Three electrode hydroquinone subcutaneous equilibrating tonometer

• US 4,803,991 A
• Filed: 09/24/1986
• Issued: 02/14/1989
• Est. Priority Date: 09/24/1986
• Status: Expired due to Fees

• Current Assignee: Baxter International Inc.
• Original Assignee: Baxter Healthcare Corporation (Baxter International Inc.)
• Inventors: Alena, Richard L., McIntyre, William H.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US06/911,277
• Time in Patent Office: 874 Days
• Field of Search: 128/635, 204/403, 204/406, 204/412, 204/415, 204/431
• US Class Current: 600/360
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence

Abstract

A closed tonometer for subcutaneous insertion is disclosed having a small closed equilibrating bath. Three noble metal electrodes, preferably platinum (Pt), communicate through electrical conductors to the bath at spacings exceeding 0.2 mm. Each noble metal electrode is typically exposed to the bath by embedding the noble metal in a dielectric and cutting both dielectric and electrode so that the exposed electrode is flush with and a part of the closed bath wall. The bath is contained within an oxygen permeable membrane -- preferably Silastic® a registered trademark of Dow Corning Corporation of Midland, Michigan. The bath contains a sodium chloride (NaCl) solution, preferably 0.9%, and small amounts of a hydroquinone such as a tenth of a gram of pure ascorbic acid per 30 ml of NaCl solution. One of the noble metal electrodes becomes a quinhydrone reference electrode preserving a precise voltage differential with respect to the electrolyte bath. This voltage of the quinhydrone reference electrode is passed through a voltage follower amplifier to a voltage adder where it is added to a reference bias voltage. Output from the adder passes to a second electrode serving as an anode. The anode supplies current to the enclosed bath sufficient to maintain the bath at constant voltage with respect to the cathode. The current at the cathode is thus solely a function of oxygen tension equilibrated from the measured tissue. There results a tonometer of miniature dimension having true analytical output.

Claims

1. A tonometer for placement subcutaneously in a patient for the measurement of oxygen tension, said tonometer comprising:

an oxygen equilibrating tube, closed at one end and open at the other end;

a solution filling said tube, said solution including an electrolyte and a hydroquinone;

a dielectric base plugging the open end of said tube to maintain said solution as a closed bath confined by said dielectric base and tube; and

,

said dielectric base having at least three nobie metal electrodes with attached conductors communicated to said closed bath,

one of said electrodes comprising a reference electrode,

said reference electrode measuring the voltage of aid solution filling said bath;

a second of said electrodes serving as an anode;

a third of said electrodes serving as a cathode;

means responsive to the voltage from said reference electrode to maintain the voltage at said anode such that the voltage between the bath and cathode remains constant and therefore the current between cathode and anode will be a function solely of oxygen tension in the equilibrated solution.

2. The invention of claim 1 and wherein said oxygen equilibraitn tube is Silastic®

.

3. The invention of claim 1 and wherein solution filling said tube includes a sodium chloride electrolyte.

4. The invention of claim 1 and wherein said hydroquinone is chosen from a group including ascorbic acid, iso-ascorbic acid and sodium ascorbate.

5. The invention of claim 1 and wherein said hydroquinone in said solution includes 0.10 of a gram per 30 ml of fluid.

6. The invention of claim 1 and wherein said three noble metal electrodes are flush with a wall of said dielectric base, said wall exposed to said closed bath.

7. The invention of claim 6 and wherein said noble metal electrodes are Pt.

8. A tonometer for placement subcutaneously of a patient having an attached circuit for the measurement of oxygen tension, said tonometer comprising:

an oxygen equilibrating tube, closed at one end and open at the other end;

a solution filling said tube, said solution including an electrolyte and a hydroquinone;

a dielectric base plugging said open end of said tube to maintain said solution as a closed bath confined by said dielectric base and tube, dielectric base having three noble metal electrodes with attached conductors communicated to said closed bath;

a circuit including a voltage follower amplifier having an input and an output, said input communicated to one of said electrodes acting as a reference electrode;

an adder amplifier having an input and an output, the input of said adder amplifier being communicated to the output of said voltage follower, the output of said adder amplifier outputting to a second one of said electrodes acting as an anode to maintain said solution at a polarographic voltage with respect to a third electrode acting as a cathode; and

means for measuring current collected to said third electrode acting as a cathode whereby said cathode electrode acts as a current measurement electrode responsive to oxygen in said solution.