APPARATUS AND METHOD FOR DETECTING AN ABDOMINAL ELECTROPHYSIOLOGICAL SIGNAL

Abstract

The invention concerns a multi-electrode patch for abdominal electrophysiological detection. The patch has a flexible substrate interconnecting multiple electrodes and a module unit for removably engaging with an electronic readout device for detecting a maternal and/or fetal electrophysiological signal from the electrodes. The module has a mechanical module unit for removable mechanical engagement with a housing of the readout device, and an electrical module unit for making an electrical connection from the electrodes to the readout device. Engaging the patch with the readout device comprises engaging both the mechanical module unit and the electrical module unit. The patch may be flexible in a manner that allows variation in the relative positioning between the electrodes. The patch and/or electronic readout device may comprise a security device for communication of an authentication code.

Claims

1-71. (canceled)

72. A multi-electrode patch for abdominal detection of maternal and/or fetal electrophysiological signals, the patch comprising: a flexible substrate interconnecting a plurality of electrodes; and a module unit connected to the flexible substrate and configured to removably engage an electronic readout device for detecting a maternal and/or fetal electrophysiological signal from the electrodes; wherein the module unit comprises a mechanical module unit for removable mechanical engagement with a housing of the readout device, and an electrical module unit comprising at least one resiliently deformable contact for making an electrical connection from the electrodes to the readout device.

73. The patch of claim 72, wherein the at least one resiliently deformable contact is a spring-loaded contact pin.

74. The patch of claim 73, wherein each spring-loaded contact pin is configured to contact a corresponding connection on the housing of the readout device when the module unit is fully engaged with the housing of the readout device.

75. The patch of claim 72, further comprising an O ring seal around the electrical module that engages the housing of the readout device when the module unit is fully engaged with the housing of the readout device to prevent the ingress of fluid.

76. The patch of claim 75, wherein the electrical module unit includes a plurality of resiliently deformable contacts arranged within the O ring.

77. The patch of claim 72, wherein the module unit further comprises a waterproof seal that isolates the at least one resiliently deformable contact to prevent the ingress of fluid.

78. The patch of claim 77, wherein the waterproof seal surrounds the electrical module unit.

79. The patch of claim 78, wherein the waterproof seal surrounds each of the at least one resiliently deformable contact.

80. The patch of claim 77, wherein the waterproof seal is a compression seal configured such that mechanical engagement of the readout device by the module unit compresses the waterproof seal against the housing of the readout device.

81. The patch of claim 80, wherein the mechanical module unit comprises a cradle that slidably engages the housing of the readout device.

82. The patch of claim 80, wherein the mechanical module unit further comprises a magnet that engages a corresponding magnet on the housing of the readout device.

83. A system for abdominal detection of maternal and/or fetal electrophysiological signals, the system comprising: a plurality of electrodes; a flexible substrate interconnecting the plurality of electrodes; an electronic readout device for receiving a maternal and/or fetal electrophysiological signal from the electrodes; and a module unit connected to the flexible substrate and configured to removably engage the readout device, wherein the module unit comprises a mechanical module unit for removable mechanical engagement with a housing of the readout device, and an electrical module unit comprising at least one resiliently deformable contact for making an electrical connection from the electrodes to the readout device.

84. The system of claim 83, wherein the readout device is configured to amplify and filter at least one signal from the electrodes and comprises: an electrical power source for storing and providing electrical power to the readout device; a housing having a mechanical module unit for mechanical engagement with the mechanical module unit connected to the patch; and an electrical module unit for electrical engagement with the electrical module unit connected to the patch.

85. The system of claim 84, wherein the at least one resiliently deformable contact is configured to contact a connection on the electrical module unit of the readout device when the module unit is fully engaged with the housing of the readout device.

86. The system of claim 83, wherein the at least one resiliently deformable contact includes at least one contact point mounted on a resiliently deformable element.

