System for measuring interface pressure

DESCRIPTIVE REPORT

Patent application for an invention related to an "INTERFACE PRESSURE MEASUREMENT SYSTEM".

The present invention relates generally to a system for measuring interface pressure, in particular pressure exerted on the skin. It finds application especially in the medical field, in compression therapy.

Compression therapy is recognized as an effective technique in the treatment of diseases related to venous insufficiency, such as thrombosis, edema, lymphedema, or leg ulcers.

This therapy is based on the application of various compression devices, such as gauze or compression bandages, whose varying elasticity characteristics allow the selection of the therapeutic pressure range to be used according to the patient and their pathologies.

A compression device, such as a bandage, must serve two purposes:

Firstly, apply appropriate pressure after application; secondly, maintain this pressure level for several days within a specific therapeutic pressure range in order to avoid having to reposition the bandage or use a new one.

For a bandage to be effective, it is therefore necessary not only that it is positioned correctly, but also that the patient agrees to keep the bandage on for several days and follows the recommendations of the clinical team, such as, for example, performing physical exercises like walking in the case of prevention of venous thrombosis.

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For maximum effectiveness, the compression system should be kept in place for 5 to 7 days, applying gradually decreasing upward pressure along the leg. The resulting pressure gradient allows blood to be forced to circulate upwards and prevents stagnation. To give an example, the pressure applied can vary between a high value, on the order of 30 to 40 mm of mercury in the malleolus region of the ankle, and a low value, on the order of 15 to 25 mm of mercury in the upper region of the calf near the knee.

Maintaining a pressure differential between the ankle and the calf is essential for the effectiveness of the treatment.

However, currently available compression systems do not include means to measure this pressure differential. Furthermore, these systems do not allow for knowing the exact pressure applied, nor for monitoring its variation over time, and consequently, for detecting any problems of underpressure or overpressure.

The medical team is therefore currently unable to monitor or verify whether the patient is following the treatment (physical exercises, use or removal of the compression system, etc.).

Therefore, the use of these known compression systems is far from ideal.

There is therefore a great demand in the field of compression therapy for the development of a pressure measurement system to:

to verify that the pressure exerted by the compression system is ideal, not only at the time of positioning, but also over time.

3/38 Check if the ankle-calf pressure gradient is ideal during treatment, detect possible problems due to over-pressure or under-pressure, record the data over time to allow the medical team to verify if the patient has followed the treatment.

However, the production of such a pressure measurement system faces a number of technical barriers.

One of the main difficulties to be resolved lies in the development of a sensor to satisfactorily measure the interface pressure exerted between the skin and the compression system.

More specifically, the sensor should:

to be highly sensitive, allowing low pressures within a range of 1 to 120 mm of mercury, and in particular 5 to 60 mm of mercury, to be measured with great precision, on the order of 1 mm of mercury; to be robust enough to withstand a 100% overload (i.e., a pressure of 250 mm of mercury) without deterioration; to exhibit good linearity; and to allow reliable measurements to be taken over a long period (several days). and be able to operate in both static mode (when the patient is stationary) and dynamic mode (when the patient is moving), and consequently, the sensor must be able to accurately measure very low pressures at frequencies on the order of 1 Hz, corresponding to the variations that must be recorded when a person is walking, and for very rapid variations in applied pressure.

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Therefore, a satisfactory sensor, in the intended application, must possess at least good sensitivity and linearity properties, both in static and dynamic modes, for measuring very low pressures.

It was determined that the linearity in the preferred measurement range (5 - 60 mm of mercury) should ideally be greater than 0.95 and even more preferably equal to or greater than 0.98. This is because, if the sensor is not linear, obtaining easily exploitable results will require the use of an associated electronic system that incorporates correction devices to make the electrical output signal proportional to variations in the measured pressure values. The resulting system will be more complex and more expensive to manufacture.

To allow very low pressures to be measured accurately for very rapid changes in applied pressure, such as those observed when a person is walking, the sensor surface should ideally have low remanence, that is, it should return to its initial shape and thickness in a very short time when the pressure is released, in order to make an accurate measurement when the next pressure is applied.

The sensor surface must also adapt to the pressure applied by the compression system, which is not rigid. Specifically, this system consists of a band that, depending on the shape and firmness of the limb being treated, will deform not only the skin but also the sensor, giving it a curvilinear shape. This phenomenon is known as the "hammock effect," referring to the shape assumed by the sensor and the skin. The compressive forces induced by the bandage are partially absorbed because of this hammock effect, and under these conditions, a conventional pressure sensor detects virtually nothing.

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This is one of the reasons why a pressure measurement system comprising many sensors is difficult to develop, as each sensor would need to have specific properties, and the associated electronic system would have to be designed to handle a multitude of complex signals.

It is therefore necessary, due to the hammock effect, to provide a pressure sensor in which curvature restrictions are minimized in order to ensure a good distribution of the forces exerted on the measuring surface.

However, this must be achieved without significantly increasing the thickness of the sensor, to avoid compromising its intrinsic properties, as described above.

Furthermore, a sensor that is too thick or too rigid carries the risk of injuring the patient's often fragile skin, particularly when treating an ulcer.

Consequently, the surface of an ideal sensor must possess specific contradictory properties in order to ensure uniform and effective contact across its entire surface, having a certain rigidity to limit the hammock effect, and sufficient resistance to compression and specific flexibility to guarantee a reproducible linear signal over a long period.

