JPS6334734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in metal electrodes for continuously measuring gas concentrations in specimens, particularly changes in oxygen partial pressure in living organisms.

Conventionally, as a method for measuring changes in oxygen gas concentration in a solution, the principle of polarography has been applied to a metal separator electrode made of gold, platinum, platinum iridium, silver, etc.
Using an indifferent electrode made of silver chloride or the like, a small voltage (0.3 to 0.7 V) is applied between these electrodes, oxygen is reduced at the indifferent electrode (cathode), and an oxygen diffusion current is generated in the solution. Methods for measuring this are widely used.

On the other hand, the influence of oxygen gas concentration, that is, oxygen partial pressure, on living organisms is important, and it is especially important to accurately and continuously monitor changes in oxygen partial pressure in neonatal surgery, cardiac surgery, brain surgery, anesthesia, etc. With the increasing awareness of the nature of oxygen, there is an increasing demand for measuring changes in oxygen partial pressure by directly inserting the above-mentioned electrodes into living tissues or blood vessels.

However, since the above method is based on a diffusion current based on the concentration gradient between the cathode surface and the solution,
If a living body moves constantly and is not in a constant stable state, it is greatly affected by this movement, making it difficult to accurately measure minute oxygen partial pressures.

In order to improve this drawback, various studies have been carried out.The electrodes are separated by an oxygen-permeable membrane, and the so-called "Clarke electrode" has a built-in electrolyte, or the surface of the electrode (cathode) is made of hydrophilic polyhydroxyethyl methacrylate, cellophane, etc. A method has been proposed in which oxygen is transferred to the surface of an electrode by coating it with a water-swollen membrane and using water surrounded between molecules as a passageway, and some of these methods have been put to practical use.

However, the former has a large form and is difficult to insert into a living body, while the latter has a water-swollen membrane that changes the measurement sensitivity, especially the response, and is inferior in accuracy and becomes brittle when dried. Practical implementation has been delayed due to the risk of the coating being damaged during removal and being left behind inside the body.

In view of these current circumstances, the present inventors have determined that even if a fine metal wire electrode is inserted into living tissue or blood vessels,
After studying metal electrodes that can continuously, stably, and accurately measure oxygen partial pressure without being affected by tissue or blood movement, we found that we could achieve our goal by protecting the electrode tip surface. I discovered that.

That is, the gist of the present invention is to insert a thin wire metal electrode for polarography into a tube made of an organic polymer with an open end so that the tip of the electrode is set back from the open tip of the tube. and the metal electrode are brought into close contact with each other, and the relationship between the retreat distance L and the electrode diameter D is L/D≧2.
A gas concentration measuring electrode for insertion into a blood vessel is characterized by the following.

The present invention will be explained in detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view of an electrode according to the invention.
The metal electrode 1 referred to in the present invention is a thin noble metal wire. There is no limit to the thickness of noble metal electrodes, and some thick ones are several centimeters in diameter, but the reason is that they will not come off from the tissue, especially when inserted into heart tissue that vibrates strongly, such as in cardiac surgery. So, the diameter
It is preferably in the range of 20 to 200μ.

The surface of the metal electrode is generally covered with an insulating layer 2,
This insulating layer 2 does not have any adverse effects on living organisms, and can be made of a soft resin with excellent insulation properties.

For example, a suitable resin such as urethane resin or modified urethane resin may be used. Note that it may be colored to make it easier to distinguish it from living tissue and blood. Examples include white and black.

The present invention is to cover this thin wire metal electrode (including both those coated with an insulating material and those not coated) with a tube 3 having an open end as shown in FIG.

The tube 3 may be made of any material such as polyethylene, polypropylene, polyester, polyvinyl chloride, polytetrafluoroethylene (Teflon), polyamide, etc., but if it is to be inserted into a living body, it has no acute toxicity and is resistant to It is desirable to have thrombogenicity and sterilization resistance. Hollow fibers made of these materials are suitable for the tube. The inner diameter of the tube may be equal to or slightly larger than the diameter including the noble metal electrode wire diameter and the insulating layer, and has a diameter into which the electrode can be inserted. Insulation material 2
If the tube 3 is not coated, the tube 3 may serve as an insulating material. In this case, the tube must cover not only the tip but also the entire length of the thin metal wire. The tube needs to be in close contact with the thin wire metal electrode. For example, if there are microscopic voids, it is difficult to remove air and the oxygen partial pressure is not stable when measuring oxygen partial pressure, and it takes a long time to stabilize.

There are various means for adhesion, but for example, after inserting an electrode into the tube, it may be heated and stretched to make it into close contact, or the insulating layer may be coated with a silicone resin or the like and then inserted into the tube.

