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POLITECNICO DI MILANO

School of Industrial and information Engineering

Master of Science in Biomedical Engineering

Department of electronics, Information and Bioengineering

FINITE ELEMENT MODEL OF AN ACTIVE

MEDICAL STOCKING

Supervisor: Prof. Josè Félix Rodríguez Matas

Master Thesis of:

Luigia < Matr. 879185

Accademic Year 2019/2020

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Abstract

The aim of this project is to create an easily editable finite element model of the active

medical sock that Dott Silvio Donelli want to produce. The main idea of Dott Donelli is to

create a sock that not is help to help the venous flow back of the lower limb but also a sock

that does not impair the arterial flow. So when the gastrocnemius muscle is contracted the

pressure in the posterior part of the leg is the one due to the sock prestress but when the

tibialis anterior is contracted the pressure should decrease in the posterior part. This is the

biggest difference with what is on the market and the device that will be modelled ant

probably the improvement that could lead to obtain a real change on the exercise

performance of athletes or of general person.

Compression therapy in the last decades has become very popular. It is very efficient for the

treatment of different pathology such as the chronic venous disease, the edema, the leg ulcer

the post thrombotic syndrome and the lymphedema even if it is sometimes associated with

other treatment. However, even if compression garments are often used in the sport world

there is no scientific evidence that compression could really improve someone performance.

It must be added that numerous scientists approached this problem but they considered

different sports, different type of stocking and the of applied pressure and different outcome

variables. Moreover in different studies there were no measurement of the pressure applied.

But, leaving aside this problems, Dott Donelli thinks that a not certain improvement could

also be due to the fact that compression helps the venous return but impair the arteriosus

flux. Thus probably with such a devise better results could be obtained even if the problem

of the wearability should be taken into better consideration.

The device described in the patent filed by Dott Donelli is constituted by a sock with a ring

of struct that are connected to the sock on their central nodes while the inferior and upper

nodes of the ring are connected to some metal lines. These lines connect the struct’s ring to

the foot, so when the tip and the heel of the subject are moved down this movement is

transmitted to the ring that opens itself realising the pressure on the leg.

An example of how the devise has been modelled is shown in Fig. 1

Since the devise is completely new and since there is no prototype yet the model has been

built so that all the geometric parameters and the mechanical properties could be modified

even by someone who doesn’t know the software used. Then the model has been created

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using the Mmatlab software. Through Matlab all the geometries and all the set are built and

then with the same program the imput file of the finite element software (Abaqus) is written.

Fig. 1 FE model

Then in order to create a new model what must be done is just to change the wanted

parameters and open the model in Abaqus.

The first lines of the Matlab code are show in Fig. 2

Fig. 2 First lines of the matlab code

Different scenarios has been tested changing the ring geometry (radius of the ring, struct

length and the number of struct), and the leg radius. The leg’s radius has been changed in

order to see the effect of the position of the ring with respect to the leg in the axial direction.

Even if all these scenarios have been testes the simulations converged in few case. In order

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to follow the movement imposed from the lines the struct part of the ring whose nodes are

not connected to the lines deform too much impairing the convergence of the simulation.

Moreover the pressure reaches really high values near the connection points between the

sock and the struct’s ring. Another problem that the simulation showed is the fact that expect

for the region near the contact point between sock and struct the pressure in the anterior part

of the model is not significantly different from the posterior side. An example of the how

the results look like is shown in Fig. 3

Fig. 3 Example of the results

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Sommario

L’obbiettivo di questo progetto è creare un medello agli elementi finite semplice e facilmente

modificabile della calza medica attiva che il Dott Donelli vuole produrre. L’idea di base del

Dott Donelli è quella di creare una calza che non solo aiuti il ritorno venoso nelle gambe ma

che anche non opponga resistenza al flusso arterioso. Quindi quando il gastrocnemio è

contratto la pressione nella parte posterior della gamba è quella dovuta al prestress della

calza ma quando il tibiale anteriore si contrae la pressione dovrebbe diminuire nella parte

posterior della gamba. Questa è la maggior differenza tra le calze presenti sul mercato e

quella che verrà modelizzata. Questo miglioramento potrebbe portare ad ottenere un vero

effetto delle calze sulla performance di atleti o di persone comuni mentre praticano sport.

La terapia con compressione è divenata molto popolare negli ultimi decenni. Viene utilizzata

con efficacia per il trattamento di diverse patologie come l’insufficienza venosa cronica, gli

edemi, le ulcere, la syndrome post trombotica e il linfedema anche se a volte viene

accompagnata da altri trattamenti

Tuttavia anche se strutture compressive vengono spesso usate nel mondo dello sport ad oggi

non c’è l’evidenza scientifica che la compressione possa realmente migliorare la

performance sportiva.

Bisogna aggiungere che un elevato numero di scienziati ha approcciato questo problema

tuttavia ogniuno ha considerato sport differenti, diversi tipi di calze e quindi di pressione

apllicata e variabili di valutazioni diverse.

Tuttavia, trasurando per ora questi problemi, il Dott Donelli pensa che il non raggiungimento

di un attuale miglioramento sia dovuto al fatto che le calze usate migliorino il ritorno venoso

ma ostacolino quello arterioso. Tuttavia, anche se con questo dispositivo si potrebbero

ottenere un efficacia maggiore, non va trascurato il problema dell’indossabilità del

dispositivo

Il dispositivo desctitto nel brevetto depositato dal dottor donelli è costituito da una calza e

da un anello di struct connessi alla prima a livello dei nodi centrali delle struct mentre i nodi

superiori e inferiori delle struct delle struct sono connessi ad alcuni fili metallici. Questi fili

connettono l’anello di struct al piede in modo che quando la punta e il tallone del soggetto

vengono spostati verso il basso il movimento sia trasmesso all’anello che in questo modo si

apre e rilascia la pressione sulla gamba.

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Un esempio del modello del dispositivo è mostrato in Fig. 4

Fig. 4 FE model

Dato che il dispositivo è una novità assoluta e dato che ancora non c’è un prototipo, il

modello è stato costruito in modo che tutti i parametri geometrici e le proprietà meccaniche

potessero essere modificate anche da qualcuno che non conosce il software usato. Quindi il

modello è stato creato usando il software Matlab. Attraverso quest’ultimo tutte le geometrie

e e tutti i set sono creati e successivamente sempre con Matlab il file input del software di

elementi finite (Abaqus) viene scritto.

Le prime righe del codice matlab sono mostrate in Fig. 5

Fig. 5 First lines of the matlab code

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Diversi scenari sono stati testati cambiando la geometria dell’anello (raggio dell’anello,

lunghezza delle struct, e numero delle struct) e il raggio della gamba. Il raggio della gamba

è stato cambiato in modo da studiare l’effetto della posizione dell’anello rispetto la gamba

nella direzione radiale.

Anche se diversi scenari sono stati testati la simulazione ha raggiunto convergenza in pochi

casi. In modo da seguire i movimenti dati dai fili, le parti delle struct che non sono collegate

ai fili devono devormarsi troppo e in questo modo compromettono la convergenza del

modello.

Inoltre livelli di pressione nei pressi del punto di incontro tra due stuct sono molto elevate.

Un altro problema mostrato dall simulazione è ll’assenza di una differenza significativa tra

la pressione nella parte anteriore e posteriore della gamba.

Un esempio dei risultati ottenuti è mostrato in Fig. 6

Fig. 6 Example of the results

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Contents

Finite element model of an active medical stocking ............................................................. 1

Abstract .................................................................................................................................. 2

Sommario .............................................................................................................................. 5

Tables .................................................................................................................................. 13

Compression therapy ........................................................................................................... 14

A brief history .................................................................................................................. 14

Medical application of compression garments ................................................................ 17

Chronic venous insufficiency ....................................................................................... 17

Inflammation and Skin Changes .............................................................................. 19

Classification of Venous Disease ............................................................................. 20

...................................................................................................................................... 23

Lower extremity oedema .............................................................................................. 23

Leg ulcers ..................................................................................................................... 24

Assessment of the patient with VLU ........................................................................ 26

Treatment options ..................................................................................................... 27

Types of compression ............................................................................................... 28

The post-thrombotic syndrome .................................................................................... 28

Clinical presentation of PTS ..................................................................................... 29

Diagnosis of PTS ...................................................................................................... 30

Treatment .................................................................................................................. 31

Lymphoedema .............................................................................................................. 31

Pathophysiology of lymphedema ............................................................................. 32

Lymphedema classification ...................................................................................... 32

Diagnosis of lymphedema ........................................................................................ 33

Therapy ..................................................................................................................... 34

Use of compression therapy in the Sports world ............................................................. 36

Muscle Strength............................................................................................................ 36

Relationship between Force Production and Instantaneous Muscle Length ................ 38

Relationship between a muscle’s moment arm and its force production. .................... 41

Effects of the magnitude of the contraction velocity on force production in muscle .. 41

Relationship between force production and level of recruitment of motor units within

the muscle ..................................................................................................................... 43

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Relationship between force production and fiber type ................................................. 43

Effect of compression on different exercise performances. ......................................... 45

Effect of compression pants on vertical jump performance, Wannop and all[58] results

...................................................................................................................................... 45

Characteristic of medical stockings ................................................................................. 48

Compression stockings types of elastomeric fibers and yarns. .................................... 48

Characteristics of Elastomeric Yarns ....................................................................... 49

Knitting Construction and Fabrication ..................................................................... 51

Fabric Mechanical Properties ....................................................................................... 52

Garment Design............................................................................................................ 53

Design System .............................................................................................................. 54

Pressure Measurement.................................................................................................. 54

In vitro measurement ................................................................................................ 55

Pressure Sensors ....................................................................................................... 56

Static Pressure Measurement .................................................................................... 56

Dynamic Pressure Measurement .............................................................................. 56

Pressure Modeling .................................................................................................... 57

Method ................................................................................................................................. 60

Part module ...................................................................................................................... 60

Part 1: The ring ............................................................................................................. 61

Part 2: Sock .................................................................................................................. 62

Part 3: Expansion cylinder ........................................................................................... 64

Part 4: Leg .................................................................................................................... 65

Part 5: Line inf.............................................................................................................. 67

Assembly module ............................................................................................................ 70

Interaction module. .......................................................................................................... 72

Material Properties ........................................................................................................... 72

Step module ..................................................................................................................... 74

Results ................................................................................................................................. 76

Mesh Convergency .............................................................................................................. 76

Case 1 ........................................................................................................................... 80

Case two ........................................................................................................................... 85

Example ........................................................................................................................ 86

Discussion ........................................................................................................................ 88

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Bibliography ........................................................................................................................ 89

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Figures

Fig. 1 FE model __________________________________________________________ 3

Fig. 2 First lines of the matlab code ___________________________________________ 3

Fig. 3 Example of the results ________________________________________________ 4

Fig. 4 FE model __________________________________________________________ 6

Fig. 5 First lines of the matlab code ___________________________________________ 6

Fig. 6 Example of the results ________________________________________________ 7

Fig. 7 oldest illustration of compression therapy ________________________________ 14

Fig. 8 Flowchart showing etiology of cutaneous venous hypertension. _______________ 17

Fig. 9 Flowchart showing etiology of cutaneous manifestations of venous hypertension. 18

Fig. 10 Leg edema _______________________________________________________ 23

Fig. 11 Leg ulcer _________________________________________________________ 24

Fig. 12 ABI measurement __________________________________________________ 26

Fig. 13 Post-thrombotic syndrome with edema, hyperpigmentation, venous ectasia, skin

induration and healed ulcer ________________________________________________ 29

Fig. 14 Physiological-cross-sectional area (green) and cross-sectional area (blue) ______ 37

Fig. 15 The length–tension curve of a sarcomere. _______________________________ 38

Fig. 16 Muscle model _____________________________________________________ 39

Fig. 17 The length–tension curve of a whole muscle. ____________________________ 39

Fig. 18 The relationship between contractile force and the velocity of contraction in

isometric and concentric contractions. ________________________________________ 42

Fig. 19 Apparel condition used during the experiment. ___________________________ 46

