SEGMENTED ELCTRODE

Abstract

Disclosed is a vital sign monitoring system. The system comprises a segmented electrode forming an in-plane electrode array, wherein the electrode comprise a skin contacting skin adhering contact layer mounted on an electrode backing material, a deformation sensor arranged for identifying deformation information of the electrode, a signal processor arranged to receive a vital sign signal from the electrode and process the deformation information to remove artefacts from the vital sign signal, wherein the electrode comprises multiple electrode segments and wherein the signal processor is arranged to select that electrode segment that has a lowest deformation of all electrode segments of the electrode.

Claims

1. A vital sign monitoring system comprising: a segmented electrode forming an in-plane electrode array, wherein the electrode comprises a skin adhering contact layer mounted on a skin facing side of the electrode; a deformation sensor arranged for identifying deformation information of the electrode; and a signal processor arranged to receive a vital sign signal from the electrode and process the deformation information to remove artefacts from the vital sign signal; wherein the segmented electrode comprises multiple electrode segments and wherein the signal processor is arranged to select that electrode segment that has a lowest deformation of all electrode segments of the electrode and measure the vital sign signal using the selected electrode segment.

2. The system of claim 1, wherein the electrode is radially segmented.

3. The system of claim 1, wherein the electrode segments form concentric rings.

4. The system of claim 1, wherein the electrode comprise a skin adhering electrode layer made of hydrogel, hygroscopic silicone gel adhesive or other medical grade skin adhesive such as polyurethane gel, acrylic adhesive, hydrocolloid, and related pressure sensitive adhesive.

5. The system of claim 1, wherein the electrode comprises either (semi-) rigid or stretchable, flexible sheet of material arranged to support the multiple electrode segments with respect to each other.

6. The system of claim 1, wherein each of the electrode segments comprise conductive carbon-filled silicone rubber (elastomer) and is further arranged for identifying the deformation information.

7. The system of claim 1, wherein the deformation sensor comprises: a strain gauge, a fibre optic sensor, a magnetic sensor, or a micro-camera.

8. The system of claim 1, wherein the deformation sensor senses the deformation in at least two dimensions.

9. The system of claim 1, wherein the processor is further arranged to process the deformation information based on a determination of the Lines of Non-extension (LoNEs).

10. A method for a vital sign monitoring comprising: identification of a deformation of a skin adhering electrode comprising multiple electrode segments by a deformation sensor; selecting an electrode segment that has a lowest deformation of all electrode segments associated with lines of non-extension, LoNEs, of the underlying soft skin tissue; and measuring a vital sign signal using the selected electrode segment.

11. The method of claim 10, wherein the electrode comprise stretchable, flexible sheet of material.

12. The method of claim 10, wherein the electrode is radially segmented.

13. The method of claim 10, wherein the electrode comprises concentric rings of electrode segments.

14. The method of claim 10, wherein the electrode comprises longitudinally arranged segments or segments forming a chessboard pattern.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In the drawings, similar reference characters generally refer to the same parts throughout different views. Also, the drawings are not necessarily to scale, with the emphasis instead generally being placed upon illustrating the principles of the invention.

[0038] FIG. 1 shows a graphical representation of a 2D deformation state, based on the Finite Strain Ellipse method according to Obropta and Newman.

[0039] FIG. 2 shows a radially segmented (stretchable) electrode array and indicated example segments associated with Lines of Non-Extension.

[0040] FIG. 3a shows a radially segmented sensor array having strain gauges incorporated therein.

[0041] FIG. 3b shows a cross section of the electrode according to the invention.

[0042] FIG. 4 shows a vital sign measurement system.

[0043] FIG. 5 shows a schematic representation of a method according to the present invention.

[0044] FIG. 6 shows a segmented (stretchable) electrode array electrode with longitudinal segments and a chessboard pattern.

[0045] FIG. 7 shows a segmented (stretchable) electrode array, wherein electrode segments are concentric rings.

