprises a complex ratio.

16. A patient monitor that processes input signals indicative of physiological parameters to determine measurements for said physiological parameters, the method comprising:

means for receiving a sensor signal from an optical sensor, said sensor signal indicative a physiological parameter of a patient;

means for demodulating said sensor signal into first and second intensity signals, each or said first and second intensity signals responsive to attenuation by body tissue of a patient of a different wavelength of said light;

means for transforming said first and second intensity signals while remaining in the time domain;

means for calculating a point-by-point ratio of a value of said time domain transformed first intensity signal and a value of said time domain transformed second intensity signal, each point-by-point ratio corresponding to a sampling point; and

means for determining a measurement for said physiological parameter.

17. The patient monitor of claim 16, wherein said means for determining said measurement comprises:

means for determining a confidence measure in said first and second intensity signals;

when said confidence measure is high, said means for determining said measurement comprises means for determining an output value of said measurement for said point-by-point ratio; and

when said confidence is not high, said means for determining said measurement comprises one or more of means for filtering, means for discarding, or means for correcting said output value of said measurement for said point-by-point ratio.