ICT-enabled Medical Compression Stocking for Treatment

of Leg Venous Insufﬁciency

Troels Fedder Jensen

, Finn Overgaard Hansen

, Jos

e Antonio Esparza Isasa

Peter Høgh Mikkelsen

, Tomi Hakala

and Timo Vuorela

Aarhus University School of Engineering, Finlandsgade 22, Aarhus, Denmark

Department of Engineering, Aarhus University, Finlandsgade 22, Aarhus, Denmark

Department of Material Science, Tampere University of Technology, Korkeakoulunkatu 6, Tampere, Finland

Department of Electronics and Communications Engineering, Tampere University of Technology,

Korkeakoulunkatu 3, Tampere, Finland

Keywords:

Compression Therapy, Leg Venous Insufﬁciency, Intelligent Medical Compression Stockings, Wearable

Devices, Independent Living.

Abstract:

This paper presents a novel approach to the treatment of leg venous insufﬁciency. This approach consists of

an ICT-enabled medical compression stocking that aims at mitigating the requirement for daily assistance and

increasing the patient’s self-sufﬁciency. More speciﬁcally, this paper presents the wearable subsystem of this

solution. In addition this paper discusses the different prototypes that have been produced to demonstrate that

this new approach is technically feasible.

1 INTRODUCTION

Leg venous insufﬁency is a serious medical condition

with severe impact on the mobility and self-sufﬁency

of patients, chieﬂy elderly people. The most practical

and efﬁcient non-invasive treatment to counteract and

prevent leg venous problems is compression therapy

by means of bandages or Graded Compression Stock-

ings (GCSs) (Partsch, 2003). GCSs, however, suffers

from a number of drawbacks: Poor conformance to

the individual patients’ legs as their size and volume

changes over time, degrading elasticity over time due

to washing and stretching, and difﬁcult to handle. The

overall consequence of this is poor levels of therapeu-

tic compliance and consequently less effective treat-

ment. This, in turn, may lead to ineffective and pro-

longed treatment, and reduced quality of life. More-

over, as GCSs are often difﬁcult to put on by patients

by themselves, the patients often depend on a visit by

home caretakers in the morning and evening to help

put the GCSs on and take them off. Apart from being

of obvious inconvenience for the patients, it is a de-

manding and time-consuming task for the caretakers,

and of substantial expense to society.

In this paper we present the current state of the

Stocking Assembly (SA) subsystem (Figure 2) of

the e-Stocking EU Ambient Assisted Living project.

The aim of this project is to develop an intelligent,

Information and Communication Technology (ICT)-

enabled graded compression stocking solution that

addresses the aforementioned shortcomings of exist-

ing GCSs. Key features of the novel stockings are

easy application and operation, compliance with indi-

vidual patient’s clinical needs; and enhanced mobility

and self-sufﬁciency.

Section 2 presents the state of the art in GCSs and

ICT-enabled compression solutions. Sections 3 to 5

yield an overview of the entire e-Stocking architec-

ture, pertaining requirements, and the design of the

SA adopted to meet these requirement. Sections 6 to 7

yield a description of SA prototypes, obtained results,

future work and conclusions.

2 STATE OF THE ART

Current approaches to treatment of leg venous insufﬁ-

ciency focus on the compression of the affected limb

through different mechanisms. Existing compression

therapy treatment is delivered by the application of ei-

ther compression bandages, compression stockings or

Intermittent Pneumatic Compression (IPC) (Hegarty

212

Jensen T., Hansen F., Esparza Isasa J., Mikkelsen P., Hakala T. and Vuorela T..

ICT-enabled Medical Compression Stocking for Treatment of Leg Venous Insufﬁciency.

DOI: 10.5220/0004903402120217

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2014), pages 212-217

ISBN: 978-989-758-013-0

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

et al., 2010). IPC is targeted primarily for the treat-

ment of venous leg ulcers and is delivered in hospitals

and daycare centers (Hegarty et al., 2008). While re-

lated in nature to the problem under study the IPC ap-

proach does not address the patients’ self-sufﬁciency

and the characteristics of the treatment are different as

IPCs provide dynamic compression while this study

aims at static compression at lower pressure levels.

