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Abstract

An apparatus for non-invasively measuring the oxygen saturation in the blood of a subject comprises light sources for irradiating a sample of blood in tissue with at least a first light beam and a second light beam having different wavelengths. A switching device drives the light sources and sequentially switches the irradiation of the sample of blood between the first and second laser beams. A photoelectric detector detects light transmitted through or reflected from the sample of blood and provides an electrical output signal indicative of the intensity of the detected light. A converter converts the electrical output signal of the photoelectric detecting device to a power spectrum, and a processor processes the power spectrum and calculates the oxygen saturation of the sample of blood. The blood oxygen saturation in the blood can be measured with high accuracy based on the detection of the light intensity transmitted through or reflected from the blood, regardless of the presence or absence of a pulsed blood flow. Additionally, by irradiating the subject by switching between laser beams of two wavelengths, the subject receives less irradiation than when two lasers are used at the same time. Thus even if the amount of irradiation at each wavelength is slightly increased, the accuracy measurement can be improved without adversely affecting the subject.

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