Measurement of forces associated with

8/7/2019 Measurement of forces associated with

http://slidepdf.com/reader/full/measurement-of-forces-associated-with 1/4

fM easurem ent o f f o rces a ssoc ia ted w i th

c o m p r e s s io n t h e r a p y

D . W e r t h e i m I J . M e l h u i s h 2 R . W i l l i a m s I K . H a r d i n g 2

1School of E lectronics, U niversi ty of Glam organ, Po ntypr idd, CF37 1DL, UK2Wound Heal ing Research Unit , Depa r tment of Surgery, Univ ersi ty of Wales C ol lege of Medic ine,

Cardi f f CF4 4XN, U K

Abstract--Compression therapy is the principal treatment for leg ulcers associated withvenous disease. The eff icacy of compression therapy can be variable, which may in partbe owing to the degree of compression appl ied. However, i f the mechanism of act ion ofthis treatment could be better understood, i t might be possible to improve i ts eff icacy. I t isnot clear whether assessment of the degree of compression should be made under stat icor dynam ic con dit ions, or both . A review of methods used previously suggests the needfo r a new method of assessment al lowing cont inuous monitor ing, even during movement.A system fo r continuous stat ic and dynamic mea surements of compression is described.Using an air chamb er and ma nome ter to test the system, agreem ent w ithin • 3 mm Hg isobserved. The system is appl ied to invest igate ch anges in force s, expressed as pressure,

u n d e r bandag es and compression stockings. Appl icat ion of f ive bandage systems byexperienced nurses to a volunteer shows a marked variat ion in appl ied pressure. Duringshort periods of walking, rapid changes in pressure und er compression stockings areobserved, including some transients of less than 0.25s. The method is simple to applyand may help to understand further the mechanism of act ion of compression therapy.

Keywords~Bandages, Compression therapy, Forces, Pressure

Med. Biol. E ng. Com put., 199 9, 37, 31-3 4

1 I n t r o d u c t i o n

VENOUS DISEASE is the m ost c om m on c ondition asso ciated

wi th chron ic u lcerat ion of the leg (BAKER e t a l . , 1992;

HARDING and LEAPER, 1994). The underly ing re asons for

the fo rm at ion of venous u lcers and thei r s low and unpred ict -

ab le rate o f heal ing are no t wel l unders tood , and there are

several theor ies regard ing the aet io logy of venous leg u lcers

(SHAMI e t a l . , 1992) . The pr incipal t reatment fo r venous leg

u l ce r s i s co mp ress io n t h e rap y , wh ich h as b een u sed fo r

cen tur ies (BLAIR e t a l . , 1988) . However , the way compression

therapy ass is t s in heal ing i s no t wel l unde rs tood (SARIN e t a l . ,

1992) , and vary ing t reatment success rates have been repor ted

(BLAIR e t a l . , 1988; MOFFATT e t a l . , 1992; FLETCHER e t a l . ,

1997).

I t has been suggested that the var iab le heal ing rates may be

due to d i f ferences in app l icat ion technique producing vary ingd eg rees o f co mp ress io n (BLAIR e t a l . , 1988; HORNER e t a l . ,

1980) . Thus there has been much in teres t in invest igat ing the

p h y s io lo g ica l e f f ec t s o f co mp ress io n t h e rap y .

The s i te o f u lcerat ion in venous leg u lcers i s most

commonly in the lower leg area (NELZI~N e t a l . , 1994;

BAKER e t a l . , 1991) , w hich i s suggest ive o f a local vu lner-

ab i l i ty . In pat ien ts wi th venous d isease, raised ambulatory

venous pressure, measured in a vein in the foo t , has been

found to be associated wi th an increased incidence of

ulceration (NICOLAIDES e t a l . , 1993).

Correspondence should be addressed to Dr D. Wertheim; ema il:

wertheim@ cardiff ac.ukFirst received 27 Ma rch 1998 and in final form 6 Au g u s t 1998

9 IFMBE:1999

M e d i c a l & B i o l o g ic a l E n g i n e e r i n g & C o m p u t i n g

1 . l C o m p r e s s i o n t h e r a p y

I t has been suggested that the p ressure g rad ien t ach ieved by

s t an din g i n a sw imm in g p o o l can a l l ev ia t e th e sy m p to ms o f

venous u lcers (MONETA e t a l . , 1995) . Compression s tock ings

were therefore designed to ach ieve a g rad ien t equ ivalen t to the

hydrostat ic p ressure g rad ien t in the pool . STEMMER e t a l .

