Patent Description:
Compression therapy (CT) via the wearing of an elasticated compression garment (CG) is widely used for the treatment and management of blood circulatory problems. These include venous deficiencies, which can cause venous leg ulcers (VLU) and deep vein thrombosis (DVT). Compression therapy also assists in the movement and removal of trapped fluid in the body's lymphatic system which can help to reduce or prevent lymphoedema. Other medical applications of compression therapy include after liposuction surgery, abdominoplasty, facelift, face compression, neck compression, Veronique compression, for the control of loose skin, after a Brazilian Butt Lift (BBL), after Caesarean section (C-section), hernia surgery or hysterectomy.

Compression garments are also known to provide ergogenic benefits during sports & athletics training and performance. Proposed benefits include an increase in strength and power as well as improved endurance performance. Advantages are thought to be achieved via a number of mechanisms, which include an increase in muscle oxygenation resulting from improved blood flow to the muscle and a reduction in blood lactate levels and muscle oscillation, thought to reduce the severity of fatigue and help in post exercise recovery.

To work optimally, compression garments should provide a predetermined amount of compression (pressure) to the relevant body part of the wearer. For this reason, compression garment, such as compression stockings, typically come in different sizes, to suit differently sized wearers. However, because different body parts have different shapes and sizes, readymade garments do not always provide the required predetermined compression. For this reason, it can be desirable to have apparatus suitable for determining information relating to the actual amount of pressure a compression garment is applying to a wearer.

It is consequently an aim of the present invention to provide a novel approach for sensing one or more properties of a compression garment.

D1 (<CIT>) relates to a compressive pressure device, having an inner compressive pressure sleeve and an overlying outer compressive pressure wrap and a sensor located (a) between the body and the sleeve, (b) within the sleeve, (c) between the sleeve and the wrap, or (d) within the wrap.

D2 (<CIT>) relates to a sensor for measuring a pressure applied by a bandage.

D3 (<CIT>) relates to a compression garment with compression applying straps, with sensors for sensing the compression applied to the straps.

When viewed from a first aspect, the invention provides a compression garment apparatus comprising a compression garment and a sensor apparatus, wherein the sensor apparatus comprises a sensor device, attached to an outer surface of the compression garment, and a controller, wherein the sensor device comprises a first mounting point, attached to a first point on the outer surface of the compression garment, and a second mounting point, attached to a second point on the outer surface of the compression garment; wherein the sensor device is arranged to sense displacement between the first and second mounting points; and wherein the controller is configured to process information representative of the sensed is placement to estimate a pressure exerted by the compression garment on a wearer of the compression garment.

From a further aspect, the invention provides a sensor apparatus comprising a sensor device, for attaching to an outer surface of a compression garment, and a controller,
wherein the sensor device comprises: a first mounting point for attaching to a first point on the outer surface of the compression garment; and a second mounting point for attaching to a second point on the outer surface of the compression garment, wherein the sensor device is arranged to sense displacement between the first and second mounting points; and wherein the controller is configured to process information representative of the sensed displacement to estimate a pressure exerted by the compression garment on a wearer of the compression garment.

Thus it will be appreciated that the present invention provides a means of determining a displacement, or stretch, in a compression garment using a sensor device attached to the outside of the compression garment. This displacement (e.g. corresponding to a change in circumference of the garment) can be used to estimate the pressure exerted by the compression garment on the wearer's body, but it does not require anything to be placed between the compression garment and the wearer. As the sensor is mounted on the outside of the compression garment, rather than between the compression garment and the wearer's skin, the sensor does not itself cause any additional expansion or distortion of the compression garment, which might otherwise lead to inaccurate pressure indications-e.g. by causing a hump in the garment over the sensor, which could create additional localised pressure or shear forces on the body. It also enables the sensor to be easily attached to and detached from the compression garment, and minimises wearer discomfort.

The controller may be configured to receive the information representative of the sensed displacement from the sensor device-e.g. as an analogue signal or as digital data.

The controller may be attached to the compression garment along with the sensor device. The controller may be integrated with the sensor device as a single device-e.g. both being on a common structure, or in a common housing or casing with the sensor device. Thus the sensor device may comprise the controller. Alternatively, the controller may be separate (e.g. remote) from the sensor device. The controller may be provided as a separate control unit. The controller may be communicatively connected to the sensor device (e.g. by a cable or other wired or wireless communication link).

The compression garment may comprise an inner surface which may be in contact with a body of the person or animal. The outer surface will then face away from the person or animal.

The compression garment may be a woven or fabric compression garment. It may be a compression stocking or other garment. It may be shaped to conform to a human or animal limb or other body part-e.g. a leg or an arm. It may be suitable for use in compression therapy-e.g. for reducing the risk of deep vein thrombosis. It may be an item of sportswear.

Each mounting point may be attached to the compression garment using a mechanical fastener and/or chemical bonding. The sensor device may be configured for attachment to the compression garment using any one or more of: hook-and-loop pads, a popper, a magnet, stitching, adhesive, riveting, welding, or any other suitable mechanism.

In some embodiments, the sensor device comprises a third mounting point attached to a third point on the outer surface of the compression garment. This additional mounting point provides additional stability to avoid twisting of the sensor.

The sensor device may be non-destructively detachable from the compression garment. This means that the garment can easily be washed and reused without damaging the sensor. Furthermore, sensor readings may be taken before and after washing of the garment in order to determine any loss of compression pressure caused by the washing process. It also allows one sensor to be used on multiple compression garments at different times, which may be more economical than disposing of the sensor with the garment.

The garment may be elongate (e.g. broadly cylindrical) and the sensor device may be attached to the garment with the first and second mounting points positioned about a common circumference of the garment. The mounting points may be the same distance from an end of the garment-e.g. from a foot of a compression stocking. They may be a common distance along a limb of a wearer when the garment is being worn. This may be a clinically recommended distance. In this way, the sensor can be used to measure circumferential displacement, or tension, in the garment. The mounting points may be just above the ankle for compression garments (e.g. a compression stocking) used for venous leg ulcer management, or any other appropriate location for other suitable or desired applications, such as lymphoedema or deep vein thrombosis management.

The sensor device may be used to sense a first displacement at a first time, which may be a time when the compression garment is not being worn. It may be used to sense a second displacement at a second time, which may be a time when the compression garment is being worn. In this way, the sensor device may be used to detect when the garment is and/or is not being worn, or may be used to determine whether the compression garment is correctly applied.

The sensor device may have an initial state, which the sensor device is in when it is attached to a slack compression garment (i.e. when the garment is not being worn). In this initial state, the first and second mounting points may be less than <NUM>, <NUM>, <NUM>, <NUM> or <NUM> apart. A relatively small initial distance can help reduce error -e.g. if there is non-uniform pressure in the garment-as well as facilitating a compact sensor device. The sensor device may be such that the first and second mounting points are less than <NUM>, <NUM>, <NUM>, <NUM> or <NUM> apart when the garment is under a maximum specified tension for the garment in normal usage-e.g. when worn by a human of an appropriate size for the compression garment,.

The sensor device may comprise a first part and a second part, wherein the first part is moveable relative to the second part. The first mounting point may be on the first part, and the second mounting point may be on the second part. The first and second parts may be connected (e.g. by a thread), or they may be unconnected. The first part may comprise a housing which may house one or more electrical components, which may include the controller.