Application of a graded pressure distribution by

means of GCS is a complex task and previous work

describes how this is true, even for ideal scenar-

ios (Liu et al., 2005). Additional studies have shown

that muscle movement during walking results in a

variation of up to 30 mmHg in exerted pressure

(Godoy et al., 2010; Partsch et al., 2006), making the

study of the pressure distribution over the leg even

more challenging. However, from a medical point

of view such variations are positive as they provide

a measure of dynamic compression that massages the

leg.

In order to measure the compression exerted at

speciﬁc locations, resistive force sensors have been

extensively evaluated (Khaburi et al., 2011a; Kawano

et al., 2005) and to some extent pneumatic force sen-

sors e.g. in the shape of the commercially avail-

able Microlab PicoPress pressure sensor instrument

(Khaburi et al., 2011b). Finally, monitoring the

swelling process of the leg as the treatment pro-

gresses has also been previously addressed using

bioimpedance techniques (Hegarty et al., 2008) and

strain gauges (Lebosse et al., 2011).

Even though extensive work has been conducted

on different aspects of the treatment of leg venous

insufﬁciency such as sensing technologies, sensor

placement and analysis of existing approaches, to our

knowledge an electronic wearable device that deliv-

ers quality compression treatment and enhances the

patient’s self-sufﬁency has not yet been developed.

3 SYSTEM ARCHITECTURE

The e-Stockings system consists of several physically

separated subsystems shown on Figure 1.

Figure 1: e-Stockings System Architecture.

The SA provides the compression to the patient’s

leg. Through the use of several air chambers the com-

pression applied to the patient’s leg can be graded

from ankle level to just below the knee. The com-

pression delivered to the leg is continuously regu-

lated through measurement of the air pressure in the

air chambers or the on-skin pressure. The compres-

sion applied is calibrated to each individual patient by

means of the E-stockings Calibration Device (ECD).

The ECD provides calibration data to the SA con-

trol unit and interfaces pressure sensors which can be

applied with the SA. The ECD is used to obtain on-

skin pressure values against which the SA can cali-

brate its target pressure values.

The Gateway consists of a smartphone device

which runs a gateway application. This provides

bridging services when the SA and ECD should be

connected as well as the graphical user interface for

use in the calibration process. The Gateway connects

wirelessly to the SA and ECD, respectively, and for-

wards sensor data requests and responses to the coun-

terpart. In the future, the Gateway is envisioned to

provide a means of remotely conﬁguring and obtain-

ing system and medical diagnostics data from the SA.

4 SYSTEM REQUIREMENTS

The requirements for the system as a whole, to which

the SA must adhere, are speciﬁed in detail in the per-

taining SysML-based Systems Requirement Speciﬁ-

cation, in which functional requirements are speciﬁed

using a set of use cases. The most important require-

ments for the SA are informally listed below. The

e-Stocking shall...

R1 promote self-sufﬁciency; the user shall be able

to apply and remove the stocking without assis-

tance.

R2 apply the correct compression proﬁle, typically

with the highest compression in the foot section

and decreasing in compression towards the knee.

R3 apply the correct compression throughout the us-

age scope of the stocking, even in the face of

changing leg size.

R4 be user-friendly in its operation.

R5 be battery powered and operable for 14 hours

without charging.

R6 be breathable and washable.

R7 be as lightweight and noiseless as possible.

R8 have a compression mechanism and control box

which is easily attached and detached.

R9 be conﬁgurable, enabling changes in compression

conﬁgurations.

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213

R10 have an aesthetically pleasing design.

R11 be certiﬁable as a medical device.

As the e-Stocking will compete with normal GCSs

in the market, which are very thin with a look and

feel as normal knitted stocking, and as the require-

ments are contradictory (e.g. lightweight, but battery-

powered, breathable but airtight), these requirements

give rise to substantial challenges.

5 SA DESIGN

The SA consists of four main parts as shown on Fig-

ure 2: an inner stocking (item 1), the compression

stocking itself (item 2), an actuator board (item 3),

and an Electronic Control Unit (ECU) (item 4). Each

of these are described in the following subsections.

5.1 Inner Stocking

The inner stocking is a commercial, knitted stocking,

which has an antibacterial property (Ag). The purpose

of this stocking is to provide a smooth, comfortable

surface to the skin. Furthermore, as this is the part

of the stocking assembly which is in immediate con-

tact with the patient’s skin, it alleviates the stocking

itself from the majority of washing required to main-

tain proper hygiene.

Figure 2: Stocking Assembly prototype 3.

