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

• US 20060080047A1
• Filed: 11/28/2005
• Published: 04/13/2006
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Mohamed K. Diab
• Inventors: Diab, Mohamed K.
• Granted Patent: US 7,440,787 B2
• Time in Patent Office: Days
• US Class Current: 702/32
• 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 attenuated by body tissue, the output signal being usable to obtain values for one or more physiological parameters of the body tissue; and

a processor configured to transform the output signal or a signal processed from the output signal, and under at least certain conditions to determine point-by-point values for the physiological parameters of the body tissue.

2. The oximeter system of claim 1, wherein the output signal includes a first signal indicative of attenuation of a first wavelength of the light by the body tissue and a second signal indicative of attenuation of a second wavelength of light by the body tissue, and wherein the processor is configured to transform the first and second signals, or signals derived from the first and second signals, into complex signals, is configured to calculate complex ratios of the first and second signals, and is configured to determine from said complex ratios the point-by-point values of said physiological parameters.

3. The oximeter system of claim 1, further comprising a phase filter configured to pass ones of said point-by-point values of said 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 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 the complex domain based on the 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 complex numbers.