Fig. 20 Core-spun yarn ____________________________________________________ 49

Fig. 21 Double covered yarn _______________________________________________ 49

Fig. 22 Texturing process __________________________________________________ 49

Fig. 23 Stress and strain relation ____________________________________________ 50

Fig. 24 Stress and strain relationship. _________________________________________ 51

Fig. 25 Knitting construction of elastic fabrics. _________________________________ 52

Fig. 26 Kowalski and all model _____________________________________________ 55

Fig. 27 McLaren and all[69] thin wearable wireless pressure monitoring device _______ 57

Fig. 28 Struct geometry. ___________________________________________________ 61

Fig. 29 Ring label ________________________________________________________ 62

Fig. 30 Ring connectivity matrix ____________________________________________ 62

Fig. 31 Sock geometry. ____________________________________________________ 63

Fig. 32 Sock labelling _____________________________________________________ 64

Fig. 33 Sock connectivity matrix ____________________________________________ 64

Fig. 34 Surface expansion geometry _________________________________________ 65

Fig. 35 Leg geometry _____________________________________________________ 66

Fig. 36 Leg Labelling _____________________________________________________ 66

Fig. 37 Leg connectivity matrix _____________________________________________ 67

Fig. 38 Straight case ______________________________________________________ 68

Fig. 39 Simple case, inferior lines ___________________________________________ 68

Fig. 40 Cross case, inferior lines ____________________________________________ 69

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Fig. 41 Straight case, superior lines __________________________________________ 69

Fig. 42 Cross case, superior lines. ___________________________________________ 70

Fig. 43 Simple case, superior lines ___________________________________________ 70

Fig. 44 Connector behaviour _______________________________________________ 71

Fig. 45 Connector example _________________________________________________ 71

Fig. 46 Interaction deactivation _____________________________________________ 72

Fig. 47 Circumferential young modulus _______________________________________ 73

Fig. 48 Longitudinal Young modulus ________________________________________ 73

Fig. 49 Poisson ratio computation ___________________________________________ 74

Fig. 50 Movement of the foot's node. _________________________________________ 75

Fig. 52 Leg mesh type 3 ___________________________________________________ 76

Fig. 51 Leg mesh type 4 ___________________________________________________ 76

Fig. 53 Pressure values for mesh 4 ___________________________________________ 77

Fig. 54 Pressure values for mesh 3 ___________________________________________ 77

Fig. 55 Effect of change of the sock mesh _____________________________________ 78

Fig. 56 Pressure when the sock is modelled as linear orthotropic. ___________________ 79

Fig. 57 Pressure when the sock is modelled as linear isotropic _____________________ 79

Fig. 58 Pameters values ___________________________________________________ 80

Fig. 59 Simple case pressure values __________________________________________ 81

Fig. 60 Simple case struct deformation _______________________________________ 81

Fig. 61 Straight case pressure values _________________________________________ 82

Fig. 62 Straight case struct deformation _______________________________________ 83

Fig. 63 Cross case initial pressure values ______________________________________ 83

Fig. 64 Cross case minimum pressure values __________________________________ 84

Fig. 65 Cross case, struct deformation ________________________________________ 84

Fig. 66 Pressure of the anterior part of the leg __________________________________ 85

Fig. 67 initial ankle's pressure ______________________________________________ 85

Fig. 68 Struct’s ring deformation ____________________________________________ 86

Fig. 69 Struct’s ring deformation ____________________________________________ 86

Fig. 70 Not converged simulation example ____________________________________ 87

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Tables

Tab. 1 CEAP classes of clinical state. ________________________________________ 21

Tab. 2CEAP definition ____________________________________________________ 23

Tab. 4Knitting method ____________________________________________________ 51

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Compression therapy

Compression garments are special clothing containing elastomeric fibers and yarns used to

apply substantial mechanical pressure on the surface of needed body zones for stabilizing,

compressing, and supporting underlying tissues. They have been used for medical

applications, athletic applications, and body-shaping applications [1].

A brief history

The oldest known illustration of compression bandages dates back to the Neolithic Age

(5000–2500 BC) Fig. 7. The ancient Hebrews, Egyptians, Greeks, and Romans used

compression therapy for treatment of wounds and ulcers, as described in the Smith Papyrus

(1650–1552 BC) and in the Book of Isaiah (Isaiah 1:6), eighth century BC[2]. Hippocrates

wrote about compression treatment in the fourth century BC, and this was followed by

further refinements from Celsus and Virgo.

Roman soldiers who marched for days at a time learned quickly that applying tight

strappings to the legs reduced leg fatigue.

The knowledge concerning the beneficial effects of compression was rediscovered by

physicians during the Middle Ages, including Guy de Chauliac (1363), Giovanni Michele

Fig. 7 oldest illustration of compression therapy

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Savonarola (1440), and Fabrizio d‘Aquapendente (1537–1619). They used compression

bandages, laster dressings, and laced stockings made from dog leather[3].

Ambroise Paré (1510–1590), Richard Wiseman (1622–1676), Christian Anton Theden

(1714–1787), and Thomas Baynton (1797) were pioneers, especially in the treatment of leg

ulcers, recommending different kinds of compression material that were mainly inelastic. In

1885, the dermatologist Paul Unna introduced his zinc paste boot for the treatment of venous

dermatitis, and in 1910, his pupil, Heinrich Fischer, recommended firmly applied ‘Unna

boots’ for treating venous thrombosis[4].

The use of elastic compression occurred with the development of elastic stockings in the mid

1800s and the discovery by Charles Goodyear in 1839 of a vulcanizing process for rubber

that would increase its elasticity and durability. In 1839, John Watson, MD, reported on the

usefulness of an elastic stocking in treating varicose veins in a 23-year-old woman with

Klippel–Trenaunay syndrome[5]. However, these stockings, made exclusively from rubber

threads, were uncomfortable. It was not until Jonathan Sparks patented a method for winding

cotton and silk around the rubber threads that elastic stockings became comfortable and

popular[5].

During the late 1800s and early 1900s, technical advances in the manufacturing process led

from the development of the frame-knitting to the flat-knitting method, which increased

production efficiency as well as providing a proper fit. Stockings became even more

comfortable and better looking when ultra-fine, rounded latex yarns became available, which

permitted the construction of seamless stockings. Two-way stretch stockings were

developed next, which led to easier application of the stocking. Finally, the development of

synthetic elastomers in the 1960s gave rise to latex-free compression stockings. Synthetic

(spandex, polyurethane and nylon) stockings are still the ideal form of material to use today

because of the relative resistance to moisture from sweat and other environmental factors as

well as the very fine threads and stretch–contraction characteristics that lead to the

production of fine stockings.

Today there are more than 200 different brands of graduated compression stockings, infact

for this project the mechanical properties of the sock that will be used to build the device has

been tested.

It was believed that the pressure exerted could reduce the side effects of gravity and uphold

posture and that it could improve the wound healing of the lower limbs. The application of

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compression with the use of bandages, was used for the first time as a treatment for varicose

veins in 1440. However, bandages were place on the market just at the end of the 19th

century. The first modern elastic compression stockings with gradual compression were also

fabricated in the 19th century in England[2]. Compression therapy has also been used for

the last 50 years for burn care and has been accepted to help minimize the formation of

hypertrophic scars and enhance the maturation process of scars[6]. Their use has become

widely common also in sports. Sportswear with moderate compression distribution is widely

used in athletics and fitness activities and is expected to enhance the performance of the

athletes, decrease the possibility of injury, and accelerate the process of recovery[7].

Likewise, compression garments with a slight pressure designed to be tight fitting for body

shaping purpose are becoming more popular. The effectiveness, safety, pressure distribution,

and retention of the compression garments are important aspects that have significant effects

on the health of users[8]. The pressure magnitude and its changes in time are the key

indicator and they are determined primarily by mechanical properties of the garment and

garment fit[9]. Pressure applied by a compression garment is one of the most important

properties used in order to evaluate the therapy efficacy, comfort, health, and security[10].

Denton[11] identified the pressure threshold of discomfort to be around 5.88–9.80 kPa

(44.1–73.5 mmHg) depending on the individual subject and the part of the body concerned.

Probably it is no accident that these values are greater but close to the average capillary blood

pressure near the skin surface (4.30 kPa, 32.3 mmHg). The pressure comfort zone for the

normal condition is 1.96–3.92 kPa (14.7–29.4 mmHg), but it also depends on the individual

condition of the subject body part and body position. An improper compression garment

would influence the energy, work efficiency, and health of the wearer. Insufficient pressure

will limit efficacy while too high of a pressure will make people feel uncomfortable, cause

numbness to the body part, or even cause breathing difficulty and other serious damage to

health. Apart from pressure performance, the physical characteristics like air permeability,

heat, moisture transmission, and tactile characteristics all have an influence on the comfort

of compression garments.

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Medical application of compression garments

Compression garments are individually designed and manufactured for a particular part of

the body, stockings, bandages, sleeves, gloves, body suits, and face masks. They have been

utilized in the areas of chronic venous disease management, scar management, orthopedic

supports, sportswear, and body shaping.

Chronic venous insufficiency

Chronic venous insufficiency may be defined as an high impedance of venous flow back to

the heart. When this occurs in the lower extremities, the normal reabsorption of perivascular

fluids by osmotic and pressure gradients is impaired, resulting in accumulation of

perivascular and lymphatic fluid. This leads to edema and impaired oxygenation of

surrounding tissue (Fig. 8).

Fig. 8

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This disruption of the normal vascular and lymphatic flow of the lower extremities may

result in pain, cramping (especially at night), restlessness, pigmentary changes, dermatitis,

and ulceration (Fig. 9).

Fig. 9 Flowchart showing etiology of cutaneous manifestations of venous hypertension.

The association of abnormal venous flow with various signs and symptoms has been noted

for centuries: first by Hippocrates in the fourth century BC and by Wiseman in England in

1676[12]. Several alterations of normal venous flow cause venous hypertension. Such

hypertension in the lower extremities is usually caused by a loss or disruption of the normal

valvular system. This may occur because of deep vein thrombosis (DVT), thrombophlebitis,

or a dilation of veins from other causes[13]. When perforating vein valvular function

becomes incompetent, there may be shunting of blood flow from the deep to the superficial

venous system through the incompetent perforating veins, with resultant adverse sequelae.

The superficial veins respond by dilating to accommodate the increased blood flow, which

produces superficial valvular incompetence leading to the development of varicosities[14].

In addition, due to the muscular movement in the lower limbs, the high venous pressure

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normally occurring within the calf is transmitted straight to the superficial veins and

subcutaneous tissues[14]. This causes venular dilation over the whole area, resulting in

capillary dilation, increased permeability and increase in the subcutaneous capillary bed[15].

This is manifested as telangiectasia and venectasia. Venous hypertension has also been

demonstrated to destroy the venous valves that are present in the subcuticular vascular

system[16]. This destruction promotes persistent and progressive changes in the venous

drainage system of the skin and subcutaneous tissues. The greater the degree of venous

hypertension, the greater the risk of venous ulcer development[17]. However venous

hypertension and subsequent insufficiency may also derive from venous obstruction, either

at lower limb level or at iliocaval level, usually associated with reflux.

Inflammation and Skin Changes

There has been progress in linking the chronic inflammatory state seen in CVD patients with

the specific skin changes typical of the condition. In lipodermatosclerosis, the skin

capillaries become elongated and tortuous, giving the appearance in histologic sections of

elevated capillary density[18].In advanced skin disease especially in the ulcerative stages,

the capillaries may take on a glomerular appearance and it seems clear that substantial

proliferation of the capillary endothelium occurs[19]. Several factors could contribute to

endothelial proliferation, but vascular endothelial growth factor (VEGF) is an obvious

candidate. VEGF is known to be involved in inflammatory and healing processes in the skin

and has been shown to increase microvascular permeability both acutely and chronically.

Plasma levels of VEGF have been shown to increase during the venous hypertension induced

by 30 minutes of standing both in normal subjects and in CVD patients. Both supine and

standing VEGF levels are higher in patients than in normal controls[20]. Furthermore,

plasma VEGF levels are higher in CVD patients with skin changes than in CVD patients

with normal skin[21].

Another feature of the skin changes associated with CVD is dermal tissue fibrosis.