5.2 Stocking

The stocking, as shown on Figure 2 item 2, covers the

lower leg of the patient from just behind the toes to

immediately under the knee. A a nonseparable zip-

per, extending the full length of the front of the stock-

ing save for the last centimeter on the foot, provides

a closing mechanism which allows the stocking to be

applied and removed with relative ease, much like a

softer version of a knee-long boot, while ensuring a

snug ﬁt. The top of the stocking consists of a soft,

elastic band which prevents the stocking from sagging

when it is zipped but not yet compressed. The stock-

ing has 3 individual compression sections mounted

laterally to cover the entire length of the stocking.

Each compression section consists of two air cham-

bers mounted at same height on the adaxial and abax-

ial sides of the leg, respectively. The air chambers are

sewn to an elastic, permeable garment on the ante-

rior and posterior sides of the leg to form the integral

stocking. Each air chamber consists of two layers of

airtight material which are high-frequency welded at

the edges to achieve air tightness. A special air chan-

nel is welded from the foot section along the front of

the middle compression section to allow a shorter tube

to connect the actuator board and the foot section. The

two layers of which each air chambers consists differ

in rigidity, the outer layer being more rigid than the

inner one, ensuring that expansion of the air chamber

is primarily directed towards the patient’s leg which

increases the compression applied to the leg per unit

volume of air in the compression section.

By controlling the compression of each compres-

sion section individually, the requirement for graded

compression can be accommodated. The expandable

compression sections provide the stocking with a cer-

tain dynamic range which is foreseen to alleviate the

need for individual tailoring of the stockings. Instead,

this may allow for the production of only a limited

number of different shapes and sizes, which will sim-

plify sizing, ordering and distributing of the stock-

ings.

5.3 Electronic Control Unit

Compression is managed by an Electronic Control

Unit (ECU). The ECU controls sensors, actuators,

user input and other external interfaces by means of

a software application running atop a FreeRTOS (RT

Engineers Ltd., 2013) Operating System (OS).

The nature of the experimental work conducted

in this project requires frequent changes in sensors

and actuators interfaced by the ECU. In order to ease

this process and shorten development time and cost

we use the Programmable System-on-Chip Cypress

PSoC5 as hardware platform. This platform imple-

ments an ARM Cortex-M3-based processor which

provides sufﬁcient processing power to run the appli-

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214

cation and OS, apart from a number of programmable

hardware blocks which provides the necessary ﬂexi-

bility, e.g. for conditioning sensors and actuators sig-

nals. Using custom hardware blocks implemented in

the PSoC5 allows a small form-factor to be main-

tained, yet preserves an open interface for experi-

menting with different sensors and actuators. Further-

more, the ECU features a dedicated Bluetooth module

to connect to remote devices, a 3-axis accelerome-

ter for motion detection and power for the complete

Stocking Assembly.

C++ was selected as implementation language.

The use of an object-oriented (OO) language

promises to minimize the gap between the employed

OO design process and the implementation. Fur-

thermore, C++ paves the way for ﬂexible and inter-

changeable implementations, a desirable feature in

light of the experimental nature of the prototyping

and subsequent frequent alterations and additions to

source code, e.g. when testing a new sensor or actu-

ator, or a new compression strategy. Finally, the use

of C++ allows source code to be tested early, often

and systematically as an integrated quality-enhancing

activity throughout software development.

While not strictly necessary, the inclusion of an

OS was desired. It was envisioned that the ECU appli-

cation would beneﬁt from running a number of con-

current threads, and the task abstraction, timing and

synchronization facilities, etc. provided by an OS

would be of substantial value. A number of OS’s

were investigated and FreeRTOS subsequently cho-

sen due to its ﬂexibility, customizability, widespread

use and small footprint. An abstraction layer was put

atop FreeRTOS to allow the application to interface

and abstract away the speciﬁc OS, and thus facilitate

a change of OS if so desired later, e.g. to SafeR-

TOS (WHIS, 2013) as required in a certiﬁcation pro-

cess.

5.4 Sensors and Actuators Board

The sensors and actuators board, mounted on the

front of the stocking as shown on Figure 2 item 3,

is equipped with four miniature solenoid valves, one

air pump and an electronic manometer, mounted on a

prototyping PCB and placed in a plexiglas housing.