(1 9 80 ) ex amin ed t h e ap p l i ca t io n o f co mp ress io n s t o ck in g s

for the t reatment o r p rophylax is o f var ious condi t ions and

suggested several p ressure p rof i les that were dependent upon

the medical condi t ion .

Ho wev er , i t i s u n c l ea r h o w th e d eg ree o f co mp ress io n

req u i r ed may v ary wi th d i f f e r en t d i sease s t a t es an d b e tween

dif feren t ind iv iduals wi th legs o f d i f feren t s izes and shapes . I f

the com pressio n app l ied i s too low, then the ef f icacy of the

t r ea tmen t ma y b e imp a i r ed (BLAIR e t a l . , 1988) . I f the ap p l ied

'p r es su re ' i s t o o g rea t , t h en t i s su e d amag e may b e cau sed(CALLUM e t a l . , 1987) . I t can be expected that the ef fect o f

co mp ress io n o v er b o n y p ar t s o f t h e l eg wi l l b e d i f fe r en t t o t h at

over sof t t i ssue, and th is i s d i f f icu lt to assess because of po in t

load ing effects .

Thus there has been m uch in teres t in evaluat ing sub-

bandage pressure o r fo rce, as wel l as p ressure and forces

u n d er g rad u a t ed co mp ress io n s t o ck in g s (BLAIR e t a l . , 1988;

R A J e t a l ., 1980; PARTSCH and HORAKOV A, 1994; SAWADA,

1993; TENNANT t a l . , 1988; DALE e t a l . , 1983; NELSON e t a l . ,

1995; BARBENEL and SOCKLINGHAM, 199 0; SOCKLINGHAM

e t a l . , 1990; STEINBERGand COOKE, 1993; LOGAN t a l . , 1992),

an d i n ev a lu a t in g t h e h aemo d y n am ics as so c i a ted wi th co m -

pression therapy (SARIN e t a l . , 1992; LAWRENCE and

KAKKAR, 1980).

1 9 9 9 , V o l . 3 7 3 1



S e v e r a l s t u d i e s o f c o m p r e s s i o n t h e r a p y a p p l i e d b y h e a l th

ca re p ro fe s s iona l s have r epo r t ed t ha t sub -bandage p r e s su re can

va ry m arked ly (B LA IR e t a l . , 1988; RAJ e t a l . , 1980; PARTSCH

and HORAKOV A, 1994; SAWAD A, 1993; TENNANTe t a l . , 1988 ;

D A LE e t a l . , 1983; NELSON e t a l . , 1995; LOGAN e t a l . , 1992) .

These s t ud i e s have been on bo th hum an and a r t i f i c i a l l egs .

H ow eve r , on ly a f ew s tud i e s have i nves t i ga t ed t he e f f ec t o f

m o v e m e n t o n t h e f o r c e s a p p l i e d b y c o m p r e s s i o n t h e r a p y

(SOCKLINGHAM e t a l . , 1990; STEINBERG and Coo KE , 1993) .

The r ea sons fo r t he va r i ab i l it y i n sub -bandage p r e s su re a r eunc l ea r bu t m ay be due t o t he app l i ca t i on t echn iques , t he

va r i ab i l i t y o f t he pa t i en t s o r vo lun t ee r s , o r t he phys i ca l

p r o p e r t ie s o f t h e b a n d a g e s y s t em s .

1. 2 M e a s u r e m e n t o f p r e s s u r e a n d f o r c e

Pres su re i s a s ca l a r quan t i t y t ha t i s gene ra l l y u sed fo r f l u id s ,

w he re t he fo r ce pe r un i t a r ea i s cons t an t a t any g iven c r o s s -

s e c t i o n ; t h i s a s sum p t ion i s c l ea r l y no t app l i cab l e fo r bandag es

on l egs , and so t he t e rm fo rce i s p r e f e r ab l e . I n add i t i on t o

n o r m a l f o r c e s , s h e a r f o r c e s m a y b e i m p o r t a n t , a s t h e y m a y

induce a t ea r i ng o r b r i ng ing t oge the r e f f ec t on vu lne rab l e

t i ssue .

T h e l a w o f L a p l a c e h a s b e e n f o u n d t o b e u s ef u l i n a n u m b e r

o f a r e a s i n m e d i c i n e (STILLWELL,1973). I t ha s been sugges t ed

t h a t L a p l a c e ' s e q u a t i o n P = T / R , wh ere R = radius , P = sub-

band age p r e s su re , and T = t ens ion , can be u sed t o e s t im a t e t he

sub -b andag e p r e s su re P , i f t he t ens ion T r equ i r ed t o p roduce a

g iven ex t ens ion i s know n , u s ing a m od i f i ed fo rm

T N x cons t an tp -CW

w he re N = nu m be r o f l aye r s , c = l im b c i r cum fe rence , w =

w id th o f bandage , and , i n t h i s ca se , T = t ens ion , i n N e w to ns

(THOMAS, 1996; NELSON, 1996) .

H o w ev e r , t he su i t ab i l it y o f t he app l i ca t i on o f the equa t i on i n

this s i tuat ion i s not c lear , as the leg i s c lear ly nei ther

cy l i nd r i ca l , no r a f l u id , and t he bandage m a y no t be a t un i fo rm

tens ion a round t he l eg . I n add i t i on , i n t he m od i f i ed fo rm , t he

t e rm in c luded fo r the nu m b er o f l aye r s a s a s im p le m u l t i p l e

appea r s ques t i onab l e .

T r a n s d u c e r s u s e d f o r m e a s u r e m e n t o f s u b - b a n d a g e f o r c e s

t end t o be o f l ow p ro f i le t o m in im i se i n t e r f e r ence i n t he

m easu rem en t . The fo r ce app l i ed on a t r ansduce r i s l i ke ly t o

v a r y i n m a n y p o s i t i o n s o n t h e l eg . I f a n a v e r a g e ' p r e s s u r e ' i s

m on i to r ed w i th a l a rge -a r ea t r ansduce r , t hen i n fo rm a t ion abou t

l o c a l h i g h - f o r c e o r p r e s s u re - a r e a s m a y b e m i s s e d , a n d a l o w -

a rea t r ansd uce r i s l ike ly t o have g r ea t e r s ens i t iv i t y t o pos i t i on .

T h u s d i f f e r e n t m e a s u r i n g s y s t e m s m a y p r o d u c e d i f f e r i n g

resul ts .A i r - f i l l ed s enso r sys t em s usua l l y a l l ow on ly i n t e rm i t t en t

m on i to r i ng (PA R TSC H a n d HORAKOVA, 1994; SAWAD A, 1993;

STEINBERG and COO KE, 1993) , an d l iquid-f i l led sens or s ys-

t em s a r e l i ke ly t o be s ens i ti ve t o m ove m en t a r t e f ac t , becau se

o f m o v e m e n t o f th e l i q u id c o l u m n (NELSON e t a l . , 1995 ;

BARBENEL a n d SOCKLINGHAM,1990; SOCKLINGHAMe t a l . ,

1990) .

W e f e e l t h a t s t u d i e s d u r i n g m o v e m e n t m a y b e u s e f u l , i n

v i e w o f t h e i m p o r t a n c e o f t h e c a l f m u s c le p u m p . F u r t h e r m o r e ,

i t ha s been found t ha t s equen t i a l -g r ad i en t , i n t e rm i t t en t pneu -

m a t i c c o m p r e s s i o n c a n e n h a n c e v e n o u s u l c e r h e a l in g (COLER-IDGE S M I T H e t a l . , 1990; MCCULLOCH e t a l . , 1994) , and a

l i m i te d r a n g e o f m o t i o n w a s f o u n d i n li m b s o f p a ti e n ts w i t h

c h r o n i c v e n o u s i n s u f f ic i e n c y ( C V I ) , w i th t h e d e g r e e o f l i m i ta -t i on appea r ing t o be r e l a t ed t o the deg ree o f C V I (BA C K e t a l . ,

1995) . Thus , t o enab l e con t i nuous m on i to r i ng du r ing m oue -

3 2

m e n t , w e d e v e l o p e d a s y s t e m i n w h i c h a t r a n s d u c e r c a n b e

p l aced d i r ec t l y on t he l eg , w i th no a i r o r l i qu id connec t i ng

link.

2 A i m

T h e a i m o f th i s s t u d y w a s t o d e v e l o p a n d a p p l y a s y s t e m f o r

c o n t i n u o u s m o n i t o r i n g o f f o r c e s u n d e r b a n d a g e s a n d g r a d u -

a t e d c o m p r e s s i o n s t o c k i n g s , b o t h u n d e r s t a t i o n a r y c o n d i t i o n sa n d d u r i n g m o v e m e n t .

3 M e t h o d

A Fon tanom e te r s enso r* , ba sed on t he s t r a in gauge

pr inc ip l e , w as u sed t o a s se s s sub -bandage p r e s su re

(WERTHEIM e t a l . , 1996) . The s enso r appea r s a s a r i g id d i s c ,

a p p r o x i m a t e l y 3 m m t h i c k a n d 1 2 . 6 m m i n d i a m e t e r . T h e

s e n s o r i s t e m p e r a t u re c o m p e n s a t e d f r o m 15 ~ t o 4 0 ~ T h e

sens i t i ve a r ea o f t he s enso r i s r ec t angu l a r and cen t r a l l y p l aced

on on e s i de o f the d i s c . The l o nge r s i de o f t he s ens it i ve a r ea i s

p l aced on t he l eg , such t ha t i t i s pa r a l l e l t o t he l ong ax i s o f the

l eg , w h ich has a l a rge e f f ec t i ve r ad ius o f cu rva tu re . B ecause

the re i s no l i qu id co lum n , bo th s t a t i c and dynam ic m easu re -

m e n t s c a n b e m a d e .

C a l i b r a t i on w as ach i eved us ing a w a t e r co lum n and a l so an

a i r c h a m b e r c o n n e c t e d t o a m e r c u r y m a n o m e t e r .

F i v e e x t e n s i b l e b a n d a g e s y s t e m s w e r e a p p l i e d b y e i g h t

nu r se s t o t he l eg o f a s i tt i ng h ea l t hy vo lun t ee r . Four o f the

b a n d a g e s y s t e m s c o n s i s te d o f t w o b a n d a g e s a p p l ie d a t t w o

d i f f e r en t ex t ens ions , a s de sc r i bed i n t he m anufac tu re r s '

i n s t ruc t i ons . The f i f t h bandage sys t em w as a m u l t i l aye r

band age sys t em . The pos i t i on o f t he l eg w as ad jus t ed a s

r equ i r ed by t he nu r se . The fo r ces exp re s sed a s p r e s su re w ere

m o n i t o r e d , u s i n g t h e s e n s o r p l a c e d 4 . 5 c m a b o v e t h e m e d i a l

m a l l eo lus . The c i r cum fe rence o f t he l eg a t t h i s pos i t i on w as

2 5 c m .

The sys t em w as a l so u sed t o i nves t i ga t e changes i n fo r ce s ,

a s s o c i a t e d w i t h m o v e m e n t , u n d e r g r a d u a t e d c o m p r e s s i o n

s tock ings . Th ree s enso r s p l a ced on t he m ed ia l a spec t o f the

l e f t l eg w ere u sed t o m on i to r f o r ce s on s i x hea l t hy vo lun t ee r s .

The s enso r s w ere connec t ed t o am pl i f i e r s t ha t w e re connec t ed

to a 12 -b i t ana logue - to -d ig i t a l conve r t e r i n a no t ebook com -

pu te r . The s i gna l f rom the am pl i f i e r s w as s am pled a t 400 H z

pe r channe l . The da t a w ere s t o r ed on ha rd d i sk and t r ans f e r r ed

to a sp r eadshee t p rog ram fo r fu r t he r ana lys i s . The s enso r s

w ere p l aced a t t h r ee pos i t i ons : 9 cm above t he m ed ia l m a l -

l eo lus ( l ow er ) ; a t t he l eve l o f g r ea t e s t p ro m inen ce o f t he ca l f

m u s c l e ( m i d ) ; a n d a t t h e u p p e r b o r d e r o f t h e c a l f m u s c le

(uppe r ) . C l a s s 2 (European /C on t inen t a l c l a s s i f i ca t i on ) com -

pre s s ion s t ock ings w ere t hen app l i ed . The vo lun t ee r s s a t w i th

bo th l egs ho r i zon t a l . D a t a w ere r eco rded du r ing p l an t a r f l ex ion

and do r s i f l ex ion o f t he l e ft f oo t . D a t a w ere a l so co l l ec t ed

d u r i n g s h o r t p e r io d s o f w a l k i n g .

4 R e s u l t s

U s i n g a w a t e r c o l u m n o r a n a i r c h a m b e r w i t h m e r c u r y

m a n o m e t e r f o r c a l i b r a t i o n o f t h e s e n s o r s , a g r e e m e n t w i t h i n

4 - 3 m m H g w a s o b s e rv e d . A n e x a m p l e o f c o m p a ri s o n w it h a n

a i r c h a m b e r a n d m a n o m e t e r i s s h o w n i n F i g . 1 .