Transforming growth factor-β1 (TGF-β1 ) is a known fibrogenic cytokine. Detailed

analysis of punch biopsy specimens has shown that skin from the lower calf and thigh of

CVD patients had significantly elevated active TGF-β1 levels compared with normal

skin[22]. Immunohistochemistry and immunogold labelling showed the TGF-β1 to be

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located in leukocytes, fibroblasts, and on collagen fibrils. Pappas el al[23] proposed that

activated leukocytes migrate out of the vasculature and release TGF-β1 , which stimulates

increased collagen production by dermal fibroblasts. Over an extended period, such a

process could contribute to the typical dermal fibrosis seen in CVD. Altered collagen

synthesis has also been reported for dermal fibroblasts taken from apparently healthy areas

of skin in patients with varicose veins[24]. It has been possible to correlate altered levels and

distributions of growth factors, including basic fibroblast growth factor (bFGF),

transforming growth factor-3 (TGF-3), and the receptor for epidermal growth factor (EGF),

with different types of skin change, including venous eczema, pigmentation,

lipodermatosclerosis, and ulceration[14].

Venous hypertension is not a benign condition. The cutaneous chain of events following the

onset of venous stasis is thought to occur in the following temporal order: localized edema,

induration, pigmentation, dermatitis, atrophie blanche, and, in untreated cases, eventual

ulceration, infection, scarring, lymphatic obstruction and sensitization to applied

medications.

Labropoulos et al[25] studied 255 limbs in 217 patients that showed superficial venous

insufficiency only, with normal perforating veins and deep veins. The color-flow duplex

imaging techniques were used. The researchers concluded that aching, ankle edema and skin

changes in limbs with reflux confined to the superficial venous system were associated

predominantly with reflux in veins below the knee. An important finding was that ulceration

occurred only when the entire great saphenous vein (GSV) was involved or when reflux was

extensive in both the great and small saphenous systems. Then changes in the skin

appearance could be a warning before venous insufficiency developed.

Classification of Venous Disease

An international ad hoc committee of the American Venous Forum developed the CEAP

classification for CVD in 1994. The goal was to stratify clinical levels of venous

insufficiency. The four categories selected for classification were: clinical state (C), etiology

(E), anatomy (A), and pathophysiology (P). The CEAP classification has been endorsed

worldwide despite its acknowledged deficiencies. It has been adopted as a standard in many

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clinics in Europe, Asia and South America and is considered the only modern method for

reporting data in the United States[26].

The first step in evaluating a patient with CVD is to establish his or her clinical class. The

CEAP classes are shown in Tab. 1.

Tab. 1 CEAP classes of clinical state.

Each clinical class is further characterized by a subscript for the presence of symptoms (S,

symptomatic) or their absence (A, asymptomatic). Symptoms include aching, pain,

tightness, skin irritation, heaviness, and muscle cramps, as well as other complaints

attributable to venous dysfunction. A basic CEAP is suggested. For the practicing physician,

CEAP is an instrument for correct diagnosis, to guide the treatment and assess the prognosis.

In the modern phlebologic practice, the vast majority of patients will undergo a duplex scan

of the venous system of the leg, which will provide data on E, A and P. In basic CEAP where

a duplex scan is performed, E, A and P should be utilized. For the anatomical classification

A in basic CEAP, the simple s = superficial, p =perforator and

d = deep descriptors should be used. Multiple descriptors should be permitted for all four

components in basic CEAP; for example a patient could be classified as C234s Ep Asd Pr.

Use of all components of CEAP is encouraged.

Definitions that apply to the CEAP classification are shown in Error! Reference source not f

ound.

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But the CEAP is a description of the disease, not an assessment of its severity. It serves for

classification, not evaluation. For this reason, several scores have been added to the CEAP,

such as the VCSS (venous clinical severity score)[11].

2.1. Chronic Venous Disease and Edema Management

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Lower extremity oedema

Introduction

An oedema (Fig. 10) is an accumulation of fluid in the interstitium it is extremely common

and generally harmless even if it may be the indication of more serious disease. The causes

can be a cardiac disfunction, an insufficient venous return or a not physiological pressure

gradient between the blood vessels and the interstitumc.

Fig. 10 Leg edema

The first thing to do is trying to understand the reason that has cause the oedema and some

question about the history (When did it start? Was it gradual?), about its evolution (Is it

getting worse? Does it come and go?) about its location (Does it involves one or two leg?).

Between the main causes of oedema there are the deep veins thrombosis (DVT), the

superficial vein thrombosis, the cellulitis, a neuropathy, the rupture of a baker’s cyst, an heart

failure, a pulmonary hypertension, the cirrhosis, a kidney disease, the malnutrition, hormonal

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changes, thyroid disease, medication, inferior vena cava thrombosis, lymphedema,

lipoedema or a chronic venous disease[27].

The first thing to do is an echocardiogram if the patient is at risk for pulmonary hypertension,

obstructive sleep apnea or heart failure or a venous ultrasound to rule out the deep vein

thrombosis[28].

The treatment require compression garment, exercise, weight loss and meticulous skin care.

The patients should elevate their leg for at least 30 minutes per day and 30 minutes of

exercise aimed to strengthening the calf muscle pumping. They should also wear a knee/high

compression stocking with 20 to 30 mmHg of pressure at the ankle. The stocking should be

worn daily particularly after being standing for long period while sleeping in them is not

necessary. The hosiery should be changed after 6 month since the fabric could have lost its

elasticity[29].

Leg ulcers

Venous leg ulcers (Fig. 11) are the most common chronic wounds, representing more than

70% of all types of leg ulcers. The patients with VLU suffer with significant changes in

their daily lives, overwhelming pain associated with dressing changes and wound surface,

Fig. 11 Leg ulcer

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daily discomfort related to edema and odor, mobility difficulties, as well as social and family

isolation[30].

Moreover, patients who suffers of CVI in general experience several episodes of ulceration

in their lives, commonly with protracted healing and recurrence because of underlying

pathophysiology[31].

Age is the most common cause of lower limb ulceration and so with an ageing population

and the growing of cardiovascular disease, diabetes, and obesity, the number of individuals

who will present a leg ulcer will increase dramatically. That is why it is important not only

for the health and quality of life of the patient but also for the treatment cost that the lowest

number of ulceration occurs[4].

The main reason of the development of venous leg ulcers (VLU) is the presence of a venous

insufficiency. Indeed the superficial and/or deep venous systems of the patient are damaged,

probably there is also a valvular dysfunction that will lead to venous hypertension and

consequent tissue hypoxia[32].

The presence of a valvular dysfunction induces an increase in the hydrostatic pressure, so in

order to reduce that the vein will dilate in order to reduce the pressure but instead this will

make the valves less functional and increase the blood back flow[17]-[33].

Also deep vein thrombosis, pregnancy, leg fractures, phlebitis or congenital weakness of

venous walls can lead to permanent damage of the superficial and/or deep venous systems,

increasing hydrostatic pressure.

Water and sodium, fibrinogen, and white and red blood cells may transudate from the vessel

lumen in the presence of venous hypertension with consequential damage to the skin,

clinically represented as edema, fibrin cuff formation, eczema, and hyperpigmentation of the

tissue. Then the cells might become ischemic and inactive, therefore the skin become fragile,

susceptible to breakdown even after minimal trauma. Finally, the combination with an

impaired healing mechanisms, will produce a chronic ulcer, that is an ulcer that need more

than 6 month to heal[34].

The most efficient way to manage venous ulcers is to address venous insufficiency in the

first place, with a strong recommendation for the use of compressive therapy as the gold

standard treatment for VLU. However, there is no consensus regarding the most effective

compressive therapy technique[25].

26

Assessment of the patient with VLU

The first thing to do is asses for signs of venous disease as the presence of varicose veins,

venous dermatitis, atrophie blanche, hemosiderin deposition, and lipodermatosclerosis.

Then the ankle-brachial index (ABI) must be checked to exclude any arterial component that

could affect the healing process. ABI is the ratio between the measure of the systolic pressure

of the affected leg (using a hand-held continuous wave Doppler ultrasound) andthe brachial

systolic pressure (the highest systolic value of both arms)[34].

A referral is recommended within 3 months after the first visit and sooner for patients with

comorbid conditions such as diabetes.

In patients with chronic VLUs, ABI must be interpreted with caution as it may under-

represent the degree of arterial disease in the lower extremity in patients with low central

systolic pressure or where there is PAD in the upper extremity. In Fig. 12 it is show how

ABI is measured

ABI contraindications include a high level of pain in lower limbs and deep vein thrombosis

as the ABPI assessment procedure may lead to thrombus dislodgement and acute embolism.

The clinical practise guidelines (CPG) do not agree on a precise value of APB for which the

27

use of compression is recommended. But several CPGs advise that compression therapy can

safely be initiated when ABPI values are >0.8 while they advise against its use if the APB

score is < 0.5[35].

There is a lack of guidance on the use of compression therapy in patients with an ABI score

of 0.6 to 0.8. But if a clinician decide to prescribe compression stockings in this last case

CPGs recommend close observation.

After the ABI assessments, the characteristics of the ulcer should be clearly described and

carefully documented over time, possibly with detailed photography. The documentation

should also include information on the area and depth of the ulcer, on the amount and the

type of exudate drainage, on its odor, on the characteristics of the edges, the bed tissue, and

the area that surround the VLU. It is important to assess the wound for infection. An infected

ulcer has at least one or more of the following symptoms and/or signs: foul odor, purulent

drainage (pus), and symptoms of inflammation such as fever, pain, redness, swelling and

warmth[30].

All chronic wounds are colonized with bacteria and/or fungi, also known as biofilm.

A lack of adequate biofilm control implies serious complications, such as delayed healing,

cellulitis, and sepsis. However removing biofilm is a major challenge for the health care

provider because of its firm adherence to the surrounding tissue.

Attinger and Wolcott emphasize that the debridement of this biofilm opens a time-dependent

window (2-3 days in wounds) where topic agents might be more effective[30].

Treatment options

The treatment of VLU consists in the choice of dressings compatible with the ulcer

characteristics, edema and exudate control, pain management, adequate compressive

therapy, dietetic education, and tight control of diabetes mellitus and hypertension[4].

The dressing must have low adherence, be unexpansive, and well tolerated by the patient.

Moreover, dressing must be capable of absorbing exudate until the next dressing change.

Compressive therapy is recommended for appropriate edema control and faster healing of

VLU.

The choice of the type of compressive device must consider size and shape of the limb,

patient‘s tolerance or preference, and the health care provider‘s level of expertise.

28

The application of compression on the limb can minimize or reverse the venous reflux

caused by valve incompetence, forcing the fluid present in the interstitial spaces to return to

the vascular and lymphatic systems, thus reducing tissue edema. However, this solution is

temporary and work only while the patient is wearing the compressive device, implying in

the use of elastic stockings even after the ulcer has healed.

In some situations, venous surgery can manage venous insufficiency and promote wound

healing, preventing recurrence of VLU. A systematic review of the literature published in

2015 concluded that surgical correction of venous insufficiency reduces recurrence rates and

extend ulcer free periods.

Types of compression

Compression therapy is considered essential for the success of VLU treatment, but it remains

unclear which type of compressive devices, techniques, and adjunct therapies are more

effective. Neither the safest and most efficient ranges of compression pressure have been

identify.

Compression therapy systems are designed to increase pressure in the ankle and underlying

structures, to counteract the force of gravity. This therapy helps the venous and lymphatic

systems to reduce tissue edema and mitigate venous hypertension.

For what concern the compression recommendations for VLU prevention suggestions

regarding the level of compression were different.

The post-thrombotic syndrome

The post-thrombotic syndrome (PTS) is a complication of deep venous thrombosis (DVT)

that is characterized by leg swelling, skin changes, pain and occasionally venous

ulceration. One of every three people with DVT will develop post-thrombotic

complications within five years and compression therapy is one of the measure used to

prevent PTS[36].

29

Clinical presentation of PTS

Patients with PTS complain of pain, heaviness, swelling, cramps, itching or tingling in the

affected limb. Typically, these symptoms are aggravated by standing or walking while they

are improved by rest and recumbency. On physical examination, edema, telangiectasiae,

hyperpigmentation, eczema, and varicose superficial veins may be found. In severe cases,

there may be thickening and induration of the subcutaneous tissue around the ankle

(lipodermatosclerosis) and evidence of healed or open ulceration[37]. The leg of a patient

suffering of PTS is show in Fig. 13.

