PROBLEM TO BE SOLVED: To precisely measure oxygen saturation in a pulse oximeter for measuring arterial blood oxygen saturation in a noninvasive manner by utilizing a difference in light absorption characteristics between two wavelengths of red light and infrared light in a living body.SOLUTION: A current/voltage conversion circuit 5 converts a current signal from a light receiving element 4 to a voltage signal by using Vref1 as a reference and amplifies it, and an amplifying circuit 6 in a second step further amplifies the voltage output. An A/D conversion circuit 7 performs A/D conversion, and an arithmetic device (CPU) 8 takes in the outcome and calculates the arterial blood oxygen saturation. The arithmetic device 8 creates the Vref1 of a level which has an eliminated pulse (AC) portion of a digital signal and corresponds to non-varied (DC) portion while considering the reference voltage Vref1 variable and imparts to the current/voltage conversion circuit 5. The current/voltage conversion circuit 5 converts the pulse (AC) portion obtained by subtracting the non-varied (DC) portion from the input current signal to a voltage with a large gain of an unsaturated level. Therefore, when the pulse is small with a small alternate current component, the oxygen saturation is precisely measured.COPYRIGHT: (C)2009,JPO&INPIT【課題】生体における赤色光と赤外光との2つの波長の吸光特性の差を利用して動脈血酸素飽和度を非観血的に測定するためのパルスオキシメータにおいて精度良く測定を行う。【解決手段】受光素子4からの電流信号を電流電圧変換回路5がVref1を基準として電圧信号に変換して増幅を行い、2段目の増幅回路6でさらに増幅し、A/D変換回路7においてA/D変換して演算装置(CPU)8が取込み、動脈血酸素飽和度を計算するにあたって、前記基準電圧Vref1を可変として、演算装置8は、デジタル信号の脈動(AC)分を除いた、非変動(DC)分に対応したレベルに前記Vref1を作成して電流電圧変換回路5に与え、該電流電圧変換回路5が、入力電流信号から前記非変動(DC)分を減算した脈動(AC)分を、飽和しないレベルの大きなゲインで電圧に変換する。したがって、脈動が小さく交流成分が小さい場合にも、精度良く測定を行うことができる。【選択図】図1