In FIG. 1, the upper end of the tube and the insulating layer are fixed with resin 4 for the purpose of complete fixation and complete airtightness. In FIG. 1, L indicates the distance from the tube opening tip to the metal electrode tip surface. D indicates the diameter of the thin wire metal electrode.

Due to the principle of polarography, when measuring the diffusion current of dissolved oxygen molecules to the cathode based on the oxygen concentration gradient generated between the solution and the cathode interface, the contact between the electrode and the solution must be kept stable. .

As in the present invention, by inserting the metal electrode so that the surface is set back from the tip of the tube, it is possible to form a stationary layer of solution on the metal electrode surface and create a stable contact state between the solution and the electrode. As a result, changes in oxygen partial pressure can be accurately captured with good responsiveness, without being affected by tissue or blood movement, with the electrode directly inserted into a living body.

The inventors studied the electrode diameter D and the retraction distance L with the aim of stabilizing the measurement, and found that
It has been found that if L/D≧2.0, the effect of oscillation is small and accurate oxygen partial pressure can be determined. On the other hand, when the electrode diameter D becomes 50μ or less, if L/D≧2.0 is followed, L becomes 100μ or less, but in this case, the surface area of the electrode decreases, so the electrolytic current also decreases, and the oscillation effect increases, making it difficult to obtain accurate It is difficult to measure the oxygen partial pressure.
Therefore, when the electrode diameter is small, L/D is preferably made larger than 2, and L is preferably at least 100 μm. On the other hand, if L is made extremely long, it will not last long and there will naturally be a limit, but this does not particularly limit the present invention. As explained above, according to the gas concentration measuring electrode of the present invention, the partial pressure of oxygen gas in a living body can be stably measured with little influence of oscillation.

In addition to measuring oxygen concentration in living organisms, the electrode of the present invention can also be used to
It is clear that this method can be used for any measurement of gas concentration in a sample that applies the principle of polarography.

Examples are shown below to clarify the effects of the present invention.

Example 1 Four types of platinum wires made of platinum with a purity of 99.9% and having diameters of 30, 50, 80, and 200μ and having a 15μ thick urethane coating layer were prepared. A 30 cm piece of each was cut out, and one end of each was cut out again at an angle close to perpendicular to the length direction to form a new electrode surface. The urethane sheath was removed from the remaining other end to connect it to the voltage application terminal.

Next is a wall thickness of 20μ inner diameter made of high-density polyethylene.
The above platinum wires are covered with tubes of 35, 55, 85, and 210μ, respectively, and the tubes protrude from the electrode surface, and the length of the protrusion, that is, the distance L from the tip of the electrode to the tip of the tube, and the electrode diameter D, respectively. The ratio L/D was adjusted to be 1.2, 2.5, 3.8, 5.0, and 12.5.

In addition, the gap between the platinum wire and the polyethylene tube is covered with chlorinated PP coated on the platinum wire urethane coating in advance.
It was filled and fixed with adhesive (Nippon Kasei Kogyo Co., Ltd. 14LB).

These coated electrodes were connected to the (-) pole as a related electrode, and an indifferent electrode made of Ag/AgCl was connected to the (+) pole, and placed in physiological saline, blown with air, and stirred (stirrer rotor 5 mmφ, length 20mm,
800r.pm), applied voltage -0.6V, electrolytic current ()
was measured.

Because the measurement system is stirred, the data fluctuates, but read the difference △I between the upper and lower limits and its average value, and calculate the fluctuation width Noise Ratio (%) using the formula below.
was calculated.

Noiseratio (%)=ΔI/I×100 FIG. 2 shows the relationship between Noise Ratio and L/D. That is, it can be seen that the noise rate becomes extremely small at L/D2. On the other hand, the diameter is 50μ
It can be seen that for smaller electrodes, excellent stability is obtained when L≧100μ.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of the electrode of the present invention, and FIG. 2 is a diagram showing the relationship between noise rate and L/D. In the figure, 1 is a metal electrode wire, 2 is an insulating layer, 3 is a tube, and 4 is a fixing resin.

Claims (1)

[Scope of Claims] 1. A thin wire-shaped metal electrode for polarography is inserted into a tube made of an organic polymer with an open end so that the tip of the electrode is set back from the open tip of the tube, and the tube is inserted into the tube. and the metal electrode are brought into close contact with each other, and the relationship between the retraction distance L and the electrode diameter D is L/D≧2. 2. The electrode for gas concentration measurement according to claim 1, wherein the retraction distance L is 100 μ or more.