The actuators and manometer are connected inside

this housing using short pieces of tubing. Three short

tubes protrude from each side of the actuator board

and are inserted into the ﬂanges of the stocking com-

pression sections prior to compression. This allows

the ECU to measure pressure in, and control inﬂation

or deﬂation of the individual compression sections.

6 PROTOTYPES AND RESULTS

This section presents three preliminary system proto-

types and the results that have been achieved so far.

6.1 Prototype 1: Resitive Sensor

Solution

In Prototype 1 resistive force sensors were used to

measure the on-skin pressure. In preparation for this,

a number of tests were conducted to screen for suit-

able sensors. This was done using a cardboard tube

of est. 10 cm diameter upon which the sensor was

mounted. On top of this, the sensor pad of a PicoPress

compression measurement system was positioned for

reference readings. To apply pressure to the sensors,

the cuff of a sphygmomanometer was wrapped around

the cardboard tube, covering the sensors.

It was evident from these experiments that a suit-

able resistive force sensor should have certain prop-

erties, most notably a large sensing area to mitigate

edge effects. It was also evident that, regardless of

the sensor used, pressure measurements below 10-15

mmHg were not consistent and could not be trusted.

As a result of the screening process, the Inter-

Link Electronics FSR 406 Square Force Sensing Re-

sistor (Interlink Electronics, 2013) was selected for

use in the prototype.

For the experiments on the prototype, three FSR

406 sensors were used to measure on-skin pressure.

One sensor was positioned on the back of the leg and

on the calf, respectively, corresponding to positions

B1 and C recommended in (Partsch et al., 2006), and

one sensor was positioned above the tuberiosity of

the third metatarsal bone on the foot. Each pressure

sensor was connected to the ECU by discrete wires.

A number of compression-regulation-decompression

cycles were executed: The ECU controlled compres-

sion build-up until the speciﬁed compression level

was reached, at which point the ECU commenced

periodic regulation of the compression level, supple-

menting compression as made necessary by any air

leakage from the sections. When commanded to do

so, the ECU controlled decompression of the stock-

ing until the compression reached a level at which the

SA was considered deﬂated.

A number of results were drawn from these exper-

iments. First, it was evident that the exact positioning

of the pressure sensors was crucial to the repeatability

of the experiments; placing the sensors even 1 cm off

caused intolerable deviations in the measured com-

pression. Second, the airtightness of the compression

sections was insufﬁcient.

The requirement for very exact positioning of the

ICT-enabledMedicalCompressionStockingforTreatment

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215

resistive force sensors was considered an unaccept-

able task to put on the patients which were to apply

the stocking on a daily basis. To alleviate this, it was

considered to permanently attach the sensors to the

inside of the stocking. This would require the sen-

sors to be washable, however, which they are not by

default. Thus, they would have to be coated in wa-

tertight material. Experiments using coated sensors

showed that the coating caused its own set of prob-

lems, as it clogged the small breathing hole in the sen-

sor necessary for air to escape from the sensor when

it is compressed.

It was also clear that the airtightness of the com-

pression sections was insufﬁcient, as the ECU had

to supplement the compression by running the pump

and valves every 5-10 seconds. This caused an audi-

ble periodic noise disturbance and signiﬁcantly higher

power consumption over time, both of which were un-

acceptable.

Based on these results it was decided to discard

resistive sensors altogether, and create and test a new

prototype which would be more airtight, and which

would use an electronic manometer to measure the

pressure in the compression sections and use this to

determine the compression on the patient’s leg.

6.2 Prototype 2: Manometer Solution

Prototype 2 was constructed to be more airtight and

using a Smartec SPD002GAsil manometer (Smartec

sensors, 2013) to gauge pressure in the air chambers.

This would have the beneﬁt that the sensor would

not need to be permanently attached at skin level and

could thus be removed along with other electronic and

pneumatic devices prior to washing.

As experiments progressed it became evident that

the air chambers were indeed more airtight due to im-

provements achieved in the high-frequency welding

process, but not entirely so. It also became evident

that the pressure measured in the compression sec-

tions did not correspond to the applied compression

on the skin as measured on-skin by the PicoPress ref-

erence sensor. It was possible to derive a second order

compression section-to-skin pressure transfer func-

tion, but such a transfer function proved susceptible

to changes in the volume and shape of the test per-

son’s leg - changes which were expected as a con-

sequence of the compression treatment itself. Con-

sidering the desire for not having to tailor the stock-

ings to individual patients, and considering that even

if tailored, any change in leg shape or volume, e.g. as

result of compression therapy, would render a trans-

fer function erroneous, the use of the manometer-and-

transfer-functions combination was discarded.