As will be seen, the development of such a pressure measurement system that satisfies all the conditions defined above is very complicated, and this is one of the reasons why the production of an interface pressure measurement system between a compression system and the skin, which allows for simple and routine use, remains an unsolved problem.

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In this situation, the objective of the present invention was to solve the technical problem of providing a pressure measurement system that can be used in the context of compression therapy treatment, making it possible to accurately measure low pressures over several days, both in static mode (patient at rest) and in dynamic mode (patient in motion). and that it is capable of providing a reproducible linear signal that can be easily exploited by an electronic system and allow the efficiency of the treatment to be controlled.

It has been discovered, and this forms the basis of the present invention, that it is possible to solve this technical problem in a satisfactory and particularly simple way by using at least two pressure sensors designed for the simultaneous measurement of the pressure exerted on two predetermined locations on the patient to be treated, the material forming the active part of the sensors coming into contact with the skin in the intended preferred application. It has a compressive elastic modulus within a selected range of values.

Thus, according to a first aspect, the present invention relates to a system for measuring the interface pressure exerted on the skin, especially useful in compression therapy, characterized by comprising:

A support that holds sensors, including at least two pressure sensors spaced apart on the support to allow measurement of the pressure exerted at two locations, one of which is predetermined; and an electronic system connected to the sensors and capable of acquiring the values ​​measured simultaneously by these sensors, and each pressure sensor comprising a transducer element, preferably

7/38 substantially flat, said transducer element having a surface intended to come into contact with the skin in the position of use, directly or by means of a layer of material covering said transducer surface, the elastic compression modulus of said transducer or said intermediate layer, measured on the surface intended to come into contact with the skin, being between 30 and 500 kPa, preferably between 80 and 400 kPa, and more preferably between 200 and 400 kPa.

According to a particular aspect of the invention, the material that constitutes said intermediate layer is selected from:

Porous materials, such as foams, preferably hydrophobic, cross-linked polyethylene foams, polyurethane, silicone, polyvinyl chloride, polyethylene-propylene diene, or neoprene;

Gels, preferably hydrophobic, such as silicone or polyurethane gels; and mixtures based on thermoplastic polymers, preferably hydrophobic, such as mixtures of tri-block polymers with plasticizer.

According to another particular aspect of the invention, each pressure sensor is substantially flat and selected from among resistive sensors, piezoelectric sensors, Hall effect magnetic sensors, and capacitive sensors.

According to another particular aspect of the invention, the aforementioned electronic system comprises:

an onboard device connected to the mount, preferably fixed to it, which allows the acquisition and processing of values ​​measured by the pressure sensors, said device

8/38 comprising means of transmitting the aforementioned values ​​measured by the sensors;

a remote device that includes:

communication means compatible with the transmission means of said onboard device and which ensure at least the transmission of data from the onboard device to the remote device; and a processing circuit connected to a display device.

Currently available compression systems also suffer from the drawback of not being able to adapt to the patient's morphology (leg size, calf size) and to changes in that morphology over time, such as in cases of edema.

In this context, the objective of the present invention is also to solve the technical problem of providing a pressure measurement system that can adapt to the patient's morphology and changes in their pathology.

To solve this second technical problem, and according to a first variant, the support for the interface pressure measurement system according to the invention is extendable.

The design of an extensible measurement system with embedded electronics presents many problems that must be solved.

The first difficulty lies in developing a system in which the functionalities of the electronic circuit and its conductive paths, which connect the various functional elements (sensors,

9/38 microprocessor, battery, etc.), should not be altered when the system is extended.

Similarly, these functional elements cannot become disconnected from the support when it is extended.

Finally, the electronic circuit should possibly be protected so that, when appropriate, it can be partially or completely reused.

These difficulties were overcome by several additional features of the invention, which will be explained in detail below.

Another objective of the invention is to solve a third technical problem.

This is because, in certain cases, particularly in the treatment of a chronic ulcer-type wound, the use of a compression system faces the additional problem of how to monitor the area to be treated, in this case the wound, which is actually covered by an absorbent layer, which in turn is hidden by the bandage of the compression system.

If, during treatment, the level of exudate from the wound becomes greater than the absorption capacity of the layer, the exudates will spread to the edge of the wound. This can result, if this phenomenon is not quickly detected, in maceration of the wound and damage to the perilesional skin, delaying or impairing the ulcer healing process. Furthermore, contact between the bandage and exudates can cause the bandage's mechanical properties, and consequently its effectiveness, to deteriorate. Additionally, the appearance of stains on the bandage can induce fear and psychological problems in the patient, which may result in their refusal to use a bandage again.

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Furthermore, in very hot weather, the expansion of the legs alters the pressure applied by the system, and the patient often tends to remove the bandage.

Measuring the humidity and/or temperature under the bandage, in parallel with pressure measurement, would consequently make it possible to improve the overall effectiveness of the treatment and allow the bandage placement to adapt to changes in the environment of the area being treated.

Thus, to solve this third technical problem, and according to a second preferred variant of the invention, the support also includes:

at least one humidity sensor, and/or at least one temperature sensor.

According to a second aspect, the present invention relates to a restriction or compression kit consisting of a restriction or compression system and an interface pressure measurement system as defined above.

Detailed description of the invention

The invention will be better understood by reading the explanatory description below with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates an interface pressure measurement system according to an embodiment of the invention, being placed on a leg, and shows points B1 and C between which the pressure differential is measured.

