Method and apparatus for improved photoplethysmographic monitoring of oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin
 An improved method and apparatus for the photoplethysmographic monitoring of blood analyte parameters, specifically oxyhemoglobin, deoxyhemoglobin (reduced hemoglobin), carboxyhemoglobin and methemoglobin, uses a plurality of beams of light having different spectral contents to trans-illuminate the tissue of a patient. Received light is measured and the normalized differential absorption is used in a forward calibration equation to generate estimated relative blood analyte concentration values. Error in the blood analyte concentration values is minimized by applying constraints to the estimated analytes. Specifically, the constraints require that all relative analyte concentration values are greater than or equal to zero and sum to one hundred percent. An alternate method of applying constraints to the determination of the stabilized analyte concentration values reduces computation time by using an inverse calibration equation and substituting the inverse equation for the forward equation in the minimization process. 
Ohmeda Inc.
A G
A61B G01N
inventional inventional
Kristin Hoyer
Jarman