Method and device for determination of concentration

• US 6,321,101 B1
• Filed: 04/19/2000
• Issued: 11/20/2001
• Est. Priority Date: 10/29/1997
• Status: Expired due to Term

• Current Assignee: Pacesetter AB (Abbott Laboratories)
• Original Assignee: Pacesetter AB (Abbott Laboratories)
• Inventors: Holmström, Nils
• Primary Examiner(s): Schaetzle, Kennedy
• Application Number:
  US09/529,842
• Time in Patent Office: 580 Days
• Field of Search: 600/309, 600/322, 600/323, 600/324-328, 600/333, 600/336, 600/345, 600/347, 600/353, 600/364, 600/365, 607/17, 607/22, 204/431, 204/416, 204/403, 204/406
• US Class Current: 600/345
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood
• CPC Class Codes: G01N 27/404 Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid , e.g. Clark-type oxygen sensors
• CPC Class Codes: G01N 33/4925 measuring blood gas content, e.g. O2, CO2 , HCO3

Abstract

In a method and a device for electrochemical determination of the concentration of at least one dissolved chemical entity in a liquid medium, a measurement voltage U is impressed on a working electrode, in contact with the liquid medium, relative to a counter electrode, thereby causing the dissolved chemical entity to react by oxidation or reduction at the working electrode, producing a measurement evoked current. The measurement evoked current is compared to a predetermined value, and the measurement voltage U is adjusted so that the measurement evoked current is substantially equal to the predetermined value, and thus remains substantially constant during measurements. A difference ΔU=U−U_min is formed, which corresponds to an oxidation/reduction reaction at the working electrode, with U_min being a minimum voltage selected as a reference level. This difference is used to calculate concentration variations of the chemical entity in the liquid. A therapy administering apparatus, such as a medical implant such as a pacemaker or the like, can be controlled dependent on the calculated concentration variations.

Claims

1. A method for electrochemical determination of a concentration of at least one dissolved chemical entity in a liquid medium, comprising the steps of:

impressing a measurement voltage U on a working electrode relative to a counter electrode, said dissolved chemical entity in said liquid being in contact with said working electrode and reacting to said voltage U by oxidation or reduction at said working electrode, resulting in a measurement evoked current;

comparing said measurement evoked current with a predetermined value;

adjusting the measurement voltage U such that the measurement evoked current is substantially equal to said predetermined value so that said measurement evoked current is substantially constant;

forming a difference Δ

U=U−

U_min which corresponds to an oxidation/reduction reaction at said working electrode, wherein U_min is a minimum voltage selected as a reference level; and

using said difference Δ

U=U−

U_min to calculate concentration variations of said chemical entity in said liquid.

2. A method as claimed in claim 1 comprising adjusting U_min in increments dU_min dependent on said measurement voltage U, such that when U−

dU_min<

0, U_min is decreased by dU_min, and after a predetermined time U_min is increased by dU_min.

3. A method as claimed in claim 2 comprising calculating dU as a function of a difference between said measurement evoked current and said predetermined value.

4. A method as claimed in claim 1 comprising supplying blood in living tissue to said working electrode as said liquid medium, said blood containing oxygen as said chemical entity.

5. A method as claimed in claim 4 comprising adjusting a pacing rate for pacing a heart as a function of said difference Δ

U=U−

U_min.

6. A method as claimed in claim 5 comprising calculating said rate adjustment according to a formula K[(U−

U_min)/(U_max−

U_min)], wherein K is a factor limiting a highest rate increase, and U_max is an adjustable value greater than U.

7. An apparatus for electrochemical determination of a concentration of at least one dissolved chemical entity in a liquid medium comprising:

a working electrode and a counter electrode, said working electrode being in contact with said liquid medium in which said at least one chemical entity is dissolved;

a voltage source for impressing a measurement voltage U on said working electrode relative to said counter electrode, said dissolved chemical entity reacting to said measurement voltage U by oxidation or reduction at said working electrode, resulting in production of a measurement evoked current;

a comparator which compares said measurement evoked current with a predetermined value;

an adjustment circuit for adjusting said measurement voltage U so that said measurement evoked current is substantially equal to said predetermined value so that said measurement evoked current is substantially constant;

a difference forming unit which forms a difference Δ

U=U−

U_min which corresponds to an oxidation/reduction reaction at said working electrode, wherein U_min is a minimum voltage selected as a reference level; and

an evaluation circuit for using said difference Δ

U=U−

U_min to calculate concentration variations of said chemical entity in said liquid.

8. A medical implant comprising:

a working electrode and a counter electrode, said working electrode being in contact with a liquid medium in which at least one chemical entity is dissolved, a voltage source for impressing a measurement voltage U on said working electrode relative to said counter electrode, said dissolved chemical entity reacting to said measurement voltage U by oxidation or reduction at said working electrode, resulting in production of a measurement evoked current, a comparator which compares said measurement evoked current with a predetermined value, an adjustment circuit for adjusting said measurement voltage U so that said measurement evoked current is substantially equal to said predetermined value so that said measurement evoked current is substantially constant, a difference forming unit which forms a difference Δ

U=U−

U_min which corresponds to an oxidation/reduction reaction at said working electrode, wherein U_min is a minimum voltage selected as a reference level, an evaluation circuit for using said difference Δ

U=U−

U_min to calculate concentration variations of said chemical entity in said liquid; and

a therapy administering unit which is supplied with said concentration variations calculated by said evaluation unit for administering a therapy dependent on said concentration variations.

9. A medical implant as claimed in claim 8 wherein said therapy administration unit is a pacemaker which administers pacing pulses having pacing parameters associated therewith which are varied dependent on said concentration variations.