11/38 Figure IA is a figure similar to Figure 1, which illustrates an interface pressure measurement system according to another embodiment of the invention, placed on a leg; Figure 2 illustrates a support provided with conductive paths according to an embodiment of the invention; Figure 3 schematically illustrates the electronic system architecture of the interface pressure measurement system according to the invention. Figures 4A to 4C illustrate various embodiments of antennas that can be used in the aforementioned electronic system, Figures 5A to 5D illustrate various embodiments of a moisture sensor or detection system that can be used in the context of the invention, Figure 6 illustrates an embodiment of an interface pressure measurement system that includes a moisture detection system, and Figure 7 illustrates another embodiment of the interface pressure measurement system shown in Figure 6.

Support

In the context of the present invention, the support for the pressure measurement system can be made of any flexible material that can be produced in sheet form and that is capable of deforming to conform to the body part being treated, such as, for example, a leg.

Such material could be, for example:

a porous material, such as a foam, a film,

12/38 a complex that combines two of these materials, a polymeric matrix, such as a silicone gel.

Examples of complex materials include those that combine a nonwoven fabric and a film. Such materials can be produced using techniques well known to those skilled in the art, for example, by applying an adhesive, by hot calendering, or by ultrasonic complexation.

In the context of compression therapy, particularly for the treatment of leg ulcers, it is important that the interface pressure measurement system does not damage the patient's skin, which is often in a very fragile state, especially around the ulcer.

The substrate must therefore be thin, flexible and, above all, non-occlusive, that is, it must have a water vapor permeability, measured according to the EM-13726 standard, equal to or greater than 1,000 g/m².²24h.

In the context of the present invention, preferred examples of supporting members are nonwovens and nonwoven films.

According to a particularly preferred embodiment of the invention, the support is extensible, preferably anisotropically extensible.

For this purpose, among the materials described above, it is preferable to choose those that have an extensibility of about 10 to 20% in the longitudinal direction and an extensibility of about 3 to 12% in the transverse direction. It has been found that an extensibility of about 10 to 20% in the longitudinal direction makes it possible to encompass, using one or two products, all types of morphology.

It is also preferable to use a stretchable material that has a low modulus of elasticity, in order to be able to reconcile the

13/38 advantages of extensibility with the ability of the support to adhere to the skin, if said support is coated with adhesive in order to facilitate its placement.

Indeed, the lower the modulus of elasticity of the stretchable material, the lower its restoring strength. A support with a relatively low modulus of elasticity, for example, around 40 N/cm or less, can therefore remain in extension for a long enough time for the medical team to be able to easily place the compression system on said support.

According to a preferred variant of the invention, this low modulus of elasticity can be obtained by forming holes or voids in the extensible material that constitutes the support. Evidently, these holes or voids will be placed on the support in suitably chosen locations so as not to interfere, while the support extends, with the electronic connections and conductive paths possibly present therein.

Examples of particularly preferred stretch materials include nonwovens or films based on polyurethanes, polyetheresters (in particular products sold under the names HYTREL® or ARNITEL®), polyamides or polyetheramides.

Pressure sensors

The interface pressure measurement system according to the invention comprises a series of sensors carried by the support described above, including at least two pressure sensors placed spaced apart on the support, so as to be able to measure the pressure exerted at two locations, one of which is predetermined.

Compression therapy is applied in most cases to the lower limbs.

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As an example, Fig. 1 shows a system designed to be placed on one leg.

In this case, the two pressure sensors mentioned will be advantageously fixed to the support, in locations chosen so that these sensors are placed respectively in the position of use of the measuring system:

in a predetermined location, such as the region indicated by Bl, where the Achilles tendon attaches to the calf muscle (approximately 10 to 15 cm above the malleolus); and in any region that is “downstream” of area Bl (i.e., above area Bl, upwards along the leg), preferably in the area indicated by C, where the calf circumference reaches its maximum.

The efficiency of a compression system depends in fact on maintaining a pressure gradient between these two areas, with the pressure in area B1 needing to be greater than the pressure in the area located downstream of it in order to ensure that the blood is forced upwards and does not stagnate. Consequently, the ability to measure the pressure in these two areas is extremely important.

Each pressure sensor advantageously satisfies certain geometric criteria (surface area and thickness) and specific metrological requirements (sensitivity and accuracy on the order of 1 mm of mercury and reproducibility of measurements over several days).

Ideally, each sensor should be able to withstand a 100% overload without damage, i.e., a pressure of 250 mm of mercury.

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To satisfy these constraints, it is preferable to choose a sensor in which the active part (a transducer optionally combined with an intermediate covering layer):

be substantially flat, have a thickness of 3 mm or less under a pressure of 20 mm of mercury, have a surface area between 0.25 and 3 cm², and make it possible to accurately measure an interface pressure across a range varying from 1 to 120 mm of mercury and in particular from 5 to 60 mm of mercury.

Thus, an ideal pressure sensor has a linearity greater than 0.95, preferably greater than or equal to 0.98, across the range of 1 to 120 mm of mercury and in particular from 5 to 60 mm of mercury.

In order to ensure reliable and reproducible measurements over time, the inventors also determined, and this constitutes an essential feature of the invention, that the material constituting the transducer or the intermediate layer covering it must possess a compressive elastic modulus measured on the surface intended to come into contact with the skin between 30 and 50 kPa.

This elastic modulus of compression can be measured using a tensile testing machine equipped with compression plates according to the procedure described in ISO 844 (2007).

