Method and apparatus for improved photoplethysmographic monitoring of oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin
First Claim
1. A method for measuring a concentration value for each of a plurality of blood analytes in a portion of tissue of a patient comprising the steps of:
- a. generating a plurality of light beams each having a distinct spectral content;
b. directing each of the plurality of light beams into the portion of tissue;
c. detecting light transmitted through the portion of tissue to generate a plurality of received light intensity signals representative of the detected light for each of the plurality of light beams;
d. calculating an estimated blood analyte concentration value from the plurality of received light intensity signals for each of the plurality of blood analytes by minimizing an error function associated with said estimated blood analyte concentration values while satisfying a predetermined set of constraints placed on said estimated blood analyte concentration values.
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Accused Products
Abstract
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.
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Citations
13 Claims
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1. A method for measuring a concentration value for each of a plurality of blood analytes in a portion of tissue of a patient comprising the steps of:
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a. generating a plurality of light beams each having a distinct spectral content; b. directing each of the plurality of light beams into the portion of tissue; c. detecting light transmitted through the portion of tissue to generate a plurality of received light intensity signals representative of the detected light for each of the plurality of light beams; d. calculating an estimated blood analyte concentration value from the plurality of received light intensity signals for each of the plurality of blood analytes by minimizing an error function associated with said estimated blood analyte concentration values while satisfying a predetermined set of constraints placed on said estimated blood analyte concentration values. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for the generation of stabilized blood analyte concentration values corresponding to the concentration of a plurality of blood analytes in a tissue portion of a patient comprising:
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one or more emitters which illuminate the tissue portion of the patient with a plurality of light signals each having a distinct spectral content; a photodetector which detects the light transmitted through the tissue portion and generates a plurality of received light intensity signals; a microprocessor; a means for communicating said plurality of received light intensity signals from the photodetector to said microprocessor; wherein said microprocessor executes a series of computer program instructions thereby calculating an estimated analyte value from the plurality of received light intensity signals while minimizing error associated with said estimated analyte values and while satisfying a set of constraints placed on said estimated analyte values. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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Specification