Method and apparatus for the measurement of dye dilution in blood

Claim 1

A method for determining cardiac volume parameters wherein a test dye is added to blood and a photometric measurement of the light absorption of the dyed blood is carried out by an electro-optical system which includes a photosensitive means to determine dye dilution in the blood, said method comprising the steps of, a. measuring the light absorption values of the blood without any dye added at a first wavelength, b. measuring the light absorption values of the blood without any dye added at a second wavelength, c. operating said electro-optical system to obtain modified light absorption values by equalizing the 02-saturation-dependent portions of said light absorption values at said first and second wavelengths by multiplying the light absorption value at said second wavelength by a factor equal to the 02-saturation-dependent portion at the minimum of 02-saturation at said first wavelength divided by the 02-saturation-dependent portion at the minimum of 02-saturation at said second wavelength, d. subtracting said modified light absorption value at said second wavelength from said light absorption at said first wavelength, the difference value thus being independent of 02-saturation to establish a first artificial isosbestic value, e. deriving a second isosbestic value by measuring the light absorption values of the blood at the wavelength of the natural isosbestic point of the blood ( lambda 0 805), f. operating said electro-optical system to equalize said first artificial isosbestic value independent of 02-saturation and said second isosbestic value independent of 02-saturation, g. forming a compensated difference value which is the difference between said first artificial isosbestic value and said second isosbestic value and this compensated difference value being zero before adding test dye and independent of 02-saturation, concentration, layer thickness and flow effect, h. adding a test dye to the blood the absorption values of which at said first and second wavelengths are different from the absorption values at said two other wavelengths and then, i. determining the light absorption values of the dyed blood by measuring the variations of said compensated difference value (under step (g)).