Pulse oximeter

• US 7,206,621 B2
• Filed: 08/27/2004
• Issued: 04/17/2007
• Est. Priority Date: 08/27/2003
• Status: Active Grant

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Kobayashi, Naoki, Fuse, Masayoshi, Aoyagi, Takuo, Ukawa, Teiji
• Primary Examiner(s): Winakur; Eric F.
• Assistant Examiner(s): Lin; Jack
• Application Number:
  US10/927,016
• Publication Number:
  US 20050049469A1
• Time in Patent Office: 963 Days
• Field of Search: 600/323, 600/336
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

In a pulse oximeter for obtaining an oxygen saturation in a blood, a light emitter irradiates a living tissue with light beams having five different wavelengths. A light receiver receives respective light beams reflected from or transmitted through the living tissue, and converts the received light beams to electric signals. A first calculator calculates five attenuation changes of the living tissue based on fluctuations of the respective electric signals. A second calculator calculates at least four attenuation change ratios from the five attenuation changes. Each of the attenuation change ratios is defined by a ratio between any two of the five attenuation changes. A third calculator calculates the oxygen saturation based on the attenuation change ratios, while taking an oxygen saturation of arterial blood, an oxygen saturation of venous blood, a ratio between changes in arterial blood and venous blood, and a tissue term as four unknown values.

Claims

1. A pulse oximeter for obtaining an oxygen saturation in blood, comprising:

a light emitter, adapted to irradiate a living tissue with light beams having five different wavelengths;

a light receiver, adapted to receive respective light beams reflected from or transmitted through the living tissue, and to convert the received light beams to electric signals;

a first calculator, operable to calculate five attenuation changes of the living tissue based on fluctuations of the respective electric signals;

a second calculator, operable to calculate four attenuation change ratios from the five attenuation changes, each of the attenuation change ratios being defined by a ratio between any two of the five attenuation changes; and

a third calculator, operable to establish four simultaneous equations each of which is associated with one of the four attenuation change ratios and takes an oxygen saturation of arterial blood, an oxygen saturation of venous blood, a ratio between changes in arterial blood and venous blood, and a tissue term as four unknown values, the third calculator operable to solve the simultaneous equations by eliminating the oxygen saturation of venous blood, the ratio between changes in arterial blood and venous blood, and the tissue term in order to obtain the oxygen saturation in arterial blood.

2. The pulse oximeter as set forth in claim 1, wherein;

the four simultaneous equations are four of the following equations;

3. A method of obtaining an oxygen saturation signal for use in indicating an oxygen saturation in blood, comprising:

placing a light emitter and a light receiver on a living tissue in a non-invasive manner;

irradiating the living tissue with light beams emitted from the light emitter and having five different wavelengths;

receiving respective light beams reflected from or transmitted through the living tissue by the light receiver;

converting the received light beams to electric signals;

calculating five attenuation changes of the living tissue based on fluctuations of the respective electric signals;

calculating four attenuation change ratios from the five attenuation changes, each of the attenuation change ratios being defined by a ratio between any two of the five attenuation changes;

establishing four simultaneous equations each of which is associated with one of the four attenuation change ratios and takes an oxygen saturation of arterial blood, an oxygen saturation of venous blood, a ratio between changes in arterial blood and venous blood, and a tissue term as four unknown values;

solving the simultaneous equations by eliminating the oxygen saturation of venous blood, the ratio between changes in arterial blood and venous blood, and the tissue term in order to obtain the oxygen saturation in arterial blood; and

generating the oxygen saturation signal based on the obtained oxygen saturation of arterial blood.

4. The method as set forth in claim 3, wherein;

the four simultaneous equations are four of the following equations;