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Abstract

An improved method and apparatus for the photoplethysmographic monitoring of blood analyte parameters, specifically oxyhemoglobin, deoxyhemoglobin (reduced hemoglobin), carboxyhemoglobin and, in addition, in a four emitter apparatus, methemoglobin, uses a plurality of beams of light having different spectral contents to trans-illuminate the tissue of a patient. The apparatus and method require the application of an emitter set comprised of four emitters. The emitters may be LED's or laser diodes. In the three analyte system the center wavelength of the emitters must fall within three specific bands. In the four emitter system (capable of measuring methemoglobin) the center wavelength of the emitters in the emitter set must fall within four predetermined bands and the emitters having the two lowest center wavelengths must be at least 5 nanometers apart. The apparatus can use emitters which are located either in a probe, or, preferably, in the monitor, as well as a photodiode which can either be located in the patient probe or in the monitor.

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First Claim