Method of analyzing and processing signals

• US 9,192,336 B2
• Filed: 08/20/2012
• Issued: 11/24/2015
• Est. Priority Date: 02/27/2003
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James Nicholas
• Primary Examiner(s): D'ANGELO, MICHAEL J
• Application Number:
  US13/590,105
• Publication Number:
  US 20130046156A1
• Time in Patent Office: 1,191 Days
• Field of Search: 600/323, 600/309, 600/310, 600/324, 600/481, 600/502, 600/529, 600/534
• US Class Current: 1/1
• CPC Class Codes: A61B 2503/06 Children, e.g. for attention deficit diagnosis
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0082 adapted for particular medical purposes
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/6896 Toys
• 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 5/726 using Wavelet 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 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence

Abstract

A physiological measurement system is disclosed which can take a pulse oximetry signal such as a photoplethysmogram from a patient and then analyze the signal to measure physiological parameters including respiration, pulse, oxygen saturation and movement. The system comprises a pulse oximeter which includes a light emitting device and a photodetector attachable to a subject to obtain a pulse oximetry signal; analog to digital converter means arranged to convert said pulse oximetry signal into a digital pulse oximetry signal; signal processing means suitable to receive said digital pulse oximetry signal and arranged to decompose that signal by wavelet transform means; feature extraction means arranged to derive physiological information from the decomposed signal; an analyzer component arranged to collect information from the feature extraction means; and data output means arranged in communication with the analyzer component.

Claims

1. A monitoring system for determining physiological information, the system comprising:

a signal acquisition unit attachable to a subject to obtain a first pulse oximetry signal corresponding to a first wavelength of received light and a second pulse oximetry signal corresponding to a second wavelength of light from the subject; and

a signal processor configured to;

decompose the first pulse oximetry signal at least in part using a first wavelet transform analysis using a signal processor to obtain a first set of values;

decompose the second pulse oximetry signal at least in part using a second wavelet transform analysis using a signal processor to obtain a second set of values;

combine the first set of values with the second set of values to obtain a Lissajous plot;

determine the physiological information based at least in part using the Lissajous plot.

2. The system of claim 1, wherein the first wavelength of received light corresponds to red light and the second wavelength of received light corresponds to infrared light.

3. The system of claim 1, wherein the first set of values comprise real values and the second set of values comprise real values.

4. The system of claim 1, wherein the first set of values comprise imaginary values and the second set of values comprise imaginary values.

5. The system of claim 1, wherein the first set of values comprise real values and imaginary values and the second set of values comprise real and imaginary values, wherein the signal processor is configured to combine the first set of values with the second set of values to obtain a Lissajous plot by combining the real values of the first set of values with the real values of the second set of values to obtain a first Lissajous plot, wherein the signal processor is further configured to:

combine the imaginary values of the first set of values with the imaginary values of the second set of values to obtain a second Lissajous plot; and

determine the physiological information based at least in part using the first Lissajous plot and the second Lissajous plot.

6. The system of claim 1, wherein the determined physiological information is oxygen saturation.

7. The system of claim 1, wherein the first set of values comprise sets of values corresponding to a plurality of scales and the second set of values comprise sets of values corresponding to the plurality of scales and wherein the signal processor is configured to:

combine the first set of values with the second set of values to obtain a Lissajous plot by combining, for each scale, the corresponding set of values of the first set of values with the corresponding set of values of the second set of values to obtain a plurality of Lissajous plots; and

determine the physiological information based at least in part using the Lissajous plot by determining the physiological information based at least in part using the plurality of Lissajous plots.

8. The system of claim 7, wherein the signal processor is configured to determine the physiological information by:

choosing one of the plurality of Lissajous plots based on a measure of spread;

determining a slope of the chosen Lissajous plot; and

determining the oxygen saturation value based on the slope.

9. The system of claim 8, wherein the signal processor is configured to choose one of the plurality of Lissajous plots by choosing the Lissajous plot having a maximum amount of spread based on a standard deviation.

10. The system of claim 8, wherein the signal processor is configured to choose one of the plurality of Lissajous plots by choosing the Lissajous plot having the lowest ratio of a standard deviation of spread along its major axis to a standard deviation of spread along its minor axis.