ORI GI N AL ARTI CLE
Correla t ion bet w een a nk le- bra chia l index before a nd a ft er shut t le w alk t est
I ná cio Te ix e ir a da Cunha- Filho; D a nie lle Apa r e cida Gom es Pe r e ir a ; André M a ur ício Bor ge s de Ca r va lho; Júlia Polca r o Ga r cia ; Lucia na M or a is M or t im e r ; I na lda Cunha Burni*
*Cent ro Universit ário de Belo Horizont e ( UNI - BH) , Belo Horizont e, MG, Brazil.
Correspondence
J Vasc Bras. 2007; 6( 4) : 332- 8.
ABSTRACT
Ba ck ground: Pat ient s wit h peripheral occlusive art ery disease ( POAD) show changes in blood flow t hat m ay im pair t heir walking abilit y. However, variabilit y bet ween inferent ial m easurem ent s of blood flow and walking perform ance is st ill high.
Obj e ct ive :To correlat e t he ankle- brachial index ( ABI ) before and aft er perform ing t he shut t le walk t est ( SWT) .
M et hods:Twent y- one pat ient s wit h claudicat ion due t o POAD had t heir ABI values regist ered before and aft er walking based on a progressive ext ernal cont rolled speed walking prot ocol.
Re sult s:Dist ance ( 261.07± 160.63 m ) , t im e ( 292.30± 122.61 seconds) and speed ( 1.23± 0.34 m / s) obt ained at claudicat ion onset and when t he lim it ing walking sym pt om st art ed ( 369.52± 157.97 m , 377.71± 104.60 seconds, 1.46± 0.29 m / s, respect ively) were regist ered. Mean ABI before and aft er t he SWT was 0.66± 0.14 and 0.42± 0.19, respect ively. There was no subst ant ial correlat ion bet ween ABI pre- and post - walking and t he variables obt ained wit h t he SWT ( dist ance, t im e and speed) . Conclusion: Tim e, speed and dist ance for claudicat ion onset and walking lim it ing sym pt om during a progressive speed walking prot ocol are independent of inferent ial blood flow m easurem ent s obt ained by ABI before and aft er exercise.
Keyw ords:Claudicat ion, walking t est , flow.
RESUM O
Obj et ivo: Est abelecer o nível de correlação ent re as m edidas do índice t ornozelo- braço ( I TB) , pré e pós- esforço, com um novo t est e de deam bulação cham ado t est e de deslocam ent o bidirecional progressivo ( TDBP) .
M ét odos: Vint e e um pacient es claudicant es, com diagnóst ico de DAOP, t iveram regist rados o I TB ant es e após a realização de um t est e de cam inhada no solo, com cont role ext erno e progressivo de velocidade ( TDBP) .
Re sult a dos:Foram regist rados a dist ância ( 261,07± 160,63 m et ros) , o t em po ( 292,30± 122,61 segundos) e a velocidade ( 1,23± 0,34 m / s) obt idos no início do surgim ent o de sint om a claudicant e, bem com o durant e o surgim ent o de sint om a lim it ant e ( 369,52± 157,97 m et ros, 377,71± 104,60 segundos, 1,46± 0,29 m / s, respect ivam ent e) . A m édia do I TB de repouso foi de 0,66± 0,14, e de pós-esforço foi de 0,42± 0,19. Não se observou nenhum a correlação im port ant e ent re as variáveis do t est e ( dist ância, t em po e velocidade) com o I TB de repouso e nem após esforço.
Conclusã o:O t em po, velocidade e dist ância de surgim ent o de sint om a claudicant e e de sint om a claudicant e lim it ant e durant e o t est e de cam inhada progressiva são independent es da m edida inferencial de fluxo sangüíneo at ravés do I TB de repouso e pós- exercício.
Pa la vr a s- cha ve:Claudicação, cam inhada, fluxo.
I nt roduct ion
Com binat ion of ankle- brachial indexes ( ABI ) and walking t est s has been used t o bet t er underst and t he degree of pat ient im pairm ent due t o peripheral occlusive art ery disease ( POAD) , since it associat es inferent ial m easurem ent of blood flow int egrit y and funct ional capacit y.1 Due t o vasodilat at ion and inabilit y t o increase flow aft er t he level of at herosclerot ic obst ruct ion, t he ABI m easured aft er physical act ivit y ( ABI - e) t ends t o drop in relat ion t o rest levels. Thus, ABI - e is considered as having bet t er prognost ic value t han rest ing ABI ( ABI- r) .2 , 3 I n addit ion, ABI - e has an addit ive value in t he diagnosis of peripheral art ery obst ruct ion for individuals whose ABI- r is norm al, but has a m aj or fall wit h effort .4 Reduct ion in syst olic pressure aft er exercises is considered one of
t he m ost sensit ive indicat ors t o det ect hem odynam ically significant st enosis.5
However, if on t he one hand t he ABI - r is universally accept ed as a clinical indicat or of blood flow im pairm ent , it does not always have sat isfact ory or significant correlat ions wit h perform ance in funct ional t est s.6 The correlat ion level bet ween ABI - r and walking dist ance unt il st art of claudicat ion
( r = 0.17) and wit h m axim um claudicat ion ( r = 0.24) , during t he prot ocol in t readm ill wit h const ant load is quit e low.7 However, when t he prot ocol is for m axim um progressive load, such levels rise t o
0.48 and 0.61, respect ively.8 , 9
ABI - e can pot ent ially have bet t er correlat ion levels wit h perform ance, since individuals wit h POAD usually have a reduct ion in ABI during effort . However, furt her invest igat ion is required t o est ablish usefulness and feasibilit y of ABI - e in walking t est s.
The t readm ill t est ( TT) provides an obj ect ive m easurem ent in walking perform ance. However, it is expensive, oft en requires specialized personnel, is not always available in clinics and does not reproduce a usual form of walking. Test- ret est reliabilit y for t im e of pain onset and lim it ing pain is low and quit e variable.8 , 9 Such variabilit y in st abilit y of dist ance m easurem ent s using t he t readm ill nat urally reflect s, in principle, t he m ult iple prot ocols and/ or form s how t est s are conduct ed.
best prot ocol for t he t readm ill and t echnical difficult ies, and cost associat ed wit h t his inst rum ent . The 6- m inut e walking t est ( 6MWT) was developed as a cheaper and alt ernat ive form of m easuring
funct ional capacit y, and it s obj ect ive is m easuring t he dist ance t he pat ient is able t o walk over a 6-m inut e period.1 0 However, t he prot ocol also has st andardizat ion problem s and higher suscept ibilit y t o
variat ion, since t he t est speed is not cont rolled and t he perform ance can be influenced by pat ient 's m ot ivat ion and encouragem ent .1 0
Anot her walking t est t o assess aerobic resist ance has been recent ly present ed in t he lit erat ure, called shut t le walking t est ( SWT) .1 1 This t est allows individuals t o develop a m ore fam iliar walking act ivit y,
i.e., walking on t he ground inst ead of walking on a t readm ill, and speed is cont rolled ext ernally by a previously recorded sound signal. Speed increases every m inut e and t he t est is only int errupt ed when t he pat ient cannot follow t he previously est ablished velocit y for a specific st age. This t est has a low cost and progressive speed, t herefore it is m ore likely t o reveal t he pat ient 's funct ional capacit y m ore reliably. Thus, SWT aggregat es values present in t readm ills ( ext ernal speed cont rol) and in t he 6MWT ( walking on a st able surface t hat is m ore represent at ive of daily walking) . SWT also has bet t er psychom et ric propert ies t han t he 6MWT and TT.1 0 , 1 2
Considering t hat t here has been no consensus on which ABI ( rest vs. effort ) is m ore adequat e t o assess t he level of blood flow im pairm ent for t he lower lim bs, and t hat prot ocols of funct ional t est s involving walking for assessm ent of claudicat ing pat ient s are variable, t here should be m ore st udies on t he associat ion of inferent ial flow m easurem ent s wit h m ore funct ional perform ance prot ocols.
