WO2008032291A2

WO2008032291A2 - Multi-electrode patches for electrophysiological impedance measurements and devices for' positioning and/or alignment of electrode- patch assemblies

Info

Publication number: WO2008032291A2
Application number: PCT/IB2007/053718
Authority: WO
Inventors: Robert Pinter; Jeroen Adrianus Johannes Thijs; Jens MÜHLSTEFF; Olaf Such
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2006-09-25
Filing date: 2007-09-14
Publication date: 2008-03-20
Also published as: WO2008032291A3

Abstract

The invention relates to an adhesive electrode patch assembly in particular for use in impedance measurements with at least one electrode patch (1) characterized in that the electrode patch (1) comprises at least one feeding electrode (F)and at least one sensing electrode (S) arranged in pairs, respectively wherein one feeding electrode (F) and one sensing electrode (S) are combined in a single electrode plate (3). Furthermore the invention is related to a device (6) for positioning and/or alignment of at least two electrode patches (1) on parts of a human body with at least two positioning heads (7), which are spaced apart from each other by a coupling (8), the positioning heads (7) comprising at least one retainer (9), wherein at least one location pin (10) arranged on each electrode patch (1) meshes with the retainer (9) in order to align the patches (1) with each other.

Description

A DEVICE FOR A MULTI-ELECTRODE PATCH IN PARTICULAR FOR ELECTROPHYSIOLOGICAL MEASUREMENTS

The present invention relates to a medical electrode arrangement, in particular for adhesive medical electrodes that can be used in impedance cardiography as well as to a device for positioning and/or alignment of such an electrode arrangement. Impedance cardiography is based on the measurement of the electrical resistance (impedance) of a human's body to electrical current by driving a defined electrical current through the human body and measuring the voltage drop resulting thereof. Usually an alternating current is used.

With impedance cardiography it is possible to detect various vital parameters such as heart beat volume, heart output, systemic vessel resistance, speed and acceleration of blood circulation, heart pump output, heart contraction etc. These parameters can be derived from a calculated change in impedance when a defined alternating current is passed through a patient's chest and the voltage changes due to changes of the blood distribution in the thorax are measured. It is a non-invasive and cost-efficient technique. Important electrophysiological measurements like impedance cardiography and bio- impedance are based on a four-point measurement. A four-point electrode setup comprises two feeding electrodes F+ and F- that feed a known current into the body, and two sensing electrodes S+ and S- located between the feeding electrodes that pick up the voltage drop generated by the known current. In one exemplary method conventional circular EKG electrodes may be used. The electrodes are applied in pairs along the vertical axis of the body, one pair of electrodes at the neck and another pair on the lower thorax, although in most cases two such four-point electrode setups are applied, one on each side of the body, in order to improve the homogeneity of the current density field inside the body. Existing products in the prior art require separate cable connections for each of the electrodes, which results in difficult handling.

The scheme according to which the electrodes have to be placed is determined by the intended measurement. In the four-point setup described above, the distance between the electrodes S+ and S- is chosen such that the voltage drop to be measured is sufficiently high, which is easily more than 15 cm. The electrodes F+ and S+ as well as the electrodes F- and S-, however, are located rather closely together in such an arrangement, e.g. 3 cm to 5 cm.

Since a proper placing of the individual electrodes is very difficult, electrophysiological impedance measurements are normally conducted by trained medical staff in a clinical surrounding.

Current studies indicate that many patients can be treated at home as part of a home-rehabilitation solution. The patients in this case have to take over tasks which normally require certain medical and technical background knowledge. For example, in a home care scenario it could be necessary that a daily electrophysiological impedance measurement comprising the proper positioning of four electrodes on the body by the patient himself at home is required. In order to obtain meaningful results from such measurements it is indispensable that the electrodes are placed according to the four- point-measurement scheme as precisely as possible.

It is therefore an object of the present invention to provide an electrode patch assembly that allows an easier handling which especially for use in a home care scenario is very important. Another object of the present invention is to provide a device for supporting a positioning and/or an alignment of at least two electrode patches for the execution of measurements concerning vital parameters, which allows a reliable handling of the electrodes and electrode patches, respectively.