The sensor device may comprise a biasing member (e.g. a spring) arranged to resist displacement of the first mounting point away from the second mounting point in one or more directions. It may be arranged to urge the first mounting point towards the second mounting point, at least when the second mounting point is displaced from the first mounting point by more than a minimum displacement. In some embodiments, the biasing member is arranged to bias the sensor device into or towards the initial state of the sensor device. The biasing member may comprise a first fixing point and a second fixing point. The first fixing point of the biasing member may be fastened to the first part. The second fixing point of the biasing member may be fastened to the second part.

In some embodiments, the biasing member is elongate (e.g. a straight or coiled spring) and a first end and a second end of the biasing member are both fastened to the first part and are separated by a fixed distance, and a third (e.g. central) point or portion of the biasing member, between the first and second ends, is fastened to the second part of the sensor device. The biasing member may be arranged such that a displacement of the first part away from the second part causes a deflection and/or elongation of the biasing member, which may be resisted by the biasing member, so as to resist the displacement.

Such a biasing member can help to ensure that, when the compression garment is removed from the wearer, the first and second mounting points reliably return to the same initial (e.g. slack) state. This can help to reduce disadvantageous effects of hysteresis when the sensor device is reused and repeatedly cycled between an initial state when the garment is not being worn, and a tensioned state when the garment is being worn.

The sensor device may generate an analogue or digital electronic signal representative of displacement between the first and second mounting points. The signal may be representative of absolute displacement and/or representative of a change in displacement (i.e. relative displacement). In some embodiments, the sensor device may generate a voltage that is representative of-e.g. proportional to-the displacement between the first and second mounting points. It will be appreciated that this signal can relate to a pressure exerted by the compression garment-e.g. on a wearer of the garment.

The sensor device may output a signal (e.g. an optical or electronic signal) that is representative of the displacement-e.g. for processing by the controller when the controller is separate from the sensor device. In some embodiments, the controller is integral with or part of the sensor device, in which case the sensor device may send such a signal to the controller over an internal connection or interface.

The controller may comprise a microcontroller or other processing device for executing software instruction, and/or dedicated hardware circuitry (e.g. an ASIC or FPGA), which may be configured for processing a signal representative of the displacement. The controller may be configured to estimate pressures in the range mHg to <NUM> mmHg. It may log data representative of the displacement and/or pressure over time at intervals, which may be regular intervals.

The information representative of displacement may be represented or encoded as an analogue or digital signal or data, in any appropriate way. The controller may process the information representative of the sensed displacement as digital data. The controller may be configured to process the information representative of displacement to determine a tension force, or a change in a tension force, in the compression garment, e.g. as a digital tension value, which it may store in a memory of the controller. The controller may be configured to process the information representative of displacement to determine an estimate of the displacement, or a change in the displacement, between the first and second mounting points, e.g. as a digital displacement value, which it may store in a memory of the controller. It may determine the digital displacement value by processing the digital tension value.

The controller may be configured to determine an absolute or relative tension force value and/or an absolute or relative displacement value using a look-up table stored in a memory of the controller. It may use the information representative of displacement to access an entry from the look-up table. The data in the look-up table may be empirically determined.

The controller may be configured to determine an absolute or relative tension force value and/or an absolute or relative displacement value by numerically evaluating a function, which may be a function of the information representative of displacement. It may do so by processing one or more algorithms.

The controller may be configured to process an absolute or relative tension force and/or an absolute or relative displacement to estimate a pressure exerted by the compression garment on a wearer of the garment.

The controller may estimate the pressure exerted by the compression garment on a wearer of the garment using a look-up table, or by evaluating an algorithm, wherein the look-up table or algorithm implement the Laplace equation.

In some embodiments, the controller is configured to calculate the pressure exerted by the compression garment by:.

The linear function of the determined displacement may be the sum of a first constant and a product. The product may be the product of a second constant and the determined displacement. The first constant may be equal to the circumference of the compression garment in a slack or un-stretched, e.g. initial, state. In embodiments where a biasing member (e.g. a spring) is provided to assist in bringing the sensor device into an initial (un-stretched) state, determining the tension in the compression garment may comprise subtracting from the tension force a biasing force provided by the biasing member. The biasing force may be determined (e.g. calculated) using the determined absolute or relative displacement between the first and second mounting points. However, in some embodiments, the biasing force provided by the biasing member may be negligible in comparison to the tension in the compression garment, and so may be disregarded in the estimation of the pressure exerted by the garment.

The sensor device or separate controller may be configured to output a signal if the displacement between the first and second mounting points and/or the pressure is greater than a predetermined value.

The sensor device may use any suitable means for sensing displacement. It may sense displacement optically and/or electronically.

In one set of embodiments, the sensor device comprises a light-emitting component (e.g. an LED) and a light-receiving transducer, such as a photo detector (e.g. a photodiode, photoresistor, or phototransistor). The sensor device may be arranged such the amount of light received by the light-receiving transducer from the light-emitting component depends on the displacement between the first and second mounting points-e.g. being proportional thereto.

Light may travel partly or entirely through free space between the light-emitting component and light-receiving transducer. However, in some embodiments, one or more optical fibres may extend at least partly between the light-emitting component and light-receiving transducer. The sensor device may comprise an optical fibre one end of which is in a fixed relationship to one of the light-emitting component and light-receiving transducer, and an opposite end of which is in a moveable relationship to the other of the light-emitting component and light-receiving transducer. The sensor device may be configured so that increased displacement between the first and second mounting points causes less light to strike the light- receiving transducer, resulting in a lower output signal from the transducer.

The sensor device may comprise a first optical fibre and a second optical fibre, which may be arranged in series. The first optical fibre may be arranged to receive light emitted from the light-emitting component and to transmit the light to the second optical fibre. The second optical fibre may be arranged to transmit the light received from the light emitting component (via the first optical fibre) to the light-receiving transducer. The sensor device may be configured so that increased displacement between the first and second mounting points causes less light to be transmitted from the first optical fibre to the second optical fibre, thereby causing less light to strike the light receiving transducer, resulting in a lower output signal from the transducer.

The first optical fibre and the second optical fibre may be coaxial (i.e. extending along the same axis), along at least respective parts or all of their lengths, in an initial (e.g. un-stretched) state of the compression garment. The first optical fibre and the second optical fibre may be moveable relative to each other- e.g. being carried respectively on the aforesaid first and second parts. They may be arranged such that relative movement between the first optical fibre and the second optical fibre causes the optical fibres to misalign, thereby reducing the amount of light transmitted from the light emitting component to the light receiving transducer via the first and second optical fibres. This can result in a lower output signal from the transducer.

The sensor device may be configured so that displacement between the first and second mounting points causes a light-emitting end of the first fibre to move relative to a light-receiving end of the second fibre. The movement may be parallel to an axis of the first and/or second fibres (e.g. increasing a separation between the ends) and/or it may be lateral or perpendicular to an axis of the first and/or second fibres (e.g. reducing an overlap area between the ends).

The second part of the sensor device may comprise an arm that extends from the second part of the sensor device towards the first part of the sensor device. The sensor device may comprise a third part, which may be arranged at the distal end of the arm (i.e. towards the first part of the sensor device). The second and third parts of the sensor device may be connected so that they are in a fixed spatial relationship. The third part may be arranged adjacent the first part. Thus, in such embodiments, displacement of the second part relative to the first part (e.g. caused by stretching of the garment), results in a corresponding displacement of the third part relative to the first part. The first optical fibre may be arranged on the first part and the second optical fibre may be arranged on the third part.

