Hematocrit measurements by electrical conductivity

• US 3,922,598 A
• Filed: 08/15/1974
• Issued: 11/25/1975
• Est. Priority Date: 08/15/1974
• Status: Expired due to Term

• Current Assignee: Glenn G. Enke, Robert R. Steuer
• Original Assignee: Glenn G. Enke, Robert R. Steuer
• Inventors: Steuer, Robert R., Enke, Glenn G.
• Primary Examiner(s): Kominski, John
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/497,553
• Time in Patent Office: 467 Days
• Field of Search: 324/29,3R,3B,65P 128/2G,2.1E 23/23B
• US Class Current: 324/442
• CPC Class Codes: G01N 33/49 Blood chemical methods for determining blood cell populations G01N33/5094; chemical analysis of blood groups or blood types G01N33/80

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.

Claims

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 IT CONSTANT CURRENT OUTPUT CONNECTED TO SAID ELECTRODES;

C. AVARIABLE GAIN AMPLIFER HAVING ITS INPUT TERMINALS CONNECTED TO SAID ELECTRODES;

D. A DIFFERENTIAL AMPLIFER 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.

2. The apparatus as in claim 1 wherein filtering means is provided to cause the input signal of said variable gain amplifier to be substantially free of the capacitative reactance component produced by said electrodes.

3. The apparatus as in claim 1 wherein a variable resistance is connected between said constant voltage output of said alternating current source and one input terminal of said differential amplifier, to achieve a null output of said differential amplifier when sAid fluid sample contains no red cells.

4. The apparatus as in claim 1 wherein said rendering means comprises a negative temperature coefficient thermistor mounted in close proximity to said fluid sample, driven by a dynamically varying DC voltage source, achieving a thermistor current jointly proportional to the temperature and the volume percentage of red cells in said fluid sample and amplifying means to convert the thermistor current to a corresponding DC voltage linearly added to the output of said attenuating network.

5. The apparatus as in claim 1 wherein said digital display means achieves the said hemoglobin estimate readout by reducing the said volume percentage of red cells readout by the ratio 3 to

6. The apparatus as in claim 1 wherein said spaced electrodes comprise first and second conductive areas each having a cylindrical shape, wherein the inner surface of the first conductive area is exposed to said fluid sample and the outer surface of the second conductive area, centered within the first conductive area and of substantially less diameter, is exposed to said fluid sample, and a fixed volume of said fluid sample is confined above said conductive areas by a planar glass cover slip normal to the axis of the cylinders and below by the top surface of an insulator separating the first and second conductive areas.