DETAILED DESCRIPTION OF EMBODIMENTS

[0046] Certain embodiments will now be described in greater details with reference to the accompanying drawings. In the following description, like drawing reference numerals are used for like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. In addition, well-known functions or constructions are not described in detail since they would obscure the embodiments with unnecessary detail. Moreover, expressions such as at least one of, when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

[0047] FIG. 2 shows a radially segmented electrode sensor and two Lines of No Extension. In this example, an electrode 100 comprises 16 multiple radially arrayed electrode segments, whereas segments 101 indicate skin stretching affected (deformed) and 103 skin stretching unaffected (undeformed) segments (FIG. 2).

[0048] Although the human skin is stretched during body motion, there is virtually no stretch along the Lines of Non-extension (LoNEs) 102.

[0049] Since the human body tends to retain its form, taking no appreciable set after ordinary body deformations, its behavior is expected to conform to the laws of physical elasticity. Deformations in an elastic body can be described by the strain ellipsoid, in which a small sphere of material deforms to nearly ellipsoidal shape under elastic deformation of the entire body. On the surface of such an elastic body, the projected deformations transform a small circle into an ellipse. Since all points on the ellipse are derived from points on the undeformed circle, in general, there may be two directions in the ellipse that are not stretched (They may be noted by superimposing the original circle on the deformed ellipse.) An extension and connection of these radial directions may be referred to as a mapping of the surface of the elastic body by lines of non-extension.

[0050] During a measurement, electrode segments 103 will experience little or no deformation as they are positioned along the Line of no extension 102 and the system will thus identify these as electrode segments that have a low deformation of all electrode segments and underlying skin. The electrode segment with the lowest deformation is subsequently selected by the system to obtain an optimised skin-stretching artefact removed vital sign signal.

[0051] Radially segmented electrode arrangement works particularly as they allow for greatest flexibility to read-out of segments associated with zero stretch (NoLE), because the angle between principal strains is normally unknown (and not constant throughout the skin or body) and needs to be measured for example with strain gauges. In a segmented electrode with longitudinal segments and a chessboard pattern (FIG. 6) only one read-out along one-line (one zero strain direction) would be accurate. In this case, the electrode does not need to be a of circle sector shape (radially arrayed) but can be designed also in other ways having straight lateral segments throughout the circle area.

[0052] FIG. 3 (a and b) depicts a radially segmented sensor having strain gauges incorporated therein. An electrode 100 comprises a stretchable radially segmented electrode with 8 segments 101(103) and a strain gauge sensor 202. The skin adhering electrode layer (100) is placed on the skin (200) of the patient and is maintained on the skin with an skin adhering electrode layer 201 as shown in FIG. 3b. The ideal electrode material (and encapsulation material of the strain gauge) is made of an elastic material to conform to the skin and matching the skin properties, i.e. one resembling the mechanical viscoelastic material behavior of skin. This can be for example a conductive ionic silicone membrane electrode onto which strain gauges are mounted to measure strains. Using suitable data acquisition and software algorithms and control loops (multiplexing) one can continuously measure strain indicated by the various strain gages and switch the measurement between electrode segments to adapt to changing skin deformations caused by (body motion, and read out that electrode segment where the lines of non-extension result in the least amount of deformation and thus a vital sign signal with the lowest amount of artefacts caused by skin deformation). Strain gauges 202 (202a, 202b, 202c) are placed on top of the stretchable electrode 101 (103). In a variant of this embodiment, the segments themselves can be used as strain (deformation) measurement system as a stretchable conductive carbon-filled silicone rubber (elastomer) is used as an electrode material so separate strain gauges or other deformation measurements means are no longer needed. In another variant of this embodiment, an array of meander-structure metal wires can be integrated in the bulk of the electrode and used as strain sensor.

[0053] There are at least 3 individual (separate) strain gauges 202a , 202b, 202c: two of the strain gauges should be placed at a 90 degree angle to each other as two orthogonal strains such as Ex and Ey should be measured. The third one can be chosen randomly as it measures a shear strain. If a rosette strain gauge is used, standardized configurations are chosen.

