Composite signal implementation for acquiring oximetry signals

• US 5,094,239 A
• Filed: 10/05/1989
• Issued: 03/10/1992
• Est. Priority Date: 10/05/1989
• Status: Expired due to Term

• Current Assignee: Omron Healthcare Company Limited (Omron Corporation)
• Original Assignee: Colin Electronics Co., Ltd.
• Inventors: Jaeb, Jonathan P., Branstetter, Ronald L.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): PONTIUS, KEVIN LANE
• Application Number:
  US07/417,320
• Time in Patent Office: 887 Days
• Field of Search: 128/633, 128/664, 356/41
• US Class Current: 600/330
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

An oximeter system for measuring blood oxygen saturation using a noninvasive optical technique is disclosed. A patient'"'"'s arterial blood is illuminated with light at two different wavelengths and the intensity of the light which is transmitted through or reflected by said arterial blood is correlated with the blood oxygen saturation of the tissue. The system provides a manner in which filtering artifacts are avoided in the oximeter signal using a high resolution analog-to-digital converter of 14 bits or more, such that, it is unnecessary to separate the DC and pulsatile components of the oximeter signal prior to processing within the microprocessor.

Claims

1. A blood oxygen saturation monitoring system for non-invasive measurement of oxygen saturation in the blood of a subject comprising:

a first source of electromagnetic radiation at a first wavelength;

a second source of electromagnetic radiation at a second wavelength;

means for positioning said first and second sources of electromagnetic radiation to illuminate a sample of blood in tissue;

detecting means for receiving electromagnetic radiation transmitted through or reflected from said sample of blood, and for providing an electrical output signal indicative of the intensity of said detected electromagnetic radiation for each of said wavelengths; and

data processing means for correlating said detected electromagnetic radiation with the blood oxygen saturation of said tissue, said data processing means comprising;

low pass filter means for removing high frequency noise from the electrical output signal of said detecting means;

amplifier means for amplifying said electrical output signal;

analog-to-digital converter means having a resolution of at least 14 bits, for converting said electrical output signal into digital data prior to any separation of said electrical output signal into a DC component and a pulsatile component; and

processing means for processing said digital data by separating said digital data into said DC component and said pulsatile component for each of said wavelengths and for producing a ratio of said pulsatile component to said DC component for each of said wavelengths and for determining said blood oxygen saturation based on said ratios.

2. A blood oxygen saturation monitoring system having a plurality of electromagnetic sources for illuminating a sample of blood in tissue, each of said sources operating at a different wavelength, having a means for attaching said electromagnetic sources proximate to said tissue and having processing circuitry, said processing circuitry comprising:

a photodetector receiving composite signals each having a DC and a pulsatile component from said electromagnetic sources reflected from or transmitted through said tissue and generating a plurality of composite current signals, each having a DC and pulsatile component, in response to detection of said composite signals;

a first converter means coupled to said photodetector for converting said composite current signals to a plurality of composite voltage signals, each of said composite voltage signals having a DC component and a pulsatile component;

a low pass filter coupled to said first converter means removing high frequency noise components from said composite voltage signals;

an amplifier coupled to said low pass filter having a gain wherein said DC component and said pulsatile component contained within said composite voltage signals are amplified by exactly said gain;

second converter means coupled to said amplifier for converting said composite voltage signals to digital data having both DC component and pulsatile component information prior to any separation of the DC and pulsatile components of said composite voltage signals; and

processing means coupled to said second converter means for processing said digital data and for determining said blood oxygen saturation based on the ratios of said DC and pulsatile components.

3. The blood oxygen saturation monitoring system of claim 2, wherein said second converter means comprises an analog-to-digital converter having at least 14 bits of resolution.

4. The blood oxygen saturation monitoring system of claim 2, wherein said low pass filter and said amplifier are low noise analog circuits.