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Development of Three-Dimensional Structures for Single-Layer Compression Therapy
DEVELOPMENT OF TElREEDIMENSIONALSTRUCTURES FOR SINGLELAYER COMPRESSION THERAPY S. Rajendran and S.C. h a n d Institute for Materials Research and Innovation,University of Bolton, Bolton BL3 5AF3,UK ABSTRhCT Venous leg ulceration is a common problem throughout the western world. The chronic nature of venous ulcers creates considerable demands upon all healthcare authorities in terms of treatment costs and nursing resources. Compression bandaging is considered as the “gold standard” for managing venous leg ulcers and treating the underlying venous insufficiency. The main function of a compression bandage is to exert external pressure onto the limb. The ability to generate and to maintain this sub-bandage pressure is determined by the bandage structure, the elastomeric properties of the yams, as well as the finishing treatments applied to the fabric. Non-woven materials are currently used in combination with compression bandages in an attempt to evenly distribute pressure and provide protection over bony prominences of the leg (tibia). However, these multilayered bandage systems are uncomfortable to wear due to their bulkiness and undesirable thermo-physiologicalcharacteristics.They are also difficult to apply and are associated with relatively high costs due to the requirement for specific bandage types for each layer. The requirement for a single-layer compression bandage that incorporates the performance characteristics of multi-layered comprasion bandage systems is of paramount importance. Three-dimensional knitted spacer fabrics are becoming increasingly important for developing novel medical textile products. In comparison to traditional woven or knitted fabrics, the range of physical and themo-physiological properties which can be achieved is considerably wider. These novel structures consist of two independent faces with interconnecting threadsjoining them. They can be exceptionally soft, incorporate large volumes of air, and provide good resilience to compression, temperature control, and moisture management. The layer of air that lies between the two independent textile faces creates a comforting, climate-controlling effect which prevents sweating and overheating of the skin. Spacer fabrics also provide an excellent cushioning effect which means that there is no need to use multiple layers of padding and compression bandages. When elasticated yarns are incorporated into the spacer fabric structure it is also possible to produce similar pressure-generating characteristics to those of traditional compression bandages. The focus of this paper is to discuss the design criteria and imporkant functional properties of three-dimensional single-layer compression systems. A range of both weft and warp knitted spacer-fabrics were tested in order to determine their basic functional properties. Mechanical testing was also undertaken in order to assess the elastic and elongation properties of these spacer-fabrics. Load elongation hysteresis is important since it not only relates to the materials ability to generate external pressure, but also how this pressure maybe affected h m any changes in tension, extension, and elastic properties. The tension, and hence external pressure, generated within traditional compression bandages normally decays slowly over an extended period of time after application onto the limb. The tension decay test simulates bandage application and 0 Woodhead Publishing Limited, 2010 279
highlights a materials ability to sustain tension throughout a pre-determined time period (15 hours). Thermo-physiological and climate-controlling properties of the spacer-fabrics will also be discussed in this paper. These tests directly relate to the functional comfort characteristics of the spacer-fabric structures which include thermal resistance, thermal absorpitivity, water vapour permeability, and evaporative heat loss. In all of the tests undertaken, comparisons are made to results obtained for traditional compression bandages and padding bandage materials.
INTRODUCTION The market potential for healthcare and medical textile devices is considerable. In the EU alone, sales of medical textiles are worth US$ 7 billion, and already account for 10% of the market of technical textiles. The EU sector consumes 100,000 tomes of fibre per annum and is growing in volume by 3% - 4% a year. The global medical device market was valued at over US$lOO billion, of which U S 4 3 billion was generated from the US market. Western Europe is the second largest market and a c ~ u n t for s nearly 25% of the global medical device industry. The UK has one of the largest medical device markets in the world. The market is dominated by the National Health Service (NHS)accounting for approximately 80% of healthcare expenditure, even though there are fewer private sectors. It is forecasted that the share of hygiene and medical textiles would be 12% of the global technical textiles market and would account for US$4.1 billion. The healthcare and medical devices market is being driven by: 0 population growth in developing countries; 0 the ageing of the population in developed countries; 0 rising standards of living and higher expectationsof quality of life, 0 changing attitudes to health, and 0 the emergence of innovations and the availability of increasingly high technology. Innovations mainly come fiom large companies which have their own research and development departments. However, many novel products will continue to be developed by small and medium size companies - albeit largely through collaboration with universities and higher educational institutions. Venous ulceration is a common disease affecting around 1% of adult population in the UK and Australia. The direct and indirect cost of the treatment in Germany is more than 1 billion DM. The estimated annual cost in Sweden is $25 million. In the US, about 2 million working days are lost each year because of leg ulcer problem and the treatment cost is enormous. It is estimated that the direct cost of management and treatment of venous leg ulcers to the National Health Service (NHS) in the UK is in excess of f8OO million. "HE TREATMENT OF VENOUS LEG ULCERS
As stated earlier, venous leg ulceration is a common problem throughout the Western world. Venous leg ulcers are the most fiequently occurring type of chronic wound accounting for over 70% of the lower extremity ulceration and the recurrence rates are as high as 72% in one year'. It should be pointed out that venous leg ulcers are chronic and there is no medication to cure the disease other than the compression therapy. A sustained 280 0 Woodhead Publishing Limited, 2010
graduated compression mainly enhances the flow of blood back to the heart, improves the functioning of valves and calf muscle pumps, reduces oedema and prevents the swelling of veins. Mostly elderly people are prone to develop Deep Vein Thrombosis @VT - popularly known as blood clot), varicose veins and venous leg ulcers. However over 40% of patients suffer prior to age 50 and 13% before the age of 30’. The chronic nature of venous ulcers creates considerable demands upon all healthcare authorities in terms of treatment costs and nursing resources. Compression bandaging is considered as the “gold standard” for managing venous leg ulcers and treating the underlying venous insufficiency. The main function of a compression bandage is to exert external pressure onto the limb. The ability to generate and to maintain this sub-bandage pressure is determined by the bandage structure, the elastomeric properties of yarns and the finishing treatments applied to the fabric. Nonwoven material is currently used in combination with multilayer bandages in an attempt to evenly distribute pressure and provide protection over bony prominences of the leg (tibia). However, these multilayered bandage systems are uncomfortableto wear due to their bulkiness and undesirable thermophysiological characteristics. The ideal requirements of pressure transference and distribution are of p a t concern. Multilayer bandages are also difficult to apply on the limb and are associated with relatively high costs due to the requirement for specific bandage types for each layer. In these circumstances, the requirement of a single-layer compression bandage regime that incorporates the ideal performance characteristics of multilayered compression bandage systems is of paramount importance. A single layer system would be simpler to apply, relatively more comfortable to patient and above all will be relatively cheaper than two to four layer systems currently available on the market.
COMPRESSION SYSTEMS Compression can be exerted to the leg either by a single-layer bandage or multilayer bandages. In the UK four-layer bandaging system is widely used whilst in Europe and Australia the non-elastic two-layer short stretch bandage regime is the standard treatment. A typical four-layer compression bandage system comprises of padding bandage, crepe bandage, high compression bandage and cohesive bandage. Both the two-layer and four-layer systems require padding bandage (wadding or orthopaedic wool) that is applied next to the skin and underneath the short stretch or long stretch compression bandages. A plaster type non-elastic bandage, Unna’s boot is favoured in the USA. However, compression would be achieved by three-layer dressing that consists of Unna’s boot, continuous gauze dressing followed by an outer layer of elastic wrap. It should be stressed that Unna’s boot, being rigid, is uncomfortable to wear and medical professionals are unable to monitor the ulcers afler the boot is applied. A variety of padding bandages are used beneath the compression bandage as a padding layer in order to evenly distribute the pressure and give protection to bony prominences. They absorb high pressures created at the tibia and fibula regions. It will be noticed that the structure of a padding bandage is regarded as an important factor in producing a uniform pressure distribution. Research has shown that the majority of commercially available bandages do not provide the desired uniform pressure distrib~~tion~.~.
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PROBLEMS WITH CURRENT BANDAGES
During the past few years there have been increasing concems relating to the performance of bandages especially pressure distribution properties for the treatment of venous leg ulcers. This is because the compression therapy is a complex system and requires two or multilayer bandages, and the performance properties of each layer differs h m other layers. The widely accepted sustained graduated compression mainly depends on the d o r m pressure distribution of different layers of bandages in which textile fibres and bandage structure play a major role. The padding bandages commercially available are nonwovens that are mainly used to distribute the pressure, exerted by the short stretch or long stretch compression bandages, evenly around the leg otherwise higher pressure at any one point not only damages the venous system but also promotes arterial disease. Therefore there is a need to distribute the pressure equally and uniformly at all points of the lower limb and this can be achieved by applying an effective padding layer around the leg beneath the compression bandage. In addition, the padding bandages should have the capability to absorb high pressure created at the tibia and fibula regions. Wadding also helps to protect the vulnerable areas of the leg h m generating extremely high pressure levels as compared to those required along the rest of the leg. The research carried out at the University of Bolton involving 10 most commonly used commercial padding bandages produced by major medical companies showed that there are significant variations in properties of commercial padding bandages*’, more importantly the commercial bandages do not distribute the pressure evenly at the ankle as well as the calfregion. The integrity of the nonwoven bandages is also of great concern. When pressure is applied using compression bandages, the structure of the nonwoven bandages may collapse and the bandage would not impart cushioning effect to the limb. The comfort and cushioning effect are considered to be essential properties for padding bandages because they may stay on the limb for several days. In the UK, multilayer compression systems are recommended for the treatment of venous leg ulcers4. ~lthoughmultilayer compression bandages are more effective than single-layer bandage in healing venous leg ulcers’, it is generally agreed by the clinicians that multilayer bandages are too bulky for patients and the cost involved is high. A wide range of compression bandages is available for the treatment of leg ulcers but each of them having Merent structure and properties and this influences the variation in performance properties of bandages. In addition, long stretch compression bandages tend to expand when the calf muscle pump is exercised, and the beneficial effect of the calf muscle pump is dissipated. It is a well established practice that elastic compression bandages that have the extension of up to 200% are applied at 50% extension and at 50% overlap to achieve the desired pressure on the limb. It has always been a problem for nurses to exactly stretch the bandages at 50% and apply without losing the stretch from ankle to calf, although there are indicators for the desired stretch (rectangles become squares) in the bandages. The elastic compression bandages are classified into four groups (3a, 3b, 3c and 3d) according to their ability to produce predetermined levels of compression and this has always been a problem to select the right compression bandage for the treatment. The inelastic short stretch bandage (Type 2) system, which has started to appear in the UK market, has the advantage of applying at full stretch (up to 90% extension) around the limb. The short stretch bandages do not expand when the calf muscle pump is exercised and the force of the muscle is directed back into the leg which promotes venous return. The limitations of short stretch bandages are that a small increase in the volume of the leg will result in a large increase 282 0 Woodhead Publishing Limited, 2010
in compression and this means the bandage provides high compression in the upright position and little or no compression in the recumbent position when it is not required. During walking and other exercises the subbandage pressure rises steeply and while at rest the pressure comparatively drops. Therefore patients must be mobile to achieve effective compression and exercise is a vital part of this form of compression. Moreover the compression is not in tact with skin when reduction in limb swelling because the short stretch bandage is inelastic, and it has already been stretched to its full extent.
