GB2056689A

GB2056689A - Measured value receiver for the transcutaneous measurement of physiological data

Info

Publication number: GB2056689A
Application number: GB8026162A
Authority: GB
Original assignee: Hellige GmbH
Current assignee: GE Medical Systems Information Technologies GmbH
Priority date: 1979-08-13
Filing date: 1980-08-12
Publication date: 1981-03-18
Also published as: DE2932739A1; JPS5628744A

Abstract

A membrane (2) of a measuring receiver for the transcutaneous determination of substances, such as oxygen, in the blood and in body tissue is clamped over the sensor 7 encircled by support port 8 of the housing (1) by a ring (3) which is releasably fitted in a groove (6) without screwing or the use of screws. The ring (3) is snap-fitted by means of a collar (10) which snaps into a grooveway (10a); alternatively the ring can have a frusto conical surface so that it thickens inwardly. The membrane is permeable to the substance to be measured but impermeable to the electrolyte between electrodes (not indicated) in the sensor part (7). The signal leads (5) from inter alia the electrodes come out at the side of the housing (1), near the working surface (11). The membrane may be formed integrally with the ring. <IMAGE>

Description

SPECIFICATION Measured value receiver for the transcutaneous measurement of physiological data The invention relates to measuring receivers for the transcutaneous determination of the concentration of substances, such as the partial pressure of gases, in the blood or in body tissue.

When it is a matter of determining the concentration of substances in the blood and in body tissue, transcutaneous measuring receivers, that is to say, measuring receivers which only have to be applied to the skin, can be used in many diagnostic and physiological measuring procedures owing to the ability of many chemical substances, which are contained in the body tissue or in the blood, or are transported by the blood, to diffuse through the walls of the arteries and veins, through the body tissue and through the skin with the result that, in time, equilibrium of the concentration of these substances in the various zones of the body is established.The measuring receivers then have to be constructed such that the substance in question also reaches the sensor part of the receiver where, corresponding to the concentration, electrical signals, or electrical signals converted to measuring signals are produced in accordance with various physical principles, for example photometrically, electrochemically, oxymetrically in the case of oxygen, and particularly polarographically. These signals are fed to an evaluation part for further processing, such as visible representation, recording or storage. Since the conventional blood-invasive diagnostic and physiological measuring procedures can be avoided by means of transcutaneous measuring receivers, these measuring receivers are being used to an increasing extent in clinical and medical fields.

Transcutaneous measuring receivers have reached a very high state of development with respect to their construction, particularly for polarographic determination of the partial pressure of gases, particularly oxygen, in the blood. Therefore, the following explanation of the invention will be based on transcutaneous, polarographic measuring receivers of this kind. However, the aim of the present invention also relates to other types of transcutaneous measuring receivers, and the invention is equally applicable to, and recommended for, these other types of measuring receivers.

In general, polarographic measuring receivers have a compact cylindrical configuration having a diameter of only a few centimetres and hitherto approximately the same height. The actual sensor part comprises at least one measuring electrode and a counter-electrode in electrical contact with one another by way of an electrolyte, and a separating membrane which is stretched over the working face of the receiver provided for contact with the skin and which seals the sensor part in an air-tight manner relative to the ambiency but which must be permeable to the substance to be analysed, so that the said substance, after passing through the skin, can also diffuse through the membrane to the electrodes of the sensor part.

Since the blood supply to the body tissue is generally increased by heating inducement of hyperaemia, thus also increasing the supply of the substance to be analysed, this effect is utilised to increase the sensitivity of measurement by electrically heating the polarographic transcutaneous measuring sensors, advantageously by means of a built-in electrical heating resistor. The heat produced is to be transmitted by way of the receiver housing and through the skin to the body tissue.Therefore, the membrane is not generally stretched across the entire face of the receiver, but only across the sensor part, and the latter is surrounded by a housing part, made particularly from metal, which serves to conduct heat to the skin from the source of heat fitted in the receiver and which also serves as a support part whose surface extending in the end face also serves as a support for securing an interchangeable adhesive ring by means of which the entire receiver is fixed to the skin during the measuring operation. Finally, this support part also includes the means and measures for securing the membrane to the sensor part in an air-tight manner.

In a recent proposal the membrane placed over the sensor part is held by a plastics ring, and the said parts are rigidly connected to the housing body of the receiver by means of an external screw ring. The end face of the screw ring forms the support surface for the receiver when applying it to the skin, and the support for the double adhesive ring by means of which the receiver is fixed to the skin.This construction requires two parts for securing the membrane to the sensor part and leads to a relatively high type of construction, so that the signal line, which connects the receiver to the evaluation unit, enters the housing relatively high either at the upper edge or at the surface of the housing which is located opposite the end face, so that a lever-arm or tilting effect readily ensues and loosens or interrupts contact of the receiver with the skin and thus adversely effects the measuring operation.

In another known embodiment of polarographic measuring receivers (see Published German Patent Specifications (Offenlegungsschrift) Nos. 21 45400, 2365477 and 2514478), although only one clamping ring is used which presses the membrane substantially flatly against the end wall of the housing and is held on the outer surface of the receiver either by a snap- or clamp-fastening or is screwed thereto, this construction has the disadvantage that, when using a snap- or clamp-fastening on the periphery of the housing, the clamping ring can be readily torn off, so that the receiver also loses contact with the surface of the skin. On the other hand, owing to the screwing operation, the fastening of a screw ring takes more time when covering the measuring electrode with the membrane.Finally, in these embodiments, in which only one clamping ring is used, the membrane is clamped very unsatisfactorily owing to the fact that the membrane extends substantially flatly only in the end face of the receiver, so that, during a measurement, the distance between the membrane and the sensitive electrodes might vary, thus also reducing the sensi tivity of the receiver.

In view of the disadvantages of these known embodiments of transcutaneous measuring receivers, the invention is based on the following aims: The exchange and the fastening of the membrane should be possible with simple means and without time-consuming measures, such as screwing, without the support part having to be removed or loosened. The functions of the support part as a contact surface for the adhesive ring or double adhesive ring, and as an element for transferring heat from the heating device of the receiver to the zone of the body, are to be retained.The support surface of the support member and the contact surface of the membrane in the zone of the body should, as far as possible, be aligned in one plane, so that, for all practical purposes, the two parts are in large-area and uniform contact with the skin of that part of the body from which measurements are to be taken, in order to obtain satisfactory heat transfer for inducing hyperaemia and low diffusion resistance to the substance to be measured. Finally, in particular, the construction in accordance with the invention is to provide the receiver with a disc-shaped configuration which is as flat as possible, instead of a compact cylindrical configuration.Nevertheless, this configuration is to permit the signal lead to be connected to the cylindrical surface of the receiver housing from the side and as close as possible above the skin, so that the signal lead cannot exert upon the receiver any lever-arm effects which could loosen contact with the surface of the skin.

Accordingly, the present invention resides in a measuring receiver for the transcutaneous determination of the concentration of substances in the blood and in body tissue, the sensor part of which measuring receiver is sealed in a gas-tight manner relative to the outside by a membrane which is permeable to the substance to be measured and which is stretched over the front or measuring surface of the sensor part of the receiver lying in the working face provided for contact between the receiver and the skin during the measuring operation, the sensor part being encircled by a support part of the receiver housing, the working face having therein an annular groove which surrounds the sensor part and which is open towards the working face-and a clamping ring being inserted in a non-screwed and releasable manner into the groove to clamp and secure the membrane by its periphery.

The invention will be further described, by way of example, with reference to the drawings, in which: Figures 1 and 2 are radial cross-sectional views of two embodiments of the receiver.

The illustrated measuring receivers for trans cutaneous polarographic measurements on the skin for the purpose of determining the concentration of various substances, such as oxygen in the blood and in the body tissue, have a receiver housing 1 which can have a flat, disc-like configuration as shown, since the signal lead 5, which connects the receiver to the evaluation, display or recording unit (not shown), can enter the outer surface of the receiver housing 1 from the side closely above the working face 11 of the receiver which is applied to the skin of the patient or subject during measurement. A membrane 2 is stretched over the sensor part (7) of the receiver housing. It serves to separate an electrolyte from the outside and is permeable to the substance, such as oxygen, being measured but impermeable to the electrolyte.Electrodes (not shown) in the housing part 7 contact the electrolyte.

The leadsfortransmitting the measuring signals from the electrodes in sensor part 7 of the receiver to the evaluation unit, the sensor leads for feeding an electrical heating resistor accommodated in the receiver housing 1, and, finally, the sensor lines for monitoring and regulating the temperature attained, can be combined in the signal lead 5. The low position at which the signal lead enters the receiver housing is rendered possible by the fact that neither the support member 8 nor a part thereof has to be removed in order to exchange the membrane 2, the support part 8 being an integral component of the housing 1.

The said structural characteristics are the result of the membrane 2 being held under tension across the.

sensor part 7 only by means of a clamping ring 3 which is pressable in a non-screwed manner into a groove 6 surrounding the sensor part and open towards the working face 11 so as to clamp the membrane 2 by its periphery, the clamping ring being releasable only manually. A large-area construction, compared with the thickness or height of the receiver, of the annular support surface 8a of the support part 8 and of the front measuring surface 7a of the sensor part which is covered by the membrane, is important for the measuring operation and also for the transmission of heat from the heat receiver 1 to the zone of the body covered thereby, and a uniform contact is ensured by virtue of the fact that these surfaces and the outer surface 3a of the clamping ring extend continuously and flush with one another.

In order to fit the clamping ring 3 in the groove 6 in a rigid, non-screwed manner, the cross sections of the groove 6 and the clamping ring 3 located in planes radially of the axis of the receiver are substantially of identical or complementary configuraton. The clamping ring is retained in the groove 6 in a non-screwed manner solely by means of a press-, clamping- or snap fastening. For this purpose, in accordance with Figure 1 for example, at least one of the inner and outer surfaces of the clamping ring 3 has a preferably continuous collar 10 which, upon pressing the clamping ring into the groove 6, snaps into a complementary grooveway 10a in the corresponding side wall of the groove 6. In the construction shown in Figure 2, the groove 6 and the clamping ring 3 have complementary, trapezoidal cross sections, such that either lateral-boundary surface with the sensor part slopes slightly inwardly from the working face 11, resulting in a reduction of that cross section of the sensor part 7 which lies at right angles to the axis of the receiver, orthatthe outer boundary face 13 of the groove with the support part slopes slightly outwardly from the working face 11, resulting in a reduction in that cross section of the support part which extends at right angles to the axis of the receiver. Thus, the mem brane 2 is also tightly sealed solely by pressing in the clamping ring.Thus, either the inner lateral boundary surface of the groove 6 with the sensor part, or its outer boundary surface 13 with the support part, is of slightly frusto-conical construction.

However, since the membrane 2 has to be changed after a certain number of measurements, the clamping ring 3 has to be separable from the groove 6 for this purpose. For this purpose, in the construction of Figure 1, a location on the circumference of the groove 6 has a small bulge or widened portion 6 which extends into the support part, so that, by way of this bulge, the clamping ring can be gripped by means of a pin, tweezers or pincers, and can be removed from the press- or snap-fit, provided that the clamping ring is made from a resiliently deformable material particularly plastics material.

Figure 2 shows another solution whereby a location on the support surface 8a of the support part 8 is provided with a radially extending auxiliary groove 15 which is open towards the working face 11, and the outer wall of the clamping ring 3 incorporates a radially extending bar 14 whose configuration is complementary to that of the auxiliary groove and which is insertable into the latter and which has a somewhat larger radial length than the auxiliary groove 15, so that an end portion of the bar 14 extends out of the outer surface of the support member 8 and can be gripped by the finger tips and released from the auxiliary groove 15, whereby the clamping ring 3 itself can also be removed from the groove 6.

Therefore, no difficulties arise either when placing the membrane 2 onto the sensor part 7, or when pressing the clamping ring 3 into the groove 6 in order to obtain a tight fit, or when releaing the clamping ring 3 from the groove 6. Only simple rapidly performable manual operations are required, this being of great importance for clinical use when it is frequently a matter of seconds. The groove 6 also forms a demarcation between the sensor part 7 and the support part 8.

In a development of the present invention, the membrane 2 cån be directly welded by its periphery to the clamping ring 3. This is possible when the membrane is made from, for example, a resiliently deformable plastics material such as polypropylene and is coated with polyethylene and thus can be injection moulded onto a clamping ring 3 of polypropylene by the methods known for the processing of plastics material. Thus, the membrane itself cannot slip out of the hold imparted by the clamping ring 3. On the contrary, it is kept in the closest possible contact with the measuring surface 7a of the sensor part 7.