This object is solved by an adhesive electrode patch assembly according to claim 1 and a device according to claim 4. The electrode patch assembly according to the invention comprises at least one electrode patch with at least one feeding electrode (F)and at least one sensing electrode (S) arranged in pairs, respectively, wherein one feeding electrode (F) and one sensing electrode (S) are combined in a single electrode plate (3).

The idea is to have electrodes F+ and S+ combined in a single patch as well as electrodes F- and S- in another patch. This is based on the fact, that the distance between the electrodes F+ and S+ is only a few centimeters. The same applies to the electrodes F- and S-.

The feeding electrode and the sensing electrode may be spaced apart from each other by 1 cm to 10 cm, preferably 3 cm to 10 cm, more preferably 3 cm to 5 cm. The distance between two sensing electrodes may be in the range of 10 cm to 50 cm, preferably 12cm to 35 cm, more preferably 15 cm to 25 cm.

Using two of the proposed electrode patches gives four separate contacts to the patient and enables a four-point measurement with only two patches. Only half as many electrode patches as for a four-point measurement with conventional electrodes are required, which reduces electrode placement errors. This makes the whole procedure much easier to complete for the patient.

Additional to halving the number of electrode patches required for a four- point measurement the electrode patch assembly proposed herein minimize the risk of swapping the neighboring electrodes F+ and S+ as well as F- and S- by fixing them in a predetermined position on one electrode patch. Furthermore in one embodiment of the present invention the electrode patch assembly minimizes the risk of swapping the feeding and sensing electrodes by providing a suitable marking on the patch or an asymmetric mechanical design of the patch. This allows a design, which leaves no doubt about how the patches have to be placed. For example, the electrode patches could be rounded at one end and cornered at the other, and the patient would be asked to apply the patches always in such a way that the cornered ends of the two patches point towards each other, thereby achieving a proper alignment.

In another embodiment of the present invention an amplifier is placed on at least one of the electrode patches, the input of which exhibits a rather high impedance and is connected to the sensing electrode, so that the current through the sensing electrode is very small, and the measurement error resulting from a voltage drop at the electrode-skin contact of the sensing electrodes is thereby minimized.

Another advantage of such an amplifier is that the current for the impedance measurement can be adapted to the properties of a patient's body. If a patient is rather obese, his body impedance is higher than that of a normal patient. In this case the current source may run into saturation, because the maximum voltage that it can supply at the feeding electrodes is limited. In such a case it would help to reduce the current, but on the other hand this reduces the precision of the measurement, for the following reason. Normally the currents through the sensing electrodes are supposed to be very small, compared to the body current provided by the current source, but if the body current is reduced, the currents through the sensing electrodes may become significant. An amplifier for the voltage measurement integrated directly in the electrode patches overcomes that problem, because it minimizes the currents through the sensing electrodes.

A device for positioning and/or alignment of at least two adhesive electrode patches on parts of the human body comprises at least two positioning heads, which are spaced apart from each other by a coupling, the positioning head comprising at least one retainer, wherein a location pin arranged on each electrode patch meshes with the retainer in order to align the patches with each other.

With this device the electrodes for a daily bio -impedance measurement are placed according to a four-point measurement scheme as precisely as possible, and a significant relief for the patient is achieved while he accomplishes this task.

In order to allow a flexible placement of the electrodes on several parts of a human body the device according to the invention is designed in one embodiment as a separate assembly so that the device is removable from the location pin at the electrode patches after the positioning and/or the alignment of the electrode patches is completed. Alternatively, the location pins may be loosely fixed to the electrode patches and may be removed after positioning and adhering the patches.

In a further embodiment of the present invention the coupling is integrated in the adhesive electrode patches. The coupling can be stiff or flexible. In case that the coupling is stiff the possibility of a misalignment of the electrode patches relative to each other is minimized. The patches are always placed "in line". On the other hand it may not be possible in this case to adapt the positioning of the electrode patches to curves or bulges, depending on the area of a human body at which the measurements should take place. Therefore, in another embodiment of the invention, the coupling is made flexible. In a further embodiment according to the invention the length of the coupling is adjustable, in particular by means of a punched tape or a clip, so that the distance between the electrode patches can be adapted to a user's stature or figure. This way a measurement is possible with a large variety of different chest circumferences, which ask for different distances between the at least two electrode patches to get exact and comparable results.