Preferably, the material constituting the transducer or the intermediate layer covering it will have a compressive elastic modulus between 80 and 400 kPa, and more preferably between 200 and 400 kPa.

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Any type of pressure sensor, except for pneumatic sensors, can be used in the context of the invention.

The following sensors can then be mentioned: resistive sensors, piezoelectric sensors and capacitive sensors, whose electrical properties vary as a function of the pressure exerted, and magnetic sensors that operate according to the Hall effect.

In general, such sensors comprise:

An active part consisting of a transducer element capable of converting pressure into a signal, and a passive part comprising contacts or conductive paths capable of transmitting the transducer's output signal to a processing unit.

In the context of the present application, the expression "pressure sensor" therefore denotes the combination of a transducer and the contacts or conductive paths mentioned.

In the pressure sensors used according to the invention, the transducer directly converts the pressure applied to it into a signal, such as an electrical or magnetic signal, by converting a variation in one of the intrinsic physical characteristics of the transducer element, such as its capacitance, its electric field, or its TQ (quantum tunneling) effect.

In these sensors, the transducer element, unlike pneumatic sensors, does not contain gases or liquids.

It should be noted that the use of pneumatic sensors cannot be conceived within the context of the present invention.

firstly because such sensors are generally expensive, bulky and complicated, and

17/38 secondly because its reliability is considered uncertain due to possible variations, for example, due to the effect of temperature, on the properties of the gas or liquid that the sensors contain, and risks of leakage if the membrane surrounding that gas or liquid ruptures.

Among the resistive sensors that can be used in the context of the present invention, the sensors sold by Tekscan under the name FLEXIFORCÈ® and those sold by International Electronics and Engineering (IEE) under the name FSR® can be mentioned. In particular, the sensors sold by IEE under the name FSR will be preferred.

Regardless of the type of sensor used, among the types mentioned above, the surface and thickness of these sensors will have to be modified by adding an intermediate layer in order to optimize the contacts between the transducer, the skin, and the compression system so as to avoid the hammock effect and thus ensure a linear and reproducible measurement over time.

The sensors sold by IEE are force-detecting resistors. Their structure is extremely simple. It is a multilayer structure formed from two laminated polymer sheets that enclose two electrodes and a resistor. The greater the pressure applied to this structure, the more its resistance decreases. These sensors are resistant to temperature, chemicals, and moisture. The technologies and implementation of such sensors are, for example, described in the publications WO 2006/79581 and WO 2006/58880 by the IEEE company.

In order to optimize the operation of these known sensors and obtain the ideal elastic compression modulus, the transducer face that enters

The 18/38 area in contact with the skin should be covered with a relatively thick layer of a material that has a compressive elastic modulus between 30 and 450 kPa.

These known sensors are flat, rigid, and very thin, so they can be used directly in the intended application.

If necessary, both sides of the transducer can be covered with identical or different materials, particularly materials with a compressive modulus between 30 and 500 kPa. This allows the negative effect of the pressure applied by the compression system on the sensor surface, on the side opposite the skin, to be reduced more significantly and achieves sensor linearity.

However, in the context of the present invention, a sensor that is excessively thick in its active part (the transducer covered with an intermediate layer), for example, with a thickness greater than 5 mm, should be avoided, as this could make it difficult to attach to the support and could damage the patient's skin, which is often fragile.

In other words, the final structure of the sensor, and in particular the thickness of its active part, will be chosen seeking the best balance between good compressibility and sensitivity. Thus, if the aim is to measure low pressures and variations in low pressure, it will be preferable to use a sensor whose transducer face that comes into contact with the skin is covered with a material that has a compressive elastic modulus between 30 and 500 kPa and particularly between 200 and 400 kPa.

Among the materials that can be used to obtain such a compressive elastic modulus, porous materials can be mentioned, such as, for example, physically cross-linked polyethylene foams and particularly the foams from the ALVEOLIT line sold by Alveo or the

19/38 marketed by Trocelen under various references. These foams exhibit excellent chemical resistance and are inert to water.

Polyurethane foams, silicone foams (for example, those sold by Poron under the references UL94HF or UL94VO), PVC (polyvinyl chloride) foams, EPDM foams and neoprene foams may also be mentioned.

All of these foams can be either open-pore or closed-pore foams.

In the context of the present invention, it will be preferable to use a hydrophobic foam in order to prevent perspiration or wound exudates from altering its elastic properties, density, compression modulus, or even its thickness, and it will be even more preferable to use a hydrophobic foam without a plasticizer in order to prevent any migration of toxic substances onto the skin or into the wound.

Generally, foams with a thickness between 0.3 and 5 mm, preferably between 0.5 and 1.5 mm, and a density between 25 and 250 g/m³ will be used.³, which will preferably be combined with transducers that have a thickness of less than 0.8 mm, preferably less than 0.5 mm, and even more preferably less than 0.3 mm.

According to the currently preferred embodiment of the present invention, each pressure sensor is an FSR® sensor comprising a transducer with a thickness of 0.4 mm and a skin contact area of ​​2.27 cm².² and containing a polyurethane foam (marketed by Poron).

According to other embodiments of the invention, this same FSR® sensor is covered with the following intermediate layers:

a) a base layer of a mixture consisting of thermoplastic polymers and a plasticizer.

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This mixture consists of:

88% by weight of a triblock copolymer marketed by Kraton under the name Kraton® G1651, and

12% by weight of a mineral oil marketed by Shell under the name Ondina® 917.

This mixture was deposited as a layer 4.24 mm thick onto the aforementioned FSR® sensor.

