Differential conductivity hemodynamic monitor

• US 5,644,240 A
• Filed: 06/07/1995
• Issued: 07/01/1997
• Est. Priority Date: 09/30/1992
• Status: Expired due to Term

• Current Assignee: Gambro Renal Products, Inc. (Baxter International Inc.)
• Original Assignee: Cobe Cardiovascular Incorporated (LivaNova Plc)
• Inventors: Brugger, James M.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US08/486,982
• Time in Patent Office: 755 Days
• Field of Search: 324/439, 324/444, 324/445, 73/861.04, 73/861.08
• US Class Current: 324/439
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/361 before treatment
• CPC Class Codes: A61M 1/3612 after treatment
• CPC Class Codes: A61M 1/3653 Interfaces between patient blood circulation and extra-corporal blood circuit
• CPC Class Codes: A61M 1/3655 Arterio-venous shunts or fistulae
• CPC Class Codes: A61M 1/3658 Indicating the amount of purified blood recirculating in the fistula or shunt
• CPC Class Codes: A61M 1/3659 Cannulae pertaining to extracorporeal circulation
• CPC Class Codes: A61M 1/3661 for haemodialysis
• CPC Class Codes: A61M 1/3669 Electrical impedance measurement of body fluids; transducers specially adapted therefor
• CPC Class Codes: G01F 1/7046 using electrical loaded particles as tracer, e.g. ions or electrons
• CPC Class Codes: G01F 1/708 Measuring the time taken to traverse a fixed distance
• CPC Class Codes: G01F 1/7088 using electrically charged particles as tracers

Abstract

A flow rate of a fluid flowing in a tube is quantitatively determined by altering the electrical conductivity of the fluid by injection of a bolus of saline. The electrical conductivity of the altered conductivity is measured over the time it takes the altered conductivity fluid to pass a conductivity measuring location. The measured conductivity is integrated over the time it take to pass the conductivity measuring location. The integral is interpreted to determine the flow rate.

Claims

1. A method for quantitatively determining a flow rate in a tube of a first fluid having a first electrical conductivity and a corresponding first concentration of conductivity producing ions, comprising:

altering the electrical conductivity of the first fluid;

measuring the electrical conductivity at a measuring location of the first fluid after the conductivity is altered;

determining the period of time over which the altered conductivity fluid passes the measuring location;

integrating the measured conductivity over the period of time; and

interpreting the time integrated value of conductivity to determine flow rate;

wherein the step of measuring the conductivity of the first fluid further comprises;

flowing the first fluid through a first conduit, said first conduit comprising a first conductivity cell through which the first fluid flows with a continuous path configuration;

inducing by electromagnetic induction a first electrical current in the first fluid in the first conductivity cell; and

sensing by electromagnetic induction the first electrical current in the first fluid in the first conductivity cell.

2. A method as defined in claim 1 wherein:

the inducing step further comprises;

positioning an exciting electromagnetic coil in proximity with the first conductivity cell at an inducing location; and

inducing the first electrical current in an electrical direction along the continuous path of the first conductivity cell; and

the sensing step further comprises;

positioning a sensing electromagnetic coil in proximity with the first conductivity cell at a sensing location.

3. A method as defined in claim 1 wherein the integrating and interpreting steps further comprise compensating for the effect of the first conductivity.

4. A method as defined in claim 1 wherein:

the step of altering the electrical conductivity of the first fluid further comprises;

injecting a predetermined volume of a marker fluid having a predetermined concentration of conductivity producing ions, different from the concentration of conductivity producing ions in the first fluid into the first fluid.

5. A method for quantitatively determining a flow rate in a tube of a first fluid having a first electrical conductivity and a corresponding first concentration of conductivity producing ions, comprising:

altering the electrical conductivity of the first fluid;

measuring the electrical conductivity at a measuring location of the first fluid after the conductivity is altered;

determining the period of time over which the altered conductivity fluid passes the measuring location;

integrating the measured conductivity over the period of time; and

interpreting the time integrated value of conductivity to determine flow rate;

wherein a second fluid flows in another tube the second fluid having a second electrical conductivity and a corresponding second concentration of conductivity producing ions, wherein the measuring step further comprises;

measuring the electrical conductivity of the second fluid; and

comparing the conductivity of the first fluid with the conductivity of the second fluid.

