Apparatus for measuring concentration of light-absorbing substance in blood

An apparatus for measuring a concentration of a light-absorbing substance in blood, comprising:

• a light emitter, adapted to irradiate a living tissue with (n) light beams, at least one of the light beams having a wavelength which is absorbed by the blood;
• a first instrument, which measures (n) first intensities of the light beams, which are to be incident on the living tissue;
• a second instrument, which measures (n) second intensities of the light beams, which are transmitted through the living tissue;
• a first calculator, which calculates at least one but at most (n−1) attenuation variation ratio, which is a ratio of attenuation variations of the respective light beams due to variation of a volume of the blood caused by pulsation, based on the second intensities of the light beams with reference to DC light levels thereof;
• and
• a second calculator, which calculates, at least one but at most, (n) third intensities of the light beams, based on the first intensities which are obtained when the apparatus is subjected to calibration, DC components of the second intensities and current values supplied to the light emitter to emit the light beams, and obtains the concentration based on the third intensities and the attenuation variation ratio.