The coupling can be fastened on a patient's chest and either remains on the chest while the measurement is conducted or can be taken off. In case that the patient is female it might be comfortable to place the coupling around the patient's back. The coupling length is different in those two cases, so that it is desirable to make the length of the coupling adjustable. Another reason to place the coupling around the back might be an injury on the front of the chest, or that the space on the chest is occupied by other medical equipment.

The device according to the invention may be employed in simple two- point bio-impedance measurements as well as in four-point measurements wherein the advantages of the device according to the invention become the more prominent the more electrodes have to be placed in a special way.

Depending on the range of application the length of the coupling which constitutes the distance between two electrode patches can be chosen in the range of 1 to 100 cm, preferably 5 to 50 cm, more preferably 20 to 30 cm. An adhesive electrode patch assembly and a device, which meet the abovementioned objects and provide other beneficial features in accordance with the presently preferred exemplary embodiment of the invention will be described below with reference to Figures 1 to 7.

Those familiar with the state-of-the-art will readily appreciate that the description given herein with respect to those figures is for explanatory purposes only and is not intended to limit the scope of the invention. Although in the present application reference is made to a patient body, in particular a human patient body, it is contemplated that only a body part may be used, for example only a torso or arm of the body. Further, a patient body may as well be an animal body. Moreover, a patient body is to be understood as any physical body, not necessarily a living body.

Figure 1 shows an electrode setup for a two-point bio-impedance measurement, according to the state-of-the-art; Figure 2 shows an electrode setup for a four-point measurement, according to the state-of-the-art;

Figure 3 shows a possible electrode setup for the four-point bio- impedance measurement on a human's body; Figure 4 shows an electrode setup for impedance cardiography; Figure 5 shows an electrode patch according to the invention;

Figure 6 shows a device for positioning and the alignment of two adhesive electrode patches according to the invention; and Figure 7 shows a device according to the invention for positioning and alignment of conventional adhesive electrode patches. Figure 1 shows an electrode setup for a two-point measurement according to the state of the art.

In the context of bio-impedance measurements several electrode setups are conceivable. Figure 1 shows the simplest one with only two electrodes. With the help of two electrodes FS+ and FS- a current source feeds a known current I into a patient's body. The voltage drop generated by the current is proportional to the body impedance.

In this simple setup the voltage is measured at the same electrodes FS+ and FS- that also feed the current into the body. It is certainly desirable to have as few electrodes as possible. However, in the simple setup according to Figure 1 the contact resistance between the electrodes and the patient's skin falsifies the impedance reading. The voltage drop at the contact resistance of both electrodes adds to the voltage drop generated along the distance D between the electrodes which is proportional to the bio -impedance. With the simple setup in Figure 1 it is not possible to measure the bio-impedance alone. The contact resistance may vary strongly and is a major source of motion artifacts in two-point bio- impedance measurement setups.