3D COMPRESSION BANDAGES Three-dimensional spacer fabrics are becoming increasingly important for developing novel medical textile products. In comparison to traditional woven or knitted fabrics, the range of physical and thermophysiological properties which can be achieved is considerably wider. These novel structures consist of two independent faces with interconnecting threadsjoining them. They can be exceptionally soft, incorporate large volumes of air, and provide good resilience to cornpression, temperature control, and moisture management. The layer of air that lies between the two independent textile faces creates a comforting, climate-controlling effect which prevents sweating and overheating of the skin. Spacer fabrics also provide an excellent cushioning effect which means that there is no need to use multiple layers of padding and compression bandages. When elasticated yarns are incorporated into the spacer fabric structure it is also possible to produce similar pressure-generating characteristics to those of traditional compression bandages. MATERIALS AND METHODS
Four spacer fabrics identified as Black (l), White (2), White (3) and Blue (4) were used to study the pressure transference at various pressure ranges. Four padding bandages (PBla to PB4a) recently available at Drug Tariff were also used for comparison. It should be mentioned that the pressure distribution of 10 commercial padding bandages were earlier studied and reported el~ewhere’.~.
Pressure mapping apparatus The electronic pressure transference apparatus (Figure 1) developed at The University of Bolton was used. The apparatus consists of a wooden platform for presentation of test specimens, a strain gauge device and an electronic circuit board. A pressure pin (9mm diameter) is attached on to the load beam of the strain gauge and a corresponding hole drilled through the wooden platform. The height of the pressure pin is adjusted so that it protrudes through the hole of the platform by lmm. The specimen is placed onto the wooden platform over the pressure pin and a series of known metal block weights are placed onto its surface. The strain gauge device detects the pressure transmitted through the specimen at each known pressure in increments created by the metal blocks. The amount of pressure absorbed and dissipated within the textile structure and the actual pressure felt immediately below the specimen ie the patient’s leg is determined. The transmitted pressure through the thickness of the specimen is the absolute pressure exerted on the patient’s leg.
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Fig 1. Pressure Transference Apparatus A fabric extension device (Figure 2) has also been developed at the University of Bolton which facilitates the extension of spacer fabrics at the required length. The pressure transference of spacer fabrics at various extensions was measured utilising this device.
Fig 2. Pressure Transference Extension Test Rig A prototype electronic mannequin leg developed at the University of Bolton was used to investigate the pressure mapping of bandages. The mannequin leg (Figure 3) simulates a lower limb and has d e h b l e tibia, calf and ankle regions.It has 8 pressuremeasuring sensors of which 2 are positioned at ankle, 3 at calf and 3 at below knee. The sensors are connected with an electronic board display unit via strain gauges.
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I
r'
L
Fig 3. Schematic Diagram of Pressure Profiling Instrument (Mannequin Leg)
RESULTS AND DISCUSSION Effect of bulk density The basic properties of padding bandages and spacer fabrics used in this study are given in Table 1. The bulk density determines the bulkiness of fabrics, higher the bulk density lower is the bulkiness. It is one of the important parameters for treating venous leg ulcers because the padding bandage is applied next to the skin around the leg, and it must be capable of protecting bony prominence and imparting comfort and cushioning effect to the patient. An appropriate bulkiness would be required to protect the bony prominences Table 1. Basic Properties of Padding Bandages (PB) and Spacer Fabrics Sample
Thickness
(mm) PBla Padding PB2a Paddini PB3a Padding PB4a Padding Black (1) Spacer White (2) Spacer White (3) Spacer Blue (4)Spacer
1.2 1.4
1.5 1.4
3.24 2.37 2.41 1.87
Area Density -2
90 93 79 72 475 295 426 279
Bulk Density (gcmJ) 0.07 0.07 0.05 0.05 0.15 0.12 0.18 0.15
in the leg. It is observed in Table 1 that all the commercial padding bandages (PBla PB4a) possess essential bulkiness and the space fabrics registered significant higher bulk densities. It should be stated that spacer fabric is a three-dimensional structure and in 3D spacer fabrics, two separate fabric layers are connected at a distance with an inner spacer yarn or yarns using either warp knitting or weft knitting route (Figure 4). The two layers can be produced from different fibre types such as polyester, polyamide, polypropylene, cotton, viscose, lyocell, wool etc and can have completely different structures6.The three-dimensional nature of spacer fabrics makes them an ideal device for application next to the skin because they have desirable properties that are ideal for the human body'. 3D fabrics are soft have good resilience that provides cushioning
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effect to the body and protects bony prominence, they are breathable and hence the ability to manage both heat and moisture generated by the body6. For venous leg ulcer applications, such attributes together with improved elasticity and recovery promote faster healing.
Fig 4. Illustration of a 3D Spacer Fabric Structure
Effect of pressure transference of commercial bandages Padding bandage is applied beneath the compression bandage. The degree of pressure that is induced into the leg by the compression bandage is of major importance. It has been demonstrated that too high a pressure on the leg not only leads to further complications of venous system but also promotes arterial disease. In contrast, inadequate pressure cannot help to heal the venous ulcers. Even if the compression bandage is applied at the correct tension it is probable that excessive pressure will be generated over the bony prominences of the leg. Therefore there is a need to distribute the pressure equally and uniformly at all points of the lower limb and this can be achieved by applying an effective padding layer around the leg below the compression bandage. The pressure distribution characteristics of commercial bandages are shown in Figure 5 . Obviously, none of the bandages provides uniform pressure distribution. It is vital that an ideal padding bandage should dissipate the pressure between 30 and 4OmmHg, exerted by a high compression bandage (Type 3c), uniformly around the limb. Earlier studies also indicated the poor pressure distribution of commercial bandages2p3.However, a significant improvement in distributing the applied pressure of the novel adding bandages developed at the University of Bolton is reported elsewhere’ In order to ascertain the pressure transference of padding bandages exerted by high compression bandage (Type 3C), a prototype electronic instrument (mannequin leg) was used. The padding bandage was wrapped around the mannequin leg at 50% overlap (two complete layers) without stretching and high compression bandage (SurePress) was wrapped over the padding bandage at 50% overlap by rotating the leg. The compression bandage was stretched at 50% extension by applying 1 kgfload when
s.