87. The system of claim 83, wherein the at least one resiliently deformable contact is a spring-loaded contact pin.

88. The system of claim 83, further comprising an O ring seal around the electrical module that engages the housing of the readout device when the module unit is fully engaged with the housing of the readout device to prevent the ingress of fluid.

89. The system of claim 88, wherein the electrical module unit includes a plurality of resiliently deformable contacts arranged within the O ring.

90. The system of claim 83, wherein the mechanical module unit comprises a cradle that slidably engages the housing of the readout device.

91. The patch of claim 83, wherein the mechanical module unit comprises a magnet that engages a corresponding magnet on the housing of the readout device.

92. The system of claim 91, wherein the module unit further comprises a waterproof seal that isolates the at least one resiliently deformable contact to prevent the ingress of fluid.

93. The system of claim 92, wherein the waterproof seal is a compression seal configured such that mechanical engagement of the readout device by the module unit compresses the waterproof seal against the housing of the readout device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] The invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

[0099] FIG. 1 is a layout diagram of a patch according to an embodiment of the invention;

[0100] FIG. 2 is a layout diagram of the overlaminate layer of the embodiment of FIG. 1;

[0101] FIG. 3 is a perspective view of a patch and readout device according to an embodiment of the invention;

[0102] FIG. 4 is a perspective view of a receiving station according to an embodiment of the invention, with three different embodiments of a readout device according to an embodiment of the invention;

[0103] FIG. 5 is a schematic of a readout device according to an embodiment of the invention;

[0104] FIG. 6 is a sectional schematic of an electrode according to an embodiment of the invention;

[0105] FIG. 7 is a block diagram of a readout device according to an embodiment of the invention; and

[0106] FIG. 8 is a schematic of a test subject and a patch according to an embodiment of the invention, in use on the subject.

DETAILED DESCRIPTION

[0107] Referring to FIG. 1, a patch 150 according to an embodiment is shown, comprising a flexible substrate 100, viewed from the side that is to be facing the abdomen, in use. The flexible substrate 100, comprises a plurality of layers 6-12. The layers 6-12 are patterned so as to define the shape of the substrate 100, and to form electrodes 1-5. Each electrode 1-5 is connected via a conducting track 15 to an electrical module unit 16, for electrically connecting the electrodes 1-5 to a readout device (not shown).

[0108] The electrodes 1-5 and/or the conducting tracks 15 are formed from the signal layer 12, which comprises silver. For example, the conducting film used can be silver chloride which provides a good stoichiometric match to saline based electrode gels. A silver-containing ink may be used in particular to print the conducting tracks 15 and/or signal layer 12.

[0109] An insulating dielectric layer 11a, 11b is arranged on each respective side of the signal layer 12. The insulating dielectric layers 11a, 11b have a similar pattern to the conducting tracks 15 of the signal layer 12. The insulating layers 11a, 11b substantially overlay the conducting tracks 15, and are oversized relative thereto. The insulating layers 11a, 11b completely cover the conducting tracks between the electrodes 1-5 and the electrical module unit 16, while leaving the signal layer 12 exposed in the electrode and electrical module unit 16 region.

[0110] A graphite layer 10a, 10b is in contact with each of the respective dielectric layers 11a, 11b. The graphite layers 10a, 10b substantially overlay the respective insulating layer 11a, 11b, and are oversized relative thereto.

[0111] A first conducting shield layer 9a is in contact with the graphite layer 10a, and a second conducting shield layer 9b is in contact with the optional graphite layer 10b. The first and second conducting shield layers 9a, 9b substantially conform to the shape of their respective graphite layers 11a, 11b. The graphite layers 10a, 10b may reduce triboelectric charging of the respective shield layers 9a, 9b.

[0112] In some embodiments the graphite layers 10a, 10b may be omitted.

[0113] A further insulating dielectric layer 8 is in contact with the first conducting shield layer 9a, and an insulating overlaminate 6a is in contact with this layer 8. An insulating base layer 6b is also in contact with the second conducting shield layer 9b. The overlaminate 6a and base layer 6b are configured to substantially encapsulate the other layers of the substrate, except in the region of the electrodes 1-5. In the region of the electrodes, the signal layer 12 is exposed so that the electrodes 1-5 can make contact with an underlying surface. The insulating overlaminate 6a and base layer 6b may comprise a plastics material, such as polyester. The insulating dielectric layers 8, 11a, 11b may comprise a plastics material, such as polyester or polyimide.

[0114] The base layer 6b defines the external shape of the flexible substrate 100, and includes a circular region corresponding with each electrode 1-5. The electrodes 1-5 are substantially rectangular, and are surrounded by each respective circular region 21-25. In will be appreciated that in other embodiments, the electrodes 1-5 can be any appropriate shape, such as circular, square or rectangular. The circular regions 21-25 may be provided with an adhesive film around their perimeter, so that the each circular region can be adhered to the skin of a subject. A conducting medium (such as ECG gel) is preferably disposed between each electrode 1-5 and the skin of the subject, thereby securely coupling each electrode 1-5 to the skin of the subject.

[0115] The conducting medium preferably comprises at least 9% (by mass) of an electrolyte such as sodium chloride or potassium chloride. The conducting medium (or gel) may be applied by a user (e.g. a nurse or doctor) to the subject's abdomen when applying the patch, or may be pre-existing on the patch when it is removed from packaging (not shown). The conducting medium may be retained in contact with the electrode by a sponge element (not shown). Each circular region 21-25 comprises a lobe, or flap, that is substantially free from adhesive film or conducting medium, protruding from the edge of the circular region 21-25. Each electrode 1-5 can thereby be detached from the subject by peeling the circular region 21-25 away from the subject by the lobe.

[0116] For any polymer layer described above, a PET material may be used and has been found to provide useful properties, i.e. resilience, for avoiding breakage of the signal layer 12 during flexing of the patch in use. The material thickness of the polymer/PET layer(s) may be matched to the properties of the signal conducting layer 12 to prevent deformation of the tracks in a manner that is likely to lead to a break in the signal layer 12.

[0117] Although not explicitly shown in the figures, a plurality of vias may be provided through one or more of the above described layers in order to allow signals to pass to/from either external surface of the patch. Thus electrical signals may pass from the electrodes to the signal layer 12 and may pass form the signal layer 12 to the module unit 6 on the exterior of the patch substrate by way of a via formation passing through the intermediate layers.

[0118] The substrate 100 comprises a reference feature 17, for lining up with an umbilicus or other suitably recognisable feature of the subject. In this case, the reference feature 17 is defined by an aperture in the flexible substrate 100. In other embodiments the reference feature 17 may be a vertex, pointer or transparent region forming in the flexible substrate 100. The reference feature 17 may be associated with an adjacent adhesive region, by which the reference feature 17 can be secured to the subject, for example adjacent to the umbilicus.

[0119] The structure lends itself to a straightforward method of application. For example, the reference feature 17 may be secured at a reference point on the patient using the associated adhesive region. The electrodes 1-5 can subsequently be moved away from the abdomen to prepare the skin. For example each electrode 1-5 can then be placed in turn around the abdomen with, if necessary, suitable abrasive skin preparation. Once any skin preparation and the subsequent placement of an electrode 1-5 has been completed the impedance of the connection between the electrode 1-5 and the patient may be measured by an electronic readout device 200 (shown in FIG. 7). If the impedance is above a desired value, further preparation of the skin may be carried out to reduce the impedance to below the desired value. The desired value may, for example, be 5 kOhms. When the impedance is below the desired value, the skin region for the next electrode may be prepared by abrading the skin and the electrode subsequently applied electrode, and the impedance tested. This method may be repeated until all of the electrodes are successfully applied.

[0120] The electrodes 1-5 comprise a first sensing electrode 1, second sensing electrode 2 and third sensing electrode 3, a drive electrode 4 and a common electrode 5. Each of the first, second and third sensing electrodes 1, 2, 3 and the drive electrode are arranged around the reference feature 17 of the patch, in this embodiment equi-angularly spaced at about the same distance from the reference feature 17. Specifically, in the orientation shown in FIG. 1, the first and third sensing electrode 1, 3 are respectively to the left and right of the reference feature, and the second sense electrode 2 and the drive electrode 4 are respectively above and below the reference feature. The length of the tracks 15 connecting each of the electrodes 1-4 to the module 16 is thereby minimised, reducing any potential for noise (which may arise from electromagnetic interference, triboelectric effects etc).

[0121] In the embodiment the circular regions 21, 23 respectively associated with the first and third sensing electrode 1, 3 are arranged symmetrically on a horizontal line passing through the centre of the reference feature 17. The circular regions 22, 24 respectively associated with the second sensing electrode 2 and drive electrode 4 are arranged on a vertical line passing through the centre of the reference feature 17.

[0122] The circular region associated with the common electrode 5 is arranged on the vertical line passing through the reference feature 17, below the drive electrode 4. The drive electrode can be placed on any other part of the abdomen.

[0123] Each of the first and third sensing electrodes 1, 3 and the common electrode 5 are attached to the region of the substrate 100 that carries the reference feature 17 by a respective flexible substructure 13a, 13b, 13c. Each flexible substructure 13a-13c is attached at a first end to a part of the substrate 100 that carries the reference feature 17, and at a second end to the circular region 21, 23, 25. Each flexible substructure is arranged to deform so as to allow the relative positions of the first and second end of each flexible substructure to be adjusted when the substrate is conformed to a surface (such as an abdomen), thereby altering the positions of the electrodes 1, 3, 5, relative at least one of: each other, the other electrodes 2, 4, and the reference feature 17. In other embodiments a similar flexible substructure can be used to connect electrodes 2 and 4 to the part of the substrate 100 that carries the reference feature 17. Such an arrangement may accommodate transverse (horizontal) stretching of the skin.

[0124] In this arrangement, the flexible substructures 13a and 13b allow adjustment of the distance between the first sensing electrode 1 and the reference feature 17 and the distance between the third sensing electrode 3 and the reference feature 17. The ability of the substrate to accommodate adjustment of the positions of these electrodes makes the patch more comfortable, because the natural movement of the subject's skin (for instance as a result of breathing) can be accommodated by the flexible substructures 13a and 13b. A similar structure may be used in relation to electrodes 2 and 4. Furthermore, the patch may be configured to fit subjects with different sizes of abdomen, so that a single patch can be used on a wide range of subjects.

[0125] Each flexible substructure 13a-13c in this embodiment comprises a serpentine arrangement, in which at least one folded elongate member is disposed substantially lateral with a direction of movement to be accommodated by the substructure. The stiffness of such a member is substantially proportional to the third power of its length, and the compliance of the substructures in each direction may readily be tailored by adjusting their length, or the number of folds in the serpentine substructure (each fold further increasing the compliance). Each substructure 13a-13c carries the conducting track 15 of the electrode associated therewith.

[0126] The flexible substructures 13a and 13b are similar, these being rotationally symmetric about the centre of the reference feature 17, and having a single folded elongate member (having an outward leg and a return leg), that extends in a substantially vertical direction. Horizontal relative movement between the first and third sensing electrode 1, 3 is thereby accommodated.

[0127] The substructure 13c that connects the common electrode 5 to the part of the substrate carrying the reference feature 17 is different, and has two folded elongate members 311, 32, each extending in a substantially horizontal direction. This substructure 13c is configured to accommodate a greater degree of relative movement than the other substructures 13a, 13b, so that the common, electrode can be positioned towards the symphis pubis at a range of gestational ages and for a range of different sized subjects. The terms horizontal and vertical will be understood as relative terms, and are not intended to refer to horizontal and vertical directions of an external reference frame.

[0128] FIG. 2 shows the shape of the overlaminate layer 6a, and substantially corresponds with the shape of the substrate 100, but with the circular regions 21-25 omitted.

[0129] FIG. 3 shows a further patch according to an embodiment, comprising the same flexible substrate 100 that is shown in FIG. 1, with a mechanical module unit 19 affixed to the substrate 100 adjacent to the electrical module unit 16. The patch 150 is shown with a separate electronic readout device 200 for detecting electrophysiological signals from the electrodes 1-5 of the patch.

[0130] The electronic readout device 200 comprises a readout device housing 201 which is substantially cuboidal in shape, and which has an upper face 202 which is substantially square. The upper face 202 is similar in extent to one of the circular regions 21-25 associated with each readout electrode. The thickness of the housing 201, in a direction normal to the upper face 202, is less than half the edge length of the upper face 202, so that the readout device 200 is compact and low profile.

[0131] The mechanical module 19 comprises a cradle for receiving the readout device housing 201 of the readout device 200. The housing 201 is removably received and held within the cradle, which allows movement of the housing 201 only in the direction of insertion/removal. The cradle comprises a stop, and the readout device 200 is fully engaged with the mechanical module unit 19 when the housing 201 is in contact with the stop. The mechanical module 19 further comprises a latch or catch to retain the readout device housing 201 in contact with the stop. In this embodiment the latch or catch comprises a magnetic catch. A permanent magnet is provided on either (or both) of the mechanical module 19 and housing 201, which attracts a corresponding magnet (or ferromagnetic element) on the other of the mechanical module 19 or housing 201. In alternative embodiments, a hook and loop arrangement (e.g. Velcro) may be used to secure the readout device 200 to the patch 150.

[0132] When the readout device housing 201 is fully engaged with the mechanical module 19, an electrical module 204 (shown in FIG. 5) of the readout device 200 is in electrical engagement with the electrical module 16 of the patch 150. The electrical module 204 of the readout device 200 may conveniently comprise a plurality of contacts mounted on resiliently deformable members (e.g. spring loaded contact pins).

[0133] The quality and reliability of the electrical contacts made to the module may be important when detecting electrophysiological signals (which are typically sub microvolt) and also for ensuring that stringent cleaning procedures associated with a hospital environment can be implemented on the readout device 200. Planar connections on the readout device 200 and resiliently biased connections on the patch 150 may be used. This arrangement allows easy cleaning of the readout device 200. The patch 150 may be disposed of after each use and hence not require cleaning, so the difficulty of cleaning the resiliently biased connections may not arise. Alternatively, either electrical module 204, 16 (of readout device 200 or patch 150) may comprise resiliently biased contacts wherein each contact pin resides inside a tube with a secure seal between the tube and the contact pin. The pins and their respective tubes may be are separated from each other by a sufficient distance to enable them to be cleaned. In this way the readout device 200 may be provided with resiliently biased contacts that may be readily cleaned.

[0134] In some situations it may be advantageous to seal the connected electrical modules 204, 16, for example to prevent the ingress of water or other fluids during a water birth delivery. One way to achieve this is to use a seal element (such as an O ring seal) around the electrical module 204, 16. The seal element may be provided on either the patch 150 or the readout device 200. The seal element may compressed when the readout device 200 is engaged with the mechanical module 19. The mechanical module 19 may be configured to urge the seal element into sealing engagement with the patch 150 and/or readout device 200 (for example by magnetic force).

[0135] A security device 101 is provided on the patch 150, for authenticating the patch 150 to the electrical readout device 200. In this embodiment the security device 101 is provided in the cradle. When the respective electrical modules 16, 204 of the patch 150 and readout device 200 are engaged, the readout device 200 checks the patch to determine whether it is authentic (i.e. checks Whether the patch is an unauthorised copy), The authentication is achieved by communication (e.g. electrical, optical, wireless) between a security device 203 of the readout 200, and a corresponding security device 101 of the patch. The security devices 101, 203 may be configured to use cryptographic and/or hash functions.

[0136] Each electrical module 16, 204 may comprise nine connections. Three connections may be provided for each of three sensing electrodes, and a common and drive connection may be provided for the common and drive electrode respectively. A connection may be provided for connection to at least one conducting shield layer of the patch. A further three connections may be provided for connection with the security device, or chip, 101 of the patch 150.

[0137] The readout device 200 is preferably configured to determine and output at least one of a: fetal heart rate, fetal ECG, maternal heart rate, maternal ECG, or uterine activity, Preferably the readout device is configured to output any two, three, four, or all five of the above. The readout device is preferably configured to transmit the output, so that it can be monitored. Preferably, the readout device 200 comprises a wireless transmitter (e.g. according to the Bluetooth standard), operable to transmit the output of the readout device 200.

[0138] In some embodiments, the readout device 200 does not determine any of a fetal heart rate, fetal ECG, maternal heart rate, maternal ECU, or uterine activity, but instead transmits raw or partially processed voltage and/or current data from the electrodes, for processing by a further device into a suitable output (such as one, two, three, four or more of a fetal heart rate, fetal ECU, maternal heart rate, maternal ECG, or uterine activity).

[0139] Referring to FIG. 7, a block diagram of a readout device 200 according to an embodiment is shown. The readout device 200 comprises an electrical module unit 204, analogue circuit 213, digital processor 2:12, wireless transmitter 2111, security device 203, battery 210 and inductive coil 214.

[0140] The analogue circuit 213 comprises an analogue to digital converter, and receives the electrical signals from the electrodes, and outputs a digitised version thereof, for processing by the digital signal processor. In some embodiments the analogue circuit 213 may comprise an amplifier and/or filter.

[0141] The processor 212 receives a digitised signal from the analogue circuit 213, and preferably processes it to determine an output, as described already. The processor 212 subsequently outputs a signal to the wireless transmitter 211 for onward transmission, for example to a receiving and display station 300 according to an embodiment of the invention.

[0142] In order to maximise the battery life of the removable electronic device it may be configured such that the power of the wireless transmitter is controlled based upon the signal strength index and/or hit error rate. This may greatly lengthen the monitoring period that can be carried under one single battery charge.

[0143] In some embodiments, one or more component of the device 200 may be combined, for example in a multi-chip module or system on chip. For example, the processor 212 may comprise any combination of the analogue circuit 213, the security device 203 and the wireless transmitter 211.

[0144] The electronic components of the readout device 200 are powered by an electrical power source, which is a battery 2:10 in this embodiment. In other embodiments the electrical power source may comprise a capacitor. The inductive coil 214 is operative to charge the battery 210, optionally under the control of the processor 210.

[0145] The readout device 200 may be configured to detect electrophysiological signals between a pair of sensing electrodes, rather than simply between a sensing electrode and the common electrode. For example, the readout device 200 may be configured to detect electrophysiological signals between sensing electrodes 1 and 3 (i.e. horizontally across the abdomen in use). This allows a further channel of UA and fetal ECG to be provided. The advantages for UA are that the separation is relatively fixed between electrodes 1 and 3 and hence this offers the potential of indicating contraction strength. Furthermore such a horizontal fECG channel (measured between sensing electrodes 1 and 3) allows breech and transverse presentations to be more carefully monitored. In addition, by providing this channel a further Maternal ECG channel can be generated that can be used for mECG removal, further reducing confusion between the mECG and MEG. Such confusion is a common problem with Doppler ultrasound whereas with abdominal fECG the percentage confusion time is considerably reduced. The use of another mECG channel (for example, measured between sensing electrodes 1 and 3) can further reduce this confusion by providing an improved template for accurate mECG removal.

