CH653236A5 - Pickup for the transcutaneous polarographic determination of the partial pressure of a gas - Google Patents

Description

The present invention has set itself the goal of improving such transducers for the transcutaneous polarographic determination of the partial pressure of gases, specifically with regard to thermostatting by heating the anode and with regard to the heat transfer to the measuring cells of the skin in order to prevent hyperaemia increase and achieve a better correlation to the arterial partial pressure of the gas.

With the formation of transducers for the transcutaneous polarographic determination of the partial pressure of gases according to the teaching of claim 1, these requirements are advantageously met without having to do without the favorable properties of previously proposed multi-cathode systems for transcutaneous polarographic transducers. Since the cross-section of the individual measuring cells is considerably smaller than the cross-section of a measuring cell that is to contain several cathodes, and since the good heat-conducting anode material remains between the individual measuring cells in a sufficiently thick intermediate layer, the heat conduction is from the heated edge of the anode block to in the middle of the anode, where the measuring cells are distributed, not obstructed. These intermediate layers form good thermal bridges and heat conductors to the individual measuring cells and to the skin areas that lie below the measuring cells, so that the process of hyperaemia is very favored. The hyperaemia of the body area covered by the sensitive parts of the sensor is therefore practically uniform and without delay.

Advantageous developments of the invention are described in the dependent claims. To take advantage of the invention, it is expedient to use at least three measuring cells of the type defined in claim 1 and to arrange them in the corners of a uniform polygon or evenly on a circumference. The thickness of the remaining intermediate layers made of the metallic anode material need not be very large, so that the mutual distance between the individual measuring cells is less than their distance from the jacket or edge of the anode block. As is known per se, this is equipped with an electrical heating resistor, preferably in the form of a heating winding surrounding the jacket of the block. For temperature monitoring and for controlling the heating output in the sense that a pre5

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certain temperature is maintained in the anode block, a temperature sensor is expediently installed directly in the anode block, which is connected via wire strands, which are accommodated in the signal line, to the control circuit for the heating power, which is accommodated in a remote measuring device, whereby the temperature is kept constant.

The invention is described below with reference to an embodiment of a measurement sensor, which is shown in the figure in a section parallel to the sensor axis. To simplify the description and drawing, this sensor has only two cathodes. In practice, there will preferably be three or more.

Polarographic sensors, the further development of which is the aim of the invention, generally have a flat disk or plate-like shape with a diameter of 1 to 2 cm. The organs that are important in terms of measurement technology are the cathodes 1, 2, ... preferably made of platinum or platinum wire and a reference electrode preferably made of silver or a silver alloy, which in the embodiment according to the invention forms an anode block 5. Although only two such cathodes 1 and 2 are shown in the figure, three or more of them will preferably be used. Between these cathodes and the anode, when a voltage is applied, a polarographic current flows in the presence of oxygen, which is fed via signal lines 1 a, 1 b and 13 a to a current measuring device or the registration and evaluation device. The lines are usually combined in a single patient line.

According to the teaching of the invention, each metal cathode 1, 2, ... is now arranged within its own insulating body, cylinder or prism made of glass and forms a measuring cell M 1, M 2, ... with each of these bodies, from which the ends of the associated ones Protrude cathodes into the electrolyte space 4. This electrolyte space is covered on the outside by a membrane 15, which comes to rest when the sensor is applied to the skin or body area, at which the oxygen partial pressure or the partial pressure of the gas to be measured is determined and continuously monitored should.

The organs mentioned are preferably inserted in a base body 11 made of plastic, via which the membrane 15 is stretched by means of a ring 8 made of plastic, leaving a thin space 4. In the latter there is the pasty or liquid electrolyte, which creates the conductive connection between the cathodes 1, 2, ... and the anode 5. An annular socket 10 made of plastic forms the outer connection into which the end of the patient line 9 opens. An electrical resistance winding 6, which is placed around the jacket of the anode block 5 and is connected via the connecting line 6a to the current source and the control circuit for the heating power, serves as the heating element. To control and regulate the temperature, a temperature sensor 7 is also inserted in the anode block 5 and is connected to the control circuit via the lines 7a. The temperature in the anode block is expediently kept at a constant value above the normal body temperature for adequate hyperaemization without endangering the skin area. The individual measuring cells M1, M2 ... from the insulator bodies 1b, 2b ... with the cathodes 1, 2 ... are inserted into bores in the anode body 5, which are arranged in a uniform distribution in the central region of the anode body.