A m a r k e d v a r i a ti o n i n r e c o r d e d p r e s su r e u n d e r c o m p r e s s i o n

b a n d a g e s a p p l i e d t o t h e v o l u n t e e r w a s o b s e r v e d , a s s h o w n i n

F i g . 2 . B a n d a g e s y s t e m 2 u s e d t h e s a m e b a n d a g e a s s y s t e m 1 .

H o w e v e r , f o r s y s t e m 2 , t h e n u r s e s w e r e a s k e d t o a p p l y t h e

*Gael tec k td, Scot land

Med ical & Biological Engineer ing & Com put ing 1999, Vol . 37



F i g . 1

10

S 4

O:

-1 00 20 40 60 80 1O0

manometer ,m m H g

Example of comparison of sensor using air chamber con-nected to manometer; (manometer reading-sensor systemreading) against manometer reading

bandage w i th g r ea t e r ex t ens ion . Even so , t he r e i s l i t t l e d i f f e r -

ence i n t he m ed ian p r e s su re app l i ed . S im i l a r l y , bandage

s y s t e m 4 u s e d t h e s a m e b a n d a g e a s s y s t e m 3 . H o w e v e r , f o r

sys t em 4 t he nu r se s w ere a sked t o app ly t he bandage w i th

g rea t e r ex t ens ion . F ig . 2 a l so show s t he app rox im a te ove ra l l

r ange o f p r e s su re o f t he bandage sys t em s ; t h is an t i c i pa t ed

range i s ba sed on m anufac tu re r s ' da t a fo r t he s i ng l e bandage

sys t em s and pub l i shed da t a fo r t he m u l t i l aye r bandage sys t em

a n d a s s u m e s a l i m b c i r c u m f e r e n c e o f 2 5 c m .

In t he s t ud ie s w i th g r adua t ed -com pres s ion s t oc k ings , p l an -t a r f l ex ion and do r s i f l ex ion o f the l e f t f oo t w i th r e spec t t o t he

r e s t i ng pos i t i on w ere a s soc i a t ed w i th changes i n r eco rded

pre s su re t ha t cou ld va ry i n t he d i f f e r en t pos i t i ons m on i to r ed

on t he l eg , a s show n in t he exam ple i n F ig . 3 . The changes i n

p re s su re a l so va r i ed i n du ra t i on f rom t r ans i en t changes t o t he

pe r iod o f the m ano euvre . C h ange s i n p r e s su re du r ing w a lk ing

w e r e a l s o f o u n d t o b e d e p e n d e n t o n w h e r e t h e y w e r e m o n -

i t o r ed and o f va ri ab l e du ra t i on , i nc lud ing som e t r ans i en t s o f

less than 0 .25 s in durat ion , as seen in the exa mp le in Fig . 4 .

D ur ing w a lk ing , t he m ed ian o f t he g r ea te s t i nc r ea se i n p r e s -

su re r eco rded by t he m id -p l aced s enso r on t he s i x vo lun t ee r s

w a s 2 2 .5 m m H g ( ra n g e 4 - 6 8 m m H g ) .

5 D i s c u s s i o n a n d c o n c l u s i o n s

The p re s su re app l i ed w i th com pres s ion t he r apy i s l i ke ly t o

va ry a round t he pe r im e te r and l eng th o f t he l eg . G radu a t ed

com pres s ion i s t hough t t o he lp venous r e tu rn bu t , a s t he r e m ay

be a dec rease i n p r e s su re t h rough t i s sue ( S H A W and M U R R A Y ,

1982) t o t he ve ins , it m a y b e i m p o r t a n t to t a k e a c c o u n t o f t h e

type and bu lk o f t i s sue a s w e l l a s t he sk in su r f ace p r e s su re . Fo r

e x a m p l e , a s t h e p e r i m e t e r a t th e l e v e l o f m a x i m u m c i r c u m -

f e r e n c e o f t h e c a l f m u s c l e i s g r e a t e r t h a n t h e p e r i m e t e r b e l o w

tha t l eve l , i t m ay be t ha t t he p r e s su re r educ t i on f rom the

su r f ace o f t he l eg t o som e ve ins i s g r ea t e r a t the l eve l o f

m a x i m u m c a l f m u s c l e c i r c u m f e r e n c e .