The elastic modulus of this layer was 240 kPa.

b) a layer based on a polyurethane foam marketed by Por on under reference 4701-50-30031-04, with a black color.

A 0.8 mm thick layer of the aforementioned foam was attached to a mentioned FSR® sensor using a 90 µm thick double-sided adhesive (acrylic/polyethylene terephthalate/acrylic adhesive).

The elastic modulus of compression of this foam layer was 380 kPa.

c) a layer based on a polyurethane foam sold by Poron, in blue color.

A 1.45 mm thick layer of the aforementioned foam was attached to a mentioned FSR® sensor using a 90 µm thick double-sided adhesive (acrylic/polyethylene terephthalate/acrylic adhesive).

The elastic modulus of compression of this foam layer was 380 kPa; and

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d) attach to each face of a mentioned FSR® sensor, using a double-sided adhesive with a thickness of 90 µm (acrylic adhesive/polyethylene terephthalate/acrylic adhesive), a 1.45 mm thick layer of the foams described in (b) and (c) above.

According to other embodiments of the invention, the FSR® sensor of the embodiments described above has been replaced by a FlexiForce sensor with reference 1-617-464-4500, marketed by Tekscan.

In all cases, the sensors modified in this way proved satisfactory for achieving the desired results.

These porous materials are attached to the sensor transducer using known techniques, for example, by hot calendering, by ultrasound if the components can be fused, or by adhesion.

Preferably, these porous materials are fixed by adhesion using a double-sided adhesive, for example, an acrylic-based adhesive, preferably with a thickness of less than 200 µm, and even more preferably less than 100 µm.

Among other materials for adjusting the elastic compression modulus of the sensor's active surface that comes into contact with the skin, gels can be mentioned, particularly silicone gels or polyurethane gels. As with foams, hydrophobic gels are preferable so that their properties are not affected by perspiration or exudates.

Compounds consisting of thermoplastic polymers and a plasticizer may also be mentioned. These thermoplastic polymers will especially be triblock polymers, such as particularly acrylic triblock polymers known as “LA”.

22/38 polymers” by Kuraray, are ABA-type triblock polymers where A represents styrene units and B represents butadiene, isoprene, ethylene-butylene or ethylene-propylene units, such as the KRATON G and KRATON D products sold by Kraton, the latter products being capable of being combined with a mineral oil.

Such compounds of thermoplastic polymers and a plasticizer are well known to those skilled in the art.

These materials can be mounted with the transducer using the techniques mentioned, and particularly by adhesion. To facilitate adhesion and ensure bond strength, it is preferable in this case to use an adhesive that has a chemical nature identical to that of the material to be bonded, such as, for example, a silicone adhesive, a polyurethane adhesive, or a hot-melt adhesive based on a triblock copolymer of acrylic or ABA in order to assemble a silicone gel, a polyurethane gel, or a material based on triblock copolymers and a plasticizer, respectively.

According to one embodiment, if it is desired to apply a gel, or a material based on a triblock copolymer and a plasticizer, to both faces of the sensor transducer, it must be encapsulated, for example, by molding, in said gel or material.

Finally, to facilitate contact between the sensor and the skin, an adhesive gel can be applied directly to the transducer. Such a gel can especially be a silicone gel or an adhesive based on a compound consisting of a triblock copolymer, a plasticizer, and a tackifying resin.

According to another approach, the sensor can be used, provided it has an appropriate elastic compression module, without the addition of...

23/38 of any other material, on the face of the transducer that comes into contact with the skin.

As an example of such sensors, one can mention a Hall effect sensor, whose transducer takes the form of a single-layer block of porous material, for example, an ethylene/vinyl acetate foam, filled with magnetic particles to convert the applied pressure into a measurable electrical quantity.

If such a sensor comprises a single-layer transducer, it is preferable to use a sensor in which the transducer has a thickness between 0.5 and 4.5 mm, preferably between 1 and 3 mm.

The electronic system

The interface pressure measurement system according to the invention also includes an electronic system connected to the pressure sensors and capable of acquiring the values ​​measured simultaneously by these sensors.

It is the acquisition of these values ​​that makes it particularly possible for the pressure differential exerted by the compression system, and consequently its effectiveness, to be controlled at any time.

In the context of the present invention, the term "electronic system" means all the elements used to allow the necessary energy and data streams to be transferred in order to obtain the measurements performed by the pressure sensors.

In general, this electronic system comprises:

at least one processing unit comprising a microcontroller and a memory, said processing unit being capable of acquiring and processing the signals representing the values ​​measured by the pressure sensors; and

24/38 at least one power supply circuit comprising a power source and a power converter/distributor device.

According to a currently preferred embodiment of the invention, this electronic system comprises:

An onboard device connected to the support, preferably fixed to it, and serving for the acquisition and processing of values ​​measured by the pressure sensors, said device comprising means of transmitting said values ​​measured by the sensors; and a remote device comprising:

communication means compatible with the transmission means of said onboard device and which ensure at least the transmission of data from the onboard device to the remote device; and a processing circuit connected to a display device.

The general architecture of this preferred electronic system is illustrated in Fig. 3.

The onboard device comprises a processing unit 11 comprising a microcontroller and transmission means 12 for transmitting the aforementioned values ​​measured by the pressure sensors Pi and P.₂, and also a power supply circuit comprising a power source 13 and a power converter/distributor device 14.

The microcontroller of processing unit 11 integrates, filters, processes, and digitizes the raw signals sent by the sensors.

