Pulse oximeter with improved accuracy and response time

• US 5,398,680 A
• Filed: 07/08/1992
• Issued: 03/21/1995
• Est. Priority Date: 11/01/1989
• Status: Expired due to Term

• Current Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Original Assignee: Gregory L. Morris, Michael J.R. Polson
• Inventors: Morris, Gregory L., Polson, Michael J. R.
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US07/910,786
• Time in Patent Office: 986 Days
• Field of Search: 128/633, 128/664-667, 128/687, 356/41, 356/39-40
• US Class Current: 600/323
• 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 5/7214 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 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: G01N 2021/3159 Special features of multiplexing circuits
• CPC Class Codes: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 2201/1244 Ambient light detector, e.g. for invalidating

Abstract

An improved pulse oximeter for the measurement of oxygen saturation in the blood, which is faster and more accurate than conventional pulse oximeters.

Improved speed and accuracy is attained by elimination of normalization and feedback circuitry and the use of analog to digital converting devices having a wide dynamic range along with a sophisticated computer analysis. The instant invention eliminates inaccuricies resulting from channel matching errors, and detects and eliminates aberrant input data.

Claims

1. A pulse oximeter for measuring and displaying average oxygen saturation levels present in pulsating blood flow in a living person, comprising:

light directing means for directing light having a first wavelength and light having a second wavelength, towards a tissue sample carrying a pulsating blood flow;

light detection means for detecting the light of said first and second wavelengths, after passage through said tissue sample, and for generating, in response thereto, a first analog electrical signal related to said first wavelength, and a second analog electrical signal related to said second wavelength;

signal conversion means for converting said first and second analog electrical signals, into first and second digital signals, respectively;

computer processing means for processing said first and second digital signals so as to compute, for each pulsation in said pulsating blood flow, (i) an oxygen saturation level data element, and (ii) an associated data element containing pulse time interval data and/or artefact data;

storage means for storing said oxygen saturation level data elements and said associated data elements computed over a predetermined period of time;

data element validation means for selectively validating certain of said oxygen saturation level data elements using said associated data elements, so as to produce validated oxygen saturation level data elements for use in computing average oxygen saturation levels for visual display; and

data element averaging means for averaging a selected number of said validated oxygen saturation level data elements so as to produce data representative of an average oxygen saturation level; and

display means for visually displaying said average oxygen saturation levels for use in monitoring said living person.

2. The pulse oximeter of claim 1, wherein said data storage means comprises a data storage queue, into which each said oxygen saturation level data element is continuously provided as input, temporarily stored, and periodically advanced so as to output said oxygen saturation level data elements.

3. The pulse oximeter of claim 2, wherein said data element validation means comprises

data element analyzing means for analyzing oxygen saturation level data elements stored in said data storage queue and based on said analysis, assigning a statistical confidence measure to each analyzed oxygen saturation level data element.

4. The pulse oximeter of claim 3, wherein said data element analyzing means uses said statistical confidence measures in order to identify and mark those analyzed oxygen saturation level data elements having one or more predefined undesired data qualities.

5. The pulse oximeter of claim 4, wherein said data element averaging means selects for averaging, oxygen saturation level data elements not marked as having one or more of said undesired data qualities.