In some embodiments the light-emitting component and light-receiving transducer are moveable relative to each other-e.g. being carried respectively on the aforesaid first and second parts.

The light-emitting component and light-receiving transducer may be elongate components and may be arranged in at least partly overlapping relationship. They may be arranged so that the length of overlap depends on displacement between the first and second mounting points. They may comprise an organic LED and/or an organic photodetector.

In some embodiments the light-emitting component and light-receiving transducer are in a fixed spatial relationship (e.g. being both on the first part), but the light- emitting component is configured to output light to an optical component (e.g. an optical fibre or a mirror) that is moveable relative to the light-emitting component or to the light-receiving transducer (e.g. being coupled to the second part). In this way, it is possible to cause the amount of light that reaches the light-receiving transducer to vary as the distance between the first and second mounting points varies. For example, the second part (e.g. the second mounting point) may be coupled to a point on an optical fibre such that relative movement of the second part causes the optical fibre to bend so that the ends of the optical fibre are drawn closer together (or are pushed further apart). In this way the amount of light transmitted from the light-emitting component to light-receiving transducer will vary.

This arrangement allows the powered components of the sensor device (e.g. the light-emitting component and the light-receiving transducer) to remain a fixed distance from each other, while a non-powered component is arranged to move as the garment is stretched. If the light-emitting component and the light-receiving transducer were attached to the first mounting point and the second mounting point respectively, a flexible power transmission system between the two components would be required in order to accommodate the changing distance between them during stretching of the garment.

In some embodiments the light-emitting component and light-receiving transducer are in a fixed spatial relationship (e.g. being both on the first part), but the sensor device comprises a light-interrupting element, such as a wedge, configured to progressively occlude an optical path between the light-emitting component and light-receiving transducer in dependence on the displacement between the first and second mounting points.

In a second set of embodiments, the sensor device uses a variable capacitance to sense displacement between the first and second mounting points. The sensor device may comprise a first capacitor plate coupled to the first point, and a second capacitor plate coupled of the second point. The plates may be in a common plane. This may help to keep the sensor device thin and unobtrusive. The plates may be thin-film plates (e.g. MEMS-type micro-fabricated capacitor plates). They may comprise a plurality of interleaved protrusions. The sensor device, or a remote controller, may comprise circuitry for measuring the capacitance between the first and second plates, and optionally for calculating a displacement value and/or pressure value therefrom.

In a third set of embodiments, the sensor device uses a variable resistance to sense displacement between the first and second mounting points. The sensor device may comprise a displacement-sensing resistor, such as a strain gauge, conductive polymer, or piezoresistive element. A first end of the resistor may be coupled to the first point, and a second end may be coupled of the second point. The sensor device, or a remote controller, may comprise circuitry for measuring thresistance across the resistor, and optionally for calculating a displacement value and/or pressure value therefrom.

In a fourth set of embodiments, the sensor device uses a variable magnetic field to sense displacement between the first and second mounting points. The sensor device may comprise a magnet and a magnetic field sensor, such as a Hall-effect or Lorentz-effect sensor, which may be a MEMS sensor. The magnet may be coupled to the first point, and the magnetic field sensor may be coupled of the second point. The sensor device, or a remote controller, may comprise circuitry for measuring the magnetic field, and optionally for calculating a displacement value and/or pressure value therefrom.

In a fifth set of embodiments, the sensor device uses a variable electric field to sense displacement between the first and second mounting points. The sensor device may comprise an electric field generator (e.g. a coil) and an electric field sensor (e.g. another coil), which may be a MEMS sensor. The electric field generator may be coupled to the first point, and the electric field sensor may be coupled of the second point. The sensor device, or a remote controller, may comprise circuitry for measuring the electric field, and optionally for calculating a displacement value and/or pressure value therefrom.

The sensor device may comprise a cover or housing, which may protect one or more optical or electrical components from damage and/or from ambient light exposure.

The sensor device may be compact, so as to be unobtrusive to use. It may have a maximum thickness of <NUM>, <NUM>, <NUM>, <NUM> or less. It may have a maximum dimension or diameter of <NUM>, <NUM>, <NUM>, <NUM> or less.

The sensor device may comprise a power supply, or it may comprise a port (e.g. an electrical connector) for receiving power from an external source.

In some embodiments, the compression garment may comprise a plurality of layers and the sensor device may be attached to an outer surface of one layer of the compression garment, which need not necessarily be the outermost layer. Thus, it is possible that the sensor device may be embedded within the compression garment.

The sensor apparatus and/or compression garment apparatus may comprise a plurality of sensor devices arranged to sense displacement between a plurality of pairs of points on the compression garment-e.g. at the ankle, mid-calf and proximate the knee. The sensor device or a separate controller may be configured to determine a graduated pressure profile, or 2D or 3D map of pressure, from data output by the plurality of sensor devices. This may be useful in a compression garment for venous leg ulcer or management where at least three sensors may be used to determine the pressure at the ankle, mid-calf and just below the knee taking the geometry of the leg into consideration and using appropriate analytical expression where the information generated by the individual sensors may be combined in an electronic device (e.g. the controller) to help generate and display a compression profile. The controller may be configured to determine a rate of blood flow or a change in muscle volume from a plurality of sensor devices; this may be useful for assessment of performance of an athlete.

A sensor apparatus according to the present invention may comprise the controller and one or more further sensor devices, each further sensor device comprising respective first and second mounting points for attaching to respective first and second points on the outer surface of the compression garment. Each further sensor device may be arranged to sense displacement between each of the respective first and second mounting points. The controller may be configured to determine a rate of blood flow or a change in muscle volume from the respective displacements. The sensor devices may be used on a properly functioning and a damaged leg to assess compartment syndrome.

The controller and/or drive electronics and/or a power supply (e.g. a battery or cell) may be an integral part of the sensor device, or may be a separate entity, e.g. worn separately from the sensor.

Information determined by the sensor device may be stored in the sensor device, e.g. in a readable memory chip, or may be transmitted (e.g. wirelessly) to a separate controller or electronic device, such as a mobile phone, PC, etc. where it may be stored and/or processed and/or displayed.

Information relating to a measure of displacement and/or pressure of the garment may be determined and stored, e.g. on the controller. Such information may be stored at intervals, which may be regular intervals.

Data derived from the sensor device may be logged. The data may be logged by the controller or by another device. By logging data representative of the pressure or tension in the compression garment, data relating to when and/or how long the garment has been worn for may be obtained. This may be used by clinicians to obtain an indication of patient compliance and/or an indication of an effectiveness of the compression garment at different pressures. For example, it may be possible to deduce from the obtained pressure measurements that a compression garment is not being worn as often as recommended, or is being worn incorrectly. This can be useful because patients suffering from medical conditions like lymphoedema, venous leg ulcers, DVT etc. may avoid wearing compression garments as prescribed by clinicians because the garments can be restrictive and uncomfortable to wear. Thus, it is often the case that patients do not wear the CGs for the prescribed duration. This not only means that the patient is likely to continue to suffer, but also that the clinician and/or nursing staff may be misled, e.g. by making an unnecessary change in treatment or, in extreme cases, performing surgery on the patient.

While the sensor apparatus of the present invention has been described above as suitable for use on a compression garment, the Applicant has appreciated that the sensor apparatus may be used for other applications.

In one set of embodiments, the object comprises a nappy (diaper). The Applicant has appreciated that, by sensing the displacement of a surface (e.g. outer surface) of a nappy (diaper), an indication of a state of fullness of the nappy (diaper) may be determined. The sensor device may thus be arranged to detect expansion of the nappy due to absorption by the nappy of urine and/or the presence of faecal matter in the nappy. In this set of embodiments, the sensor device may implement any of the features disclosed herein. It may be permanently or detachably fastened to an outer surface of the nappy. It may comprise an integral controller and power supply as disclosed herein.

The sensor device may comprise an output for providing an indication of fullness of the nappy (diaper). The output may comprise a speaker or a light-emitting component, e.g. an LED. The output may comprise electronic circuitry, such as a radio transmitter, configured to transmit a signal, e.g. to a smartphone e.g. of a parent, guardian or carer. The indication may be binary (e.g. full or not full), or may indicate a degree of fullness of the nappy.

The sensor device may be configured to determine when the sensed displacement in the nappy (diaper) exceeds a predetermined threshold. The output of the sensor device may be configured to provide an indication, e.g. transmit a signal, in response to determining that the sensed displacement exceeds the predetermined threshold. In this way, the sensor device may be used to provide an alert to a parent, guardian or carer that a nappy (diaper), e.g. worn by a baby, infant, toddler, child, adult or animal, has been filled, e.g. by urine or faeces, and needs to be replaced.

A plurality of sensor devices may be attached to different locations on the outer surface of the nappy (diaper). This may improve the accuracy of the indication of the fullness of the nappy. Furthermore, the displacements measured by the plurality of sensor devices may be used to determine whether the nappy has been filled by liquids (e.g. urine) or solids (e.g. faeces).

The nappy (diaper) may be disposable or reusable.

However, the object may be any object of which it is suitable or desirable to sense the displacement or stretch.

The sensor device may be used to determine information relating to a pressure exerted by the object on another entity such as a human or animal which is in contact with the object.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:.

<FIG> shows a compression garment apparatus according to an embodiment of the present invention. The apparatus comprises a compression garment <NUM> and a sensor device <NUM>. The sensor device <NUM> comprises a plastic housing <NUM> and a stud <NUM>. The plastic housing <NUM> and the stud <NUM> are affixed to different respective points (i.e. a first mounting point and a second mounting point respectively) on the outer surface of the compression garment <NUM> (i.e. the surface that faces away from the wearer when the garment is worn). The fastening may be achieved using hook-and-loop fastening pads, adhesive, stitching, riveting, or any other suitable mechanism.

The apparatus also comprises an electronic controller (not shown), such as the electronic control and power supply unit described below with reference to <FIG>, which may be at least partly contained within the housing <NUM>, or which may be separate from the housing <NUM> and stud <NUM> (e.g. connected by an electrical cable). A light-emitting diode (LED) <NUM> is mounted on the plastic housing <NUM>, opposite a photodetector <NUM>, which is also mounted on the plastic housing <NUM>. A first rigid tube <NUM> and a second rigid tube <NUM> are mounted rigidly on the plastic housing <NUM>, along respective portions of a path between the LED <NUM> and the photodetector <NUM>. An optical fibre <NUM> extends through the first and second tubes <NUM>, <NUM>, with a first end adjacent the LED <NUM> and a second end adjacent the photodetector <NUM>, so as to direct light produced by the LED <NUM> to the photodetector <NUM>. The optical fibre has an outer diameter in the region of <NUM> - <NUM>. The first <NUM> and second tubes <NUM> each have an outer diameter of up to <NUM> and an inner diameter very slightly (e.g. between <NUM> and <NUM>) larger than the outer diameter of the optical fibre <NUM>. The first <NUM> and second tubes <NUM> may be constructed from metal, ceramic, glass or plastic. The photodetector <NUM> is arranged to generate an electrical output signal corresponding to the amount of light it receives from the LED <NUM>, through the optical fibre <NUM>.

The first end of the optical fibre <NUM> is fixed to the front of the LED <NUM> (e.g. to a lens of the LED <NUM>), while the second end of the optical fibre <NUM> is located at a distance <NUM> from the front of the photodetector <NUM> (e.g. spaced around <NUM> away). The second end of the optical fibre <NUM> is not fixed and is free to move longitudinally through the second tube <NUM>. In other embodiments, the first end of the optical fibre <NUM> may instead be fixed adjacent the front of the photodetector <NUM> and the second end of the optical fibre <NUM> may be located adjacent the LED <NUM> but free to move longitudinally within the first tube <NUM>.

A central portion of the optical fibre <NUM> is not contained within either the first tube <NUM> or the second tube <NUM>. This exposed central region is approximately <NUM> in length. The first <NUM> and second tubes <NUM> are used to encase the optical fibre <NUM> and restrain it from lateral movement, apart from in the exposed central portion of the optical fibre <NUM>.

A thread <NUM> comprises a first end and a second end. The first end of the thread <NUM> is attached to the stud <NUM> and the second end of the thread <NUM> is attached to the central portion of the optical fibre <NUM> that is not covered by either the first tube <NUM> or the second tube <NUM>, approximately centrally between the first and second tubes <NUM>, <NUM>.

A device <NUM> further comprises a spring <NUM> having a first end and a second end. The first and second ends of the spring <NUM> are attached to the housing <NUM> adjacent the LED <NUM> and the photodetector <NUM> respectively, such that the spring <NUM> extends parallel to the optical fibre <NUM>. The spring <NUM> is linked to the central portion of the optical fibre <NUM> by the second end of the thread <NUM>.

The housing <NUM> further comprises locator studs <NUM>, <NUM> for connecting a protective casing (not shown) around the optical fibre <NUM>, LED <NUM>, spring <NUM> and photodetector <NUM>.

<FIG> respectively show cross-sectional front and plan views of the device <NUM> of <FIG> when the compression garment <NUM> is in a slack state-i.e. before stretching of the garment <NUM> over a patient's body.

In use, the stud <NUM> and housing <NUM> of the sensor device <NUM> are attached to the compression garment <NUM>, with the thread <NUM> minimally taut, before the assembled compression garment apparatus is put on the wearer. In this state, the wire spring <NUM> is also minimally taut and thus exerts a zero or minimal biasing force on the thread <NUM> and the optical fibre <NUM>. Typically, the stud <NUM> will be circumferentially displaced from the housing <NUM>, so that the sensor measures circumferential displacement (e.g. displacement around a limb of the wearer). Before the garment <NUM> is applied, power is supplied to the device <NUM> (from an internal or external power supply such as a battery), causing light from the LED to pass through the optical fibre <NUM> to the photodetector <NUM>, with the optical fibre <NUM> following a straight path.

The photodetector <NUM> produces an output signal that corresponds to an un-stretched state of the garment <NUM>. The garment <NUM> is then applied to the wearer.

The garment <NUM> is stretched once it is put on the wearer, and so the distance between the stud <NUM> and the housing <NUM> increases, causing the thread <NUM> to pull the exposed central portion of the optical fibre <NUM> in the direction of the stud <NUM>. This causes the distance <NUM> between the second end of the optical fibre <NUM> and the photodetector <NUM> to increase. This increase in distance <NUM> reduces the amount of light received by the photodetector <NUM> from the LED <NUM> via the optical fibre <NUM>. The proportion of the emitted light that strikes the photodetector <NUM> reduces with increasing distance. Therefore, the electrical output signal produced by the photodetector <NUM> is lower once the garment <NUM> is fitted than when it was slack.

The movement of the stud <NUM> away from the housing <NUM> also causes the thread <NUM> to pull the central portion of the spring <NUM> in the direction of the stud <NUM>, thus causing the spring <NUM> to extend. As a result of this extension, the spring <NUM> exerts a biasing force on the optical fibre <NUM> and the stud <NUM> via the thread <NUM>. This biasing force acts against the tension in the thread <NUM>, tending to restore the position of the stud <NUM> and the optical fibre <NUM> to the initial "un-stretched" position shown in <FIG>. This biasing force helps to reduce the effects of hysteresis in the fibre when the garment is stretched and un-stretched repeatedly-e.g. when the garment <NUM> is repeatedly taken on and off.

If the stretch in the garment <NUM> is reduced, the separation between the stud <NUM> and the housing decreases, allowing the optical fibre <NUM> to extend towards the photodetector <NUM>, thus reducing the distance <NUM> between the second end of the optical fibre <NUM> and the photodetector <NUM>. This increases the amount of light received by the photodetector <NUM> from the LED <NUM> via the optical fibre. Therefore, the output signal produced by the photodetector <NUM> increases in this situation.

<FIG> respectively show cross-sectional front and plan views of the device <NUM> with the garment <NUM> in a stretched state. As can be seen, the increase in the distance between the stud <NUM> and the housing <NUM> causes the thread <NUM> to pull on the exposed central portion of the optical fibre <NUM> and the central portion of the spring <NUM> such that the optical fibre <NUM> and the spring <NUM> deflect. The initial (un-stretched) position of the optical fibre <NUM> is shown by a semi-dashed line in Figured 2d. This deflection in the optical fibre <NUM> results in a change in the distance <NUM> between the second end of the optical fibre <NUM> and the photodetector <NUM>, from d-, in a slack state, to a larger value, d<NUM>, in the stretched state. As described above, while in the stretched state shown in <FIG>, the spring <NUM> exerts a biasing force on the fibre <NUM> and the thread <NUM> that helps to restore the stud <NUM> and the fibre <NUM> to their original (un-stretched) positions once stretching of the garment is relaxed.

The change in distance <NUM> depends on the properties of the material from which the compression garment <NUM> is made, and on the properties of the optical fibre <NUM>. The deflection of the optical fibre <NUM> in the exposed region in the direction of stretch is expressed analytically by the following equation: <MAT> in which on,,, is the deflection of the fibre <NUM> in the direction of the stretch, F is the pulling force in the thread <NUM>, L is the length of the exposed central region of the optical fibre <NUM>, E is the Young's Modulus of the material of the optical fibre <NUM>, and I is the moment of inertia of the optical fibre <NUM>.

When the garment <NUM> is stretched, the force F (where the force of the spring <NUM> is considered in the force F) exerted on the optical fibre <NUM> by the thread <NUM> increases, thus increasing the deflection on,,, of the fibre <NUM> according to equation (<NUM>). This deflection results in an increase in the distance d<NUM> between the second end of the optical fibre <NUM> and the photodetector <NUM>. As the intensity of the light received by the photodetector <NUM> is proportional to d<NUM> the electrical output signal produced by the photodetector <NUM> decreases. Therefore, the electrical output of the photodetector <NUM> is proportional to the stretch distance on,,, of the garment <NUM>.

The electronic controller of the device <NUM> may, in some embodiments, accordingly map the output of the photodetector <NUM> to a value of stretch distance on,,,, e.g. using a lookup table of empirically determined data stored in a memory of the controller.

The stretch distance <NUM>n,,, of the garment <NUM> is equal to the difference between the initial distance of the stud from the housing x<NUM> and the distance from the stud to the housing after the garment <NUM> has been stretched x<NUM>. This difference is also proportional to the change in circumference of the garment <NUM> from an initial (un-stretched) circumference C<NUM> to a final (stretched) circumference C2, and to the tension Tin the garment <NUM> (as shown by the factor F in equation (<NUM>) above and by T in equation (<NUM>) below).

The pressure exerted by the compression garment <NUM> on the body is determined by the well-known Laplace Law: <MAT> in which P is the pressure, T is the tension in the garment <NUM> material, and r is the radius of curvature of the garment. However, the circumference of the garment <NUM> may be used instead of the radius of curvature. As the tension T is proportional to the stretch distance of the garment <NUM>, the tension T may be determined from the output of the photodetector <NUM>.

The controller connected to the device <NUM> may, in some embodiments, map the output of the photodetector <NUM> to a value of tension T, e.g. using a lookup table of empirically determined data.

The method for determining an accurate value of compression pressure from the measurements obtained by the sensor device is explained below with reference to <FIG>.

The pressure can be calculated by the electronic controller-e.g. using software executed by a processor, or using custom hardware logic such as an FPGA or ASIC. A data logger (not shown) can then record the values of the pressure at intervals. Data may be logged as frequently as required and either displayed in real-time or retrieved via a USB port <NUM> (shown in <FIG>).

<FIG> schematically represents the change in circumference of the compression garment when stretched. The un-stretched garment is represented by a circle <NUM> and the stretched garment is represented by a larger circle <NUM>. The initial and final circumferences of the garment, before stretching and after stretching, are Ci and C2 respectively. The initial circumference Ci of the garment is typically specified by the manufacturer of the garment. It can be stored as a constant by the controller.

The circumference CI, C<NUM> of each circle <NUM>, <NUM> has been equally divided into eight arcs. The difference between the length xi of an arc <NUM> of the circle <NUM> prior to stretching and the length x<NUM> of the same arc <NUM> of the circle <NUM> after stretching is given by Ax = x<NUM> - x<NUM>. Thus, the arc <NUM> corresponds to a respective displacement between the stud <NUM> and the plastic housing <NUM>. It will be appreciated that Ax may correspond to an increase or a reduction in distance, depending on whether the amount of stretching of the garment is increasing or decreasing.

If N<NUM> = C<NUM>/x<NUM>, where N<NUM> is the number of arcs, and N<NUM> = N<NUM> = C<NUM>/ X<NUM>, then C<NUM>/x<NUM> = C<NUM>/x<NUM>. This may be rearranged to C<NUM> = cix2.

Furthermore, Ax = x<NUM> - x<NUM> may be rearranged to give x<NUM> = Ax +.

Thus: <MAT> <MAT>
<MAT>
<MAT> <MAT> where A is a constant defined by A = -, which may be pre-stored in a memory of the controller.

Consequently, the pressure applied by the garment when stretched is given by the following equation: <MAT> Both T and Ax are proportional to the amount of stretch and may be determined from the change in the output signal produced by the photodetector <NUM> when the garment is stretched. As the change in change in arc length Ax is likely to be very small in comparison to the radius of the garment, Ax may be assumed to be equal to the linear displacement omax of the stud from the housing, as discussed above.

Thus, in order to calculate the pressure P applied by the garment, the controller may calculate a value of tension T in the garment, and a value of the linear displacement on,,, = /x of the stud <NUM> from the housing <NUM>, from the change in the output signal produced by the photodetector <NUM>, e.g. using a lookup table. The controller then calculates the pressure P as the determined tension T divided by a linear function of the determined displacement ,Ax. It preferably does this by numerically evaluating a function of T and /x (e.g. using floating point arithmetic operations), but it could determine an approximate pressure estimate by using a multi-dimensional look-up table of pre-calculated pressures for sets of possible
values for T and ,Ax.

In some embodiments the apparatus may determine a qualitative measure (e.g. a binary determination of whether the garment is sufficiently stretched or not). The controller may compare the calculated pressure estimate against a threshold value, or it could directly compare the voltage output of the photodetector <NUM> with a predetermined threshold value, to detect when it passes below the threshold, as being indicative of having sufficient tension in the garment. This may be used to provide an indication of whether or not the garment is being (or has been) worn. In other embodiments, (instead of, or as well as, a voltage input), a capacitance, resistance, magnetic field strength or other electrical or optical signal as appropriate may be compared to a predetermined threshold value to determine whether there is sufficient tension in the garment.

<FIG> respectively show cross-sectional front and plan views of a sensor device <NUM> in accordance with an alternative embodiment of the present invention, in which an obscuring element <NUM> is moved by the stretching of a compression garment (not shown) to interrupt an optical beam.

In this embodiment, a housing <NUM> retains a first optical fibre <NUM>, which receives light at a first end from an LED <NUM>, and a second optical fibre <NUM>, arranged coaxially with the first optical fibre <NUM> such that it receives light, at first end, from a second end of the first optical fibre <NUM> and outputs the light from a second end to a photodetector <NUM>. An elongate arm <NUM> is arranged between the second end of the first optical fibre <NUM> and the first end of the second optical fibre <NUM>. The arm <NUM> is perpendicular to the shared axis of the first <NUM> and second optical fibres <NUM>. The arm <NUM> is arranged to move longitudinally relative to the housing <NUM>. The arm <NUM> comprises an obscuring element <NUM>, which has a substantially triangular, wedge-shaped cross-section, an end-stop <NUM> and an extended portion <NUM>. The distal end of the extended portion <NUM> is fixedly mounted on an anchor block <NUM>.

The anchor block <NUM> and the housing <NUM> are affixed to respective points of the outer surface of a garment, around a circumference of the garment. Prior to the stretching of the garment, they are separated by a distance x<NUM>.

The housing <NUM> further comprises a void <NUM> through which light from the first optical fibre <NUM> is directed into the second optical fibre <NUM>. The arm <NUM> is movable relative to the housing <NUM> between an un-stretched position (shown in <FIG>) and a stretched position (shown in <FIG>).

In the un-stretched position, the obscuring element <NUM> is arranged to interrupt the beam of light as it passes through the void <NUM> between the first <NUM> and second optical fibres <NUM> to small degree, or not at all. Thus, in this position, the photodetector <NUM> receives a maximum amount of light from the LED <NUM>.

<FIG> respectively show cross-sectional front and plan views respectively of the device <NUM> of <FIG> with the garment in the stretched position. The stretch in the garment causes the anchor block <NUM> and the housing <NUM> to move apart by a distance -max = x<NUM> - x<NUM> such that the anchor block <NUM> and the housing <NUM> are separated by a distance x<NUM>, as shown in <FIG>.

In the stretched state, the obscuring element <NUM> is arranged to interrupt the beam of light between the first <NUM> and second optical fibres <NUM> to a greater extent, due to its wedge shape. Thus, in this position, the photodetector <NUM> receives a lesser amount of light from the LED <NUM>. The photodetector <NUM> is arranged to produce an electrical output signal that is proportional to the amount of light received from the LED <NUM>.

A high resolution analogue signal is produced by the photodetector <NUM>. This signal may optionally be converted to a digital signal by an analogue-to-digital converter for display and/or data logging purposes.

The change in output signal from the photodetector <NUM> corresponds to the change in circumference of the garment. Therefore, the compression pressure may be determined, and optionally logged by an electronic controller, in a similar way to that described above.

<FIG> show cross-sectional views of a pressure sensor device <NUM> according to an alternative embodiment of the present invention in which an organic photodetector <NUM> is arranged to detect light emitted from an organic LED <NUM>.

Organic devices have a very low profile, which is convenient for applications where the devices are arranged on a garment. Furthermore, such devices are inexpensive to manufacture in large quantities.

In this embodiment, a first end <NUM> of an elongate organic LED <NUM> can be fixed to a first region of a compression garment (not shown), and a first end <NUM> of an elongate organic photodetector <NUM> can be fixed to a second region of the compression garment, such that the LED <NUM> and the photodetector <NUM> are in a side-by-side overlapping arrangement, both oriented parallel with a circumferential direction of the compression garment, and with first ends <NUM>, <NUM> distal from each other. Stretching of the compression garment thus causes the first end <NUM> of the organic LED <NUM> and the first end <NUM> of the organic photodetector <NUM> to move
apart, reducing the length of overlap.

The LED <NUM> is arranged such that an elongate light-emitting portion of the LED <NUM> is alongside an elongate light-detecting portion of the photodetector <NUM>. Thus, light emitted from this portion of the LED <NUM> can be received by the photodetector <NUM>. Light emitted from portions of the LED <NUM> that are not overlapping the light-detecting portion of the photodetector <NUM> is not detected by the photodetector <NUM>.

The photodetector <NUM> is arranged to produce an output signal that is proportional to the amount of light received by the photodetector <NUM> from the LED <NUM>. As with the other embodiments herein, the sensor device may comprising a casing (not shown) which may shield the photodetector <NUM> from ambient light.

<FIG> shows the arrangement of the device <NUM> before the garment is stretched. As can be seen, a region of the LED <NUM> of initial length x<NUM> is opposite the photodetector <NUM>. Thus, in <FIG>, the photodetector <NUM> receives incident light from this portion of the LED <NUM> alone and produces a corresponding output signal.

<FIG> shows the arrangement of the device <NUM> during stretching of the garment. As can be seen, the region of the LED <NUM> that is opposite the photodetector <NUM> has decreased in length to x<NUM>. Thus, the amount of light received by the photodetector <NUM> from the LED <NUM> is reduced, in proportion with the displacement of the two ends <NUM>, <NUM>, which means that the photodetector <NUM> produces a lower output signal.

Thus, the change in output signal corresponds to a change in circumference of the garment and may therefore be used to determine a compression pressure, as disclosed above.

In alternative embodiments, the optical elements may be replaced by an inductive or magnetic sensor having appropriate fixed and movable parts where the inductive and magnetic sensing elements may be of a small footprint MEMS (micro electromechanical systems) type.

<FIG> show plan views of a pressure sensor device <NUM> according to an alternative embodiment of the present invention in which a variable capacitor is used to determine the change in circumference of a compression garment after stretching.

<FIG> shows a capacitor comprising a first plate <NUM> and a second plate <NUM>. The capacitor may be a thin film MEMS-type micro-fabricated capacitor. As can be seen in <FIG>, the first <NUM> and second capacitor plates <NUM> comprise a number of interdigitated 'fingers', which may be up to <NUM> wide. The capacitor plates <NUM>, <NUM> may be around <NUM> in thickness and are separated by an initial (un-stretched) distance x<NUM> of up to <NUM>.

Capacitor plates <NUM>, <NUM> are connected to electronic circuitry (not shown) via arms <NUM>, <NUM> that terminate at mounting pads <NUM>, <NUM>. The electronic circuitry is configured to measure the capacitance of the capacitor. The mounting pads <NUM>, <NUM> may be constructed from thin films (which may be deposited, screen printed etc.). Each of the mounting pads <NUM>, <NUM> is mounted on a structure (not shown) that can be affixed to the outer surface of a compression garment, e.g. by a detachable hook-and-loop connecting mechanism.

<FIG> shows the device <NUM> of <FIG> after stretching of the garment. As can be seen, the stretching of the garment causes the mounting pads <NUM>, <NUM> to move apart, thus causing the capacitor plates <NUM>, <NUM> to move apart such that the distance between the capacitor plates <NUM>, <NUM> increases to x<NUM>.

The increase in distance between the capacitor plates <NUM>, <NUM> reduces the capacitance of the capacitor that is measured by the electronic circuitry. The capacitance will change in some proportion to the change in circumference of the garment caused by stretching. Therefore, a correlation may be determined between
the change in capacitance and the change in circumference of the garment during stretching. Thus, Equation <NUM> may be used to calculate a compression pressure from a determined change in circumference of the garment, if required.

<FIG> is a schematic view of a sensor device <NUM> according to an alternative embodiment of the present invention in which a variable resistor <NUM> is used to determine the change in circumference of a compression garment.

The device <NUM> comprises a first <NUM> and second mounting pad <NUM> that can be affixed to the outer surface of a compression garment, typically along a circumferential path. The device <NUM> further comprises a variable resistor <NUM>, the resistance of which is arranged to vary according to the application of a mechanical load. The variable resistor <NUM> may be a strain gauge, conductive polymer, piezoresistive element or similar. The variable resistor <NUM> is fixedly connected to the first <NUM> and second <NUM> mounting pads by a first <NUM> and second wire <NUM> respectively.

The variable resistor <NUM> is electrically connected to an electronic circuit (e.g. comprising a Wheatstone-Bridge circuit) (not shown) that is arranged to measure the resistance of the variable resistor <NUM>. The variable resistor <NUM> may comprise an inductor, piezoelectric element or similar, that is connected to the electronic circuit such that the strain on the sensing element during stretching of the garment produces a change in the output signal.

During stretching of the garment, the first mounting pad <NUM> is moved away from the second mounting pad <NUM>. As a result, the first <NUM> and second wires <NUM> exert a tension on the variable resistor <NUM> such that the resistance of the variable resistor <NUM> changes. The change in resistance of the variable resistor <NUM> is proportional to the tension exerted by the first <NUM> and second wires <NUM> and is therefore proportional to the amount by which the garment is stretched. Consequently, a change in circumference of the garment may be determined and subsequently used to calculate a compression pressure according to Equation <NUM>.

<FIG> shows an exemplary arrangement of three sensor devices, each embodying the invention, positioned on a compression stocking <NUM> worn on a leg <NUM> of a patient. These may communicate with one or more controllers in one or more of the sensor devices, or with a controller that is remote from the sensor devices. The sensor devices and controller(s) may embody a sensor apparatus as disclosed herein.

Compression stockings <NUM> have several uses including the management of venous leg ulcers. The compression applied to the leg <NUM> may be 'graduated', meaning that the compression pressure is higher (e.g. <NUM> Hg) at the ankle and is gradually decreased towards the knee (e.g. to <NUM> Hg). If the compression pressure is too high, it may cause problems with the patient's skin. On the other hand, if the compression pressure is too low, the effectiveness of the compression treatment is reduced. Correct application of compression allows faster healing. Therefore, it is important for clinicians to know the amount of compression applied.

In this example, before the compression stocking <NUM> is put on the leg <NUM> of the patient, sensor devices <NUM>, <NUM>, <NUM> are positioned on the outer surface of the compression stocking <NUM> at various locations along the length of the stocking <NUM>. The first sensor device <NUM> is positioned just above the ankle <NUM>. The second sensor device <NUM> is positioned at the mid-calf <NUM> area. The third sensor device <NUM> is positioned just below the knee <NUM>.

The sensor devices <NUM>, <NUM>, <NUM> may be used to determine the distribution of pressure over the compression garment <NUM>. The data generated by the sensor devices <NUM>, <NUM>, <NUM> may then be analysed to establish whether then compression garment is performing as required.

<FIG> shows an exemplary arrangement of sensor devices according to any embodiment of the present invention when positioned on a compression sleeve <NUM>.

In some circumstances, it may be desirable to measure the swelling of a part of the body. For example, this is required in case of patients suffering from lymphedema. Compression sleeves are used after a surgical procedure to remove trapped fluid from the lymphatic system and reduce swelling. The decrease in swelling in the affected area is used as an indication of the patient's improvement.

As a further example, athletes may wish to measure the volume change in a body part when performing certain exercises, e.g. to determine muscle growth. The volume change may be related to a change in blood flow to or from the body part or a change in muscle volume.

<FIG> shows an exemplary compression garment <NUM> that may be worn on, for example, an arm or leg. The compression garment <NUM> has an upper radius r<NUM>, measured at a distal end of the compression garment <NUM>, a lower radius r<NUM>, measured at a proximal end of the compression garment <NUM>, and a height h.

The volume (V) contained within the compression garment <NUM> may be determined according to the equation: <MAT>.

A first sensor device <NUM> is located on the surface of the distal end of the compression garment <NUM> (e.g. located just below the knee of the wearer). A second sensor device <NUM> is located on the surface of the proximal end of the compression garment <NUM> (e.g. located around the ankle of the wearer).

A change in the lower radius r<NUM>and the upper radius rI caused by a stretching of the compression garment <NUM> may be determined according to any of the methods discussed above. Thus, Equation <NUM> may be used to determine a change in volume of the compression garment <NUM> that corresponds to a change in volume of the body part around which the compression garment <NUM> is worn.

For higher accuracy, additional sensor devices may be located at an intermediate locations (e.g. at the mid-calf area). In this case, the above equation would be used multiple times and the results summed to determine the total volume.

Where multiple sensor devices are used (e.g. between two and twenty) on a single compression garment, the sensor devices may be linked electronically to facilitate the construction of a map of the pressure distribution. The sensor devices may be distributed linearly along the length of the compression garment or around a circumference. Each sensor device may be accessed individually or simultaneously to detect pressure distribution.

In the case of a muscular volume change, it may also be possible to determine a blood flow rate from the change in volume of the muscle, as the change in volume of a muscle is related to the rate of blood flow in the leg.

<FIG> shows an electronic control and power supply unit <NUM> (i.e. a controller) that may be used with any embodiment of the invention. The control and power supply unit <NUM> may comprise signal amplifiers, an analogue-to-digital converter, a microcontroller or other processor, memory, a data logger, a wireless transmission (e.g. Bluetooth™) system, discrete or integrated electronic components, FPGAs, DSPs, ASICs, etc. It may have a digital display <NUM> which is configured to display instantaneous pressure readings. The electronic control and power supply unit may comprise an audio indicator-e.g. for signalling an alert if the pressure applied by the compression garment is outside a target range-e.g. if the garment is pressing too loosely and/or is pressing too tightly. The entire electronic control and power supply may be contained within a housing of the unit <NUM>.

Measurements determined by the sensor device can be captured at intervals and stored in the data logger prior to processing in the microprocessor. Measurements may be taken and recorded in the data logger as frequently as desired-e.g. every minute or every hour. Data from the data logger or the microprocessor may be transmitted by the transmission system to a remote device or server. This may be a smartphone, laptop, pager or other device. The remote device can keep a record of pressure data that can be used for clinical evaluation or performance assessment by athletes.