These signs are probably due to venous hypertension. During the first month after the

development of a thrombus, a complex process involving the dissolution of the blood clot

and the proliferation of new vessel, named recanalization, occurs. However this process can

induce the valves malfunction that combined with the possible presence of occluded veins

cause an increase of the pressure within the veins. The valvular malfunction induce venous

hypertension that leads to the appearance of telangiectasiae and venous ectasia, and causes

capillary leakage of plasma proteins, erythrocytes and leukocytes, with resultant edema,

tissue hypoxia and damage, and ultimately, in some cases, skin ulceration[38].

Fig. 13 Post-thrombotic syndrome with edema, hyperpigmentation, venous ectasia, skin induration

and healed ulcer

30

Diagnosis of PTS

The diagnosis of PTS should be based primarily on the presence of typical clinical features.

In fact the majority of patients with symptomatic PTS have valvular incompetence, but many

with valvular incompetence do not have symptoms and even if evidence of venous valvular

reflux can help to confirm the diagnosis in symptomatic patients, subjects who have venous

reflux on objective testing but who are asymptomatic do not have PTS. Moreover the

diagnosis should be made after 3.6 month after DVT since this is the time that pain and

swelling due to venous obstruction and inflammation need to heal[39].

If a patient has some symptoms of PTS without a diagnosis of DVT, a DVT should be

suspected moreover if he has undergone surgery, prolonged immobilization or episodes of

leg pain and swelling that could also resolved by their own. In this case the presence of vein

reflux on Doppler ultrasound, or the evidence of recanalized veins, collateral channels on

venography or outflow obstruction on plethysmography could confirm the presence of a

previous DVT[40].

It is important but difficult to distinguish PTS from a recurrent DVT. If the pain and swelling

increase rather than improve in 24h, this could be a clue of a recurrent DVT. But an objective

testing is problematic. In fact the venography that can be used to diagnosis DVT, can be

misinterpret because of the venous abnormalities that have been generated by the previous

DTV. The same can be said for the compression ultrasonography since persistent

abnormalities are still present after 1 year in the 50% of patient. The presence of a new non-

compressible venous segment or the increase in the diameter of the common or of the

popliteal vein indicate a recurrent DVT but not always there is an old imaging that can be

used for the comparison. In the end the d-dimer test can excludes a recurrent DVT if there is

no presence of d/dimer that is a degradation product of the fibrinolysis of a clot[38].

Three scales exist that can help the evaluation of PTS: the one developed by Villalta, the one

created by Ginsberg and colleagues and the CEAP (Clinical, Etiologic, Anatomic,

Pathophysiologic) classification.

The PTS scale developed by Villalta rates the severity, from 0 to 3, of five symptoms (pain,

cramps, heaviness, pruritus and paresthesia) and 6 signs (edema, skin induration,

hyperpigmentation, venous ectasia, redness, pain during calf compression). A total score of

31

5–14 indicates mild/moderate PTS, and a score of 15 or more or the presence of a venous

ulcer indicates severe PTS[41].

While Ginsberg diagnose PTS if the patient has pain and swelling for at least a month that

worsen at the end of the day or after prolonged sitting or standing, and improve after a night‘s

rest and leg elevation), and that occurs 6 months or more after the acute DVT[42].

CEAP is a classification system used for chronic venous insufficiency that could also be

used for PTS. It categorises patients into one of seven classes based on clinical signs, with

modifiers that reflect the underlying cause (congenital, primary, or secondary to DVT),

anatomic distribution (superficial, deep, or perforating veins), and pathophysiologic

condition (reflux, obstruction, or both). But symptoms are not considered[42].

Treatment

The best way to prevent PTS is by the prevention of DVT in high-risk patients with use of

thromboprophylaxis But thromboprophylaxis is still underutilized, particularly among non-

orthopedic surgery patients and medical in-patients. So if the patient has suffered of DTV it

is important to prescribe to him an adequate intensity and duration of anticoagulation in order

to minimize both the risk of recurrence and of bleeding.

It has become common clinical practice to prescribe knee-length compression stockings to

patients with DVT, particularly proximal DVT[38].

Lymphoedema

The lymphatic system is responsible for ensuring homeostasis of interstitial tissue fluid and

plays a vital role in the immune system. Any impairment to the flow of lymph, which is

composed mainly of interstitial fluid, will cause a lymphoedema.

Consequently, lymphoedema is the accumulation of interstitial fluid when the lymphatic

system is no more capable of sustaining its natural homeostasis.

As lymphoedema progresses in morbidity, lymphangions are obliterated, whilst tissue

swelling and fibrosis take place along with muscle atrophy and increased fatty tissue.

Lymphangions first enter a dilated stage, then a contracted stage and finally a fibrotic stage

where they lose their ability to contract[43].

32

Pathophysiology of lymphedema

Several anatomic problems can lead to lymphatic stasis, including lymphatic hypoplasia and

functional insufficiency or absence of lymphatic valves[44]. Some patients may have an

impairment in the intrinsic contractility of the lymphangion (the segmentally contracting,

functional vascular unit of the lymphatic circulation[44].

Secondary lymphedema, which is much more common than the primary form, can develop

as a consequence of any surgical, traumatic, inflammatory, or neoplastic disruption or

obstruction of lymphatic pathways.

Once established, lymphatic stasis fosters the accumulation of protein and cellular

metabolites, such as macromolecular protein and hyaluronans, within the extracellular

space[45].

This is followed by an increase in the tissue colloid osmotic pressure, which leads to water

accumulation and increased interstitial hydraulic pressure.

Chronic lymph stasis often produces an increase in the number of fibroblasts, adipocytes,

and keratinocytes in the edematous tissues determining often there is an increase in collagen

deposition, with adipose and connective tissue overgrowth in the edematous skin and

subcutaneous tissues. Mononuclear cells (chiefly macrophages) often demarcate the chronic

inflammatory response. Histopathologic findings in chronic lymphedema include thickening

of the basement membrane of lymphatic vessels, fragmentation and degeneration of elastic

fibers, increased numbers of fibroblasts and inflammatory cells, and increased amounts of

ground substance and pathological collagen fibers. Ultimately,

these processes lead to progressive subcutaneous fibrosis[46].

Lymphedema classification

The simplest classification of lymphedema relies upon a differentiation between primary and

secondary causes[47]. Primary lymphedemas are generally classified according to the age at

which the edema first appeared. Congenital lymphedema is apparent at birth or becomes

recognized within the first 2 years of life. Lymphedema praecox is most commonly detected

at the time of puberty, but may appear as late as the third decade of life. Lymphedema tarda

typically appears after age 35 years. Recent advances within the genetic investigation of

33

hereditary suggests that the disease can be ascribed to a mutation that inactivates the

VEGFR3 tyrosine kinase signalling mechanism that is felt to be specific to lymphatic

vessels[48].

Lymphedema praecox, the most common form of primary lymphedema, is responsible for

as many as 94% of the cases in large reported series. The estimated 10:1 ratio of females to

males suggests that estrogenic hormones are involved[49]. The edema is usually unilateral

and is limited to the foot and calf in the majority of patients[49].

Lymphedema tarda is relatively uncommon, and accounts for fewer than 10% of cases of

primary lymphedema.

Secondary lymphedema develops after disruption or obstruction of lymphatic pathways by

other disease processes, or as a consequence of surgery or radiotherapy and is much more

common than the primary form. Lymphedema of the leg may occur after pelvic or genital

cancer surgeries, particularly when there has been inguinal and pelvic lymph node dissection

or irradiation.

Diagnosis of lymphedema

In most patients with advanced lymphedema, the characteristic clinical presentation and

physical findings establish the diagnosis with near certainty[50]. However, early in the

natural history, or with presentations of mild or intermittent swelling, it may be more

difficult to distinguish lymphedema from other edematous states. Several physical features

distinguish lymphedema from other causes of chronic edema of the extremities. Among

these are the classic changes of cutaneous and subcutaneous fibrosis (peau d‘orange), and

the Stemmer sign, which is an inability to tent the skin on the dorsum of the digits of the

feet. Although the Stemmer sign has not been validated, it was initially reported to

discriminate patients with lymphedema[48]. Lymphedema in the legs often produces

preferential swelling of the dorsum of the foot, as well as the characteristic blunt, ‘squared-

off ‘ appearance of the digits in the involved extremity.

When the physical examination does not conclusively support the diagnosis of lymphedema,

additional evidence may be necessary to confirm impaired lymphatic function. Available

tests include isotopic lymphoscintigraphy, indirect and direct lymphography, lymphatic

capillaroscopy, magnetic resonance imaging (MRI), axial tomography, and ultrasonography.

34

Direct lymphography is generally limited to the evaluation of candidates for lymphatic

surgery. Isotopic lymphoscintigraphy is the most commonly used test and is generally

considered to be the gold standard for the diagnosis of lymphedema. A radiolabelled

macromolecular tracer (eg, sulfur colloid) is administered into the subdermal, interdigital

region of the affected limb. The lymphatic transport of the radiolabelled macromolecule can

be monitored in a semiquantitative fashion with a gamma camera. Major lymphatic trunks

and lymph nodes can be visualized. Typical abnormalities in lymphedema include absent or

delayed transport of tracer, absent or delayed visualization of lymph nodes, crossover filling

with retrograde backflow, and dermal backflow. Magnetic resonance imaging and

computerized tomographic(CT) imaging allow the objective documentation of structural

changes attributable to lymphedema[51].

The characteristic absence of edema within the muscular compartment helps to distinguish

lymphedema radiographically from other forms of edema. In addition, the honeycomb

distribution of edema within the epifascial plane, along with thickening of the skin, is

characteristic of lymphedema. The anatomic delineation of lymphatic and nodal architecture

derived from MR imaging can complement the functional assessment provided by

lymphoscintigraphy[52].

Less commonly employed techniques include tissue tonometry and bioelectric impedance

analysis . These techniques allow detection of small changes in tissue turgor and may have

utility in the detection of subclinical states of lymphatic impairment, as well as in the serial

assessment of the response to treatment.

Therapy

Lymphedema is a chronic condition that requires lifelong attention. Meticulous attention to

control of edema may reduce the likelihood of disease progression and limit the incidence

of soft-tissue infections[50]. Aggressive implementation of decongestive lymphatic therapy

is the mainstay of most therapeutic recommendations. This complex form of physical

therapy integrates meticulous skin care, massage, exercise, and use of compressive elastic

garments. Decongestive lymphatic therapy can acutely reduce limb volume as well as

provide long-term benefits owing to the acceleration of lymph transport in the edematous

limb and the dispersal of accumulated protein[53] .

35

During the acute approach to volume reduction, nonelastic, compressive wrappings should

be applied after each session of manual lymphatic drainage and worn during exercise to

prevent accumulation of fluid and to promote lymph flow during exertion.

.

36

Use of compression therapy in the Sports world

Muscle Strength

Before considering the effect of compression on a performance it is important to review

some mechanical concept that regard the muscle. This review will help understand why it is

so difficult to prove if compression has or not a positive effect on a performance.

The number of skeletal muscle fibers in a given muscle is genetically determined and does

not change. Muscle strength is directly related to the amount of myofibrils and sarcomeres

within each fiber and on the number of fibers. So the maximum tensile force produced by an

individual muscle is a function of its area. However, the overall size of a muscle may be a

poor indication of the number of fibers contained in that muscle.

The relationship between muscle size and force of contraction is complicated by the muscle’s

architecture. The anatomical cross-sectional area of the muscle is the cross-sectional area at

the muscle’s widest point and perpendicular to the length of the whole muscle. In a parallel

fiber muscle this cross-sectional area cuts across most of the fibers of the muscle however,

in a pennate muscle the anatomical cross-sectional area cuts across only a portion of the

fibers composing the muscle. Thus the anatomical cross-sectional area underestimates the

number of fibers contained in a pennate muscle and hence its force production capabilities.