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1 sheet of drawings

Claims (9)

653 236 1. Transducer for the transcutaneous polarographic determination of the partial pressure of a gas, in particular oxygen, with at least two cathodes (1 and 2), which are arranged within a common anode (5), and a space filled with electrolyte (4), which is closed with a membrane (15) which is permeable to the gas to be measured, characterized in that each metal cathode (1, 2, ...) is arranged within its own electrically insulating body 1b, 2b, ...) which is provided by the metal of the anode (5) is surrounded and with which each cathode forms a measuring cell Ml, M2, ...), and that the metal body of the anode is equipped with an electrical heater (6) and a temperature sensor (7), with the help of which it is kept at a constant temperature. 2. Sensor according to claim 1, characterized in that the electrically insulating bodies 1b, 2b, ...) are cylindrical. 2nd PATENT CLAIMS 3. Sensor according to claim 1, characterized in that the electrically insulating body (lb, 2b, ...) are prismatic. 4. Sensor according to claim 1, characterized in that the electrically insulating body (lb, 2b, ...) consist of glass. 5. Sensor according to claim 1, characterized in that the electrically insulating body (lb, 2b, ...) consist of plastic. 6. Sensor according to claim 1, characterized in that at least three measuring cells (Ml, M2, ...) are arranged within the block-like anode (5), and that the measuring cells (Ml, M2, ...) are viewed in cross section Form corners of an even "square. 7. Sensor according to claim 1, characterized in that at least three measuring cells (Ml, M2, ...) are arranged within the block-like anode (5), and that the measuring cells (Ml, M2 ...) viewed in cross section, evenly are arranged on a circumference. 8. Sensor according to one of the preceding claims, characterized in that the measuring cells (Ml, M2, ...) are arranged in a central zone of the block of the anode (5) in such a way that their mutual distance is less than the distance from the jacket or edge of the anode block (5). 9. Sensor according to claim 1, characterized in that the diameter of the individual cathodes (1,2, ...) is 10 µm to 50 µm. There are known transducers for the transcutaneous polarographic determination of the partial pressure of gases, in particular oxygen in living tissue or in the blood (US Pat. No. 3,929,603 and DE-OS 2,835,730), which have one or more cathodes and are equipped with an anode. In the cases mentioned, all cathodes, e.g. consist of platinum or gold, formed as thin cylindrical tubes or as wires and arranged inside a common, heated anode block made of silver. They are insulated against the anode block using glass or an epoxy resin. The insulation also serves to hold and fix the cathodes. Furthermore, transducers for transcutaneous polarographic determination of the partial pressure of gases have already been proposed (KIMMICH, HP; SPAAN, VG; KREUZER, F .: Transcoutaneous Measurement of pa02 at 37 ° C with a Triple Electrode System, Acta Anesthetic Scand. Suppl. 68; 28 ... 32 (1978)), in which several cathodes are each arranged in their own insulating body, each of which is surrounded by a heated anode, these anodes being thermally and electrically insulated from one another. Finally, with such sensors, several cathodes have already been arranged in their own insulating body within a common anode that is not heated (FATT, I. and HELEN, R. St., A Multicathode Polarographic Oxygen Sensor and its Performance. J. Appi. Physiol. 27: 435 ... 437 (1969)). The advantages of the multi-cathode system with individual micro-cathodes for transcutaneous sensors are as follows: The measured value, i.e. the partial pressure e.g. oxygen is averaged over a larger area of the skin. According to the number of cathodes, the measuring current is multiplied without the favorable properties of the microcathodes (low 02 consumption, short time constant) deteriorating, as would be the case if one wanted to achieve the same multiplication of the measuring current by enlarging a cathode. However, the prerequisite is that the distance between the cathodes is greater than the diameter of the individual cathodes.