Normalization method for a chronically implanted optical sensor
First Claim
1. A method for accurately estimating an oxygen saturation metric for a volume of blood by an optical sensor measurement, comprising:
- deploying a dual wavelength optical sensor into fluid communication with a volume of blood, wherein said volume of blood is characterized by a blood flow rate condition, said flow rate condition comprising one of;
relatively low, stasis, substantially stagnant;
determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in the dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of saturated oxygen present in said volume of blood and said second wavelength of radiation is substantially independent of the amount of saturated oxygen present in the volume of blood;
determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of blood having known optical properties;
determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation;
measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of blood; and
calculating a saturation metric for the saturated oxygen based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval.
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Abstract
A system and method are provided for estimating blood oxygen saturation independent of optical sensor encapsulation due to placement in blood, where the blood includes a blood flow characteristic of: a relatively low, a stasis, a stagnant value. The method includes determining tissue overgrowth correction factor that includes optical properties of the tissue that cause scattering of the emitted light to a detector and relative amplitudes of the emitted light wavelengths. A corrected time interval measured for infrared light is based on an infrared signal and a corrected time interval for red light is determined by subtracting red light signal due to presence of tissue overgrowth. The red light signal due to tissue overgrowth is proportional to total infrared signal less nominal infrared signal. Oxygen saturation is estimated based on standard calibration factors and the ratio of the corrected infrared time interval and the corrected red time interval.
15 Citations
18 Claims
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1. A method for accurately estimating an oxygen saturation metric for a volume of blood by an optical sensor measurement, comprising:
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deploying a dual wavelength optical sensor into fluid communication with a volume of blood, wherein said volume of blood is characterized by a blood flow rate condition, said flow rate condition comprising one of;
relatively low, stasis, substantially stagnant;determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in the dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of saturated oxygen present in said volume of blood and said second wavelength of radiation is substantially independent of the amount of saturated oxygen present in the volume of blood; determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of blood having known optical properties; determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation; measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of blood; and calculating a saturation metric for the saturated oxygen based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for accurately estimating an oxygen saturation metric for a volume of blood, comprising:
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means for determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in a dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to saturated oxygen present in a volume of blood and said second wavelength of radiation is substantially independent of saturated oxygen; means for determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to the volume of blood having known optical properties; means for determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation; means for placing the dual wavelength optical sensor in the volume of blood, wherein said volume of blood is characterized by a blood flow-rate condition, said flow-rate condition comprising one of;
relatively low, stasis, substantially stagnant;means for measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of blood; and means for calculating a saturation metric for a metabolite of interest based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification