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Abstract

A method is disclosed for the determination of the saturation of the blood of a living organism with oxygen and an electronic circuit for performing this method is also disclosed. The method resides in red light and infrared radiation being simultaneously beamed into living tissue and the mixed residual radiation emanating from the irradiated tissue being received by a phototransistor 18 and the infrared radiation contained in the mixed residual radiation being received by an identical phototransistor 17 with a green filter 20 arranged in front of it. The measured intensity of the residual infrared radiation is subtracted from the measured intensity of the mixed residual radiation by an electronic circuit so as to obtain the intensity of the residual red light radiation and the residual infrared radiation. The saturation of the blood with oxygen can be computed from the values represented by these intensities of the residual infrared and red light radiations. The electronic circuit includes two light-emitting diodes 15 and 16 for infrared radiation and for red light, respectively, and two identical phototransistors 17 and 18. A green filter 20 is arranged in front of the phototransistor 17. Via a comparator, photocurrents are generated in the phototransistors 17 and 18 which have DC components of equal value for the infrared radiation, on the one hand, and for the red light, on the other hand. The photocurrents generated by the mixed residual radiation in the photo transistor 18 and by the infrared radiation in the photo transistor 17 are modulated by the heartbeat. The electric signal derived from the modulation of the photocurrent of the phototransistor 17 is subtracted in a subtracting circuit 41 from the electric signal derived from the modulation of the photocurrent of the phototransistor 18.

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First Claim