In order to avoid the abovementioned disadvantages of the two-point impedance measurement setup a four-point measurement is used, comprising four electrodes. Figure 2 shows an example for such an electrode setup for a four-point measurement. The current is fed into the body with the help of the two feeding electrodes F+ and F-. In order to prevent the varying contact resistance of these electrodes from falsifying the measurement result, the voltage drop that is representative of the bio-impedance is not measured at the feeding electrodes as in the two-point measurement setup, but at two extra sensing electrodes S+ and S-. The voltage measurement does not require a large current to flow through the sensing electrodes. It is possible to use an amplifier with rather high impedance in the Giga-Ohm range for example, so that the current I_meas is extremely small. Therefore the voltage drop generated by I_meas at the sensing electrodes is accordingly small, such that the bio- impedance measurement error caused by electrode-skin contact resistance is minimized. The measurement signal is proportional to the distance D between the sensing electrodes S+ and S-. In order to obtain a sufficiently high signal-to-noise-ratio the distance D is usually chosen around 15 cm or more. The distance d between the electrodes S+ and F+, and also the distance between the electrodes S- and F-, may be smaller. A feeding electrode F+, F- could be placed 3 to 5 cm away from the associated sensing electrode S+, S-, such that there is enough place for the electric current to distribute equally in the body part under investigation. In Figure 2 this is indicated with the help of the current density streamlines 2 between the feeding electrodes F+, F-. While the streamlines 2 are bended strongly at the feeding electrodes F+, F-, where they enter the body, they are almost parallel to the body surface when they pass the locations of the sensing electrodes S+, S-. This indicates a rather homogeneous current distribution in the region between the two sensing electrodes S+, S-. The four-point measurement technique is state-of-the-art for ICG and bio-impedance measurements today. As far as the signal quality and the reliability of the measurement results are concerned the four-point bio-impedance measurement is absolutely superior to the two- point measurement. However, the number of electrodes doubles with respect to the two- point electrode setup shown in Figure 1. The proper placing of four individual electrodes at home is not easy for a medically untrained person.

Figure 3 shows a possible electrode setup for a bio-impedance measurement. It is meant to capture the retention of fluid in the lung of patients suffering from chronic heart failure (CHF). In order to obtain meaningful results from such measurements it is indispensable that the electrodes are accurately placed according to the four-point measurement scheme.

Furthermore, it is not yet verified whether a single four-point measurement is sufficient to reliably detect a decline of a CHF patient's health status. Other applications like impedance cardiography for example employ two or even more four-point measurements simultaneously, as shown in Figure 4.

Figure 4 shows an electrode setup that is required for a bi-literal bio- impedance measurement of the thorax. In this case there is a four-point measurement on each side of the body. The feeding electrodes on each side are marked as F, the sensing electrodes as S. As can be seen it is necessary to attach eight electrodes as precisely as possible to the body. It is unreasonable to expect patients to be able to achieve a proper placement of such an electrode configuration regularly if they need to do it themselves at home without help by others. Measurement errors due to inappropriate electrode placement have to be expected. Another typical mistake while setting up a four-point measurement is to swap the electrodes S and F. All of these will give measurement results that are wrong but still reasonable, so the mistake can not be detected easily. Figure 5 shows an adhesive electrode patch 1 for use in an impedance measurement according to the invention. The electrode patch 1 comprises one feeding electrode F and one sensing electrode S combined in a single electrode plate 3, wherein the feeding electrode F and the sensing electrode S are spaced apart from each other by 3 cm. The electrodes F, S are electrically isolated from each other and are connected with two wires, which are combined in a single cable 4 such that a patient needs to handle only one cable per electrode patch 1 which makes the handling much easier. The electrode patch 1 has an asymmetric mechanical design with two slanted edges 5 on one side of the patch 1 in order to prevent swapping of the sensing electrode S and the feeding electrode F. This way, swapping of the electrodes S and F as well as swapping of the electrode patches as a whole is prevented, since there is no doubt about how the patches have to be placed. Those sides of the electrode patches with the slanted edges 5 should point towards each other, indicating that the electrode patches are positioned in the right direction.

The invention is useful for the single four-point measurement explained above, but also for various four-point measurements in general. The number of electrode patches 1 that have to be applied is halved in either case. In principle it would even be possible to put all four electrodes F+, S+, F-, S- in a single patch, but a patch would then be rather large, causing discomfort for the patient when the patch has to be removed. Figure 6 shows a device 6 for positioning and alignment of at least two electrode patches 1 on parts of the human body according to the invention.

The device 6 comprises two positioning heads 7, which are spaced apart from each other by a coupling 8. The positioning heads 7 respectively comprise two retainers 9, in which two location pins 10 arranged at each electrode patch 1 mesh, in order to align the patches 1 with each other. The device 6 is built as a separate module that is removable from the location pins 10 after a proper positioning and alignment of the electrode patches 1 is achieved. In this embodiment the location pins 10 are integrated in the two electrodes F, S on the electrode patch 1.