Therefore, t his st udy aim s at invest igat ing t he degree of associat ion of ABI aft er effort wit h a walking t est t hat is closer t o funct ional act ivit y and t hat has m ore st abilit y in relat ion t o occurrence of
sym pt om s.
M et hods
I ndividuals of bot h genders, independent of et hnic group or age, wit h POAD confirm ed clinically or by ult rasound were cont act ed t o part icipat e in t he st udy. The pat ient s were part of a vascular
rehabilit at ion program at t he Cent er of St udies of Peripheral Vascular Diseases of Clínica Escola do Cent ro Universit ário de Belo Horizont e ( UNI - BH) . The st udy st art ed aft er approval by t he Hum an Research Et hics Com m it t ee of Hospit al SOCOR and each part icipant j oined t he program aft er signing a consent form cont aining all inform at ion regarding t he st udy.
I nclusion crit eria were adult pat ient s wit h POAD who present ed ABI- r bet ween 0.9 and 0.4, wit h no pain at rest and wit h int erm it t ent claudicat ion.
Exclusion crit eria were pat ient s who had ABI - r > 0.9 or < 0.4, or t hose wit h pain at rest ; pat ient s unable t o perform exercises, such as t hose wit h severe congest ive heart failure, unst able angina, arrhyt hm ias, who did not cooperat e wit h perform ing t he t est ; pat ient s whose ABI was inaudible and, consequent ly, not m easurable; and diabet ic pat ient s, except t hose who had sym pt om s of pain.
Pr oce dur e s
ABI m easurem ent
A specific cuff for lower lim bs was placed above t he m alleolus and inflat ed at 20 m m Hg above t he SAP t o m easure syst olic pressures of each lim b. A Doppler probe was placed on t he post erior t ibial and dorsal foot art eries. Alt hough ABI is usually obt ained t hrough t he rat io bet ween t he highest syst olic pressure values recorded for t he lower and upper lim b, t his st udy used t he lowest syst olic pressure value in t he lower lim b, because t he aut hors consider t hat t he largest obst ruct ion had a great er im pact on t he funct ioning of t he lower lim b.2 The lower lim b t hat generat ed t he lowest ABI was used as a reference lim b t o record t he ABI aft er t he walking t est .
Aft er t he walking t est , t he pat ient was im m ediat ely placed in a supine posit ion and t he pressures in t he lower and upper lim bs were recorded in t hat order. However, at t hat m om ent , only t he lim b previously ident ified wit h t he lowest ABI was assessed.
Shut t le walking t est ( SWT)
For t his t est , each part icipant walked a 10- m et er dist ance, lim it ed by t wo cones placed on t he ground. The part icipant m ade consecut ive laps around bot h cones, wit h speeds t hat increased progressively unt il exhaust ion, presence of claudicat ing sym pt om or inabilit y t o m aint ain t he previously est ablished rhyt hm . Speed was increased at every m inut e ( 0.17 m / s) and cont rolled by audio signals, generat ed by a port able sound device. The SWT consist ed of 12 levels last ing 1 m inut e each, and init ial speed was 0.5 m / s unt il a m axim um speed of 2.37 m / s.1 1
During t he SWT, t he pat ient used a belt over his chest t hat cont ained a port able t ransm it t er. A Polar TM ( m odel Sport Test er, USA) heart rat e m onit or capt ured all signals em it t ed by t he t ransm it t er at t ached t o t he pat ient 's chest t o record heart rat e ( HR) during t he whole walking t est . By t he end of each m inut e, HR was recorded.
The variables of int erest in t his t est were dist ance, t im e and speed recorded at t he pain onset and at t he lim it ing sym pt om at which t he pat ient could no longer follow t he prot ocol.