25/38 pressure Pi and P₂It performs the analog-to-digital conversion of these signals. It can also analyze these signals using Fourier transforms or digital filters, which can be used in combination with software to verify the data at certain events. It stores the standardization and calibration data from the pressure sensors and the data measured by these sensors. It controls the transmission of data to the remote device and correctly manages the distribution of power through the power converter/distributor device 14.

In the context of the present invention, any type of microcontroller (or microprocessor) commonly used in the construction of electronic and microelectronic systems can be used. Such products are, for example, marketed by Texas Instruments, Microchip and NXP under the names 8150, 16F690 and Coolflux respectively.

The remote device 20 comprises a processing unit 21, which comprises a microcontroller, a memory 22, communication media 23 compatible with the transmission media 12 of the onboard system, a display device 24 and a power supply circuit comprising a power source 26 and a power converter/distributor device 27.

Communication between the onboard system and the remote system can be wired or wireless (radio module and antenna) as in the example shown.

The energy source

In the context of this description, the term "power source" should be understood as any device capable of providing sufficient power to supply all elements of the interface pressure measurement system (sensors and electronic system).

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In the case of a wired system, this energy can be distributed, for example, from an electrical outlet via a cable.

In the case of a wireless system, any type of energy source commonly used in measuring instruments can be employed, such as, in particular, disposable batteries, rechargeable batteries, or devices capable of capturing energy from the environment, these being denoted by the term "scavengers". A scavenger can specifically collect solar energy or energy produced by temperature gradients, vibrations, movements, especially the movement of a person, or electromagnetic phenomena. A scavenger converts the energy thus captured into electrical data (voltage, frequency, etc.). This energy can be stored in a battery or in a supercapacitor that can be incorporated into the interface pressure measurement system.

The media

According to a currently preferred embodiment of the invention, communication between the onboard device and the remote device can be wireless, and preferably radio frequency communication.

Communication systems generally comprise a communication module that incorporates the electronics to perform the communication and an antenna with appropriate software and hardware.

The onboard device's communication module can be: unidirectional, in which case it merely transmits data sent by the sensors and the microcontroller to the outside, and bidirectional (transmitter/receiver), in which case it also receives data from the outside, as in the example shown.

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Wireless communication can possibly be carried out in two stages.

In the first stage, data communication occurs between the onboard system and a portable control module. This could, for example, take the form of a wristwatch or a mobile phone-type device. In this case, the range between the system and the module will preferably be on the order of 10 mA, with a maximum transfer rate of less than 1 Kbyte per second. Advantageously, communication will be via radio frequency (for example, at a frequency of 2.4 GHz) and can utilize specifically for this purpose the communication module marketed by Nordic Semiconductor under reference nRF24L01. Alternatively, communication can also be achieved through magnetic induction, with the corresponding advantage of a very low level of interference with the human body, and it is possible to use for this purpose the communication module marketed by NXP under the reference “Coolflux radio module”.

In a second stage, communication occurs between this portable control module and a computer. In this case, it is preferable to use a 2.45 GHz radio frequency link, allowing a larger volume of data to be transferred over greater distances. In this case, the transfer rate is on the order of 1 Mbyte per second and the range on the order of 100 m. Several devices can be used for this purpose. For example, the Zigbee®, Bluetooth®, and Wifi® protocols can be mentioned.

Two-step communication is particularly suitable for use of the interface pressure measurement system according to the invention by medical staff or even by the patient themselves.

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The portable control module is used to control the system and record data. This data can then be accessed by the doctor on their computer to adjust the treatment and verify the patient's adherence.

Clearly, direct data communication between the onboard system and a computer is also conceivable.

When radio frequency communication is used, the onboard device will include an antenna. This antenna may have various configurations depending on the frequency used, the waveform of the signal to be processed, and the available power.

Generally, a copper or aluminum antenna will be used, but it is also possible to use an antenna made from conductive paint.

According to a preferred embodiment, the antenna has the form of a cylindrical coil wound around a ferrite core (with a diameter of 4 mm or less) or a coil in the form of a snail shell (with a diameter of 10 mm or more).

Like the other components of the onboard device, the antenna can be fixed to a rigid or flexible printed circuit board along with these other components, or it can be mounted independently on the support. Similarly, it can be encapsulated independently or together with these other components.

If the support is extendable, it is preferable to fix the antenna directly onto this support or onto an extendable circuit, as will be described later, for example, on a stretchable polyurethane film.

Figures 4A, 4B, and 4C illustrate various antenna shapes that can be placed directly on the extendable bracket.

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The guiding paths

According to a currently preferred approach, the onboard device will be connected to the pressure sensors via conduit pathways.

If the substrate is not extensible, conductive paths can be produced by techniques well known to those skilled in the art, such as, in particular, screen printing using a conductive ink, for example, a silver-based ink or an ink based on a silver-copper alloy.

These techniques can also be used when the aforementioned support is extensible.

The conduction pathways can also be integrated within the support when it is in the form of a stretchable polymer sheet, such as a silicone or polyurethane gel.

Alternatively, conductive paths made of, for example, copper, can be formed on the substrate when it is in the form of a film, such as a polyurethane film. In practice, this can be achieved by coating one side of a copper sheet with a polyurethane film, applying a mask over the exposed side of the sheet (with the solid parts of said mask taking the shape of the paths to be obtained), and destroying the unmasked copper by acid etching.

