Electrical liquid conductivity measuring system

• US 4,303,887 A
• Filed: 10/29/1979
• Issued: 12/01/1981
• Est. Priority Date: 10/29/1979
• Status: Expired due to Term

• Current Assignee: United States Surgical Corporation (Medtronic Plc)
• Original Assignee: United States Surgical Corporation (Medtronic Plc)
• Inventors: Hill, Jeremy R., Meyer, Allen E.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US06/089,087
• Time in Patent Office: 764 Days
• Field of Search: 324/441, 324/442, 324/446, 324/447, 324/448, 324/450, 324/65 R, 324/64, 128/637, 128/669, 29/592 R, 29/876, 29/877, 73/344, 73/343.5
• US Class Current: 324/441
• 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
• CPC Class Codes: G01R 27/22 Measuring resistance of fluids

Abstract

An electrical system for measuring a parameter of a liquid sample such as the hematocrit and an approximation of hemoglobin for a blood sample. The system basically comprises an instrument and a disposable sample card. The instrument is a hand-held, battery-operated device used for the fast and simple measurement of a parameter such as blood conductivity. The instrument accepts the disposable sample card, which is used for the one-time conveyance and application of a liquid sample, such as blood, to the instrument. The instrument has provision for digital displays for read-outs. There are no external switches on the instrument, and power is automatically applied when the disposable sample card is inserted into the instrument.

The instrument basically comprises an electronic portion for processing data obtained from the liquid sample on the sample card, a front-end mechanism for positioning the sample card within the instrument, and a digital display for displaying in eye-readable form the results of a parameter measurement made in the instrument.

Claims

1. An electronic device for measuring conductivity of a blood sample of predetermined volume, said device comprising:

generating means for generating a signal of predetermined frequency;

electrode means for passing said signal through said blood sample;

control means for activating and deactivating said generating means at regular predetermined time intervals chosen to prevent polarization of said blood sample about said electrode means;

first monitoring means connected to said electrode means for monitoring the conductivity of said blood sample;

second monitoring means for monitoring the temperature of said blood sample; and

temperature-compensating means responsive to said monitored conductivity and said monitored temperature for producing a conductivity signal indicative of the temperature-compensated conductivity of said blood sample, said temperature-compensating means including computer means having a memory, said memory storing information relating to a predetermined range of temperature-compensated conductivity.

2. The device of claim 1, wherein said generating means is a square wave generator.

3. The device of claim 2, wherein said square wave generator includes means for generating a square wave having a frequency of approximately 25 Khz.

4. The device of claim 1, wherein said first monitoring means comprises a peak detector.

5. The device of claim 1, wherein said second monitoring means comprises a thermistor.

6. The device of claim 1, further comprising means for issuing an error signal when said temperature-compensating means determines that said temperature-compensated conductivity of said blood sample is outside of the range of the information stored in said memory.

7. The device of claim 6, further comprising means responsive to said error signal for indicating a visual alert.

8. The device of claim 6, further comprising means responsive to said error signal for indicating an audible alert.

9. The device of claim 1, further comprising display means for converting said temperature-compensated conductivity signal into an eye-readable format.

10. The device of claim 1, further comprising means for converting said monitored conductivity into a signal indicative of hematocrit percentage.

11. A circuit for measuring the true value of a first parameter of a liquid sample of predetermined volume, the value of the first parameter being dependent on the true value of a second parameter of the liquid sample, said circuit comprising:

generating means for generating an electrical signal;

electrode means for passing said signal through said liquid sample;

first monitoring means connected to said electrode means for monitoring said first parameter of said liquid sample;

second monitoring means for measuring said second parameter; and

compensating means responsive to said monitored first and second parameters for producing a signal indicative of the true value of said first parameter, said compensating means including computer means having a memory, said memory storing information relating to a predetermined range of true values of said first parameter, the specific one of said true values for conversion into a signal being determined by the monitored values of said first and second parameters.

12. The circuit of claim 11 wherein said first parameter is conductivity and wherein said second parameter is temperature.

13. The circuit of claim 11 wherein said generating means is a square-wave generator.

14. The circuit of claim 13 wherein said square-wave generator includes means for generating a square-wave having a frequency of approximately 25 KHz.

15. The circuit of claim 11 wherein said first monitoring means is a peak detector.

16. The circuit of claim 11 wherein said second monitoring means is a thermistor.

17. The circuit of claim 11 further comprising control means for activating and deactivating said generating means at regular predetermined time intervals.

18. An electronic device for measuring conductivity of a blood sample of predetermined volume, said device comprising:

generating means for generating a signal of predetermined frequency;

electrode means for passing said signal through said blood sample;

first monitoring means for monitoring the conductivity of said blood sample;

second monitoring means for monitoring the temperature of said blood sample; and

means for comparing the temperatures monitored by said second monitoring means and for issuing a temperature signal when the difference between two successive monitored temperatures is less than a predetermined value.

19. The device of claim 18, further comprising means responsive to said temperature signal for displaying said monitored conductivity in an eye-readable form.

20. The device of claim 18, further comprising means responsive to said temperature signal for displaying said monitored conductivity as hematocrit percentage.