[0146] The readout device 200 may comprise sensors 215, which may comprise an inertial sensor such as accelerometer and/or gyroscope. Preferably, the sensors 215 comprise a one, two or three axis accelerometer, and/or a one, two or three axis gyroscope. The sensors 215 may be MEMS (micro-electromechanical systems) devices. The readout device 200 may comprise an inertial measurement unit. The accelerometers and gyroscopes may be used to track the movement of the readout device 200, thereby allowing both fetal ECG and electrohysterogram algorithms to differentiate between maternal/fetal movements and genuine contractions and fetal ECG signals. A gyroscope can provide useful additional rotational information that an accelerometer cannot provide, thereby allowing further separation of fetal movement from the acquired data. This fetal movement is a highly useful indicator that provides further fetal well-being indication. Additionally the use of the pair of devices allows separation of the maternal breathing signal which is a further indication of maternal health.

[0147] In FIG. 4, a signal receiving and display station 300 is shown, comprising a screen 302, and two dock areas 301. The receiving station is operable to receive and display output signals from the readout device 200 on the screen 302. The dock areas 301 are arranged to receiving part of the housing 201 of the readout device 200, and are provided with a wireless charging device, that is operable to charge a readout device 200 placed in the dock area 301. The wireless charging device preferably operates by inducing a current in a conductor of the readout device 200 using a coil. A number of alternative embodiments 200a, 200b, 200c of readout devices 200 are shown in front of the receiving station, each having slightly different designs of housing 201. The housing 200 is preferably waterproof, and is preferably IP57 rated.

[0148] The receiving and display station 300 can have two significant functions. The first is to display the full set of fetal and maternal parameters (i.e. ERR, MHR, UA, fetal movement etc) to the clinical care team or community midwife. A second significant function is that of an interface device that connects to existing installed CTG (cardiotocograph) machines. This latter function allows hospitals/health care units to efficiently use its existing resources without making equipment redundant whilst benefiting from the advantages of abdominal electrophysiological monitoring i.e. increased FHR accuracy; improved reliability of FHR/UA with BMI; maternal mobility; reduced FHR/MHR confusion etc.

[0149] At least two readout devices 200 are preferably allotted for a single patient. When one readout device 200 is connected to the patch 150 it sends the patch unique ID to the receiving and display station 300 so that the second readout device 200 can only be connected to the same patch 150 when the readout devices 200 are eventually swapped over. Readout devices may be swapped when the battery becomes discharged or when routine maintenance is required. The number of readout devices 200 associated with each patient, patch, or receiving and display station 300 is not limited to two or three (as shown in FIG. 4) as labour or a maternal antenatal recording session can extend over a considerable time, for example from a few hours to several weeks.

[0150] The use of at least two readout devices 200 allows a seamless swapping of the readout devices 200. The subsequent readout device 200 may already have the appropriate patch ID loaded into its local memory so as to reduce set up time.

[0151] Referring to FIG. 6, an electrode 400 is shown. The electrode 400 is for use as an electrode of a patch according to an embodiment of the invention, and comprises a substrate 402, from which extend a plurality of electrically conductive needles 401. The needles are formed from a bio-compatible material (such as doped silicon), and are configured to penetrate the stratum corneum to provide an electrical connection to the more conductive underlying layers, without penetrating far enough to stimulate nerves so as to cause pain. The needles therefore have a length of between 20 m and 200 m, preferably between 50 m and 100 m. The needles may be formed by reactive ion etching or wet etching of silicon, or may be formed by any other suitable process, from any other suitable material. The electrode 400 may be used as each electrode of a patch according to an invention. A patch 150 that comprises such electrodes 400 may obviate the careful preparation of the skin that is usually necessary to achieve a low enough impedance contact to the subject, because the needles facilitate contact to be made through the stratum corneum.