6. A method as defined in claim 5 wherein:

the step of altering the electrical conductivity of the first fluid further comprises;

injecting a predetermined volume of a marker fluid having a predetermined concentration of conductivity producing ions, different from the concentration of conductivity producing ions in the first fluid into the first fluid.

7. A method as defined in claim 5 wherein the steps of measuring the conductivity of the first fluid and the second fluid further comprise:

flowing the first fluid through a first conduit, said first conduit comprising a first conductivity cell through which the first fluid flows with a continuous path configuration;

flowing the second fluid through a second conduit, said second conduit comprising a second conductivity cell through which the second fluid flows with a continuous path configuration;

inducing a first electrical current in the first fluid in the first conductivity cell and a second electrical current in the second fluid in the second conductivity cell;

sensing the first electrical current in the first fluid in the first conductivity cell and the second electrical current in the second fluid in the second conductivity cell; and

subtracting the second electrical current from the first electrical current to produce a signal representative of the difference in the conductivity between the first and the second fluids.

8. A method as defined in claim 7 wherein:

the inducing step further comprises;

positioning an exciting electromagnetic coil in proximity with the first and second conductivity cells at an inducing location;

inducing the first electrical current in an electrical direction along the continuous path of the first conductivity cell; and

simultaneously inducing the second electrical current to flow in the same electrical direction along the continuous path of the second conductivity cell as the direction of the first electrical current; and

the sensing and subtracting steps further comprise;

positioning a sensing electromagnetic coil in proximity with the first and second conductivity cells at a sensing location with the first conductivity cell oriented at the sensing location with the first electrical current in an opposite electrical direction with respect to the sensing electromagnetic coil from the electrical direction of the second electrical current with respect to the sensing electromagnetic coil.

9. A method as defined in claim 5 wherein the integrating and interpreting steps further comprise compensating for the effect of the first and the second conductivity.

10. A method as defined in claim 5 wherein:

the step of altering the electrical conductivity of the first fluid further comprises;

injecting a predetermined volume of a marker fluid having a predetermined concentration of conductivity producing ions, different from the concentration of conductivity producing ions in the first fluid into the first fluid.

11. A method as defined in claim 5 wherein the integrating and interpreting steps further comprise compensating for the effect of the first conductivity.

12. An apparatus for determining a rate of flow of a first fluid in a tube, said first fluid having a first electrical conductivity and a first concentration of conductivity producing ions, comprising:

means for altering the electrical conductivity of the first fluid;

means for measuring the electrical conductivity of the first fluid after the conductivity is altered;

means for determining the period of time over which the altered conductivity fluid passes the measuring location;

means for integrating the measured conductivity over the period of time; and

means for interpreting the time integrated value of conductivity to determine flow rate;

wherein the means for measuring the conductivity of the first fluid further comprises;

a first conduit through which the first fluid flows, said first conduit comprising a first conductivity cell through which the first fluid flows with a first conductivity cell upstream connection, a first conductivity cell downstream connection, and two branches connecting the upstream connection to the downstream connection with a continuous path configuration from the upstream connection to the downstream connection through one of the two branches and returning to the upstream connection through the other one of the two branches;

means for inducing by electromagnetic induction a first electrical current in the first fluid in the first conductivity cell;

means for sensing by electromagnetic induction the first electrical current in the first fluid in the first conductivity cell.

13. An apparatus as defined in claim 12 wherein:

the inducing means comprises an exciting electromagnetic coil in proximity with the first conductivity cell at an exciting location; and

the sensing means comprises;

a sensing electromagnetic coil in proximity with the first conductivity cell at a sensing location.

14. An apparatus as defined in claim 12 wherein the means for integrating and means for interpreting further comprise means for compensating for the effect of the first conductivity.

