Optical measurement of blood hematocrit incorporating a self-calibration algorithm
First Claim
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1. A method for determining hematocrit of a blood sample, comprising the steps of:
- measuring absorbance of said blood sample at a first isobestic wavelength;
measuring absorbance of said blood sample at a second isobestic wavelength; and
determining hematocrit of said blood sample in accordance with the algorithm;
space="preserve" listing-type="equation">Hct=(T.sub.i,1 -R*T.sub.i,2)/(K.sub.1 -R*K.sub.2),wherein;
Ti is total absorbance at an isobestic wavelength;
K is a constant that includes a molar extinction coefficient Hb at that wavelength, a red blood cell scattering factor, and path length;
Hct is hematocrit; and
R is the ratio of light scattering from a plasma component measured at two wavelengths.
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Abstract
An optical method for obtaining hematocrit values of blood uses the light transmittance properties of blood as a means of acquiring information about the blood sample. An algorithm is used to calculate the hematocrit value based on the absorbance spectra obtained at wavelengths of approximately 500 nm and 800 nm. These absorbance wavelengths are selected for their insensitivity to the oxygen saturation level of hemoglobin. Additionally, the algorithm has demonstrated insensitivity to plasma and other blood constituent scattering effects.
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Citations
21 Claims
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1. A method for determining hematocrit of a blood sample, comprising the steps of:
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measuring absorbance of said blood sample at a first isobestic wavelength; measuring absorbance of said blood sample at a second isobestic wavelength; and determining hematocrit of said blood sample in accordance with the algorithm;
space="preserve" listing-type="equation">Hct=(T.sub.i,1 -R*T.sub.i,2)/(K.sub.1 -R*K.sub.2),wherein; Ti is total absorbance at an isobestic wavelength; K is a constant that includes a molar extinction coefficient Hb at that wavelength, a red blood cell scattering factor, and path length; Hct is hematocrit; and R is the ratio of light scattering from a plasma component measured at two wavelengths. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for determining hematocrit of a blood sample, comprising:
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a first detector for measuring absorbance of said blood sample at a first isobestic wavelength; a second detector for measuring absorbance of said blood sample at a second isobestic wavelength; and means for determining hematocrit of said blood sample in accordance with the algorithm;
space="preserve" listing-type="equation">Hct=(T.sub.i,1 -R*T.sub.i,2)/(K.sub.1 -R*K.sub.2),wherein; Ti is total absorbance at an isobestic wavelength; K is a constant that includes a molar extinction coefficient Hb at that wavelength, a red blood cell scattering factor, and path length; Hct is hematocrit; and R is the ratio of light scattering from a plasma component measured with two wavelengths. - View Dependent Claims (8, 9, 10, 11, 12)
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13. An apparatus for determining hematocrit of a blood sample, comprising:
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a first detector for measuring absorbance of said blood sample at an isobestic wavelength of 506 nm; a second detector for measuring absorbance of said blood sample at an isobestic wavelength of 805 nm; and means for determining hematocrit of said blood sample in accordance with the algorithm;
space="preserve" listing-type="equation">Hematocrit=(Absorbance.sub.805 nm -Absorbance.sub.506 nm)/K,wherein K is a cell constant for a probe that provides said first detector and said second detector. - View Dependent Claims (14, 15, 16, 17)
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18. A method for determining hematocrit of a blood sample, comprising the steps of:
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measuring absorbance of said blood sample at an isobestic wavelength of 506 nm; measuring absorbance of said blood sample at an isobestic wavelength of 805 nm; and determining hematocrit of said blood sample in accordance with the algorithm;
space="preserve" listing-type="equation">Hematocrit=(Absorbance.sub.805 nm -Absorbance.sub.506 nm)/K,wherein K is a cell constant for a probe that provides said first detector and said second detector. - View Dependent Claims (19, 20, 21)
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Specification