Electrode device

© Beginning of patent period: June 15, 1973 Longest possible duration;

© Issued on: 25.Feber 1974 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

OE 313480 - 2 -

Nr.313480

The invention relates to a bloodless measurements in connection with the concentration or the

Partial pressure of a gas in the blood suitable electrode arrangement.

It is known to measure the partial pressure of a gas in the blood, for example of oxygen or CO2, with bloodless blood. For this purpose, an electrode is applied to a suitable site of the body surface of the subject such as the scalp, a wrist, the inner canthus of an eye, etc. With a suitable bias of the electrode, an electrochemical reaction takes place on its surface with the gas diffused from the blood through the tissue, in the case of oxygen, for example, its reduction to OH ions. The occurring current is measurable and under certain conditions is proportional to the concentration or partial pressure of the gas in the blood.

Depending on the particular measurement requirements, bare or membrane-covered electrodes are suitable, with platinum being the preferred electrode material. As a material for the membrane, for example, polypropylene, polyethylene, polytetrafluoroethylene, polyester, etc., has proved advantageous.

It has been found that the measured values ​​are not only a function of the actual partial pressure of a gas in the blood, but also depend on the local perfusion of the tissue in the measuring range of the electrode. It may therefore be advantageous for certain measurements to reduce the influence of the perfusion on the measurement results by hyperaemicizing the skin in the measurement area. It has already been proposed to use for this purpose suitable vasodilators, for example histamine, papaverine, nicotinic acid, etc. However, the use of such preparations is problematic in certain cases, for example when measuring on the inner canthus of the eye.

Accordingly, the invention has for its object to provide an electrode assembly of the type described above, with the local circulation in the measuring range of the electrode is increased without additional use of hyperemic preparations.

According to the invention this is achieved in that the electrode assembly is provided with a measuring electrode and a heater for heating the measuring electrode for thermal stimulation of the local blood circulation.

In the following, exemplary embodiments of the invention are described with reference to the drawings. 1 shows a longitudinal section through an electrode arrangement according to the invention with a bare electrode for detecting a substance dissolved in the blood, for example a gas, and FIG. 2 shows a section through an electrode arrangement according to the invention for partial pressure measurements.

The electrode arrangement shown in Fig.l is particularly suitable for detecting a transported through the circulation gas, such as hydrogen, on the inner canthus of an eye. Thus, for example, the transport time of an inhaled gas in the bloodstream from the lungs to the inner canthus can be measured with it. It has a short response time.

A platinum electrode - 11 - is intended to be placed on the skin of the inner canthus of an eye. For this purpose, a cylindrical shape with about 3 mm diameter and a spherical rounded support surface at the top is advantageous. The platinum electrode -11- is solid and good heat-conducting in one

Copper socket -12- used. The copper socket -12 - also has a substantially cylindrical

Shape of about twice the diameter of the platinum electrode with an axial bore for receiving the platinum electrode. On the opposite side of this bore a second axial bore of smaller diameter is attached, which leads to the vicinity of the platinum electrode -11-. This second axial bore serves to receive a temperature measuring element - 14-, for example, a thermistor and its

Supply line -17-.

The lateral surface of the copper socket -12- is interrupted by a circumferential, wide depression, which serves to receive a heating coil -13--, for example, from a resistance wire. The supply line

--18- to the heating coil is led from the front side of the copper socket -12- through an eccentric bore. A lead -16- for the electrode current is fixed in another eccentric bore.

The entire assembly is of a substantially cylindrical capsule - 15- plastic, eg PVC,

Polyamide, surrounding only the tip of the platinum electrode -11- and on the opposite side of the supply lines -16, 17, 18-, which are conveniently combined to form a cable, leaves open.

The electrode arrangement shown in Fig. 2 is especially for quantitative partial pressure measurements of O2, H₂etc. suitable for the skin. A disc-shaped platinum electrode -21- is in thermoconductive contact with a substantially cylindrical copper block -22- of the same diameter as the platinum electrode

--21-. The lateral surface of the copper block -22 - has a circumferential recess in which a

Heating coil -23- is located. The supply line - 28- leads to the heating coil through a bore which connects the platinum electrode -21- opposite end face of the copper block -22- with the circumferential recess. Another eccentrically arranged bore in this end face is used to attach the feed line -26- for the electrode current. In addition, from the same side of the copper block, an axial bore is made in the vicinity of the platinum electrode -21-, in which there is a temperature measuring element -24- with the leads -27-.

A silver ring serving as a reference electrode, which is chlorinated on one of its flat surfaces - 3 -

No.313480 and having an inner diameter greater than the diameter of the platinum electrode is arranged so that its chlorinated surface lies in a plane with the surface of the platinum electrode -21- opposite the copper block -22-. A lead -31- to the silver ring is guided parallel to the leads -26,27,28- on the same page and conveniently combined with these to form a cable. The entire assembly is surrounded by a flat cylindrical capsule -25- of a suitable plastic such as PVC, nylon, etc., with one end face of the capsule -25- in the plane defined by the platinum electrode and the silver ring and the corresponding platinum surface and leaves the chlorinated silver surface. The entire face including the platinum or AgCl surface is coated with an electrolyte film -32- and covered with a suitable membrane -33-, eg Teflon. This diaphragm serving as the bearing surface of the electrode arrangement is held in place with a substantially annular capsule. In order to exclude the gas from the outside, the gap between the two capsules -25 and 34- is sealed by an O-ring -35-, which is embedded in corresponding annular grooves.

It has been shown that a heating of the skin in the region of the measuring electrode to about 40 to 42 ° C makes sense. A noticeably higher temperature is usually not allowed because of the skin lesions caused by them. In operation, the heating coil is supplied with a current whose intensity is regulated by means of the temperature determined by the temperature measuring element. For this purpose, any known temperature control circuit is suitable if it is sufficiently sensitive.

The electrode according to the invention is particularly advantageous since it allows hyperemia in the region of the tissue and the skin in which the measurement is made, without the need for additional preparations. This is particularly advantageous if the measurement of such body surface sites in question in which the application of hyperemic preparations is problematic. Even in the case of mass examinations in the sense of preventive medicine, it is advantageous if the examined persons do not have to be prepared before the measurement.

A significant additional advantage of the inventive electrode is that the increased stabilized working temperature, a significant stabilization of the electrode reaction and thus the measurement is achieved by the influence of fluctuations in ambient temperature, ie the temperature of the ambient air and / or the skin is turned off.