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Abstract

A liver function testing apparatus measures n-times the values .DELTA.logT.sub.1 and .DELTA.logT.sub.2 corresponding to pulse wave signals obtained upon passage through a prescribed optical path in vital tissue. A sensor (30) having first and second light sources (3, 4) and a light receiving element (6) is attached to a testee (5) before injection of a specific dye. A value .alpha..sub.0 is calculated by using a statistical computation with two variables as to n .DELTA.logT.sub.1 and .DELTA.logT.sub.2 on the basis of an equation of .DELTA.logT.sub.1 =.alpha..sub.0..DELTA.logT.sub.2..DELTA.logT.sub.1 and .DELTA.logT.sub.2 corresponding to pulse wave signals are measured in response to intensity levels of first light and second light passing through the vital tissue during a prescribed time following an injection on the basis of decision outputs representing levels of the first light and the second light from the light sources after the specific dye is injected. A value Cg corresponding to a specific dye concentration in the blood is calculated from .alpha..sub.0 , .DELTA.logT.sub.1 and .DELTA.logT.sub.2. A simulation curve as a function of time changes of the result of the measurements is calculated by the application of the least squares method, thereby to obtain a blood plasma disappearance rate K and a T-minute retention rate R % of the specific dye on the basis of the simulation curve.

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