[0054] In FIG. 3b a cross section of the electrode according to the invention is shown. In this embodiment, strain gauges 202 are placed on top of the stretchable electrode 101(103). The skin adhering electrode layer (100) is placed on the skin (200) of the patient and is maintained on the skin with an adhesive 201.

[0055] FIG. 4 depicts a vital sign measurement system showing a conceptual schematic describing the spatial selection of stretchable electrode segments 101 (103). As shown in this example, the system 100 contains 16 electrode segments 101. Each segment 101 is connected to an analog multiplexer 305 which is controlled by a processor 303 (typically a microcontroller). The processor 303 selects electrode segments 101 that are being measured by the read out electronics 306. The read out electronics comprises for instance sampling unit, amplification unit, and analog-to-digital conversion unit. The processor 303 estimates the deformation level applied to each electrode based on the deformation measurements obtained from the strain gauges 202 that are shown separately in FIG. 4 for clarity reasons but are actually as explained in FIG. 3, part of the electrode sensor 100. The electrode segment selection is then based on this estimation. The processor 303 can for example select each electrode showing a strain lower than a certain threshold value or select the one segment with the lowest deformation associated. The specific and number of electrode segments that are being selected can vary over time based on the deformation level variations that are being measured. The wearable device is therefore adapting its measurements based on the specific body movement.

[0056] If the deformation on each electrode segment 101 is unknown, it may still be possible to determine which of the segments are reporting reliable information based upon the fact that there are 2 LoNE axes. For this reason, if a sufficiently dense mesh of radial electrodes is defined (must be radially spaced by at most half the closest angle between 2 LoNE axes), then there should be 2 sets of radial electrode segments which qualitatively show the same or similar skin stretching artefact reduced biosignal output (all others should show deviating results). In addition, analysis may allow identification of an artefact as it is a component of the signal and varies from segment to segment, reaching a minimum in one of the electrode segments. The electrode segments thus found can be defined as the correct measurement. Again, criteria can be defined to reject measurements in situations where either difference between any 2 measurements exceeds a certain threshold or radial electrodes with the same result are too close together to form the 2 LoNE axes (i.e. if 2 adjacent electrodes indicate the same value).

[0057] In addition a calibration could be performed where the patient is asked to move through a series of motions while observing the resulting artefacts and identifying for the applied sensor which electrode segments are positioned at a Line of No Extension.

[0058] In a further embodiment, concentric rings of electrode segments (FIG. 7) are used in order to account for non-uniform strains. For example, the smaller the electrode segment (inner ring 103) the more likely that an area of low strain may be measured, however at a lower signal accuracy. A larger electrode segment delivers higher quality measurement but of course with a higher chance of artefacts introduced by deformation. Again, comparisons between smaller (103) and larger (101) electrode ring segments can considered.

[0059] Another embodiment of a vital sign monitoring system according to the present invention is a combination of the deformation measurement for example using a strain gauge with electrode segments output signals to make the identification of zero-stretch electrode segments more robust/reliable. An alternative to this embodiment is to exclude electrode segments with signal levels above a certain threshold (i.e. above typical physiological signal levels). This processing step should be applied after having filtered out common-mode interferences (e.g. 50/60 Hz).

[0060] The method according to the invention is depicted in FIG. 5. Specifically, in FIG. 5a after beginning of the vital sign measurement in step 401 by the vital sign monitoring system, the next step 402 is the identification of a deformation of an electrode comprising multiple electrode segments by the system using a deformation sensor. Then in step 403 the system selects that electrode segment that has a lowest deformation of all the segments of that electrode and using the selected electrode segment start measuring a vital sign signal of the patient (404). Then subsequently the vital sign signal of the patient is stored (405). FIG. 5b shows alternative version of method according to invention. A loop from step 405 back to step 402 so that the deformation information is again obtained and the selection changed if another electrode segment turns out to be more optimal.

[0061] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variation of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0062] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. Also, reference numerals appearing in the claims in parentheses are provided merely for convenience and should not be viewed as limiting in any way.