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"1
Fig 5. Pressure Transferenceof CommercialPadding bandages wrapping around the leg. It should be stressed that nurses normally apply the bandages at 50% overlap, and at 50% extension for treating the venous leg ulcers. The pressure developed at ankle, calf and below knee positions in the mannequin leg was determined from the display unit and the values were corrected using the regression equations. Prior to the measurement, the pressure sensors in the leg were calibrated to the known pressure range of 0 to 300 mmHg by making use of a sphygmomanometer. The pressure mapping is depicted in Figure 6.
..I
m.m
Fig. 6 Pressure Mapping of Commercial Bandages on Mannequin Leg The interpretation of the results is summarised based on the following two major phenomena.
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1. A sustained graduated compression,higher pressure at the anMe which gradually reduces to calf and upper calf according to Laplace's Law', aids the treatment of venous leg ulcers'. f i e graduated compression mainly enhances the flow of blood back to the heart, improves the functioning of valves and calf muscle pumps, reduces oedema and prevents the swelling of veins". 2. Approximately 30-40 mmHg at the ankle that reduces to 15-20 mmHg (50%) at the calf is generally adequate for healing most types of venous leg ulcers". The ideal pressure just below the knee is around 17 mmHg".
It is obvious from Figure 6 that the bandages do not fulfil the requirements of a sustained graduated compression of an ideal bandage system. The pressure measured by sensor 2 at the ankle is very high although the pressure is graduating down to the knee. It is obvious, however, that all padding bandages exhibited relatively lower compression values than the type 3C high compression bandage when applied on its own without orthopaedicwadding below it. In Figure 6 type 3c Sure Press compression bandage was applied alone and on top of padding bandages PBla to PB4a It is obvious fiom Figure 6 that type 3c Sure Press when applied in conjunction with padding bandages PB2a and PB3a produced the closest results to the theoretical values.
Effed of presswe transferenceof space bandages Pressure transference appamtus and extension test rig were used to study the pressure transference of spacer bandages both at unrestrained and stretch conditions. It will be observed in Figure 7 that the pressure transference of Merent spacer bandages at any one point varies, and it mainly depends on the structure and fibre content of the material. It is interesting to note that spacer bandages distributed the applied pressure much more uniformly around the leg than the four commercial padding bandages PBla to PB4a, see Figure 5. For instance, the White (2) spacer bandage absorbed the applied pressure of 43.9 mmHg and transfer 2 mmHg at one point. In other words the absorbed pressure of 41.9 mmHg is uniformly distributed inside the fabric structure which is one of the essential requirements for venous leg ulcer treatment. On the other hand, the commercial padding bandage (F'B4a) absorbed 43.9 mmHg and transferred 35 mmHg at one point (Figure 5) and this means the bandage distributed only 8.9 d g uniformly inside the structure. The higher out put pressure fiom the bandage at one point is undesirable and may slow down andor block the blood flow in arteries.
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1200
,
-m-Elack
+Blw
(I)
(4)
zml Fig 7. Pressure Transference of Spacer Bandages (Relaxed) Figures 8 to 1 1 represent the pressure transference of spacer bandages at known pressures under extension up to 120%.
o
10
20
x)
a
w
40
m
I
RI
im
i i o r m
--1w
Fig 8. Effect of Extension on Pressure Transference of Spacer Bandages - Black (1)
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4.m
,
4m.
am.
I
f KI om o
10
20
10
u)
HI
~ J I
m
m
m
Im
-m Fig 9. Effect of Extension on Pressure Transference of Spacer Bandages - White (2) It will be noticed that increase in applied pressure does not influence the pressure transference at any one point and the variation is marginal in all the samples. This affirms that these spacer fabrics can be used as ideal padding bandages, and by controlling the tension it will be possible to generate the required pressure for the treatment of venous leg ulcers.
Fig 10. Effect of Extension on Pressure Transference of Spacer Bandages - White (3)
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Fig 11. Effect of Extension on Pressure Transferenceof Spacer Bandages - Blue (4)) It should also be stated that according to Laplace equation the pressure generated on to the limb by a bandage is directly proportional to the tension of the bandage and the number of layers but inversely proportional to the width of the bandage and the circumference of the limb. Utilising this concept, the research and development programme into the mathematical modelling of spacer fabrics to achieve the required pressure mapping for the treatment of venous leg ulcer is in progress at the University of Bolton. SUMMARY
The effective management of venous leg ulcer involves careful selection of bandages to reverse the venous blood flow back to the heart. The paper has discussed the significant contribution of padding as well as compression bandages in healing the ulcer. The advantages and limitations of the existing two-layer to four-layer bandaging regimens are discussed in this paper. It is obvious that the pressure transference of commercial padding bandages varied and none of the padding bandages investigated satisfied the requirements of an ideal padding bandage. The study also demonstrated the need for developing a single-layer bandaging regimen for the benefit of elderly and cutting the cost of treatment. 3D spacer technology has been investigated and the results affirmed that spacer bandages would be utilised to design and develop a single-layer system that could replace the currently used cumbersome four-layer system. A suitable spacer structure can combine the desirable attributes of both the padding and 2-dimentional compression bandages into one composite 3-dmentiod structure.
ACKNOWLEDGEMENTS The research and development programme is funded by Engineering and Physical Sciences Research Council (EPSRC), UK. The authors are grateful to EPSRC for finding and supporting the research programme.
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REF’ERENCES 1 P N Kimbrell and V Larson-Lohr, ‘Venous Disease’, in P J Sheffield, C E Fife and A P S Smith (Eds), Wound Care Practice, Best Publishing Co,2004,267.