[0152] Referring to FIG. 8, a patch 150 according to an embodiment of the invention is shown in use, applied to the abdomen of a pregnant human subject 500. The skin is preferably prepared to ensure a good contact is made between each electrode and the skin, and gel is preferably applied to electrically couple the electrodes to the skin. The reference feature 17 of the patch is aligned with the umbilicus 501 of the subject 500, and the first sensing electrode 1 and drive electrode 4 are arranged on the abdomen on the median plane of the subject. The common electrode 5 is placed facing the symphis pubis, by extending the flexible substructure 13c if necessary. The patch 150 is comfortable and low profile, and relative movement of the electrodes (e.g. as a result of breathing and locomotion) is accommodated.

[0153] The readout device 200 is engaged with the module of the patch 150, so that their respective electrical modules 16, 204 are connected. In order for the readout device to work with the patch 150, and provide any useful output, the patch is preferably first authenticated by the readout device, using the respective security devices 101, 203.

[0154] Once the patch 150 is authenticated, the readout device 200 amplifies and filters the electrophysiological signals detected by the sensing electrodes 1-3 to determine and output all of: a fetal ECG, a fetal heart rate, a maternal ECG, a maternal heart rate, and a uterine activity. More specifically, the voltage difference between the sensing electrodes and the common electrode is sensed and processed by the readout device to create an output signal from the readout device 200. The common mode voltage of the three sense electrodes 1-3 is applied to the shield layers 9a, 9b of the patch 150, to minimise leakage currents to the shield layers. The inverse of the common mode voltage is applied to the drive electrode 4 to minimise common mode voltage noise. The term common mode is used in the conventional sense of a signal that is shared by more than one conductor.

[0155] The integration of the readout circuit 200 and patch 150 allows the subject to move freely, without having to worry about leads, and minimising any deleterious cable noise that can arise due to triboelectric effects when leads are flexed. Furthermore, the short length of the connections to the readout circuit minimise the potential for other sources of noise.

[0156] The readout device 200 preferably comprises a wireless transmitter (not shown), and is operable to wirelessly transmits the output, via the wireless transmitter, substantially in real time, to a monitoring station that is operable to display the output. The readout device 200 is compatible with a number of monitoring stations, but is preferably used with a receiving and display station 300 according to an embodiment of the invention.

[0157] When the need for monitoring abdominal electrophysiological signals has passed, the readout device 200 is removed from the patch 150, and the patch can disposed of. The readout device 200 can be subsequently re-used with a different patch 150, preferably after the readout device 200 is sterilised (e.g. by immersion in a sterilising fluid). The patch 150 may therefore be made relatively cheaply, and the readout device 200 may include relatively sophisticated electronics without compromising the cost of using the system. When the readout device 200 is not in use with a patch 150, it may preferably be placed on a docking area 301 of the receiving and display station 300, so that it charges ready for another use. There may be two or more readout devices 200 associated with each monitoring station 300, so that one readout device 200 is always charging while the other is in use, thereby ensuring that a charged device is always ready for use.

[0158] It will be appreciated that the patch, readout, monitoring device and systems comprising combinations of these address a number of the problems with prior art devices.

[0159] Although an embodiment of the patch has been described in which each flexible substructure comprises a serpentine flexure, any suitable arrangement may be used. For example, in some embodiments the flexible substructure may comprise a corrugated region of the substrate that can accommodate movement parallel to the plane of the substrate. Other compliant planar arrangements may also be used. For example, the electrode may be coupled to the remainder of the patch via a ring shaped element, wherein the ring has geometry selected (e.g. large diameter, narrow width) to accommodate movement in the plane of the substrate.

[0160] In any examples of the invention, the patch may be provided with a backing material layer which is removable, e.g. by peeling, to expose the patch adhesive region(s) for attachment of the patch to the abdomen of a wearer. Separate or individual backing sheets may be applied to different electrodes/portions of the patch such that individual portions can be adhered and/or replaced as necessary.

[0161] A number of other modifications and variations may be made, without departing from the scope of the invention, as defined by the appended claims.