Tissue oximetry apparatus and method

Abstract

An apparatus and method for determining tissue oxygenation such as arterial and venous oxygenation and cerebral oxygenation. In one embodiment, the optical properties of tissue are determined using measured light attenuations at a set of wavelengths. By choosing distinct wavelengths and using light attenuation information, the influence of variables such as light scattering, absorption and other optical tissue properties can be minimized.

1 . Apparatus and sensor for measuring constituents of blood in tissue in vivo with a sensor connected to said apparatus determining light attenuation at a combination of light emitters and detectors comprising the following means:
 a light emitter and at least two detectors, said light emitter including at least three wavelengths, wherein a peak spectrum of one of said at least three wavelengths is about the geometric mean value of the two other of said three wavelengths;   means for calculating at least two values of differential attenuation vs. time Rw1, w2, Rw2,w3 with w1, w2,w3 representing the selected wavelengths;   means for eliminating influences on calibration by subtracting and adding measured light attenuations to generate a signal; and   means for generating a resulting output signal for a constituent of blood in vivo depending on said signal; wherein said means for generating a resulting output minimizes the error on said resulting output.   
     
     
         2 . The apparatus of  claim 1 , wherein said constituent is selected from the group consisting of carboxyhemoglobin, methemoglobin, glucose in blood, Hb, SvO2, SaO2 and bilirubin. 
     
     
         3 . An apparatus for measuring constituents of blood in tissue, including a sensor with a combination of two light emitters and two light detectors, said apparatus comprising:
 means for emitting a light wavelength combination including at least two wavelengths with at least one emitter, wherein the peak spectrum of one of said at least three wavelengths is about the geometric mean value of the two others of said three wavelengths to generate a first output signal;   means for calculating differential attenuation vs. time Rw1, w2, Rw2, w3;   means for eliminating influences on calibration by an operation which corresponds to subtracting and adding measured light attenuations to generate an output signal for optical properties;   means for encoding information about the sensor for compensating influences of varying optical tissue properties related to said sensor interface;   means for generating a resulting output signal for at least one of said constituents of blood in vivo depending on said means measured on the forehead or back or chest or arm of the body; and   means for generating an output signal for cardiac output depending on said blood constituents, wherein said means for generating the resulting output signal for at least one of said constituents minimizes the error on said resulting output.