This data logging may be used by clinicians to monitor the healing response of an individual under different compression conditions. However, such logging is not essential, and the control unit <NUM> may simply provide an instantaneous indication of displacement of the compression garment.

The control and power supply unit <NUM> further comprises a rechargeable coin cell for supplying electrical power to the claimed pressure sensor device and the electrical components of the control and power supply unit <NUM>. The power supply unit <NUM> supplies a voltage of 5V or less. The control and power supply unit <NUM> further comprises a USB port <NUM> by which data may be retrieved from the data logger.

The control and power supply unit <NUM> may be attached to a garment via adhesive pads, a hook-and-loop connecting mechanism or similar, or it may be integrated into a housing or casing of the sensor device, or it could be connected by a cable and located remotely-e.g. in a pocket of clothing worn by the wearer, or on a bedside trolley.

Although the above embodiments describe the sensor device of the present invention with regard to uses on a compression garment, where compression forces are relevant, any features of the above-described embodiments can also be applied to embodiments that deduce the expansion of a garment more generally, e.g. expansion of a nappy.

<FIG> shows a sensor device <NUM> in accordance with an embodiment of the present invention, attached to the outer surface of a nappy <NUM> (diaper) that is being worn by a baby <NUM>. It will be appreciated that the nappy could instead be worn by an adult.

The first and second mounting points (not shown) of the sensor device <NUM> are attached to respective first and second points on an outer surface of the nappy <NUM>. These points may be any appropriate distance apart-e.g. around <NUM> apart when the nappy is dry and unsoiled.

A first displacement between the first and second mounting points is measured before or soon after the nappy <NUM> has been put onto the baby <NUM>, or is preconfigured. This first displacement is representative of the state or stretch in the nappy <NUM> when the nappy <NUM> is in an unsoiled 'empty' state.

Subsequently, the sensor device <NUM> records, at intervals, further measurements of the displacement between the first and second mounting points of the sensor device <NUM>. Each further measurement of displacement can be compared with the first displacement. If the device <NUM> records a displacement measurement that is greater than the first displacement by a predetermined threshold, indicating a significant expansion of the nappy <NUM>, the device <NUM> determines that the nappy <NUM> has been filled, e.g. by urine or faeces. Consequently, the device <NUM> may be arranged to issue an alert to the parent or guardian of the baby <NUM> that the nappy <NUM> has been soiled and therefore requires changing-e.g. by sending a radio message to a baby monitor device, or to an app on a phone belonging to the parent or guardian. In some embodiments, more complex processing of the displacement measurement may be performed, e.g. to filter out changes arising due to movement of the baby (e.g. crawling).

<FIG> respectively show cross-sectional front and plan views of a sensor device <NUM> in accordance with an alternative embodiment of the present invention, in which a light emitting diode (LED) <NUM> is connected to a first optical fibre <NUM>, and a photodetector <NUM>, connected to a second optical fibre <NUM>, is arranged to detect light emitted from the LED <NUM> through the first optical fibre <NUM>.

In this embodiment, the sensor device <NUM> comprises a first anchor block <NUM> and a second anchor block <NUM> that are attached to respective first and second mounting points on an outer surface of a garment <NUM>, such as a compression stocking or a nappy (diaper), around a circumference of the garment <NUM>. A rigid elongate arm <NUM> is arranged to connect the second anchor block <NUM> to a third anchor block <NUM> so as to maintain a fixed displacement between the second anchor block <NUM> and the third anchor block <NUM>. The third anchor block <NUM> lies adjacent the outer surface of the garment <NUM> such that the third anchor block <NUM> and the first anchor block <NUM> are adjacent. The third anchor block <NUM> is not fixedly mounted on the garment <NUM>. Thus, displacement of the second anchor block <NUM> relative to the first anchor block <NUM> (e.g. owing to stretching the garment <NUM>) results in a corresponding displacement of the third anchor block <NUM> relative to the first anchor block <NUM>.

The first anchor block <NUM> defines a first through-bore <NUM> that extends from an LED <NUM>, mounted on the first anchor block <NUM>, through the first anchor block <NUM>. The third anchor block <NUM> defines a second through-bore <NUM> that extends from a photodetector <NUM>, mounted on the third anchor block, through the third anchor block <NUM>. The first anchor block <NUM> and the third anchor block <NUM> are mounted adjacent one another on the garment <NUM> such that, prior to stretching of the garment <NUM>, the first through-bore <NUM> and the second through-bore <NUM> are coaxial (i.e. they extend along the same axis).

The sensor device <NUM> comprises a first optical fibre <NUM>, retained within the first through-bore <NUM>, and a second optical fibre <NUM>, retained within the second through-bore so as to be in alignment with the first optical fibre <NUM> in an un-stretched state of the garment <NUM>. A first end of the first optical fibre <NUM> receives light from the LED <NUM>. A first end of the second optical fibre <NUM> is arranged to receive light (from the LED <NUM>) from a second end of the first optical fibre <NUM>. The photodetector <NUM> is arranged to detect light transmitted through the second optical fibre <NUM>. Thus, the photodetector <NUM> is arranged to detect, via the first optical fibre <NUM> and the second optical fibre <NUM>, the light emitted by the LED <NUM>.

Prior to stretching of the garment <NUM>, the first anchor block <NUM> and the second anchor block <NUM> are separated by a distance <NUM> (x<NUM>), in a direction perpendicular to the axis along which the first optical fibre <NUM> extends through the first anchor block <NUM>. When the garment <NUM> is stretched (e.g. when it is being worn), the distance <NUM> between the first anchor block <NUM> and the second anchor block <NUM> increases from x<NUM> to x<NUM>. This is shown in <FIG>.

The displacement between the first anchor block <NUM> and the second anchor block <NUM> results in a corresponding displacement between the first anchor block <NUM> and the third anchor block <NUM> and, thus, a misalignment of the first optical fibre <NUM> and the second optical fibre <NUM>. The misalignment in the fibres <NUM>, <NUM>
means that cross-sectional area of the second optical fibre <NUM> that is exposed to the cross-sectional area of the first optical fibre <NUM> (and, thus, the light transmitted through the first optical fibre <NUM> to the second optical fibre <NUM>) is reduced. As a result, the photodetector <NUM> measures a decrease in the received light intensity.

The photodetector <NUM> is arranged to produce an electrical output signal that is proportional to the amount of light received from the LED <NUM>. A high resolution analogue signal is produced by the photodetector <NUM>. This signal may optionally be converted to a digital signal by an analogue-to-digital converter for processing by a controller as disclosed herein. In particular, the change in output signal from the photodetector <NUM> corresponds to the change in circumference of the garment <NUM>; therefore, the compression pressure exerted by the garment <NUM> can be determined, and optionally logged by an electronic controller, in ways described herein.

Claim 1:
A sensor apparatus comprising a sensor device (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>), for attaching to an outer surface of a compression garment (<NUM>; <NUM>), and a controller, wherein the sensor device comprises:
a first mounting point for attaching to a first point on the outer surface of the compression garment; and
a second mounting point for attaching to a second point on the outer surface of the compression garment,
wherein the sensor device is arranged to sense displacement between the first and second mounting points; and
wherein the controller is configured to process information representative of the sensed displacement to estimate a pressure exerted by the compression garment on a wearer of the compression garment.