The sys t em desc r ibed above , w h ich use s a sm a l l t em pera -

t u r e c o m p e n s a t e d s e n s o r , h a s a l l o w e d c o n t i n u o u s d i r e c t m e a -s u r e m e n t o f f o r c es a s s o c i a te d w i t h c o m p r e s s i o n t h e r a p y , e v e n

80 84

~ 6 0E

~ 4 ~

~. 20

F i g . 2

t I I I I

1 2 3 4 5b a n d a g e system

Variation in pressure observed on human leg with differentbandage systems. Broken lines indicate anticipated range ofpressure from bandage data. (-- ) rain, max, (0) median

Medical & Biological Engineer ing & Comput ing

60

F i g . 3

a~ 30 r ~ ~ ~ ~ ~ ~ _

= 20~" 10 ~ ~ l ~ . . . . .

I dorsi f lex plantar lex0 I I I I I I ] I I I I I I I I I I I I I

1 2 3 4 5 6 7 8 9 10time, s

Example o f changes in pressure und er compress ion s tock-ings associated with dorsiflexion a nd plan tar f lexion of left

f o o t

Q .

F i g . 4

7 0 -standing walking

6o. n~,d / ~ / 1

5040- .................. ..-. /~ ~

3 0 - upper

1o L L L

0 ~ I I I I I I I I I t I I I

1 2 3 4 5 6 7t ime, s

Example of changes in pressure under compression stock-ings when walking. 'L ' marks show when highest orces wererecorded under left Joot when walking (using two Force

Sensing Resistors)

dur ing m ovem en t . The re i s , how eve r , l im i t ed ev idence a s t o

t h e a p p r o p ri a te l e v el o f c o m p r e s s i o n a n d ' w h e t h e r a n d h o w t h isshou ld va ry i n d i f f e r en t peop l e and i n d i f f e r en t d i s ea se s t a t e s .

T h u s t h e i m p l i c a ti o n s o f th e o b s e r v e d v a r i a t io n i n b a n d a g e

app l i ca t i on a r e d i f f i cu l t t o a s se s s , a l t hough i t m ay accoun t , a t

l ea s t i n par t , f o r t he p r ev ious ly ob se rved va r i a t i on i n e f f i cacy .

In add i t i on , i t i s c l ea r t ha t com pres s ion ach i eved va r i e s ove r

the l eg , va r i e s w i th pos i t i on and du r ing m ovem en t , and m ay

va ry w i th t im e .

The sys t em i s su it ab l e fo r c l in i ca l u se and m ay t hus be o f

v a l u e i n c o m p a r i n g t r e a t m e n t s t r a te g i e s a n d i n c o m p a r i n g t h e

w a y i n w h i c h t h e y a r e a p p l i e d b y d i f f e re n t p e o p l e . T h e s y s t e m

i s be ing fu r t he r deve loped t o de t ec t shea r fo r ce s .

The r e su l ts o f t h is s t udy su gges t t ha t t he fo r ce s app l i ed by

e x p e r i e n c e d n u r s e s u s i n g c o n v e n t i o n a l c o m p r e s s i o n b a n d a g e s

c a n v a r y m a r k e d l y . F u r t h e r m o r e , t h is s t u d y h a s d e m o n s t r a t e dt h a t f o r c e s u n d e r g r a d u a t e d c o m p r e s s i o n s t o c k i n g s c a n v a r y

w i t h m o v e m e n t a n d w i t h f o o t p o si t io n . T h u s t h i s s y s t e m m a y

h e l p t o f u r th e r u n d e r s ta n d i n g o f t h e m e c h a n i s m o f a c t i o n o f

c o m p r e s s i o n t h e r a p y .

A c k n o w l e d g m e n t s - - T h i s study was funded by a grant from the HigherEducation Funding Council fo r Wales.

We are grateful for the help given to us by the nursing sta ff of theW oun d Healing Research Unit, University o f Wales College ofMedicine.

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A u t h o r s ' b i o g r a p h i e s

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assessm ent o f com press ion therapy . Th is research i s par t o f aco l labora t ive m ul t id isc ip l inary p ro jec t be tween the M edica l E lec-

t ron ics and S igna l P rocess ing Research Uni t (MESPRU), Schoolo f E l e c t r on i c s, U n i v e r s i t y o f G l a m o r g a n a n d t h e W o u n d H e a l i n g

R e s e a rc h U n i t ( W H R U ) , D e p a r t m e n t o f S u r g e r y , U n i v e r s it y o f W a l e s

C o l l eg e o f M e d i c in e .

3 4 M e d ic a l & B io log ic a l E ng ine e r ing & C o m p ut ing 1 9 9 9 , V o l . 3 7

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Measurement of forces associated with