Electrode arrangement suitable for measuring the concentration of a gas in blood

Electrode arrangement suitable-for measuring the concentration of a gas in blood

SPARAMEDICA A.Gi7.,.4 4701/34

This invention relates to an electrode arrangement. in vivo suitable for bloodless measurement in connection with the concentration or the partial pressure of a gas in blood.

It is known to measure bloodlessly the partial pressure of a gas in the blood (for example of oxygen or CO^) with electrodes. For this purpose, an electrode is applied to a suitable position of the body surface of the patient, for example on the scalp, a wrist or the inner can thus of an eye. With a suitable initial electrode potential an electrochemical reaction takes place on the electrode surface with gas diffused through the tissue from the blood (in the case of oxygen, for example, its reduction to OH״ions). - The current which is thereby generated is measurable and under certain, circumstances is proportional to the concentration or to the partial pressure of the gas in the blood.

Bare electrodes or electrodes covered with a membrane are suitable, depending on the particular measurement requirements, platinum being generally eminently suitable as the electrode material. Polypropylene, polyethylene, Teflon״ and Mylar, for example, have proved to be advantageous as the membrane material. The words Teflon and Mylar are Trade Marks. ״

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 in addition also further depend on the local blood circulation of the tissue in the region of the electrode. For certain measurements, it may, therefore, be of advantage to decrease the influence of the blood circulation on the results

Bu/12.8.71. ' ’ -237643/2

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by hyperaemising the skin in this region. It has already been proposed to use suitable vasodilating preparations (for example, histamine, papaverine or nicotinic acid) for this purpose. However, the application of such preparations is problematical in certain cases, for example in the case of measurement on the inner canthus of the eye*’

It is an object of the present invention to provide an electrode arrangement suitable for bloodless in vivo measurements, in connection with the concentration or the partial pressure of a gas In blood, with which the local blood circulation in the measuring region of the electrode is increased without additional application of hyperaemising preparations^

According to the present invention there is provided an electrode arrangement suitable for bloodless in vivo measurement in connection with the concentration or the partial pressure of a gas in blood, said electrode arrangement comprising in . combination heating means for the direct contact thermal stimulation of the local blood circulation, and means for the continuous monitoring of blood gas concentration or blood ׳gaspartial pressure, both said means capable of being operated simultaneously,

For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawing, in whichjFigure 1 shows a longitudinal sectional view through an electrode arrangement according to the invention with a bare electrode for detecting a substance (for example, a gas) dissolved in blood, and

Figure 2 shows a sectional view through an electrode arrangement according to the invent ion for partial pressure measurements. ,

Referring now to the drawings, the electrode arrangement shown in Figure 1 is particularly suitable for detecting at the inner canthus of an eye a gas (for example, hydrogen) transported by the circulation. With this electrode arrangement there can accordingly be measured, for example, the transport time of an inhaled gas in the blood stream from the lung to the inner canthus. This electrode displays a short response time.

A platinum electrode 11 is for applying to the skin of the inner canthus of an eye. A cylindrical shape, ca 3 mm diameter and having a spherically rounded-off application surface at the tip, is advantageous for this purpose. The platinum electrode 11 is inserted firmly and with, good heatconduction in a copper socket 12. The copper socket 12 likewise has a substantially cylindrical shape, the diEime ter being about double that of the platinum electrode, with an axial bore to receive the platinum electrode. On the face opposite the axial bore is provided a second axial bore of smaller diameter which leads to the vicinity of the platinum electrode 11. The second axial bore is for receiving a temperature measuring element 14, for example a thermistor, and a lead 17 therefor.

The outer surface of the copper socket 12 is interrupted by an encircling, bread recess which receives a heating winding 13, for example of resitance wire. A lead 18 to the heating winding 13 passes from the end-face of the copper socket 12 through an eccentric boring. A lead 16 for the electrode current passes through a further eccentric boring. The whole arrangement is surrounded by a substantially cylindrical capsule 15 of plastics material (for example of PVC or nylon) which only leaves exposed the tip of the platinum electrode--וו and, at the opposite end, the leads 16, 17, 18, which are expediently united into a cable »

The electrode arrangement shown in Figure 2 is especially suitable for quantitative partial pressure measurements of 0₂, Hg etc on the skin. A disc-shaped platinum electrode 21 is in heat-conducting contact with a substantially cylindrical copper block 22 of the same diameter as the platinum electrode

21. The outer surface of the copper block 22 is provided with an encircling recess in which is located a heating winding 23« A lead 28 to the heating winding passes through an eccentric bore which connects the end-face of the copper block 22 opposite the platinum electrode 21 with the encircling recess« A further eccentrically disposed bore in the end-face is for the attachment of a lead 26 for the electrode current. In addition, directed from the same end-face of the copper block into the vicinity of the platinum electrode 21 is an axial bore in which is located a temperature-measuring element 24 having leads 27.

A silver ring 29» serving as a reference electrode, which is chlorinated on one of its flat faces and which has an internal diameter greater than the diameter of the platinum electrode, is so arranged that the chlorinated face lies in a common plane with the face of the platinum electrode 21 opposite the copper block 22. A lead JI to the silver ring is directed parallel with the leads 26, 27 and 28 and expediently united with these leads into a cable. The whole arrangement is surrounded with a smoothly---------------------------------------5 cylindrical capsule 25 of a suitable plastics material (for example, PVC or nylon), one end-face.of the capsule 25 lying in the common plane of the platinum electrode and the silver ring and the corresponding platinum surface and the chlorinated silver surface not being covered thereby. The whole end-face, including the platinum and chlorinated silver surface, is coated with an electrolyte film 32 which is itself covered with a suitable membrane 33 (for example of Teflon). The membrane 33» serving as the application surface of the electrode arrangement, is retained by a substantially annular capsule 34. In order to exclude the ingress of gas from outside,the gap between the. two capsules 25 and 34 is sealed with an O-ring 35 which is fitted in corresponding ring grooves.

Xi has been found that heating of the skin in the region of the measuring electrode to about 40-42°C is reasonable. A markedly higher temperature is as a rule not admissible because of skin lesions caused thereby. In operation, the heating spiral is provided with a current the strength of which is regulated with the aid of the temperature measured by the temperature-measuring element. Any suitable temperatureregulation circuit may be used for this purpose, so long as it is sufficiently sensitive.

An electrode arrangement in accordance with the invention is particularly advantageous since it makes it possible to hyperaemise in the region of the tissue and the skin in which the measurement is undertaken without additional preparations having to be applied. This is particularly favourable when the measurement is_ to be made at positions on the body surface at which the application of hyperaemising preparations is problematical. Also, in the case of mass investigations, as is often used in preventive medicine, it is advantageous when the investigated persons to not have to be prepared before the required measurement may be taken.

׳ ׳ .

A substantial additional advantage of the electrode arrangement in accordance with the invention is a considerable stablisation of the electrode reaction and therewith of the measurement which is achieved through the elevated statilised working temperature, since the influence of fluctuations of the ambient temperature, that is both of the surrounding

' ’ .. ־ ׳ ־ ־ ' ¹ air and of the skin, is virtually eliminated.