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

• US 8,948,835 B2
• Filed: 05/17/2013
• Issued: 02/03/2015
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Cercacor Laboratories
• Inventors: Diab, Mohamed K.
• Primary Examiner(s): Winakur, Eric
• Application Number:
  US13/896,731
• Publication Number:
  US 20130324817A1
• Time in Patent Office: 627 Days
• Field of Search: 600/310, 600/322, 600/323, 600/336
• US Class Current: 600/336
• 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. A physiological monitoring system that computes arterial oxygen saturation in tissue material, the physiological monitoring system comprising:

a light emitter which emits light of at least first and second wavelengths;

a light detector responsive to light from said light emitter attenuated by body tissue, said light detector providing an output signal indicative of at least first and second intensity signals associated with said at least first and second wavelengths; and

a signal processor responsive to the first and second intensity signals to encode said first and second intensity signals in a complex time domain, to calculate arterial oxygen saturation from complex ratios of said encoded signals, and to output said arterial oxygen saturation for caregiver review.

2. The physiological monitoring system of claim 1, wherein said processor determines point-by-point ratios from said encoded signals without concern for zero crossing in said ratios.

3. The physiological monitoring system of claim 2, wherein said processor phase filters said ratios to reduce an effect of noise.

4. The physiological monitoring system of claim 3, wherein said processor phase filters said ratios based on a measure of confidence.

5. The physiological monitoring system of claim 4, wherein said measure of confidence comprises a complex cross correlation between said encoded signals.

6. The physiological monitoring system of claim 4, wherein said measure of confidence comprises a measurement of phase.

7. The physiological monitoring system of claim 1, comprising a display displaying information indicative of said saturation.

8. A method of determining measurements of oxygen saturation of a monitored patient in a patient monitoring system, the method comprising:

receiving at the patient monitoring system from a noninvasive optical sensor an input signal indicative of detected light after attenuation by body tissue;

electronically demodulating, using a processor of the patient monitoring system, said input signal into at least first and second intensity signals corresponding to first and second wavelengths of said detected light;

electronically transforming said first and second intensity signals into a complex time domain;

electronically generating complex ratios of said transformed first and second intensity signals;

electronically determining oxygen saturation of said monitored patient from said complex ratios; and

outputting said oxygen saturation for caregiver review.

9. The method of claim 8, comprising determining a complex cross correlation and wherein said determining of said measurements uses said complex cross correlation.

10. The method of claim 8, comprising filtering using phase information to reduce an effect of noise.

11. A patient monitor comprising:

an input configured to receive sensor output signal from a noninvasive optical sensor, the sensor output signal responsive to attenuation of light of at least first and second wavelengths by a body tissue; and

a processor configured to;

receive said sensor output signal including a first intensity signal associated with the first wavelength and a second intensity signal associated with the second wavelength;

encode said first and second intensity signals into a complex domain; and

calculate oxygen saturation from a complex ratio said encoded first and second intensity signals.

12. The patient monitor of claim 11, wherein the processor is further configured to:

determine point-by-point ratios from said encoded first and second intensity signals without concern for zero crossing in said ratios.

13. The patient monitor of claim 12, wherein the processor is further configured to phase filter said ratios to reduce an effect on noise.

14. The patient monitor of claim 12, wherein the processor is further configured to phase filter said ratios based on a measure of confidence.

15. The patient monitor of claim 14, wherein said measure of confidence comprises a complex cross correlation between said encoded signals.

16. The patient monitor of claim 14, wherein said measure of confidence comprises a measurement of phase.

17. The patient monitor of claim 11, further comprising a display configured to display information indicative of said physiological parameter.

18. The patient monitor of claim 11, wherein encoding said first and second intensity signals into a complex domain comprises encoding said first and second intensity signals into a complex time domain.

19. The patient monitor of claim 11, wherein encoding said first and second intensity signals into a complex domain comprises encoding said first and second intensity signals into a complex frequency domain.

20. The patient monitor of claim 11, wherein the physiological parameter comprises arterial oxygen saturation.