2 S Rajendran and S C Anand, ‘Design and development of novel bandages for compression therapy’, British JNursing, 2003 11 1300-1307. 3 S Rajendran and S C Anand, ‘The contribution of textiles to medical and hdthcare products and developing innovative medical devices’ Indian J Fibre & Text Res, 2006 31 215-229. 4 EHC, ‘Compression Therapy for Venous Leg Ulcers. University of York NHS Centre for Review and Dissemination’, E’ective Healthcure, 1997 3 1-12. 5 N Cullum et al, ‘Compression for venous leg ulcers’, Cochrane Review: The
Cochrane Library,Oxford, 2002,l. 6 S C Anand ‘Spacers- at the technical frontier’, Knit International, 2003 110 38-41.
7 Anon, ‘Spacerfabric focus’, Knit International,2002 109 20-22. 8 C Moffat and P Harper, Leg Ulcers, Churchill Livingstone, Edinburgh, 1997. 9 RCN, Clinical Practice Guidelines. The Management of Patients with Venous Leg Ulcers. RCN Institute,London, 1998. 10 M Collier, Venous Leg Wceration: In Wound Management: Theory and Practice, Edited by M Miller and D Glover, London. Nursing Times Books, 1999. 11 D Simon, ‘Approachesto venous leg ulcer care within the community: compression, pinch skin grafts and simple venous surgery’, Ostomy Wound Management, 19% 42 2 34-40.
12 R Sterner et al, ‘Compression mabnent for the lower extremities particularly with compression stockings’, The Dermatologist, 1980 31 355-365.
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highlights a materials ability to sustain tension throughout a pre-determined time period (15 hours). Thermo-physiological and climate-controlling properties of the spacer-fabrics will also be discussed in this paper. These tests directly relate to the functional comfort characteristics of the spacer-fabric structures which include thermal resistance, thermal absorpitivity, water vapour permeability, and evaporative heat loss. In all of the tests undertaken, comparisons are made to results obtained for traditional compression bandages and padding bandage materials.
INTRODUCTION The market potential for healthcare and medical textile devices is considerable. In the EU alone, sales of medical textiles are worth US$ 7 billion, and already account for 10% of the market of technical textiles. The EU sector consumes 100,000 tomes of fibre per annum and is growing in volume by 3% - 4% a year. The global medical device market was valued at over US$lOO billion, of which U S 4 3 billion was generated from the US market. Western Europe is the second largest market and a c ~ u n t for s nearly 25% of the global medical device industry. The UK has one of the largest medical device markets in the world. The market is dominated by the National Health Service (NHS)accounting for approximately 80% of healthcare expenditure, even though there are fewer private sectors. It is forecasted that the share of hygiene and medical textiles would be 12% of the global technical textiles market and would account for US$4.1 billion. The healthcare and medical devices market is being driven by: 0 population growth in developing countries; 0 the ageing of the population in developed countries; 0 rising standards of living and higher expectationsof quality of life, 0 changing attitudes to health, and 0 the emergence of innovations and the availability of increasingly high technology. Innovations mainly come fiom large companies which have their own research and development departments. However, many novel products will continue to be developed by small and medium size companies - albeit largely through collaboration with universities and higher educational institutions. Venous ulceration is a common disease affecting around 1% of adult population in the UK and Australia. The direct and indirect cost of the treatment in Germany is more than 1 billion DM. The estimated annual cost in Sweden is $25 million. In the US, about 2 million working days are lost each year because of leg ulcer problem and the treatment cost is enormous. It is estimated that the direct cost of management and treatment of venous leg ulcers to the National Health Service (NHS) in the UK is in excess of f8OO million. "HE TREATMENT OF VENOUS LEG ULCERS
As stated earlier, venous leg ulceration is a common problem throughout the Western world. Venous leg ulcers are the most fiequently occurring type of chronic wound accounting for over 70% of the lower extremity ulceration and the recurrence rates are as high as 72% in one year'. It should be pointed out that venous leg ulcers are chronic and there is no medication to cure the disease other than the compression therapy. A sustained 280 0 Woodhead Publishing Limited, 2010
graduated compression mainly enhances the flow of blood back to the heart, improves the functioning of valves and calf muscle pumps, reduces oedema and prevents the swelling of veins. Mostly elderly people are prone to develop Deep Vein Thrombosis @VT - popularly known as blood clot), varicose veins and venous leg ulcers. However over 40% of patients suffer prior to age 50 and 13% before the age of 30’. The chronic nature of venous ulcers creates considerable demands upon all healthcare authorities in terms of treatment costs and nursing resources. Compression bandaging is considered as the “gold standard” for managing venous leg ulcers and treating the underlying venous insufficiency. The main function of a compression bandage is to exert external pressure onto the limb. The ability to generate and to maintain this sub-bandage pressure is determined by the bandage structure, the elastomeric properties of yarns and the finishing treatments applied to the fabric. Nonwoven material is currently used in combination with multilayer bandages in an attempt to evenly distribute pressure and provide protection over bony prominences of the leg (tibia). However, these multilayered bandage systems are uncomfortableto wear due to their bulkiness and undesirable thermophysiological characteristics. The ideal requirements of pressure transference and distribution are of p a t concern. Multilayer bandages are also difficult to apply on the limb and are associated with relatively high costs due to the requirement for specific bandage types for each layer. In these circumstances, the requirement of a single-layer compression bandage regime that incorporates the ideal performance characteristics of multilayered compression bandage systems is of paramount importance. A single layer system would be simpler to apply, relatively more comfortable to patient and above all will be relatively cheaper than two to four layer systems currently available on the market.
