Hematocrit measurements by electrical conductivity
First Claim
1. An apparatus for displaying in digital form the volume percentage of red cells in a conducting fluid sample comprising:
- a. 2 spaced electrodes cooperating with said fluid sample;
b. a sinusoid alternating current source having its constant current output connected to said electrodes;
c. a variable gain amplifier having its input terminals connected to said electrodes;
d. a differential amplifier having its input terminals connected between the output of said variable gain amplifier and the constant voltage output of said alternating current source;
e. rectifying means and DC amplifier connected to the output of said differential amplifier;
f. a dynamic attenuating resistive network, whose output voltage approximates the volume percentage of red red cells in said fluid sample, driven by the output of said DC amplifier;
g. means operable to render said attenuating network output substantially independent of temperature variations of said fluid sample; and
h. digital display means driven by the output of said attenuating network to provide direct readout of either the volume percentage of red cells in said fluid sample or the hemoglobin estimate of said fluid sample.
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Abstract
Method and apparatus for determining the hematocrit of blood samples from the electrical conductance of whole blood by means of a portable, simple to use instrument with a digital readout. A dip-electrode-probe and/or a "fingerstick"-probe, requiring one drop of blood, have been developed to provide an easy to use and clean electrode system. Electronic improvements further provide for uniformity of readings between observers, automatic operator alert when poor sample contact or insufficient battery power, an exponential solution to the Fricke, Curtis and Maxwell equations and further eliminates electrode polarization by providing a separate DC path to conduct any DC component in the sine-wave signal. A provision is also made to estimate the hemoglobin value from the measured hematocrit.
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Citations
6 Claims
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1. An apparatus for displaying in digital form the volume percentage of red cells in a conducting fluid sample comprising:
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a. 2 spaced electrodes cooperating with said fluid sample; b. a sinusoid alternating current source having its constant current output connected to said electrodes; c. a variable gain amplifier having its input terminals connected to said electrodes; d. a differential amplifier having its input terminals connected between the output of said variable gain amplifier and the constant voltage output of said alternating current source; e. rectifying means and DC amplifier connected to the output of said differential amplifier; f. a dynamic attenuating resistive network, whose output voltage approximates the volume percentage of red red cells in said fluid sample, driven by the output of said DC amplifier; g. means operable to render said attenuating network output substantially independent of temperature variations of said fluid sample; and h. digital display means driven by the output of said attenuating network to provide direct readout of either the volume percentage of red cells in said fluid sample or the hemoglobin estimate of said fluid sample. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification