WO2001050953A1

WO2001050953A1 - Suction contact sensor, in particular for non-invasive measurements of a foetus such as the pulse rate

Info

Publication number: WO2001050953A1
Application number: PCT/EP2000/000089
Authority: WO
Inventors: Alfons Schmid
Original assignee: Agilent Technologies Inc.
Priority date: 2000-01-07
Filing date: 2000-01-07
Publication date: 2001-07-19

Abstract

The invention relates to a foetal suction electrode (200) for non-invasive measurements of a foetus, in particular of the pulse rate. The suction electrode has a suction head (210) for providing suction contact with the foetus by the formation of a negative pressure in said suction head. In addition, the suction head has bellows for reducing the volume, by compression during mechanical actuation. The bellows are configured elastically in such a way that they oppose the volume reduction and endeavour to return substantially to their initial position, thus increasing their volume once more. The suction electrode can also have an elastic contact mass (220) with at least mild adhesive characteristics, said contact mass having an adhesive effect during the formation of the contact, thus sealing in the negative pressure. The contact mass can be electrically conductive and a corresponding appropriate electrical contact can be established with the foetus, using the contact mass (220).

Description

SENSOR WITH SUCTION CONTACT, IN PARTICULAR FOR NON-INVASIVE FETAL MEASUREMENTS LIKE THE PULSE RATE

The present invention relates to sensors with suction contact, in particular for non-invasive fetal measurements such as the pulse rate.

In order to be able to assess the physiological condition of a fetus, it is advantageous in medical birth monitoring to be able to measure the changes in the pulse rate when the fetus is under stress.

Only invasive methods are currently available as marketable solutions for performing this pulse rate measurement. Around 95% of all applications are so-called spiral electrodes (or scalpel electrodes). These spiral electrodes have a single or double spiral (helix) at their upper end, which is intended to make electrical contact with the fetus, which is screwed or screwed into the fetus with a manipulator.

Surgicraft-Copeland offers another solution, primarily in Great Britain, which makes electrical contact via a curved needle as a closed ring.

All these solutions have the disadvantage that the unborn child, even if only slightly, sustains an injury (open wound) to the head as a result of this process, which in turn means an increased risk of infection. Problems arise in particular if the scalpel electrode is not placed vertically, so that a crack wound occurs when turning. If the scalpel electrode is turned too far, it can be pulled out completely and a larger wound is created. In addition, injuries to the mother can also occur during the induction of the scale electrode or if the scale electrode has come loose. Recently, non-invasive measurement methods have been described as further solutions, all of which are based on the suction effect due to negative pressure. Solutions of this type, as shown in FIG. 1 as a schematic diagram, are described, inter alia, in WO 91/15996 and WO 96/41570. These solutions are a suction electrode 10, in which a soft (latex, elastomer), conical and outwardly opening suction body 20, which seals at the edges with a sealing lip 25, is sucked in by a negative pressure and thus adheres to the fetus 30 sucks. To generate negative pressure in the absorbent body 20, either a bellows 40 or a piston / cylinder version 50 is proposed, each of which generates the negative pressure in the absorbent body 20 from outside the womb with the aid of a hose 60. '

An electrical contact to the fetus 30 is generated with a metal body 70 with a cable connection 80. When the conical soft part of the suction body 20 is sucked in, the metal body 70 located in the middle of the suction body is pressed against the body of the fetus 30.

These suction electrode solutions shown in FIG. 1 and not yet available on the market have several serious disadvantages:

In addition to the electrical cable 80, the suction element 40 or 50 for generating the negative pressure and the associated connecting hose 60 must remain connected to the suction body 20 in order to

Maintain negative pressure. This not only makes this solution very uncomfortable for expectant mothers, it also hinders doctors and midwives during examinations.

The electrical contact between the fetus 30 and the metal body 70, which is produced by pressing the absorbent body 20 with the aid of the negative pressure, has proven to be very unsafe in practice and, above all, cannot be achieved or can only be brought about poorly in fetuses with heavy hair become. In addition, there is the problem of having the absorbent body sealed, especially in fetuses with heavy hair.

Very high accuracy requirements with regard to the sealing lip 25 are placed on the absorbent body 20.

The most serious disadvantage, however, has been shown to be that if the negative pressure is too strong, hematomas can appear on the fetus, which can even be more serious than the cuts caused by the invasive scalp electrode.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved non-invasive electrode for determining the fetal pulse rate.

The object is achieved by the features of the independent claims. Advantageous embodiments are set out in the dependent claims.

The invention solves this problem on the one hand by providing an improved structure of the electrode suction head, which does not require any further external means for producing and maintaining a negative pressure, and on the other hand by using a contact compound for mechanical sealing of the absorbent body and / or for electrical contacting. These two aspects are preferably used in combination, but they can also be used independently.

The improved construction of a fetal electrode according to the invention works in a similar way to the known electrodes shown in FIG. 1 with the principle of creating a negative pressure for establishing a contact between the

Electrode and the fetus. However, while in the conventional electrodes 10 (see FIG. 1) the negative pressure in the suction head 20 of the electrode facing the fetus 30 is generated and maintained by external means 40 or 50 located outside the womb, according to the invention such external means are completely eliminated, and the negative pressure in the suction head becomes brought about solely by mechanical actuation of the suction head.

The suction head according to the invention allows a volume reduction, e.g. by squeezing, its elastic structure, however, opposes the volume reduction and essentially tries to return to its starting position and thereby increase its volume again. By reducing the volume of the suction head, e.g. while the suction head is pressed against the fetus, the air in the suction head is displaced and pushed out of the suction head via a valve. After the contact pressure has been removed, the elastic body of the suction head expands again counter to the pressing direction, thereby increasing its volume. Now, however, the valve blocks the gas supply back into the suction head, so that due to the volume expansion of the suction head, a negative pressure is created in the suction head, which can be used to attach the suction electrode to the fetus.

This negative pressure is maintained until air, for example, penetrates the suction head through the seal between the fetus and the suction head. No special measures or external means to maintain the negative pressure are required. If the negative pressure subsides, the electrode can be re-attached by pressing or the negative pressure can be increased.

In a preferred embodiment, the suction head is provided with a bellows which, when compressed, elastically reduces the volume of the suction head and, when the contact pressure is removed, again endeavors to return to its starting position. The suction electrode according to the invention thus leads to smaller and easier-to-apply units which, because of the lack of external means for producing a negative pressure, can also withstand greater tensile and bending stresses. As a result, the birth process is hampered as little as possible, both technically and emotionally. Finally, the suction electrode according to the invention can also be easily released again by opening the valve.

In order to produce an improved contact between the fetus and the electrode, the suction head is sealed according to the invention with the aid of an elastic sealing compound with at least a slight adhesive effect, which leads to sticking when contact is formed and can thus also sealingly enclose possibly existing hair. Ductile, biocompatible substances are particularly suitable. Alternatively or in addition, an electrically conductive contacting compound can also be used to improve the electrical contact between the fetus and the electrode. When using an electrically conductive material for the sealing and contacting compound, this can take on the task of both mechanical sealing and electrical contacting. Because of the possibly overlapping properties, no distinction should be made in the following between the terms' sealing compound 'and' contacting compound 'and the term' contacting compound 'is used uniformly, depending on the application, these are referred to as' sealing compound' and 'contacting compound ¹ or both understand is.

So-called hydrogels have been shown to be particularly favorable as a use for the contact mass. Hydrogels are highly hydrated, ductile, biocompatible, electrically conductive, sticky, slimy and organic. They meet two conditions:

• they bring the releasable adhesive connection between body and push button contact, and • They create the electrical conductivity between the body and the contact.

Hydrogels adapt perfectly to any surface shape and have been tested for many applications on and in the human body. Hydrogels consist of water-insoluble polymer molecules, the structural form of which is such that water molecules are built in between the individual polymer molecules in order to obtain a polymer chain.

As a requirement for the contact material, it must be biocompatible, be able to adapt to the shape of the head and, if necessary, the hair, and thus provide the appropriate sealing effect. In addition, the contact mass should also have an adhesive effect in order to improve the holding force. Depending on the application, the contact mass should also be electrically conductive so that electrical contact can be made with the fetus. Various hydrogels have been shown to be particularly advantageous:

Polyacrylamides (PAA),

Polyhydroxyethyl methacrylates (PHEMA), as are used, for example, for soft contact lenses or for moisture absorption in diapers,

• polysaccharides (alginates), as sugar solutions in jelly form, or

• Polyhydroxypropylmethacylanide, as they are used in the coating of delay pills.

In a preferred embodiment of the invention, an outer edge of the suction head facing the fetus is provided with a sealing ring consisting of the contact material. This significantly improves the adhesive properties of the suction head. This not only allows reliable contacting even in the case of fetuses with thicker hair, but overall also a reduction in the required negative pressure, since the negative pressure is better sealed from the environment, and therefore no increased negative pressure is generated 'in stock' got to. A reduction in vacuum in turn counteracts the formation of hematomas.

If an electrically conductive contact mass (preferably a hydrogel) is used as the contact mass for the sealing ring, the electrical contact formation can also take place directly via the outer sealing ring without any further special electrode contact to the fetus being required. This not only allows a further reduction in components, but also makes it unnecessary to make another contact in addition to the sealing contact. From a mechanical point of view, too, the electrical contact along the sealing contact is cheaper than, for example, an extra contact in the center area of the suction head. In addition, if the sealing contact diminishes, as a result of which the electrical contact is also reduced, this is also noticeable to the outside by a reduction in the adhesion of the entire suction head. If the seal and the electrical contact are separated, however, the seal can be intact while the electrical contact is released. By simultaneously sealing and making electrical contact, the safety and reliability of the electrical contact is significantly increased.

The use of a contact compound according to the invention thus not only leads to a significantly increased application safety by improving the adhesive property, but in turn also allows the vacuum requirement to be reduced in order to burden the baby as little as possible. Finally, the electrical contact of the electrode to the fetus can be significantly improved in order to get the electrophysiological signal in better quality or to improve the pulse rate measurement by an optical measuring method (such as a pulse sensor, SpO2 sensor). Due to the improved sealing properties of the contact mass, a lower suction volume is usually sufficient to suction the electrode. By suitable selection of a soft ductile material for the contact mass, sufficient electrical contact can be made even with strong hair growth. It can be seen that the inventive provision of the suction head with a contact mass is independent of the principle chosen for producing a negative pressure. Thus, the use of a contact material according to the invention can be used in particular in the embodiment of a fetal electrode which is improved according to the invention, but also in the conventional suction electrodes known in the prior art.

Individually or in combination, the aspects according to the present invention lead to a significant improvement in the quality in the determination of the pulse rate of the unborn child and this with improved comfort for mother and clinic staff.

Although the invention has been described with regard to the application for fetal pulse rate measurement, it can be seen that the invention is not restricted to these, but for any form of fetal measurement in which a more or less permanent contact with the fetus is to be established, can be applied. In addition, the inventive principles can generally be extended to other applications of sensors with suction contact. Examples are: the SpO2 measurement in the reflection method, optical absorption and reflection methods for measuring medical parameters, pH measurement, transcutaneous measurements of oxygen partial pressure (pO2) and carbon partial pressure (pC02) or other transcutaneous parameters, or intracranial pressure when applied the Fontanelle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained below using the drawings, the same reference symbols referring to functionally identical or similar features.

Figure 1 shows the structure of known fetal suction electrodes, and Figure 2 shows the structure of a preferred embodiment of a fetal suction electrode according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 2 shows the structure of a preferred exemplary embodiment of a fetal suction electrode 200 according to the invention. The suction electrode 200 has a suction head 210 which is applied to a fetus (not shown) with the aid of an insertion tube 420. The suction head 210 has a sealing ring 220 which is preferably wrapped around on three sides and, in the application, is pressed against the unborn child with the open fourth side. The sealing ring 220 is a simple ring, the cross-sectional shape of which can have any shape, but is preferably round or has a rectangular cross-section, preferably with the narrower side up / down, that is to say the wider side in diameter.

The sealing ring 220 is preferably made of an elastic material with at least a slight adhesive effect, which leads to easy bonding when contact is formed and thus also sealingly encloses any existing hair. The sealing ring 220 is preferably made of a hydrogel, but other materials can also be used accordingly, which ensure sufficient sealing properties, in particular even in the presence of hair.

The suction head 210 also has a suction body 230, which preferably has a shape as a bellows. The absorbent body 230 reduces its volume under the influence of a force in the direction of the arrow. The absorbent body 230 is preferably a soft elastomer part, e.g. B. made of silicone. Other preferred materials for the absorbent body 230 can also be soft PVC, polyurethane (PUR) or (preferably sprayable) elastomers. The undercuts resulting from the shape and the bellows can preferably be molded in silicone.

The absorbent body 230 closes off from the fetus with a sealing lip 240. Within the inner area of the Absorbent body 230, the sealing ring 220 nestles against the sealing lip 240. The sealing lip 240 preferably projects slightly beyond the sealing ring 220. The sealing effect of the absorbent body 230 can be decisively improved by the combination of the sealing lip 240 and the sealing ring 220.

In order to reduce lateral pushing of the sealing ring 220 or so that the sealing ring 220 cannot be pulled inward by the suction effect, it is preferably embedded in the suction body 230 between a retaining ring 250 and the sealing lip 240 of the suction body 230 and is thus held in position ,

In a bottom region 260 (that is, in a region facing away from the fetus) of the absorbent body 230 there is a valve 270, which preferably consists of a valve

There is a recess 280 in the base region 260 and a flap 290, such as a pressure lip, which presses against the recess 280. With this type of

Flap valve 270 becomes the pressure lip 290 when an overpressure builds up in the

Absorbent body 230 opened, and the gases in the absorbent body 230 can escape. On the other hand, if the volume of the absorbent body 230 expands again, so that a negative pressure is created in the absorbent body 230, the

Pressing lip 290 pressed against the recess 280 so that no gases can penetrate into the absorbent body 230 through the recess 280. As a result, the negative pressure required for the suction effect of the absorbent body 230 is built up and maintained.

It is clear that instead of the flap valve 270 shown in FIG. 2, any type of valve can be used, the valve 270 being adapted to the corresponding application and environmental conditions and to the geometric embodiment of the absorbent body 230.

A holding ring 300, which serves to let the suction head 210 rest on the insertion tube 420, also adjoins the bottom region 260. At the same time, the retaining ring 300 allows the insertion tube 420 to be easily removed by pulling the insertion tube 220 against the direction of the arrow shown in FIG. A reference contact 310 is also connected to the bottom region 260, which is preferably located in the insertion state between the bottom region 260 and the insertion tube 420. The reference contact 310, preferably a metal ring, serves to establish the electrical contact of the reference electrode. The reference contact 310 is followed, preferably via a metallic connection such as a soldered or welded connection, by a cable 320 which is guided to the outside in a protected manner via the insertion tube 420.

Another cable 330 for making electrical contact with the fetus is preferably led into the absorbent body 230 through a recess in the base region 260. In an arrangement with a metal body 70 as an electrode opposite the fetus, as shown in FIG. 1, the cable 330 is conductively connected to the metal body 70. In a preferred embodiment (as shown in FIG. 2), however, the sealing ring 220 is made electrically conductive by suitable material selection and itself serves as an electrode opposite the fetus. In this case, the cable 330 is connected to the sealing ring 220 in an electrically conductive manner. By pressing the absorbent body 230 against the fetus, the sealing ring 220 now not only provides a seal for the absorbent body 230, but also establishes electrical contact with the fetus. This interaction of densities and electrical contacting of the sealing ring makes it unnecessary to attach a special electrode contact (such as the metal body 70 in FIG. 1) in the absorbent body 230. The cable 330 can of course also be routed outside the absorbent body 230.

The insertion tube 420 is used for the targeted and simple insertion of the suction head 210 into the womb towards the fetus. When the suction head 210 has touched the body of the fetus, the suction head 210 is pressed by means of the insertion tube 420, whereby the volume of the suction body 230 is reduced. The valve 270 opens under the influence of excess pressure when the absorbent body 230 is compressed. During this compression (in the direction of the arrow), the sealing lip 240 and the sealing ring 220 are also pressed against the fetus. If the insertion tube 420 is withdrawn again, the suction body 230 tries to follow this movement. Due to the adhesive effect of the sealing ring 220, the suction head 220 initially adheres to the fetus. Since the valve 270 now closes, but at the same time the suction body 230 strives to return to its original shape, that is to say expands, a negative pressure is created in the suction body 230, which in turn presses it more firmly against the fetus.

By pressing the suction head 210, the sealing lip 240 is opened and the sealing ring 220 mechanically (and possibly also electrically) makes contact with the body of the fetus. Electrical contact to the fetus is made via the electrical conductor of the cable 330 (and the sealing ring 220) and the pulse rate can be measured in a known manner.

The suction head 210 is preferably produced by spraying technology, parts such as the cable 330, the reference contact 310 and the valve 270 being able to be injected into the suction body 230 when the latter is being sprayed. The sealing ring 220 must be inserted later.

The pressure lip 290 is preferably a simple preformed elastomer plate (preferably silicone). The conductors of the two cables 320 and 330 are preferably treated galvanically in order to avoid corrosion, particularly in a hydrogel environment used as a sealing ring 220.

At the distal end of the insertion tube 420 there is preferably a button part 340 which can be pressed, glued or otherwise attached to the insertion tube 220. The button part 340 serves to facilitate the application process.

Claims

PA TEN TA NSPRÜ CHE

1. Sensor (200), in particular for non-invasive fetal measurements of physiological parameters such as the pulse rate of a fetus, comprising:

a suction head (210) for establishing a suction contact with a measurement object, in particular a patient or a fetus,

characterized,

that a vacuum in the suction head (210) is brought about solely by mechanical actuation of the suction head.

2. The sensor (200) according to claim 1, characterized in that the suction head (210) means (230) for reducing the volume under the mechanical

Actuation, preferably by pressing together, wherein the means (230) is constructed to be elastic in such a way that it opposes the reduction in volume and essentially attempts to return to its starting position, thereby increasing its volume again.

3. The sensor (200) according to claim 2, characterized in that the means (230) for reducing the volume is a bellows.

4. The sensor (200) according to any one of the preceding claims, characterized by a valve (270), wherein the valve (270) opens at excess pressure in the suction head (210) and closes at negative pressure.

5. The sensor (200) according to one of the preceding claims, characterized by a measuring sensor (330, 220) for recording measured values on the measurement object, preferably for recording measured values of a physiological parameter of the patient or the fetus.

6. The sensor (200) according to any one of the preceding claims, characterized by a sealing ring (220) on a side of the suction head (210) facing the measurement object for sealing the negative pressure in the suction head (210).

7. The sensor (200) according to claim 6, characterized in that the sealing ring (220) has an elastic contact mass, preferably a hydrogel, with at least a slight adhesive effect, which leads to sticking when contact is formed.

8. The sensor (200) according to claim 7, characterized in that the contact mass is electrically conductive.

9. The sensor (200) according to claim 8, as far as related to claim 5, characterized in that the measuring sensor (330, 220) makes an electrical contact to the measurement object via the contact mass.

10. Fetal suction electrode (200) for non-invasive measurements, in particular the pulse rate, on a fetus, with a suction head (210) for producing a

Suction contact to the fetus,

characterized,

11. Fetal suction electrode (200) for non-invasive measurements, in particular the pulse rate, on a fetus, with a suction head (210) for producing a suction contact with the fetus,

characterized in that

the suction head (210) means (230), preferably a bellows, for reducing the volume under mechanical actuation, preferably by

Compressing, wherein the means (230) is so elastic is constructed so that it opposes the volume reduction and essentially tries to return to its starting position, thereby increasing its volume again.

12. The fetal suction electrode (200) according to claim 10 or 11, characterized by a valve (270), wherein the valve (270) at excess pressure in the suction head

(210) opens and closes at negative pressure.

13. suction electrode (200), in particular for non-invasive measurements such as the pulse rate, for example on a fetus, with a suction head (210) for producing a suction contact by forming a negative pressure in the suction head (210),

characterized by an elastic contact mass (220) with at least slight adhesive effect, the contact mass (220) leading to sticking when contact is formed and thus serves to seal the negative pressure.

14. The suction electrode (200) according to claim 13, characterized in that the contact mass (220) is electrically conductive and an electrical contact is made to the application site of the electrode via the contact mass (220).

15. suction electrode (200), in particular for non-invasive measurements such as the pulse rate, for example on a fetus, with a suction head (210) for producing a suction contact by forming a negative pressure in the suction head (210),

characterized by an elastic contact mass (220), the contact mass (220) bringing about an electrical measurement contact to the application site of the electrode when contact is formed.

16. Use of an elastic contact mass (220) with at least slight adhesive effect in a sensor (200), in particular for non-invasive fetal

Measurements such as the pulse rate of a fetus, the sensor (200) having a suction head (210) for establishing suction contact with a measurement object by forming a negative pressure in the suction head (210), in particular a patient or a fetus, and the contact mass (220) leads to sticking when contact is formed and thus serves to seal the negative pressure.

17. The use of an elastic contact mass (220) according to claim 16, wherein the contact mass (220) is electrically conductive and an electrical contact to the measurement object is made via the contact mass (220).

18. Use of an elastic contact mass (220) in a sensor (200), in particular for non-invasive fetal measurements such as the pulse rate of a fetus, the sensor (200) having a suction head (210) for producing a

Has suction contact to a measurement object, in particular a patient or a fetus, and the contact mass (220) brings about an electrical contact to the measurement object when contact is formed. *