COMPRESSION SYSTEMS Compression can be exerted to the leg either by a single-layer bandage or multilayer bandages. In the UK four-layer bandaging system is widely used whilst in Europe and Australia the non-elastic two-layer short stretch bandage regime is the standard treatment. A typical four-layer compression bandage system comprises of padding bandage, crepe bandage, high compression bandage and cohesive bandage. Both the two-layer and four-layer systems require padding bandage (wadding or orthopaedic wool) that is applied next to the skin and underneath the short stretch or long stretch compression bandages. A plaster type non-elastic bandage, Unna’s boot is favoured in the USA. However, compression would be achieved by three-layer dressing that consists of Unna’s boot, continuous gauze dressing followed by an outer layer of elastic wrap. It should be stressed that Unna’s boot, being rigid, is uncomfortable to wear and medical professionals are unable to monitor the ulcers afler the boot is applied. A variety of padding bandages are used beneath the compression bandage as a padding layer in order to evenly distribute the pressure and give protection to bony prominences. They absorb high pressures created at the tibia and fibula regions. It will be noticed that the structure of a padding bandage is regarded as an important factor in producing a uniform pressure distribution. Research has shown that the majority of commercially available bandages do not provide the desired uniform pressure distrib~~tion~.~.
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PROBLEMS WITH CURRENT BANDAGES
During the past few years there have been increasing concems relating to the performance of bandages especially pressure distribution properties for the treatment of venous leg ulcers. This is because the compression therapy is a complex system and requires two or multilayer bandages, and the performance properties of each layer differs h m other layers. The widely accepted sustained graduated compression mainly depends on the d o r m pressure distribution of different layers of bandages in which textile fibres and bandage structure play a major role. The padding bandages commercially available are nonwovens that are mainly used to distribute the pressure, exerted by the short stretch or long stretch compression bandages, evenly around the leg otherwise higher pressure at any one point not only damages the venous system but also promotes arterial disease. Therefore there is a need to distribute the pressure equally and uniformly at all points of the lower limb and this can be achieved by applying an effective padding layer around the leg beneath the compression bandage. In addition, the padding bandages should have the capability to absorb high pressure created at the tibia and fibula regions. Wadding also helps to protect the vulnerable areas of the leg h m generating extremely high pressure levels as compared to those required along the rest of the leg. The research carried out at the University of Bolton involving 10 most commonly used commercial padding bandages produced by major medical companies showed that there are significant variations in properties of commercial padding bandages*’, more importantly the commercial bandages do not distribute the pressure evenly at the ankle as well as the calfregion. The integrity of the nonwoven bandages is also of great concern. When pressure is applied using compression bandages, the structure of the nonwoven bandages may collapse and the bandage would not impart cushioning effect to the limb. The comfort and cushioning effect are considered to be essential properties for padding bandages because they may stay on the limb for several days. In the UK, multilayer compression systems are recommended for the treatment of venous leg ulcers4. ~lthoughmultilayer compression bandages are more effective than single-layer bandage in healing venous leg ulcers’, it is generally agreed by the clinicians that multilayer bandages are too bulky for patients and the cost involved is high. A wide range of compression bandages is available for the treatment of leg ulcers but each of them having Merent structure and properties and this influences the variation in performance properties of bandages. In addition, long stretch compression bandages tend to expand when the calf muscle pump is exercised, and the beneficial effect of the calf muscle pump is dissipated. It is a well established practice that elastic compression bandages that have the extension of up to 200% are applied at 50% extension and at 50% overlap to achieve the desired pressure on the limb. It has always been a problem for nurses to exactly stretch the bandages at 50% and apply without losing the stretch from ankle to calf, although there are indicators for the desired stretch (rectangles become squares) in the bandages. The elastic compression bandages are classified into four groups (3a, 3b, 3c and 3d) according to their ability to produce predetermined levels of compression and this has always been a problem to select the right compression bandage for the treatment. The inelastic short stretch bandage (Type 2) system, which has started to appear in the UK market, has the advantage of applying at full stretch (up to 90% extension) around the limb. The short stretch bandages do not expand when the calf muscle pump is exercised and the force of the muscle is directed back into the leg which promotes venous return. The limitations of short stretch bandages are that a small increase in the volume of the leg will result in a large increase 282 0 Woodhead Publishing Limited, 2010
in compression and this means the bandage provides high compression in the upright position and little or no compression in the recumbent position when it is not required. During walking and other exercises the subbandage pressure rises steeply and while at rest the pressure comparatively drops. Therefore patients must be mobile to achieve effective compression and exercise is a vital part of this form of compression. Moreover the compression is not in tact with skin when reduction in limb swelling because the short stretch bandage is inelastic, and it has already been stretched to its full extent.
3D COMPRESSION BANDAGES Three-dimensional spacer fabrics are becoming increasingly important for developing novel medical textile products. In comparison to traditional woven or knitted fabrics, the range of physical and thermophysiological properties which can be achieved is considerably wider. These novel structures consist of two independent faces with interconnecting threadsjoining them. They can be exceptionally soft, incorporate large volumes of air, and provide good resilience to cornpression, temperature control, and moisture management. The layer of air that lies between the two independent textile faces creates a comforting, climate-controlling effect which prevents sweating and overheating of the skin. Spacer fabrics also provide an excellent cushioning effect which means that there is no need to use multiple layers of padding and compression bandages. When elasticated yarns are incorporated into the spacer fabric structure it is also possible to produce similar pressure-generating characteristics to those of traditional compression bandages. MATERIALS AND METHODS
Four spacer fabrics identified as Black (l), White (2), White (3) and Blue (4) were used to study the pressure transference at various pressure ranges. Four padding bandages (PBla to PB4a) recently available at Drug Tariff were also used for comparison. It should be mentioned that the pressure distribution of 10 commercial padding bandages were earlier studied and reported el~ewhere’.~.
Pressure mapping apparatus The electronic pressure transference apparatus (Figure 1) developed at The University of Bolton was used. The apparatus consists of a wooden platform for presentation of test specimens, a strain gauge device and an electronic circuit board. A pressure pin (9mm diameter) is attached on to the load beam of the strain gauge and a corresponding hole drilled through the wooden platform. The height of the pressure pin is adjusted so that it protrudes through the hole of the platform by lmm. The specimen is placed onto the wooden platform over the pressure pin and a series of known metal block weights are placed onto its surface. The strain gauge device detects the pressure transmitted through the specimen at each known pressure in increments created by the metal blocks. The amount of pressure absorbed and dissipated within the textile structure and the actual pressure felt immediately below the specimen ie the patient’s leg is determined. The transmitted pressure through the thickness of the specimen is the absolute pressure exerted on the patient’s leg.