The standard measure used to approximate the number of fibers of a whole muscle is its

physiological cross-sectional area (PCSA)Fig. 14Error! Reference source not found.. The P

CSA is the area of a slice that passes through all the fibers of a muscle and in a parallel fiber

muscle the PCSA is approximately equal to the anatomical cross-sectional area. However,

in a pennate muscle the PCSA is considerably larger than its anatomical cross-sectional area.

Although their anatomical cross-sectional areas are very similar, the pennate muscle has a

much larger PCSA, thus if all the factors are equal, the pennate muscle can generate an

higher contraction force than the muscle with parallel fibers. The angle at which the fibers

insert into the tendon also influences the total force that is applied to the limb by a pennate

muscle. This angle is known as the angle of pennation.The tensile force generated by the

whole muscle is the vector sum of the force components that are applied parallel to the

muscle’s tendon, therefore as the angle of pennation increases, the tensile component of the

contraction force decreases. However, the larger the pennation angle is, the larger the PCSA

37

is. Resistance training increases the fibers’ angle of pennation and the muscle’s PCSA. Also

factors, such as hormones and stress (and artificial anabolic steroids), acting on the muscle

can increase the production of sarcomeres and myofibrils within the muscle fibers, a change

called hypertrophy, which results in the increased mass and bulk in a skeletal muscle.

Likewise, decreased use of a skeletal muscle results in atrophy, where the number of

sarcomeres and myofibrils disappear, but not the number of muscle fibers.

Muscle architecture demonstrates how muscles exhibit specializations that enhance one

performance characteristic or another. Long fibers in a muscle promote the excursion

producing capacity of the muscle, however, spatial constraints of the human body prevent a

muscle with long fibers from having a very large cross-sectional area and hence a large force-

production capacity. On the other hand, muscles with a large PCSA can be fit into small

areas by arranging the fibers in a pennate pattern. However, the short fibers limit the

excursion capacity of the muscle. Thus fiber arrangement suggests that pennate muscles are

specialized for force production but have limited ability to produce a large excursion.

Conversely, a muscle with parallel fibers has an improved ability to produce an excursion

but produces a smaller contractile force than a pennate muscle of the same overall size. Thus

the intrinsic structural characteristics of a muscle help define the performance of the muscle

by affecting both the force of contraction and the amount of the resulting joint excursion.

Fig. 14 Physiological-cross-sectional area (green) and cross-sectional area (blue)

38

Relationship between Force Production and Instantaneous Muscle Length

Since the strength of muscle contraction is a function of the number of cross-links made

between the actin and myosinchains within the sarcomeres, alterations in the proximity of

the actin and myosin chains also influence the force of contraction. The maximum number

of cross-links between he actin and myosin myofilaments and hence the maximum

contractile force in the sarcomere occurs when the full length of the actin strands at each end

of the sarcomere are in contact with the myosin molecule. This length is operationally

defined as the resting length of the muscle. The sarcomere can shorten slightly from this

point, maintaining the maximum cross-linking, however, increased shortening reduces the

number of available sites for cross-bridge formation, and the force of contraction decreases.

Similarly, when the sarcomere is stretched from its resting length, contact between the actin

and myosin myofilaments decreases consequently the force of contraction decreases Error! R

eference source not found.(Fig. 15)

However a muscle’s response to stretch is affected also by the elastic properties of the

noncontractile components of the muscle, including the epimysium, perimysium,

endomysium, and tendons. Some studies, performed on whole muscle, consistently

demonstrate that as a muscle is stretched in the absence of a contraction, there is some

length at which the muscle begins to resist the stretch Fig. 16. As the stretch of the muscle

increases, the muscle exerts a larger pull against the stretch. This pull is attributed to the

Fig. 15 The length–tension curve of a sarcomere.

39

elastic recoil of the passive structures within the muscle, such as the investing connective

tissue. These components are known as the parallel elastic components. The tendons at either

end of the muscle also provide a force against the stretch in fact they can be described as the

series elastic components (Fig. 16)

The combined effects of muscle contraction and stretch of the elastic components are

represented mechanically by a contractile element in series and in parallel with the elastic

components Fig. 17

The response of both the contractile and elastic components together is examined by

measuring the resistance to increasing stretch while simultaneously stimulating the muscle

to induce a contraction. Such experiments reveal that when the muscle is very short, allowing

no passive recoil force, stimulation produces a small contractile force. As the stretch

increases and stimulations continue, the tension in the muscle increases. In the middle region

Fig. 17 The length–tension curve of a whole muscle.

Fig. 16 Muscle model

40

of stretch, the force plateaus or even decreases, even with stimulation. This plateau occurs

at approximately the resting length of the muscle. With additional stretch, the tension in the

whole muscle begins to increase again and continues to increase with further stretch. By

subtracting the results of the passive test from the results of the combined test, the

contribution of the active, or contractile, component to muscle tension is determined. The

active contribution to muscle tension in the whole muscle is similar to the length–tension

relationship seen in the individual sarcomeres. These results demonstrate that while the

contractile contribution to muscle tension peaks in the mid region of stretch, the passive

components of the muscle make an increasing contribution to force after the midrange of

stretch. Thus the overall tension of the muscle is greatest when the muscle is stretched

maximally.

It is important to recognize that the experiments described above are performed on

disarticulated muscles then the extremes of shortening and lengthening tested are non-

physiological.

An intact human muscle functions somewhere in the central portion of the length-tension

curve, although the precise shape of the length-tension curve varies across muscles. The

response to stretch depends on the architecture of the individual muscle as well as the ratio

of contractile tissue to connective tissue in the muscle. In addition, the exact amount of

stretch and shortening sustained by a muscle depends on the individual muscle and the joint.

Muscles that cross two or more joints undergo more shortening and lengthening than muscles

that span only one joint.

The classic length-tension relationship described so far has been studied by altering the

length of a muscle passively and then assessing the strength of contraction at the new length.

More recent studies have investigated the effects of length changes on isometric strength

while the muscle is actively contracting. These studies consistently demonstrate that the

traditional length-tension relationships are amplified if the length changes occur during

contraction. Specifically, if a contracting muscle is lengthened and then held at its lengthened

position, the force generated at the lengthened position is greater than the strength measured

at that same position with no preceding length change. Similarly, shortening a muscle as it

contracts produces more strength reduction than placing the relaxed muscle at the shortened

position and then measuring its strength[54].

41

Relationship between a muscle’s moment arm and its force production.

The ability of a muscle to rotate a joint depends upon its force of contraction and on its

moment arm, the perpendicular distance from the muscle force to the point of rotation. The

muscle’s moment arm is critical in determining the moment generated by the muscle

contraction. The larger the moment arm, the larger the moment created by the muscle

contraction. The moment arm is determined by the sine of the angle of application and the

distance between the muscle’s attachment and the joint’s axis of rotation.

A muscle with a large moment arm produces a larger moment than a muscle with a shorter

moment arm if both muscles generate equal contractile forces.

The moment arms of some muscles such as the hamstrings change several centimeters

through the full ROM of the joint, while others such as the flexor digitorum profundus

demonstrate very little change. Therefore, a muscle’s ability to produce a moment varies

with the joint position. For example, elbow flexion lengthens the elbow extensor muscles

and shortens the elbow flexors. The angle of application of the biceps brachii is almost zero

with the elbow extended and increases to over 90°, with the elbow flexed. In this case, the

muscle’s moment arm is at a minimum when the muscle’s length is at a maximum. In

contrast, the angle of application is greatest when the length is shortest. The optimal angle

of application, 90°, occurs when the elbow is flexed to approximately 100°. Thus the

muscle’s ability to generate a large contractile force as a result of stretch is maximum in the

very position in which the muscle’s ability to produce a moment is smallest by virtue of its

moment arm. Consequently, the biceps produces peak moments in the midrange of elbow

flexion where neither the muscle’s length nor angle of application is optimal. The relative

contribution of moment arm and muscle length to a muscle’s ability to produce a moment

varies among the muscles of the body and depends on the individual characteristics of each

muscle and joint.

Effects of the magnitude of the contraction velocity on force production in muscle

Until know only in isometric contractions, contractions with no visible change in muscle

length, have been considered. However in nonisometric contractions, the speed of

contraction influence the muscle’s output.

42

A concentric contraction, also known as a shortening contraction, is defined as a contraction

in which there is visible shortening of the muscle. Thus a concentric contraction has a

positive contraction velocity. While an eccentric contraction, also known as a stretching

contraction, is defined as a contraction in which there is visible lengthening of the muscle.

Thus an eccentric contraction has a negative contraction velocity.

The relationship between contractile force and speed of contraction in isometric and

shortening contractions has been studied for most of the 20th century and is well understood.

A plot of a muscle’s force of contraction over contractile velocity for isometric and

concentric contractions reveals that contractile force is maximum when contraction velocity

is zero and decreases as contraction velocity increases. Thus an isometric contraction

produces more force than a concentric contraction of similar magnitude. Similarly, a rapid

shortening contraction produces less force than a slow shortening contraction (Fig. 18)

Eccentric contractile strength is less understood than isometric and concentric strength, at

least in part because it is difficult to study lengthening contractions over a large spectrum of

speeds in intact muscles. Eccentric contractions produce more force than either isometric or

concentric contractions

Fig. 18 The relationship between contractile force and the velocity of contraction in isometric and

concentric contractions.

43

Relationship between force production and level of recruitment of motor units within the

muscle

The force of contraction of a whole muscle is modulated by the frequency of stimulation by

the motor nerve and by the number of motor units active. A motor unit consists of the

individual muscle fibers innervated by a single motor nerve cell. A single stimulus of low

intensity from the motor nerve produces depolarization of the muscle and a twitch

contraction of one or more motor units. As the frequency of the stimulus increases, the twitch

is repeated. As in the single fiber, if the stimulus is repeated before the muscle

relaxes, the twitches begin to fuse, and a sustained, or tetanic, contraction is elicited. As the

intensity of the stimulus increases, more motor units are stimulated, and the force of

contraction increases.

In an isometric contraction, there is a strong relationship between the electrical activity of

the muscle, its EMG, and the force of contraction. As isometric force increases, the EMG

also increases. The EMG reflects the number of active fibers as well as their firing frequency

however, the relationship of the muscle’s EMG and its force of contraction is more

complicated when the muscle is free to change length and the joint is free to move.

The EMG merely serves to indicate the electrical activity in a muscle. Thus a larger muscle

produces a larger EMG pattern during a maximal contraction than a smaller muscle

performing a maximal contraction, since there are more motor units firing in the larger

muscle. However, within the same muscle, a maximal eccentric contraction elicits an EMG

pattern similar to that produced during a maximal concentric contraction, even though the

force of contraction is greater in the eccentric contraction.

There are also several technical factors that influence the magnitude of EMG produced

during muscle contraction. These include the type and size of the recording electrodes and

the signal-processing procedures. Thus the clinical interpretation of EMG and comparisons

across studies must proceed with caution.

Relationship between force production and fiber type

The last characteristic of muscle influencing the force of contraction is the type of fibers

composing an individual muscle. Different types of muscle fibers possess different

44

contractile properties. Therefore, their distribution within a muscle influences the contractile

performance of a whole muscle.

There are a variety of ways to categorize voluntary muscle fibers based on such

characteristics as their metabolic processes, their histochemical composition, and their

phenotype. Oxidative fibers rely on aerobic respiration to fuel muscle contractions, they are

also called slow-twitch (type I) fibers, and they are characterized by of muscles with long

contraction duration and they are associated with endurance. Slow-twitch fibers are used to

maintain posture. A large concentration of myoglobin provide them the steady supply of

oxygen they need to perform oxidative phosphorylation, and this is the reason of their red

colour. This process is slower than glycolysis, but much more efficient, which is why slow-

twitch muscles do not tire easily thus slow-twitch fibers contain less sarcoplasmic reticulum,

facilitating a slower release of calcium, then muscle contraction happens at slower rates.

Glycolytic fibers rely on glycolysis to fuel muscle contractions and are also known as fast-

twitch (type IIb) fibers, which are characterized by fast muscle contractions of short duration.

Fast-twitch fibers are constituents of white muscles and have less myoglobin due to their

primary reliance on glycolysis to fuel muscle contractions. Although glycolysis is very

quick, it is also produces lactic acid as a by-product, which leads to fatigue, in fact fast-

twitch muscles tire out quickly. Type IIa fibers relies both on glycolysis and aerobic

respiration so their contraction force, their contraction velocity and their fatigability Type I

fibers are innervated by motor nerve with small-diameter axons and thus they are recruited

first in a muscle contraction. Type IIb fibers are innervated by large axons and are recruited

after type I and type IIa fibers. The velocity of contraction also differs among fiber types.

Consequently, the force–velocity relationship also varies among the fiber types. Data from

human muscles suggest that type IIb fibers exert larger forces at higher velocities, while type

I fibers have slower maximal contractile velocities as well as lower peak forces [14]. Thus

muscles with a preponderance of type II fibers have a higher rate of force production and a

higher contractile force than muscles with more type I fibers.

Postural muscles typically are composed largely of type I fibers, while muscles whose

functions demand large bursts of force consist of more type II fibers. However, as already

noted, human muscles contain a mixture of fiber types. Therefore, the contractile properties

of whole muscles reflect the combined effects of the fibers types. Consequently, the other

factors influencing force production such as muscle size and mechanical advantage appear

45

to have a larger influence on contractile force. However, muscle fibers demonstrate different

responses to changes in activity and thus play a significant role in muscle adaptation. The

adaptability of muscle is discussed briefly below.

Effect of compression on different exercise performances.

The purpose of the garment is to mitigate exercise-induced discomfort or aid aspects of

current or subsequent exercise performance[55]. Potential benefits may be mediated via

physical, physiological or psychological effects, although underlying mechanisms are

typically not well elucidated[8]. Despite widespread acceptance of CGs by competitive and

recreational athletes, convincing scientific evidence supporting ergogenic effects remains

somewhat elusive. The literature is fragmented due to great heterogeneity among studies,

with variability including the type, duration and intensity of exercise, the measures used as

indicators of exercise or recovery performance/physiological function, training status of

participants, when the garments were worn and for what duration, the type of garment/

body area covered and the applied pressures[56]. Little is known about the adequacy of

current sizing systems, pressure variability within and among individuals, maintenance of

applied pressures during one wear session or over the life of the garment and, perhaps most

importantly, whether any of these actually influence potential compression-associated

benefits[57].

During exercise, relatively few ergogenic effects have been demonstrated when wearing

CGs. While CGs appear to aid aspects of jump performance in some situations, only limited

data are available to indicate positive effects on performance for other forms of exercise[1].

Effect of compression pants on vertical jump performance, Wannop and all[58] results

John W. Wannop and all[58] asked ten male athletes to perform countermovement vertical

jumps in eight concept apparel conditions and one control condition (loose fitting shorts).

Four apparel condition (Fig. 19) consisted of alterations in the amount of upper leg

compression while minimally altering the hip joint stiffness while the other four apparel

condition altered the hip joint stiffness while minimally altering the compression of the soft

tissues.

46

Fig. 19 Apparel condition used during the experiment.

The best performance was reached with a differ value of compression and joint stiffness for

each athlete. For what concern the effect of a change of compression when the athletes were

grouped based on the compression apparel in which they had their best performance

significant jump and reach height increases were obtained (308.7 cm compared with 306.8

cm in the control, p =0.005, 95% CIDiff = 0.58–3.27). And a significant increase in their

peak hip flexion angle was observed (88.78 compared with 79.78 for the control, p = 0.004,

95% CIDiff = 3.20–14.80) while no differences were seen in the peak hip extension angular

velocity or regarding the angle or angular velocity of the ankle or knee joint.

For what concern the effect of a change of stiffness still hen the athletes were grouped based

on the stiffness apparel with which they had their best performance, a significant increase in

their vertical jump and reach height was achieved (307.6 cm compared with 306.5 cm, p =

0.005, CIDiff = 0.33–1.96). In their best stiffness condition, there were trends toward a

reduction in the peak hip flexion angle (p = 0.022, CIDiff = 222.12 to 20.33) and a reduction

in the peak hip extension angular velocity (p = 0.018, CIDiff =295.47 to 25.12). The authors

also find out that although most athletes (9 of 10) had their best performance in one of the

compression apparel conditions, most athletes also had their worst performance in

compression apparel as well (6 of 10). This may indicates not only that an optimal amount

of compression can improve the performance, but also that a suboptimal compression can

impair the last one.

47

The mechanisms by which compression acts to aid performance remain unknown but when

the athletes were performing in their optimal compression apparel the peak hip joint flexion

angle was significantly increased, whereas in their worst compression condition, it was

unchanged from the control. Maybe the increase in the peak hip joint flexion angle may have

shifted the hip extensors of the athletes to a more advantageous region along the force-length

curve, thereby allowing them to produce a greater amount of force during the initiation of

the concentric phase of the push-off.

While comparing the best and worst stiffness conditions, the first one produced an increase

in the jump height, a reduction of the peak hip flexion angle, of the peak hip joint extension

velocity, and an increase in the passive joint moment. Conversely, the worst stiffness

condition showed no change in jump height, a reduction of the peak hip flexion angle, an

increase in the passive hip joint moment, and no change in hip extension angular velocity.

The only measured variable that was different was the angular velocity of the hip joint. Then

probably the best stiffness condition optimized or controlled the angular velocity of

the hip joint to increase the force production/power output of the hip joint extensors by

shifting the athlete to a region on the force-velocity curve where greater power could be

produced.

During recovery, CGs have had mixed effects on recovery kinetics or subsequent

performance. Various power and torque measurements have, on occasions, benefitted from

the use of CGs in recovery, but subsequent sprint and agility performance appears no better.

Results are inconsistent for postexercise swelling of limb segments and for clearance of

myocellular proteins and metabolites, while effects on plasma concentrations are difficult to

interpret. However, there is some evidence for local blood flow augmentation with

compression. Ratings of post-exercise muscle soreness are commonly more favourable when

CGs are worn, although this is not always so. In general, the effects of CGs on indicators of

recovery performance remain inconclusive. More work is needed to form a consensus or

mechanistically insightful interpretation of any demonstrated effects of CGs during exercise,

recovery or perhaps most importantly fitness development. Limited practical

recommendations for athletes can be drawn from the literature at present, although this

review may help focus future research towards a position where such recommendations can

be made.

48

Characteristic of medical stockings

Compression stockings types of elastomeric fibers and yarns.

The most important characteristic of the compression garment is its elastic mechanical

properties. To achieve this, elastic fibers and yarns that exhibit good extensibility and elastic

recovery have been used. Elastomeric or spandex fibers and their continues filament yarns

are chosen for this purpose. Some examples are: polyurethane fibers, polyester ether fibers,

polyester fibers, like polybutylene terephthalate (PBT) fiber and polytrimethylene

terephthalate (PTT) fiber, olefin based elastomeric fibers, and bio-component fiber[59].

According to the extension, they can be classified into low elastic fiber if their elongation

range from 20% to 150%, medium elastic fiber with elongation in the range of 150% to

390%, and the high elastic fiber with elongation up to 400% to 800%. Commercial synthetic

elastic fibers used in compression garments normally have an extension break over 200%

and exhibit rapid recovery when tension is released.

Lycra™ is the most popular commercial elastomeric fiber[59]. It is a synthetic linear

macromolecule with a long chain consisting of at least 85% of segmented polyurethane along

with the alternating hard and soft segments linked by urethane bonds[60]. The soft chain

segments provide elasticity to fiber while the hard segments supply a molecular interaction

force to fiber and guarantee the strength and stability of fiber[61]. More than 90% of the

spandex fibers are produced with the method of solution dry spinning since this method

supplies better heat resistance and tenacity than other methods like melt extrusion, reaction

spinning, and solution wet spinning.

Also other fibers such as nylon 6 or nylon 66 filaments or cotton are employed to make

elastic yarns. Covered yarn, core-spun yarn, and textured (or air-covered) yarn are the

common elastic yarns used. In a covered yarn, the elastomeric core yarn is wrapped by a

covering filament yarn with Z or S twist. There are on the market also double covered yarn

(Fig. 21), in this case the second wrapping is follow the opposite direction with respect to

the first one in order to achieve torque balance and stability. While a core-spun yarn (Fig.

20) is achieved using a ring spinning machine where short staple fibers like cotton are around

an elastomeric core yarn.

49

The textured yarn consists of elastomeric yarn and false-twisted covering yarn. It is made

by a combined process of false twist texturing and air-jet mingling. This application of this

method is schematized in Fig. 22

Among the three kinds of yarns, the covered and core-spun elastomeric yarns are

recommended for high extension applications while textured yarns are best to use for low to

medium stretch requirements[60].

Characteristics of Elastomeric Yarns

The mechanical properties that most effect the performance of a compressive garment are

the tensile properties and elastic recovery properties of the yarns. In addition, elastomeric

fibers should also show an high stability under dyeing, finishing conditions and under normal

Fig. 21 Double covered yarn Fig. 20 Core-spun yarn

Fig. 22 Texturing process

50

washing conditions[61]. There are usually two types for the elastomeric fibers inserted in

the fabrics. One type is a bare threads inserted together or interlace with other yarns and the

second kind is covered or core-spun elastomeric yarns. Their tensile properties are

influenced by material composition, processing, and process parameters. An analysis based

on the superposition of the two material explain the elongation performance. Fig. 23 shows

the stress and strain relationship of an elastomeric yarn wrapped with nylon (continuous

purple curve)[59]. From the beginning to ε0, the strain is mainly acquired from the

elastomeric yarn with high elastic modulus, as shown by the red dashed curve. While the

contribution of the polyamide yarn with high plastic properties, the blue dotted curve, occurs

progressively and between a given range of elongation ε3 and ε5. Therefore the properties of

the elastomeric yarn become dominant at an extreme degree of elongation.

The mechanical properties of elastomeric core-spun yarns were significantly affected by

spandex and the outer yarns. Fig. 24 shows the force-strain curve of the 100% cotton yarn

(purple curve), the spandex (blue curve), and of the elastomeric core-spun yarn (red

curve)[62] . It was found that the elastomeric part of core-spun yarns, the spandex in this

case, did notcontribute much to yarn strength while the non-elastic part of core-spun vortex

yarns limited the stretch limit of core-spun yarns[59].

It is crucial that the pressure is the wanted one and that it stays stable. For sportswear or

body shaping garments, the low or medium elastomeric fibers could meet the elastic

requirements while, for a medical purpose, high elastomeric fibers should be used to obtain

Fig. 23 Stress and strain relation

51

the desired pressure. Within the usage range the tensile strain is expected to increase slowly

when the tensile stress rose. Therefore, the pressure would be stabilized in a relative range.

This also means there is a wide range of applications for the compression garments to satisfy

different sizes and movements[59].

Knitting Construction and Fabrication

Elastic knitted fabrics are the most used in order to create a compression garment. There are

two categories of the knitting technology, the weft and the warp kitting. For the weft one,

the flat knitting machine and circular knitting machine consists of a single jersey, interlock,

Tab. 3Knitting method

52

a double jersey, and rib machines, which are always used.

The knitting method, the most used machine and their application are show in Tab. 3.

While Fig. 25 shows the typical knitting construction for elastic fabrics. The red line is elastic

yarn and yellow line is ground yarn.

Compression garments are usually knitted with at least two types of yarn including a ground

yarn to ensure thickness and stiffness and an inlay-yarn to generate compression. The

elastomeric inlay-yarn can be inlayed, floated, or plated into a knitted structure. Higher

levels of compression could be achieved by increasing thickness of the elastic core of the

inlay-yarn or by changing the knitting construction and elastic yarn insertion density[62].

Fabric Mechanical Properties

Extensibility and elastic recovery are the most important characteristics of a compression

garment, in fact they allow the fabric to exert continuous pressure on the human body.

However the actual compression is also influenced by the hysteresis of the fabric and its

dynamic elastic properties. Studies have been done to prove that elastomeric yarns and

knitting construction all influence the elasticity of the fabric. Cooper et all[63] tested the

stretch and recovery properties of different stretch fabrics with all-cotton, nylon, and

polyester/spandex core yarns and indicated that yarn type and inter fiber friction may play a

significant part in the stretch and recovery properties. Wang et all[64] studies also indicated

Fig. 25 Knitting construction of elastic fabrics.

53

that elastic recovery depends on the compression force provided, the time of application of

the force, and time period for which the fabric is allowed to recover. Hysteresis reflects the

stress relaxation of an elastic fabric when it has been subjected to repeated stretching and

recovery[59]. The hysteresis phenomenon was first discovered by Ng[65]. He found that

elastic fabrics had relaxed their stress significantly under stretching and the degree of stress

relaxation would increase with prolonged time under stretching. Studies also found that

fabrics containing elastomeric yarns had severe hysteresis problems under constant

deformation. And thus the stress relaxation will result in pressure degradation[66].

Stiffness is also affects the compression performance. It is defined as the change of

compression exerted by a garment when the body girth is increased or decreased. Stiffness

is related to the elasticity of the material and the construction of the fabric. Both the dynamic

and the static stiffness effect the compression performance. A research showed that there is

a positive correlation between the static and dynamic stiffness indices, but the dynamic

stiffness has a slightly higher value[59].

Most of the compression garments have to be worn about 23 hours per day, so the fabric it

is stretch at a given extension level for a long and continuous time before tension was

released[67]. Practical applications verify that slackening occurs in compression garments

when patients wear them over a prolonged period of time and pressure decay affects the

effectiveness of compression therapy.

Garment Design

Generally compression garments are produced in a regular cut-and-sew method. First, flat

knitted elastic fabrics are knitted to the correct size and then they are sew them together.

Most of sportswear with low compression are produced with this method[59].

So they are cheap and easy to product but the seams produce skin irritation and the garments

are easier to break.

While a one-piece constructions is commonly utilized in the high compression garments

design. Double needle bar warp machine, flat knit machine, and circular knit machine have

can knit whole seamless compression garments with minimal or no cutting and sewing

processes.

54

However not all compression garments are properly fit to achieve the optimal effects and an

excessive improper compression could make the subject wearing them feel uncomfortable

and even restrict blood supply and cause debilitation. Therefore, customized compression

garments are becoming more prevalent[68].

Design System

In order to design system a customized compression garment, three important steps should

always be made. The first step is to acquire an exact measurement of the human body. The

second stage is to investigate a mathematical model to determine the size and type of fabric

in order to exert a certain pressure. The last stage is to develop a computerized system that

use the mathematical model in order to design the garments and to verify the system.

Usually, a 3D digital scanning is used to get body information such as curvature of body

parts. Then when the fabric mechanical properties, the wanted pressure and the body

curvature are inserted in a computerized system a 3D model of the garment will be generated.

Then the 3D garment model is flattened into a two-dimensional (2D) pattern design to

construct the compression garment[68].

However this design tool does not take in consideration that different part of the body, such

as bone, muscle or fat, sustain the pressure differently. So these tool could still be improve.

Pressure Measurement

It is important to verify that the static and dynamic pressure that the garment apply are the

desired one. The could be measured using an in vitro or an in vivo method. The in vitro

pressure is calculated from the combination of the Laplace‘s Law and the fabric

properties[32]. While the measurement in vivo is always conducted with various interface

pressure devices.

55

In vitro measurement

Kowalski and all[32] used the Laplace law in order to find a relationship between the

circumference of the knitted fabric in the free state and the pressure and the circumference

of the body part.

The Laplace law is obtained imposing the equilibrium of the force and it can be written as:

𝑝 =2𝜋𝐹

𝐺1𝑠

Where:

P is the pressure,

G1 is the circumference of the body part

s is the bandwidth

Then if we consider the relationship between force and elongation in the compression

phase after the 5th cycle to be

𝐹 = 𝑎𝜀𝑏

Where the elongation 𝜀 is defined as

𝜀 =𝐺1 − 𝐺0𝐺0

and G0 is the circumference in the free state.

So in the end by substitution we obtain

𝐺0 =(2𝜋𝑎)

1𝑏

(𝑝𝐺1𝑠)1𝑏 + (2𝜋𝑎)

1𝑏

𝐺1

Fig. 26 Kowalski and all model

56

The same equation, if rearranged, can be use to compute the pressure as a function of the

radius of curvature R. So the value of pressure can be obtain also if the body shape is not

modelled ad a perfect circle.

This method is a basic and convenient tool to calculate the rough pressure, but the main

disadvantage is that it does not take the elastic modulus of the human body and body motion

into consideration. Therefore, the pressure calculated does not reflect the real condition.

Pressure Sensors

Initially electro pneumatic and fluid filled pressure transducers were used but they had a law

accuracy and showed a poor conformity to the body curvature.

By using strain gauge or force-sensing resistor with piezoelectric element the accuracy of

the device was improved but the sensors were too sensitive to pressure and showed a limited

sensitivity under 10 mmHg of pressure.

The capacitive pressure sensor showed the best characteristic. They display higher

sensitivity and flexibility, lower temperature dependency and also lower power consumption

than piezoresistive devices.

Static Pressure Measurement

Current devices for measuring garment static pressure that are principally used in the

medical field are the Kikuhime® pressure monitor, the SIGaT tester®, and the PicoPress®

pressure monitor. Despite they show an high sensitivity, they are flexible, small and exhibit

a good measurement range they are not well suited to dynamic pressure measurement due

to their limited portability, memory communication, and power capacity during sports

conditions[69].

Dynamic Pressure Measurement

During activity and exercise, the size of the body limb experiences great changes so the

pressure between the body and garments is dynamic. So in order to improve the device

efficacy the dynamic value of pressure should be known.

57

The PicoPress® transducer, which is a kind of pneumatic pressure transducer, could be used

as a dynamic pressure tracing in but the measured value is higher than the actual value

because the radius of curvature is affected by the presence of the sensor..

McLaren and all[69] developed a thin wearable wireless pressure monitoring device ()of six

18mm diameter low that could measure pressures in the range of 5-50 mmHg.

The authors tested the device response by applying a series of known for few second then

they confronted the value of pressure measured with the one obtained by a Kikuhime ™ and

PicoPress sensor. The performance of these sensors was deemed acceptable whilst not

necessarily as precise as the kikuhime ™and Picopress ™devices, particularly at pressures

below 5mmHg. After this test some sensors have been used to explore the performance of

the device during running. The average pressure and peak pressures detected with the

wearable dynamic pressure monitoring device (WDPMD) were generally consistent with the

garment pressure measured with a conventional static pressure instrument.

But even in this case there might me a disadvantage. Since the sensor are attached on the

body they have a potential to shift during strenuous exercise. The ideal but more challenging

way is inserted or integrated sensors and circuit in compression garments improve

practicability and acceptability.

Pressure Modeling

Direct measurement of the garment pressure on the human body has several limitations and

so should only be used during the first stages of the design of a compression garment. Then

numerical method should be used.

Fig. 27 McLaren and all[69] thin wearable wireless pressure monitoring device

58

There are mainly two tools, known as the finite element method and the volumetric

subdivision scheme that could be used.

An example of simulation using the finite element method is the one performed by Liu et

al[70]. They obtained the anatomy of the leg of an healthy female subject of 25 year using

the magnetic resonance imaging. For what concern the material properties they distinguished

between bone, considered as a rigid and incompressible material, and soft tissue, described

as homogeneous, isotropic and linear elastic. They model the sock as an orthotropic and

linear elastic material with different mechanical property in the longitudinal direction. They

use the automated surface to surface contact option of ABAQUS/CAE to simulate the

interface interactions between leg and stocking. The friction is ignored but a penalty contact

algorithm is employed to avoid the penetration of the nodes of the sock surface into the leg

surface nodes. In the end they applied a displacement to the upper part of the sock to simulate

the wearing, while they fixed the position of the bones.

They analysed three different values: the pressure on the surface, the displacement of

different cross-section and the stress distribution. Each of these quantities is evaluated at the

ankle, at the calf, at the knee and at the thigh region.

The highest surface pressure were found at the anterior side, the region with greater

curvatures and less underlying soft tissue layers. The thigh and the knee showed the biggest

variation of pressure between the anterior, posterior, medial and lateral region. The first

differences are probably due to high presence of soft tissue, while the variation near the knee

are probably due to its irregular cross-section. What is interesting about the cross-section

displacement is that its pick value were found during the wearing. In the end they showed

the changes in stress (Von Mises stress) in time and space. As expected the highest stress

were at the ankle with the stress decreasing from the centre to the peripheral of each cross-

section. The author idea is that the gradually increased inner stress can help venous

contraction by reducing their cross-sections, avoiding venous hypertension and reflux and

pumping the venous blood up toward the heart. In order to validate the model they asked the

same subject to wear the sock and they directly measure the pressure. The pressure along the

leg was higher at the ankle in the simulated case. The reasons could be many: the

simplification of the soft tissue mechanical properties, large non-linearity geometric

deformation of stocking hose, hard-controlled wearing states (standing, lying, walking, etc.),

and the limitation of the pressure sensor.

59

Another example of simulation using the finite element method is the one performed by Lin

et all[70]. They used the FE model and the response surface method (RSM) in order to find

the values of the socket mechanical and geometrical properties that generate the wanted

pressure. First they developed the FE model. It consist of two cylinder, one that represent

the leg modelled as rigid and the stocking described by using a first order Ogden strain

energy function. The sock is modelled as fully incompressible. Then the a displacement is

applied to the fabric tube. Then the model was validated through the comparison of the mean

contact pressure of the simulation and the one of an experimental test. They performed a

sensitivity analysis in order to find the factor that most effect the contact pressure distribution

and the range of interest of different variable such as the fabric mechanical properties, the

thickness, the strain, the density and the friction coefficient. The last two were found to be

the less effective. In the end the

RSM method was applied in order to find the values of the previous parameters that best

fitted the wanted pressure distribution using a second order polynomial model.

60

Method

The aim of this project is to create a finite element model (FEA) through which the effect of

various parameters on the change of pressure can be analysed.

FEA is a numerical method for solving partial differential equation as well as integral

equations generated from complex structure. It starts the analysis by dividing the interested

object into non-uniform regions (finite elements) that are connected to associated nodes. For

each typical element, there exit dependent variables at the nodes such as displacement. Then

an interpolation function is defined relative to relate the value variables in the element and

their values at the nodes. Next the governing equation that describe the physical problem is

added. In the end, after the application boundary condition, the governing algebraic

equations can be solved for the dependent variable at each node. The strain and stress can be

calculated based on the displacement of nodes associated with the element.

Abaqus is one of the most famous FEA commercial software in the world. It can provide

muti-discipline solution across a number of areas such as Aerospace, Architecture,

Automotive, Consumer goods, Energy, Life sciences, et al. It can provide the solutions about

stress and strain, natural frequencies and mode shape, forced response, fatigue and lifetime

estimation, plastically and nonlinear material, et al.

Generally the model is built through the software interface, but since between the editable

parameters there is also the parts geometry a Matlab code has been created so that the

geometry of the object could be easily modified just by the change of the geometric

parameter, for example the number of struct of the ring, the radius of the leg, the one of the

sock, without the need of drawing again each part every time we want to change the model

geometry. Thus in the first part of the code there is the list of the editable parameters, in the

second the matrixes that contains the coordinates of the nodes of the different part of the

model or the label of the nodes that constitute the set will that will be created. In the last part

input file of Abaqus is written.

Part module

The first step of any Abaqus model is the creation of the part that describe the physical

problem. The coordinate of all the nodes of each part have been listed in order to build each

object. In order to assign the material property and add some geometrical feature (for

61

example the beam’s profile or the membrane thickness) a section must be created. In the part

module also the mesh has been created by the construction of the connectivity matrix. In this

matrix all the nodes that compose an element has been listed, the order through which the

node label has been written will be responsible of the element shape. In the next section all

the part will be listed and described.

Part 1: The ring

The ring is composed by an even number of struct element that cross each other in their

middle. First each beam has beam has bean than in a following section connectors will be

built in order to constrain the relative motion of the upper, lower and central node of each

struct. In order to compute the coordinate of each node the spiral equation has been used.

The final geometry can be seen in Fig. 28.

Fig. 28 Struct geometry.