In an alternative embodiment (not shown) the location pins may be provided as separate parts and may be designed fixed to the electrodes or detachable, such that they can be removed from the patch after the positioning of the patches is completed.

The coupling 8 in this embodiment is stiff, so that the possibility of a misalignment of the electrode patches 1 relative to each other is minimized since the patches 1 are always placed "in line". In this embodiment the location pins 10 are formed equally. Another embodiment (not shown) provides an electrode patch, in which the location pins and therefore also the retainers which should mesh with the location pins are formed differently. This way it is only possible to insert the pins into the retainers if the patch is oriented properly with respect to the positioning head, and not 180° rotated.

Figure 7 shows an alternative embodiment of the device according to the invention for use as a positioning and alignment support for the positioning of conventional electrode patches known in the state-of-the-art, which can be used in electrocardiography measurements for example. The device is very similar to the device shown in Figure 6 and also the functionality is very similar, so that a further description is not necessary and will not be given in order to avoid a repetition.

Claims

CLAIMS:

1. Adhesive electrode patch assembly in particular for use in impedance measurements with at least one electrode patch (1) characterized in that the electrode patch (1) comprises at least one feeding electrode (F)and at least one sensing electrode (S) arranged in pairs, respectively wherein one feeding electrode (F) and one sensing electrode (S) are combined in a single electrode plate (3).

2. Adhesive electrode patch assembly according to claim 1, characterized in that the feeding electrode (F) and the sensing electrode (S) are spaced apart from each other by 1 cm to 10 cm, preferably 3 cm to 10 cm, more preferable 3 cm to 5 cm.

3. Adhesive electrode patch assembly according to claim 1 or 2,characterized in that the distance between two sensing electrodes (S) is in the range of 10 cm to 50 cm, preferably 12cm to 35 cm, more preferably 15 cm to 25 cm.

4. Adhesive electrode patch assembly according to claim 1 to 3, comprising at least two electrode patches (1) characterized in that it includes a marking or an asymmetric mechanical design (5) to minimize the risk of swapping the feeding and sensing electrodes.

5. Adhesive electrode patch assembly according to any preceding claim, characterized in that it comprises at least one amplifier, the input of which exhibits a rather high impedance and is connected to the sensing electrode (S).

6. Device (6) for positioning and/or alignment of an electrode patch assembly according to any of claims 1 to 5 on parts of a human body with at least two positioning heads (7), which are spaced apart from each other by a coupling (8), the positioning heads (7) comprising at least one retainer (9), wherein at least one location pin (10) arranged on each electrode patch (1) meshes with the retainer (9) in order to align the patches (1) with each other.

7. Device (6) according to claim 6, characterized in that it is removable from the at least one location pin (10) after the positioning and/or the alignment of the electrode patches (1).

8. Device (6) according to claim 6, characterized in that the coupling (8) is integrated in the electrode patches (1).

9. Device (6) according to any of claims 6 to 8, characterized in that the coupling (8) is stiff or flexible.

10. Device (6) according to any of claims 6 to 9, characterized in that the length of the coupling (8) is adjustable, in particular by means of a punched tape or a clip.

11. Device (6) according to any of claims 6 to 10, characterized in that that the length of the coupling (8), which constitutes the distance between two electrode patches (1) can be chosen in the range of 1 cm to 100 cm, preferably 15 cm to 40 cm, more preferable 20 cm to 30 cm.

12. Device (6) according to any of claims 6 to 11, characterized in that the location pin (10) is built as an integral part of the electrodes (F+, F-, S+, S-) on the electrode patches (1).

13. Device (6) according to any of claims 6 to 12, characterized in that at least two location pins (10) are placed on one electrode patch (1) wherein the location pins (10) are formed differently.

14. Device (6) for positioning and/or alignment of at least two adhesive electrode patches (1) on parts of a human body with at least two positioning heads (7), which are spaced apart from each other by a coupling (8), the positioning heads (7) comprising at > least one retainer (9), wherein at least one location pin (10) arranged at each electrode patch (1) meshes with the retainer (9) within the positioning heads (7) in order to align the electrode patches (1) with each other.