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Fig 1. Pressure Transference Apparatus A fabric extension device (Figure 2) has also been developed at the University of Bolton which facilitates the extension of spacer fabrics at the required length. The pressure transference of spacer fabrics at various extensions was measured utilising this device.
Fig 2. Pressure Transference Extension Test Rig A prototype electronic mannequin leg developed at the University of Bolton was used to investigate the pressure mapping of bandages. The mannequin leg (Figure 3) simulates a lower limb and has d e h b l e tibia, calf and ankle regions.It has 8 pressuremeasuring sensors of which 2 are positioned at ankle, 3 at calf and 3 at below knee. The sensors are connected with an electronic board display unit via strain gauges.
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I
r'
L
Fig 3. Schematic Diagram of Pressure Profiling Instrument (Mannequin Leg)
RESULTS AND DISCUSSION Effect of bulk density The basic properties of padding bandages and spacer fabrics used in this study are given in Table 1. The bulk density determines the bulkiness of fabrics, higher the bulk density lower is the bulkiness. It is one of the important parameters for treating venous leg ulcers because the padding bandage is applied next to the skin around the leg, and it must be capable of protecting bony prominence and imparting comfort and cushioning effect to the patient. An appropriate bulkiness would be required to protect the bony prominences Table 1. Basic Properties of Padding Bandages (PB) and Spacer Fabrics Sample
Thickness
(mm) PBla Padding PB2a Paddini PB3a Padding PB4a Padding Black (1) Spacer White (2) Spacer White (3) Spacer Blue (4)Spacer
1.2 1.4
1.5 1.4
3.24 2.37 2.41 1.87
Area Density -2
90 93 79 72 475 295 426 279
Bulk Density (gcmJ) 0.07 0.07 0.05 0.05 0.15 0.12 0.18 0.15
in the leg. It is observed in Table 1 that all the commercial padding bandages (PBla PB4a) possess essential bulkiness and the space fabrics registered significant higher bulk densities. It should be stated that spacer fabric is a three-dimensional structure and in 3D spacer fabrics, two separate fabric layers are connected at a distance with an inner spacer yarn or yarns using either warp knitting or weft knitting route (Figure 4). The two layers can be produced from different fibre types such as polyester, polyamide, polypropylene, cotton, viscose, lyocell, wool etc and can have completely different structures6.The three-dimensional nature of spacer fabrics makes them an ideal device for application next to the skin because they have desirable properties that are ideal for the human body'. 3D fabrics are soft have good resilience that provides cushioning
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effect to the body and protects bony prominence, they are breathable and hence the ability to manage both heat and moisture generated by the body6. For venous leg ulcer applications, such attributes together with improved elasticity and recovery promote faster healing.
Fig 4. Illustration of a 3D Spacer Fabric Structure
Effect of pressure transference of commercial bandages Padding bandage is applied beneath the compression bandage. The degree of pressure that is induced into the leg by the compression bandage is of major importance. It has been demonstrated that too high a pressure on the leg not only leads to further complications of venous system but also promotes arterial disease. In contrast, inadequate pressure cannot help to heal the venous ulcers. Even if the compression bandage is applied at the correct tension it is probable that excessive pressure will be generated over the bony prominences of the leg. Therefore there is a need to distribute the pressure equally and uniformly at all points of the lower limb and this can be achieved by applying an effective padding layer around the leg below the compression bandage. The pressure distribution characteristics of commercial bandages are shown in Figure 5 . Obviously, none of the bandages provides uniform pressure distribution. It is vital that an ideal padding bandage should dissipate the pressure between 30 and 4OmmHg, exerted by a high compression bandage (Type 3c), uniformly around the limb. Earlier studies also indicated the poor pressure distribution of commercial bandages2p3.However, a significant improvement in distributing the applied pressure of the novel adding bandages developed at the University of Bolton is reported elsewhere’ In order to ascertain the pressure transference of padding bandages exerted by high compression bandage (Type 3C), a prototype electronic instrument (mannequin leg) was used. The padding bandage was wrapped around the mannequin leg at 50% overlap (two complete layers) without stretching and high compression bandage (SurePress) was wrapped over the padding bandage at 50% overlap by rotating the leg. The compression bandage was stretched at 50% extension by applying 1 kgfload when
s.
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Fig 5. Pressure Transferenceof CommercialPadding bandages wrapping around the leg. It should be stressed that nurses normally apply the bandages at 50% overlap, and at 50% extension for treating the venous leg ulcers. The pressure developed at ankle, calf and below knee positions in the mannequin leg was determined from the display unit and the values were corrected using the regression equations. Prior to the measurement, the pressure sensors in the leg were calibrated to the known pressure range of 0 to 300 mmHg by making use of a sphygmomanometer. The pressure mapping is depicted in Figure 6.
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m.m
Fig. 6 Pressure Mapping of Commercial Bandages on Mannequin Leg The interpretation of the results is summarised based on the following two major phenomena.
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1. A sustained graduated compression,higher pressure at the anMe which gradually reduces to calf and upper calf according to Laplace's Law', aids the treatment of venous leg ulcers'. f i e graduated compression mainly enhances the flow of blood back to the heart, improves the functioning of valves and calf muscle pumps, reduces oedema and prevents the swelling of veins". 2. Approximately 30-40 mmHg at the ankle that reduces to 15-20 mmHg (50%) at the calf is generally adequate for healing most types of venous leg ulcers". The ideal pressure just below the knee is around 17 mmHg".