For what concern its mechanical property the struct has been described as a linear elastic

material. For the simulation the mechanical properties of the Kevlar49 have been chosen but

all the geometrical properties and both the Young modulus and the Poisson ration could be

modified.

62

In Fig. 29 the node labelling can be seen while in it is shown the first lines of the ring

connectivity matrix. The thirteen element has been highlighted to show the change in the

pattern.

Fig. 29 Ring label

Fig. 30 Ring connectivity matrix

Part 2: Sock

The sock is composed by membrane element. The sock has been described as a cylinder and

its geometry can be seen in be changed easily.

63

.

For what concern its mechanical property the sock could be described as a linear elastic

material or as an orthotropic material subjected to plane strees. For the simulation the

mechanical properties are the one computed by the results of a tensile text performed in the

axial and circumferential direction. Even in this case all the geometrical and mechanical

properties could be changed easily.

Fig. 31 Sock geometry.

64

In Fig. 32 the node labelling can be seen while in Fig. 33 is shown the first lines of the sock

connectivity matrix. The first element of the part has been highlighted.

Part 3: Expansion cylinder

In order to simulate the prestress of the sock the initial radius of the sock is lower than the

one of the sock so first the sock must be expand until it reaches the radius of the leg. It is

like simulating the stocking wearing. But the expansion will be applied to this infinitely rigid

surface and not directly to the sock. This surface then is a cylinder higher but with a smaller

Fig. 32 Sock labelling

Fig. 33 Sock connectivity matrix

65

radius than the one of the sock. Its geometry can be seen in Fig. 34.The labelling and the

connectivity matrix have been built following the same method used for the sock.

Fig. 34 Surface expansion geometry

Part 4: Leg

The leg is composed by solid element. The leg has been represented as a cylinder with a

cylindrical hole. It has been built determining the Nr_leg-1 centre and radius of the

circumferences that passes through the points that divides equally both the segment between

the leg cylinder circumference and the tibia cylinder circumference. The leg geometry can

be seen in

Fig. 35. The mash is equal to the one that Abaqus would have created and can be been in

Fig. 36

66

The first lines of the connectivity matrix of the leg are shown in Fig. 37

Fig. 35 Leg geometry

Fig. 36 Leg Labelling

67

Fig. 37 Leg connectivity matrix

Part 5: Line inf.

Once the sock is expanded it will connect to line. The lower nodes of the lines will be moved

to simulate the foot movement transmitting the movement to the sock. Two different part

has been creates because the lines connected to the upper part of the ring can not sustain

compression while the one connected to the lower part of the ring can.

The lines are composed by beam element. Once the position of the lowest nodes is chosen

considering the subject foot shape the lines are the spirals that connect the lowest foot nodes

of the foot and the chosen nodes of the struct’s ring. The coordinates of nodes of the struct’s

ring are the one that the ring riches after the expansion, when it is in contact with the leg.

These coordinates have been computed considering that the central nodes of the ring

maintain their axial coordinate and considering just the change of radius of the ring. This

mean that the struct are not lengthened, what is responsible for the change of radius is only

the rotation between the structs.

Three different lines geometry have been represented.

In the first one the lines are straight (Fig. 38), in the second case, that from now on will be

called the simple case, the foot point of the anterior part are connected to the nearest posterior

part of the ring, the same regard the foot posterior point (Fig. 39) In the third case he, the

68

foot point of the right anterior part are connected to the left posterior part of the ring, the

same regard the foot posterior point (Fig. 40).

Fig. 39 Simple case, inferior lines

69

Fig. 40 Cross case, inferior lines

Part 5: Line sup.

Also the lines connected to the upper part of the ring are composed by beam element.

Three different lines geometry have been represented.

In the first one the lines are straight (Fig. 41), in the second case, that from now on will be

called the simple case, the foot point of the anterior part are connected to the nearest posterior

part of the ring, the same regard the foot posterior point (Fig. 43).

In the third case he, the foot point of the right anterior part are connected to the left posterior

part of the ring, the same regard the foot posterior point (Fig. 42).

Fig. 41 Straight case, superior lines

70

Fig. 43 Simple case, superior lines

Assembly module

In the assembly module, all the part become an hole. In this part also the connector are listed.

The connectors introduce a relative motion constraint between two elements. The first

connector are between two structs, in this case the connector are called ‘hinge’, then all the

motion are constrained except for the rotation in the radial direction. The second type of

connectors are between the central nodes of the ring and the sock, in this case the connector

are called ‘Join, Cardan’, then all the motion are constrained except for the rotation.

71

The third type of connectors are between the superior and inferior nodes of the ring and the

lines. A behaviour has been added so that during the expansion there is no constraint between

struct and lines but as the ring radius reaches the one of the leg the constrained is applied.

As long as the distance in the radial direction is between 51.6549 and 0.1the connector are a

‘Cartesian, Cardan’ type. Their distance can not be higher than, in fact their initial distance

is 17.5070 but when the distance become lower than 0.1 all the relative movement except

for the radial one are blocked. This behaviour ca be obtain as shown in Fig. 44.

Fig. 44 Connector behaviour

An example of a connector is can be built is in Fig. 45. The first number is the connector

label, then the instance name and the label of the first and second node must be written.

Fig. 45 Connector example

Also a node set with the list of all the node that will be connected must be created, a set for

each instance. In this module are also created the surfaces needed to create the interaction.

The surfaces type could be node or element.

72

Interaction module.

First the interaction property must be written. The interaction could be between two element

surface or between a node and an element surface. The second type has a lower

computational cost. Two pressure-overclosure have been use the exponential and the hard

one. The difference regard how quickly the pressure between the two surface could change.

In the first case the change is exponential, in the second the change is fast.

Five interaction have been built. The first is between the sock and the struct and it is always

active. The second is between the expansion surface and the sock, it is active only in the first

and second step. The third interaction is between the leg and the sock, it is active only from

step two. The fourth interaction is between the superior part of the struct’s ring and the lines,

it is active from step two. The fifth interaction is between the inferior part of the struct’s ring

and the lines, it is active from step two. Since the model has been created writing the inp file

all the interaction are created in the initial step if they want to be disactivated the method

shown in must be followed. This procedure is done in the Step module.

Fig. 46 Interaction deactivation

Material Properties

The material properties of the sock have been computed. First five specimen have been

obtained in the axial and in the circumferential direction. All the specimen have been tested

by an axial machine and the force and change in length in the axial direction have been

obtained. The stress has been computed as the ratio between the force and the specimen

width while the strain has been computed as the ratio between the change of length and the

specimen height. The initial values of stress and strain have been subtracted to all the stress

and strain values. The computed stress is computed as the product between the Yung

modulus and the strain. The Young modulus in the circumferential direction has been

computed using the excel solver tool as show in Fig. 47. In the same figure also the final

value of the Young modulus is shown.

73

Fig. 47 Circumferential young modulus

The Young modulus in the longitudinal direction has been computed using the excel solver

tool as show in Fig. 48. In the same figure also the final value of the Young modulus is

shown.

74

The Poisson ratio has been computed as the ratio between the change of length in the

circumferential direction and the change of length in the axial direction. The final value of

the Poisson ratio in show in Fig. 49

Fig. 49 Poisson ratio computation

Step module

In this step the boundary condition are applied. In step one the cylinder is expanded until the

sock exceeded the leg surface. In the second step the sock is free to accommodate on the leg.

In the third step the foot point are moved first down and then back to their initial position.

First the posterior nodes of the foot are moved in the axial direction then once they come

back to their initial position the nodes of that represent the anterior part of the foot are moved.

The movement is the one of an half sinusoid (

Fig. ).

All the nodes of the internal surface of the leg are blocked in the radial, tangential and axial

direction, this is like considering the tibia as infinitely rigid during all the step. The central

node of the ring are block in the axial direction during step one and step two. The nodes of

the sock with the biggest x coordinate are blocked in the y direction and the ones with the

biggest y coordinate are blocked in the x direction in order to avoid the sock rotation around

75

the axial rotation. The movement in the radial direction of all the lines is blocked during Step

3

Fig. 50 Movement of the foot's node.

76

Results

Mesh Convergency

In order to be sure that the results obtained were accurate, a mesh convergency analysis has

been performed. Different parameters have been changed. The first one is the number of

element of the mesh of the leg, the second the number of beam element of each struct. Thus

the last parameter was linked also to the number of element of the sock mesh. The two typer

of leg geometry are shown in Fig. 51 and Fig. 52.

Fig. 52 Leg mesh type 3

Fig. 51 Leg mesh type 4

77

As we can see from Fig. 53 and F the effect of the leg mesh on the mean pressure is

very small in all the three configuration (straight, cross and simple), the from now on the

type 3 mesh of the leg will be used.

Fig. 54 Pressure values for mesh 3

While the number of element of the sock has a bigger effect. In fact convergence has been

reach only with a sock mesh of type 10. The values of pressure obtained using the type of

mesh 10 and 12 are shown in Fig. 55

78

Fig. 55 Effect of change of the sock mesh

While if we make a comparison between results obtained when modelling the sock as a linear

isotropic (Fig. 57) material and when modelling as an orthotropic material (Fig. 57) there is

no effect on the mean pressure. There from now on we will use the linear elastic mechanical

properties

79

Fig. 56 Pressure when the sock is modelled as linear orthotropic.

80

Case 1

The values of the editable variable used in this model are the one showed in Fig. 58.

Fig. 58 Pameters values

Let’s consider the simple case

Fig. 59 shows respectively when it is in his initial position and when the ring is opened. The

mean pressure at both time is 15.0015 mmHg with a difference in pressure of 0.2100 mmHg.

While how the struct is deformed is shown in Fig. 60.

81

Fig. 59 Simple case pressure values

Fig. 60 Simple case struct deformation

82

Let’s consider the straight case

Fig. 61 shows respectively when it is in his initial position and when the ring is opened. The

mean pressure at both time is 15.00 mmHg with a difference in pressure of -0.751 mmHg.

While how the struct is deformed is shown in Fig. 62

Fig. 61 Straight case pressure values

83

Fig. 62 Straight case struct deformation

Let’s consider the cross case

Fig. 63 and Fig. 64 shows respectively when it is in his initial position and when the ring is

opened. The mean pressure at both time is 15.00 mmHg with a difference in pressure of

0.765 mmHg.

While how the struct is deformed is shown in Fig. 65

Fig. 63 Cross case initial pressure values

84

Through a comparison between Fig. 64 and Fig. 66 it can be see that except for the region

there the struct are connected to the sock there is no evident pressure change between the

posterior and the anterior part of the leg. An equivalent result has been obtained in the other

two case

Fig. 65 Cross case, struct deformation

Fig. 64 Cross case minimum pressure values

85

Fig. 66 Pressure of the anterior part of the leg

Case two

In the next simulation the radius of the leg and the one of the leg have been changed in order

to see what is the pressure applied by the devise near the ankle

Fig. 67 andFig. 68 shows respectively when it is in his initial position and when the ring is

opened. The mean pressure at both time is 18.7533 mmHg with a difference in pressure of

3.7503 mmHg.

While how the struct is deformed is shown in Fig. 69

Fig. 67 initial ankle's pressure

86

Example

Other simulation has been performed for example changing the lines geometry (simple or

cross case) but no convergence has been reached. There are a lot of combination of struct’s

length, number of struct, leg’s radius and struct-s radius that does not allow the simulation

to converge. An example is show in Fig. 70.

Fig. 69 Struct’s ring deformation

Fig. 68 Struct’s ring deformation

87

Fig. 70 Not converged simulation example

88

Discussion

In the first case treated in both the three lines configuration the mean pressure before the

lines are moved is of 15 mmHg. In the simple case there is no evident change in the

pressures’ values when the ring is at his maximal opening while a difference of about 0.750

mmHg is reached. The main difference between this three different case are the values of

the pressure near the zone where the struct and the sock are connected. As expected in the

second case the mean pressure is higher infact normally the medical stocking have their

maximum pressure in the anckle region. T

The last paragraph of the results chapter has shown that even if the physic of the problems

seems easy in reality it is not. This evidence the need of a model that once validated could

become a really useful tool to check if the pressure values are the wanted one and how they

could change. This tool could also be used in order to make patient specific stocking allowing

the reduction of time and money cost need to produce a device.

89

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