Patent ID: 6104938
Filing Date: 2000-08-15
Classification: A61B,G01N

Abstract:
A method for non-invasively determining the amount of a light absorbing substance in the blood of a subject, the blood having at least two light absorbing substances, said method comprising the steps of:(A) applying light of a first wavelength to tissue of the subject containing blood to obtain a first transmitted light quantity, the first transmitted light quantity having a pulsatile component and a non-pulsatile component;(B) applying light of a second wavelength to tissue of the subject containing blood to obtain a second transmitted light quantity, the second transmitted light quantity having a pulsatile component and a non-pulsatile component;(C) ratioing the pulsatile component of the first transmitted light quantity to the total first transmitted light quantity and ratioing the pulsatile component of the second light quantity to the total second transmitted light quantity to obtain first and second percentage modulation quantities (% mod 1, 2 . . . );(D) ratioing the first and second percentage modulation quantities (% mod 1, 2 . . . ) to obtain a modulation ratio quantity (Z');(E) formulating substance concentration determining equations (Eq 8, 9) for wavelengths corresponding to the first and second light wavelengths;(F) altering one of a modulation ratio term (Z', Z) or extinction coefficient terms (.epsilon.', .epsilon.) in the equations in accordance with the percentage modulation quantities to account for the application of the light of the first and second wavelengths to the tissue as well as the blood of the subject;(G) solving the equations for at least one selected substance present in the blood; and(H) determining, from the solution of the equations, the amount of the selected substance in the blood.