The individual elements of the sensor part, the elements serving for heating and temperature control, are not shown in detail.

The construction of the measuring receivers in accordance with the present invention fulfils the important requirements, set forth above, for practical use in the medical clinical field, the construction being simplified compared with embodiments known hitherto. It therefore constitutes a substantial practical advance. This construction is not only suitable and advantageous for transcutaneous polarographic measuring receivers, but is also suitable and advantageous for other kinds of transcutaneous receivers.

Claims

1. A measuring receiver for the transcutaneous determination of the concentration of substances in the blood and in body tissue, the sensor part of which measuring receiver is sealed in a gas-tight -manner relative to the outside by a membrane which is permeable to the substance to be measured and which is stretched over the front or measuring surface of the sensor part of the receiver lying in the working face provided for contact between the receiver and the skin during the measuring operation, the sensor being encircled by a support part of the receiver housing, the working face having therein an annular groove which surrounds the sensor part and which is open towards the working face and a clamping ring being inserted in a non-screwed and releasable manner into the groove to clamp and secure the membrane by its periphery.

2. A measuring receiver as claimed in claim 1, in which a signal or patient lead for connecting the receiver to the evaluation unit enters the wall of the support part from the side and closely behind the working face.

3. A measuring receiver as claimed in claim 1 or 2 in which the contact surface of the support part the measuring surface of the sensor part which is covered by the membrane and the outer surface of the clamping ring extend in the working face of the receiver and are flush with one another.

4. A measuring receiver as claimed in claim 1,2 or 3, in which the groove is disposed between the sensor part and the support part.

5. A measuring receiver as claimed in any preceding claim, in which the support part forms an integral part of the receiver housing and is not releasable therefrom for the purpose of servicing the receiver.

6. A measuring receiver as claimed in any preceding claim, in which the clamping ring has a cross section complementary to that of the groove and is retained in the groove in a non-screwed manner means of a press-, clamp- or snap- fastening and is releasable only by a manual operation.

7. A measuring receiver as claimed in claim 6, in which at least one of the inner and outer surfaces of the clamping ring has a preferably continuous collar which, upon pressing the clamping ring into the groove snaps into a grooveway of complementary configuration which is formed in the corresponding side wall of the groove.

8. A measuring receiver as claimed in claim 6, in which the groove has a trapezoidal cross section such that either its lateral boundary surface with the sensor part slopes slightly inwardly from the working face so as to reduce the cross section of the sensor part, or that the outer boundary surface of the groove with the support part slopes slightly outwardly from the working face to reduce the cross section of the support part, while the clamping ring has a cross section complementary to that of the groove, so that a secure fit is obtained solely by pressing the clamping ring into the groove.

9. A measuring receiver as claimed in any of claims 1 to 8, in which the support part- has at one location of its support surface a radially extending auxiliary groove open towards the working face, and the clamping ring has mounted on its outer surface a radially extending bar which is of complementary configuration to the auxiliary groove and which is pressable into the latter and is somewhat longer than the auxiliary groove, so that a portion of the bar extends out of the outer surface of the support part to enable the clamping ring to be readily removed.

10. A measuring receiver as claimed in any of claims 1 to 8, in which a location on the circumference of the groove is provided with a small widened portion which extends into the support part, so that, by means of this bulge, the clamping ring can be engaged by a tool, such as a pin, forceps or tweezers.

11. A measuring receiver as claimed in any preceding claim, in which the clamping ring is made from a resiliently deformable plastics materials.

12. A measuring receiver as claimed in any preceding claim, in which the membrane is made from a resiliently deformable plastics material.

13. A measuring receiver as claimed in any preceding claim, in which the membrane is made from polypropylene and is coated with polyethylene.

14. A measuring receiver as claimed in claim 13, in which the clamping ring is made from polyethylene and is injection moulded onto the polyethylene-coated polypropylene membrane.

15. A measuring receiver as claimed in any of claims 1 to 12, in which the membrane is directly welded to the clamping ring.

16. A measuring receiverforthe transcutaneous determination of the concentration of substances in the blood and in body tissue, constructed substantially as herein described with reference to and as illustrated in the drawings.