When the support is extensible, it is important that there are no breaks in these conductive paths when the support is extended. To this end, the paths will preferably be in the form of Ω-shaped elements connected in successive pairs. When the support extends, each Ω-shaped element may deform longitudinally.

30/38 thus preventing the path from breaking. Such Ω-shaped structures are, for example, described in publication WO 2004/107973.

Alternatively, the risk of breakage can be avoided by attaching extension limiters to the extendable support.

These extension limiters can, for example, consist of stiffening strips. These strips will be formed from a material that has an extensibility lower than that of the extensible support. Thus, when the support is stretched, it will be "locked" by said strips above a certain extension. Preferably, these strips will have a longitudinal extensibility of about 20% or less. The materials that can be used to produce these strips can be similar to those mentioned for the support, in particular they can be fabrics, foams or films. These strips can be fixed to the stretchable support using conventional techniques adapted to the nature of the support. Examples of such techniques include compounding and needle punching, in the case of a fabric backing such as a nonwoven fabric or foam; in the case of a film-based backing, ultrasonic welding, bonding, thermal complexation, or fixation with the aid of an adhesive.

Extension limiters may also consist of one or more wires integrated within the plane of the support, over all or part of it, in a sinusoidal wave configuration and possessing a tensile strength greater than that of the support. Thus, when the support is stretched, the wire becomes taut and interrupts the extension of the support. Such wire or wires may be integrated within or fixed to the extendable support using the techniques described above for fixing the strips.

Generally, all components of the onboard device will be positioned between the two pressure sensors in order to reduce the

31/38 risk of breakage of the conductor paths placed on the support. The shorter these paths are, the lower the risk of breakage.

Fig. 2 shows an embodiment of a support S comprising two series of conductive paths 1, IA and 2, 2A formed from Ω-shaped elements and intended to be connected to pressure sensors P] and P₂, respectively.

The connections

The functional elements of the onboard device and the sensors will be connected to the conduit paths of the support using conventional techniques employed for non-extendable supports.

These connections can be conventional welded joints or they can be manufactured:

using Z-shaped conductive adhesives such as, for example, the adhesives sold by Adhesive Research under the names ARcare 90366 or ARcare 90447;

or even using conductive velcro.

These connections will link the conductive terminals of these functional elements and sensors to the conductive terminals placed on the conductive paths of the support.

Alternatively, these connections can be made using micro-connectors, which are widely used for making connections in computers or cell phones.

When the measuring system is a disposable system, tamper-evident connections, such as welded joints, may be used.

However, when the measuring system is intended to be partially reused, it is preferable to use "reactivatable" connections, such as connections made using adhesives or micro32/38 connectors. In this case, the support can be discarded after use and the functional elements reused with a new support to which said elements will be fixed by means of new adhesives or microconnectors. Alternatively, only certain functional elements of the system may be reused, for example, when it is desired to replace the sensors or the power source.

When the measurement system is intended to be entirely reused, all functional elements of the system (sensors and onboard system) may be encapsulated or integrated, like conventional electronic devices, in silicone or polyurethane polymers, as described, for example, in publication WO 2006/094513. In this case, a system will be obtained that can be cleaned after use and can be reused many times.

In the context of the present invention, it is preferable to encapsulate only the most sensitive elements, and particularly the electronic components, so as not to impair the “breathing” properties of the system.

Similarly, in order not to restrict the extensibility of the support, it is also preferable to encapsulate only the connections between the 20 electronic components and the extensible support.

The various components of the onboard device (power supply, antenna, microprocessor) and the conductive paths that connect them can, depending on their nature and size , be connected directly to the terminals produced on the extendable support or mounted on one or more "interposed" elements or printed circuit boards that will be connected to the terminals of the extendable support.

Alternatively, some of these elements, such as the power source or the antenna, can be connected directly, or through

33/38 elements are interposed, in an extension of the support, beyond the part that extends between the pressure sensors, so as not to impair the extensibility of the support. This extension of the support is not necessarily extensible.

As indicated above, this extension of the support and the elements connected to it can be encapsulated in a suitable material, such as a silicone-based material, for example, a polydimethylsiloxane.

The materials that can be used to produce the interposed elements on which electronic components are mounted are those commonly used in the production of conventional electronic circuits. Although it is possible to use rigid materials, it is preferable to use flexible, foldable or semi-rigid conformable materials for these purposes, so that they adapt to the patient's morphology and the critical curvature radius of an ankle, which is around 25 mm.

Among the materials that can be used to produce these foldable or semi-rigid interposed elements, polyimides can be mentioned, such as the products sold by DuPont under the name Kapton®, and epoxy films with a thickness of around 0.1 to 0.4 mm, such as the products sold under the name "epoxy FR4".

If necessary, and particularly in the context of treating skin ulcers, a varnish can be applied to the surface of these interposed elements in order to prevent any short circuits or electrical malfunctions that could be caused by contact with wound exudates or moisture in the gauze under the bandage during use of the interface pressure measurement system. Varnishes that

Products 34/38 that can be used for this purpose are, for example, the Propocure products, for example, from the 520-530 series, marketed by PC/S.

The other sensors

According to alternative embodiments, the interface pressure measurement system according to the invention may comprise sensors other than pressure measurement sensors in order to measure additional parameters useful in the context of compression therapy treatment, such as acceleration (to detect and assess the patient's physical activity). Temperature (which plays an important role in venous circulation) and moisture (to detect perspiration under the bandage and problems due to the level of wound exudation in the case of leg ulcers).

