Patent ID: 6400972
Filing Date: 2002-06-04
Classification: A61B

Abstract:
A non-invasive method of optical measurements for determining the concentration of at least one substance in patient's blood, the method comprising the steps of:(a) applying an over-systolic pressure to the patient's blood perfused fleshy medium with a normal blood flow at a first location on the patient's body, such as to cause a state of temporary blood flow cessation at a second location on the patient's body located downstream of said first location with respect to a normal blood flow direction for a cessation time period being insufficient for irreversible changes in the fleshy medium; (b) releasing the over systolic pressure at the first location to cause a state of transitional blood flow terminating with the normal blood flow at the second location; (c) selecting at least two timely separated sessions for performing the optical measurements on the blood perfused fleshy medium at said second location, wherein the selected sessions are such that light response of the medium at said at least two sessions substantially differs from each other, at least one of said at least two sessions being selected within a time period including the state of temporary blood flow cessation and the state of transitional blood flow, wherein said selecting includes distinguishing the normal blood flow from the state of temporary blood cessation by detecting that at least one optical characteristic associated with the light response of the blood has changed by a predetermined threshold value, and that the character of its change corresponds to a time-dependent function; (d) effecting the measurements at said at least two sessions successively, each session including illumination of the second location with at least two different wavelengths of incident light and detection of light responses of the medium; and (e) determining for each of said at least two sessions a corresponding value of the concentration of said at least one substance, analyzing the determined values and obtaining a corrected value of said concentration.