Patent ID: 7206621

Claim:
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.