6.3 Prototype 3: Hybrid Solution

Prototype 3 was constructed to leverage the experi-

ence gained from prior prototypes; to use on-skin cal-

ibration periodically, e.g. monthly, to obtain accurate

reference results, and to use the corresponding ECU

manometer values as target values on a day-to-day ba-

sis.

The ECD was introduced to provide a means of

gauging the on-skin pressure through the use of three

FSR 406 resistive force sensors, identical to the ones

used in Prototype 1 and placed in the same positions.

The stand-alone ECD was to be operated by skilled

personnel which would mitigate the risk of false com-

pression readings due to errornous positioning of the

sensors. The ECU would be commanded into a spe-

cial ”calibration” mode in which it would control the

compression of the leg as hitherto, but take its com-

pression readings from the ECD over a Bluetooth con-

nection established by a Gateway device (Smartphone

app). When the on-skin compression level as read by

the ECD was in accordance with the target compres-

sion conﬁgured for the ECU, the ECU would stop

compression of the leg, gauge the level of compres-

sion in the individual compression sections by means

of its own electronic manometer and store these in

non-volatile memory for future use when operating in

its ”normal” mode. Thus, using the ECD and ECU in

conjunction, the stocking could be calibrated by the

help of skilled personnel periodically (e.g. monthly)

to accomodate changes in the shape and volume of

the patient’s leg, but be used with relative ease by the

patients themselves, as there would be no need for ac-

curate placement of sensors on a day-to-day basis.

Experiments were conducted using this strategy

and, while the principle appeared sound, it again be-

came evident that the spot measurements given by the

resistive sensors were not sufﬁciently reliable. It was

therefore decided that a number of ﬂat stand-alone

air chambers (dubbed ”calibration pads”) each the

size of a compression sections, should be produced.

For calibration, the calibration pads would be slightly

inﬂated, connected to electronic manometers on the

ECD and placed under the stocking before it was

closed. When compression was initiated, the same

pressure would be exerted on the calibration pads as

on the skin. Thus, by measuring the pressure in the

calibration pads, a measure for the on-skin pressure

could be derived. While similar to the resistive sen-

sors in application, the prominent advantage of the

calibration pads is their larger area; pressure readings

taken from a calibration pad corresponds to the mean

compression exerted on the area covered by the pad

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216

and thus mitigates the requirement for very ex-

act positioning of the sensors.

7 FUTURE WORK AND

CONCLUSIONS

Initial tests have been conducted using the calibration

pads. The results indicate a correlation between com-

pression measured with the pads and with a PicoPress

reference, but further experiments must be conducted

to fully understand and have conﬁdence in the corre-

lations, especially in terms of consistency over time.

Clinical testing is planned to take place during the

ﬁnal year of the project. This test shall primarily re-

veal if the stocking has the required clinical effect on

the patient’s legs. Before this testing phase can take

place, however, certiﬁcation by legal authorities in the

country where the test is to be performed - in our

case in Switzerland - must be obtained. Another sim-

ilar task, end-user testing, is planned to be conducted

in three different countries to investigate and accom-

modate for cultural differences and habits. The end-

user testing shall primarily test the main requirements

of enabling independent living and usability aspects.

End-user tests also require certiﬁcation to be obtained

prior to the tests.

Based on the results of clinical and end-user tests,

the prototype will be further developed and, at the end

of the project period, result in a workable prototype

which fulﬁls the stated set of requirements. At this

time, the experiences obtained and the ﬁnal prototype

will form the foundation for further product develop-

ment and maturing, in which manufacturing and pro-

duction issues will be addressed and CE-marking ob-

tained for the end product, paving the way to intro-

duction into the market.

This paper has listed the main requirements of

an ICT-controlled medical compression stocking, and

described the design, implementation, and tools ap-

plied in the development of a stocking assembly to

meet these requirements. Furthermore, it has de-

scribed the technical challenges posed and how they

were overcome.

ACKNOWLEDGEMENTS

This research is funded by the EU Ambient Assisted

Living Joint Programme, eStockings Project under

grant agreement no. AAL-2011-4-020.

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