15. An apparatus as defined in claim 12 wherein:

the means for altering the electrical conductivity of the first fluid further comprises;

means for injecting a marker fluid having an electrical conductivity and concentration of conductivity producing ions different than the first conductivity and first concentration of conductivity producing ions of the first fluid into the first fluid.

16. An apparatus as described in claim 12 further comprising an apparatus adapted for the determination of a degree of flow recirculation within a zone of a vessel.

17. An apparatus for determining a rate of flow of a first fluid in a tube, said first fluid having a first electrical conductivity and a first concentration of conductivity producing ions, comprising:

means for altering the electrical conductivity of the first fluid;

means for measuring the electrical conductivity of the first fluid after the conductivity is altered;

means for determining the period of time over which the altered conductivity fluid passes the measuring location;

means for integrating the measured conductivity over the period of time; and

means for interpreting the time integrated value of conductivity to determine flow rate;

wherein a second fluid having a second conductivity and a second concentration of conductivity producing ions is flowing in another tube, further comprising;

means for measuring the electrical conductivity of the second fluid, and for comparing the conductivity of the first fluid with the conductivity of the second fluid.

18. An apparatus as defined in claim 17 wherein:

the means for altering the electrical conductivity of the first fluid further comprises;

means for injecting a marker fluid having an electrical conductivity and concentration of conductivity producing ions different than the first conductivity and first concentration of conductivity producing ions of the first fluid into the first fluid.

19. An apparatus as defined in claim 17 wherein the means for measuring the conductivity of the first fluid and the second fluid and comparing the conductivities further comprises:

a first conduit through which the first fluid flows, said first conduit comprising a first conductivity cell through which the first fluid flows with a first conductivity cell upstream connection, a first conductivity cell downstream connection, and two branches connecting the upstream connection to the downstream connection with a continuous path configuration from the upstream connection to the downstream connection through one of the two branches and returning to the upstream connection through the other one of the two branches;

a second conduit through which the second fluid flows, said second conduit comprising a second conductivity cell through which the second fluid flows with a second conductivity cell upstream connection, a second conductivity cell downstream connection, and two branches connecting the upstream connection to the downstream connection with a continuous path configuration from the upstream connection to the downstream connection through one of the two branches and returning to the upstream connection through the other one of the two branches;

means for inducing a first electrical current in the first fluid in the first conductivity cell and a second electrical current in the second fluid in the second conductivity cell;

means for sensing the first electrical current in the first fluid in the first conductivity cell and the second electrical current in the second fluid flowing in the second conductivity cell, and subtracting the second electrical current from the first electrical current to produce a signal representative of the difference in the conductivity between the first and the second fluids.

20. An apparatus as defined in claim 19 wherein:

the inducing means comprises an exciting electromagnetic coil in proximity with the first and second conductivity cells at an exciting location, the first conductivity cell being oriented at the exciting location with respect to the second conductivity cell with first electrical current in an electrical direction with respect to the exciting electromagnetic coil and the second electrical current in the same electrical direction with respect to the exciting electromagnetic coil; and

the sensing and subtracting means further comprises a sensing electromagnetic coil in proximity with the first and second conductivity cells at a sensing location, the first conductivity cell being oriented at the sensing location with respect to the second conductivity cell with the electrical direction of the first electrical current with respect to the sensing electromagnetic coil opposite the electrical direction of the second electrical current with respect to the sensing electromagnetic coil.

21. An apparatus as described in claim 17 further comprising an apparatus adapted for the determination of a degree of flow recirculation within a zone of a vessel.

22. An apparatus as defined in claim 17 wherein:

the means for altering the electrical conductivity of the first fluid further comprises;

means for injecting a marker fluid having an electrical conductivity and concentration of conductivity producing ions different than the first conductivity and first concentration of conductivity producing ions of the first fluid into the first fluid.

23. An apparatus as defined in claim 17 wherein the means for integrating and means for interpreting further comprise means for compensating for the effect of the first conductivity.