Method for digitally processing signals containing information regarding arterial blood flow

• US 5,299,120 A
• Filed: 09/15/1989
• Issued: 03/29/1994
• Est. Priority Date: 09/15/1989
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Kaestle, Siegfried
• Primary Examiner(s): Hayes, Gail O.
• Application Number:
  US07/408,001
• Time in Patent Office: 1,656 Days
• Field of Search: 364/413.09, 364/413.03, 356/41, 128/664, 128/633, 128/666
• US Class Current: 600/310
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method for digitally processing signals containing information regarding arterial blood flow in a living body is disclosed enabling a more accurate determination of the oxygen saturation. The method comprises the steps of identifying a first edge based on a first derivation of the signal, disregarding same if it does not fulfill certain criteria, determining a window based on said identified first edge, identifying the second edge falling within said window, disregarding same if it does not fulfill certain criteria, and replacing the second edge by the first before repeated these steps.

Claims

1. Apparatus for processing a signal of varying amplitude so as to detect systolic edges comprising:

first means for determining if edges in the signal have a MAX1 and MIN1;

second means for determining the maximum absolute value DMIN of the first derivative of edges having MAX1 and MIN1;

third means for determining the time tMIN1 between MAX1 and MIN1;

fourth means for determining the time tDMIN1 between MAX1 and the occurrence of DMIN;

means for accepting an edge as a first edge if MAX1-MIN1>

a given value and for determining the MAX1 and MIN1 of a subsequent edge if MAX1-MIN1 is not >

said given value;

means for defining the following upper and lower values of windows, ##EQU4## means for determining if a second edge has been subjected to the operation of the first through the fourth means so as to derive MAX2, MIN2, tMIN2 and tDMIN2;

means for determining if the second edge has values within said windows; and

means for storing the values MAX2 and MIN2 if the second edge has values within said windows.

2. Apparatus for processing a signal for arterial blood flow so as to identify systolic edges more reliably comprising:

means for identifying a portion of said signal as a first systolic edge when it meets given criteria;

means for determining the maximum value of the first derivative of the portion of the signal in said first systolic edge;

means for determining the time of occurrence of the maximum value of said first derivative relative to one end of said first systolic edge;

means responsive to said time of occurrence for deriving a range of times of occurrence for the maximum value of the first derivative;

means for providing an indication when a later portion of said signal meets given criteria for a potential second systolic edge;

means for determining the maximum value of the first derivative in the signal in said potential second systolic edge;

means for determining the time of occurrence of said latter maximum value of the first derivative relative to one end of said potential second systolic edge; and

means for providing further indication that the potential second systolic edge is a true systolic edge if the time of occurrence of the maximum value of its first derivative falls within said range.

3. A method for processing a signal corresponding to arterial blood flow so as to identify systolic edges more reliably comprising:

identifying a portion of the signal as a potential first systolic edge when it meets certain criteria;

deriving the first derivative of the portion of the signal in said first systolic edge;

determining the maximum value of said first derivative;

determining the time of occurrence of said maximum value of said first derivative with respect to one end of said first systolic edge;

deriving a range of times of occurrence of a maximum value of a first derivative in response to at least the time of occurrence of the maximum value of the first derivative in said first systolic edge;

providing an indication when a later portion of said signal meets given criteria for a potential second systolic edge; and

providing further indication that the second systolic edge is a true systolic edge when the time of occurrence of the maximum value of its first derivative with respect to an end thereof falls within said range.