It is obvious from Figure 6 that the bandages do not fulfil the requirements of a sustained graduated compression of an ideal bandage system. The pressure measured by sensor 2 at the ankle is very high although the pressure is graduating down to the knee. It is obvious, however, that all padding bandages exhibited relatively lower compression values than the type 3C high compression bandage when applied on its own without orthopaedicwadding below it. In Figure 6 type 3c Sure Press compression bandage was applied alone and on top of padding bandages PBla to PB4a It is obvious fiom Figure 6 that type 3c Sure Press when applied in conjunction with padding bandages PB2a and PB3a produced the closest results to the theoretical values.
Effed of presswe transferenceof space bandages Pressure transference appamtus and extension test rig were used to study the pressure transference of spacer bandages both at unrestrained and stretch conditions. It will be observed in Figure 7 that the pressure transference of Merent spacer bandages at any one point varies, and it mainly depends on the structure and fibre content of the material. It is interesting to note that spacer bandages distributed the applied pressure much more uniformly around the leg than the four commercial padding bandages PBla to PB4a, see Figure 5. For instance, the White (2) spacer bandage absorbed the applied pressure of 43.9 mmHg and transfer 2 mmHg at one point. In other words the absorbed pressure of 41.9 mmHg is uniformly distributed inside the fabric structure which is one of the essential requirements for venous leg ulcer treatment. On the other hand, the commercial padding bandage (F'B4a) absorbed 43.9 mmHg and transferred 35 mmHg at one point (Figure 5) and this means the bandage distributed only 8.9 d g uniformly inside the structure. The higher out put pressure fiom the bandage at one point is undesirable and may slow down andor block the blood flow in arteries.
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1200
,
-m-Elack
+Blw
(I)
(4)
zml Fig 7. Pressure Transference of Spacer Bandages (Relaxed) Figures 8 to 1 1 represent the pressure transference of spacer bandages at known pressures under extension up to 120%.
o
10
20
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a
w
40
m
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im
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Fig 8. Effect of Extension on Pressure Transference of Spacer Bandages - Black (1)
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4.m
,
4m.
am.
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10
20
10
u)
HI
~ J I
m
m
m
Im
-m Fig 9. Effect of Extension on Pressure Transference of Spacer Bandages - White (2) It will be noticed that increase in applied pressure does not influence the pressure transference at any one point and the variation is marginal in all the samples. This affirms that these spacer fabrics can be used as ideal padding bandages, and by controlling the tension it will be possible to generate the required pressure for the treatment of venous leg ulcers.
Fig 10. Effect of Extension on Pressure Transference of Spacer Bandages - White (3)
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Fig 11. Effect of Extension on Pressure Transferenceof Spacer Bandages - Blue (4)) It should also be stated that according to Laplace equation the pressure generated on to the limb by a bandage is directly proportional to the tension of the bandage and the number of layers but inversely proportional to the width of the bandage and the circumference of the limb. Utilising this concept, the research and development programme into the mathematical modelling of spacer fabrics to achieve the required pressure mapping for the treatment of venous leg ulcer is in progress at the University of Bolton. SUMMARY
The effective management of venous leg ulcer involves careful selection of bandages to reverse the venous blood flow back to the heart. The paper has discussed the significant contribution of padding as well as compression bandages in healing the ulcer. The advantages and limitations of the existing two-layer to four-layer bandaging regimens are discussed in this paper. It is obvious that the pressure transference of commercial padding bandages varied and none of the padding bandages investigated satisfied the requirements of an ideal padding bandage. The study also demonstrated the need for developing a single-layer bandaging regimen for the benefit of elderly and cutting the cost of treatment. 3D spacer technology has been investigated and the results affirmed that spacer bandages would be utilised to design and develop a single-layer system that could replace the currently used cumbersome four-layer system. A suitable spacer structure can combine the desirable attributes of both the padding and 2-dimentional compression bandages into one composite 3-dmentiod structure.
ACKNOWLEDGEMENTS The research and development programme is funded by Engineering and Physical Sciences Research Council (EPSRC), UK. The authors are grateful to EPSRC for finding and supporting the research programme.
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REF’ERENCES 1 P N Kimbrell and V Larson-Lohr, ‘Venous Disease’, in P J Sheffield, C E Fife and A P S Smith (Eds), Wound Care Practice, Best Publishing Co,2004,267.
2 S Rajendran and S C Anand, ‘Design and development of novel bandages for compression therapy’, British JNursing, 2003 11 1300-1307. 3 S Rajendran and S C Anand, ‘The contribution of textiles to medical and hdthcare products and developing innovative medical devices’ Indian J Fibre & Text Res, 2006 31 215-229. 4 EHC, ‘Compression Therapy for Venous Leg Ulcers. University of York NHS Centre for Review and Dissemination’, E’ective Healthcure, 1997 3 1-12. 5 N Cullum et al, ‘Compression for venous leg ulcers’, Cochrane Review: The
Cochrane Library,Oxford, 2002,l. 6 S C Anand ‘Spacers- at the technical frontier’, Knit International, 2003 110 38-41.
7 Anon, ‘Spacerfabric focus’, Knit International,2002 109 20-22. 8 C Moffat and P Harper, Leg Ulcers, Churchill Livingstone, Edinburgh, 1997. 9 RCN, Clinical Practice Guidelines. The Management of Patients with Venous Leg Ulcers. RCN Institute,London, 1998. 10 M Collier, Venous Leg Wceration: In Wound Management: Theory and Practice, Edited by M Miller and D Glover, London. Nursing Times Books, 1999. 11 D Simon, ‘Approachesto venous leg ulcer care within the community: compression, pinch skin grafts and simple venous surgery’, Ostomy Wound Management, 19% 42 2 34-40.
12 R Sterner et al, ‘Compression mabnent for the lower extremities particularly with compression stockings’, The Dermatologist, 1980 31 355-365.
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