Obviously, other parameters can be evaluated, such as pH, using physicochemical sensors.

Preferably, in order not to impair the extensibility properties of the interface pressure measurement system, these sensors are positioned on an extension of the support, beyond the part that extends between the pressure sensors. This support extension may or may not be extensible.

In the context of treating leg ulcers, detecting the degree of moisture in the gauze covering the wound and hidden under the bandage is an important factor in promoting sufficient adherence to treatment and ensuring that the treatment is effective.

Many well-known devices for detecting humidity (or humidity sensors) exist.

In the context of the present invention, however, it is preferable to use a system consisting of two electrodes (one acting as an anode and the other acting as a cathode) spaced apart by a distance

35/38 of a few millimeters (preferably 2 to 20 mm and more preferably 2 to 5 mm). This spacing should be adapted according to the desired objectives: detection limit; location on the stretchable support; size of the gauze and the stretchable support, and according to the patient's morphology.

These electrodes can consist of various materials that are deposited, like conductive paths, onto the support. Advantageously, they will be electrodes formed from copper paths, whose surfaces may or may not have been subjected to a chemical or electrolytic treatment, with an addition of gold or platinum, or even electrodes obtained by screen printing using conductive inks, such as inks filled with a salt of silver, carbon, etc.

If the substrate is made from a fabric, electronically conductive fibers can also be used as electrodes.

The length, width, and configuration of these electrodes can vary. Thus, two parallel sinusoidal electrodes, two mutually intertwined combs, two concentric rings, or even two parallel spirals can be designed. Such configurations are shown in Figs. 5A, 5B, 5C, and 5D, respectively.

These two electrodes can be connected to the electronic system via conductive paths 3, 4, as shown in Fig. 6.

The measurement principle of such a moisture detector is based on the change in resistivity between the anode and cathode with hydration.

This resistivity value will be compared to a calibrated value according to the adopted detection limit, and recorded in the electronic system.

The analysis of this comparison can then trigger an alarm, such as a visual alarm (LED) or an audible alarm (a

36/38 horn), or a change of state per bit if the electronic system incorporates a microprocessor.

The alarm can, for example, be located in the portable control module described above.

Another important parameter to be evaluated in the context of compression therapy may be temperature.

Temperature can be conventionally measured using a temperature sensor, such as a thermistor, whose resistance varies with temperature.

These temperature sensors are well known to technicians in the field and are used in the textile industry.

Both the form factor and the configuration of the interface pressure measurement system according to the present invention may vary.

In the context of the present invention, and in particular for the treatment of leg ulcers by compression therapy, two particular shapes illustrated in Figs. 6 and 7 are preferred.

The first format, of the "sock" type, is shown schematically in Fig. 7.

Support S includes:

a first part S1 that extends substantially longitudinally and is limited by the two pressure sensors P1 and P2 to be positioned at points B1 and C (see Fig. 1), for example, on the outer surface of the leg, and a second part S2 that extends the first part substantially perpendicularly and comprises the two electrodes H that form the moisture detector, the second part being intended to be

Fold the 37/38 gauge gauze into the position for use on the inside of the leg so as to cover the upper surface of the gauze positioned over the leg ulcer.

In the example shown, the onboard components of the device (power supply, communication module, antenna, microprocessor) are mounted on a single printed circuit board E placed between the two sensors Pi and P.₂This arrangement is particularly advantageous because, when support S is extended, it maximizes the integrity of the conductive paths 1, IA and 2, 2A that supply power to sensors Pi and P.₂ and the integrity of pathways 3 and 4 that supply energy to electrodes H.

This "sock" design requires that two separate versions (left and right) be produced, depending on which leg is being treated.

The second format is shown schematically in Fig. 6.

The two parts Si and S₂ The components that form the support are aligned here, so that this unique shape is suitable for whichever leg (left or right leg) is being treated.

The support can be bent in the region that separates its two constituent parts, Si and S.₂This allows the moisture detector to be positioned on the left or right side during use, depending on the leg being treated (see Fig. IA). The fold can therefore be advantageously sized according to the patient's leg size and wound location.

Similarly, the length of the electrodes that make up the moisture measuring device makes it possible to measure, if necessary, excess moisture on the outer surface of the gauze and/or on its periphery if exudates are released through the edges of the gauze.

Obviously, the humidity detector can be replaced by a temperature sensor or any other type of sensor.

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According to one embodiment, a humidity detector and a temperature sensor can be placed in the second part S2 of the support.

According to another embodiment, it is possible to place a humidity detector in the second part S2 of the support and a temperature sensor in a third part of the support (not shown) that forms an extension of the first part SI of the support on the opposite side to the second part.

As indicated above, the second and third parts of the support may or may not be extendable. However, to facilitate manufacturing, it is preferable to use a support that is extendable along its entire length.

The interface pressure measurement system according to the invention can be attached to the limb being treated using any known means of attaching a device to the human body, such as a Velcro-type fastener or an adhesive.

In the context of compression therapy treatment, it is particularly preferable to use a non-traumatic adhesive that, if necessary, can be repositioned in the same way as those commonly used for the production of absorbent gauze intended to be placed on the skin or on leg ulcers. This adhesive can cover, for example, totally or partially, the surface of the support system that comes into contact with the skin or wound. The reader may, for example, refer to publication WO 2006/094513 regarding the choice of such an adhesive. If necessary, this adhesive may be used to encapsulate some or all of the components of the interface pressure measurement system.