St at ist ical analysis
For t he descript ive st at ist ics, t he dat a were present ed as m ean and st andard deviat ion. Pearson's correlat ion coefficient was used t o est ablish a correlat ion bet ween ABI values and t he variables evaluat ed in t he SWT. A significance level equal or higher t han 5% was used t o det erm ine whet her t he associat ion bet ween m easurem ent s differed from zero. St udent 's t t est was used t o com pare
SWT variables at t he st art of claudicat ing sym pt om s and during lim it ing claudicat ing sym pt om s.
Result s
Twent y- nine pat ient s were cont act ed t o part icipat e in t he st udy, but only 21 were included. The ot her eight pat ient s did not show up for t he procedures. Out of 21 part icipant s, 15 were m ales and six were fem ales, aged bet ween 35- 80 years ( m ean 61.95± 10.21 years) . Mean height was 163.00± 7.00 cm and m ean body weight was 70.16± 14.68 kg. All pat ient s t olerat ed t he procedures and t here were no com plicat ions or m edical em ergency during t he st udy.
The pat ient s had t heir diagnosis of POAD confirm ed clinically ( presence of int erm it t ent claudicat ion) and by ult rasound exam inat ion ( Doppler scan) . Five pat ient s had obst ruct ive lesion in one lim b and 16 had it in bot h lower lim bs. Mean diagnost ic t im e of POAD was 54.4 m ont hs ( 12- 216 m ont hs) .
problem s. Eleven pat ient s were sm okers, eight ex- sm okers and t wo pat ient s had never sm oked cigaret t es. Hypert ension and diabet es m ellit us were t he m ost frequent ly found associat ed diseases am ong t he part icipant s ( Table 1) . Drugs in use are list ed in Table 1.
Of t he 21 pat ient s included in t he st udy, only one could not have his ABI aft er effort recorded. Mean ABI - r value was 0.66± 0.14 ( 95% CI 0.38- 0.94) ; and m ean ABI - e value was 0.42± 0.19 ( 95% CI 0.24-0.61) . There was a reduct ion of 0.24± 0.14 in m ean ABI obt ained aft er effort in relat ion t o rest ing ABI ( p < 0.0005) . Mean values of dist ance, t im e, speed and HR of claudicat ing pain onset , as well as occurrence of lim it ing claudicat ing sym pt om are described in Table 2. One pat ient did not report init ial claudicat ing sym pt om and, t herefore, was not included in correlat ion st at ist ics.
The correlat ion bet ween ABI - r wit h dist ance, t im e and speed of claudicat ing sym pt om onset and lim it ing claudicat ing sym pt om was sm all and not significant , ranging from 0.19 t o 0.25. The ABI- e did not show m aj or correlat ion wit h any of t he variables obt ained, bot h at claudicat ing sym pt om onset and during lim it ing claudicat ing sym pt om ( ranging from - 0.01 t o 0.12) .
Funct ional variables had m ore significant correlat ions bet ween t hem selves when claudicat ing sym pt om onset was com pared wit h lim it ing claudicat ing sym pt om . The correlat ions bet ween
dist ance, t im e and speed at claudicat ing sym pt om onset wit h t ot al dist ance, t im e and speed achieved at t he lim it ing sym pt om were 0.92 ( p < 0.0005) , 0.91 ( p < 0.0005) , and 0.89 ( p < 0.0005) ,
There was no st at ist ical difference bet ween HR recorded at claudicat ing sym pt om onset and during t he lim it ing sym pt om HR ( Table 2) . HR was not significant ly correlat ed wit h dist ance, t im e and speed during occurrence of claudicat ing sym pt om . On t he ot her hand, HR during lim it ing sym pt om had a 0.55, 0.55 and 0.49 ( p < 0.0005) correlat ion wit h dist ance, t im e and speed during lim it ing
claudicat ion, respect ively.
Discussion
The m ain obj ect ive of t his st udy was t o det erm ine t he level of associat ion of ABI- e wit h a new walking t est , t he SWT. Choice for ABI aft er perform ing physical act ivit y was due t o t he fact t hat t he lit erat ure has variable correlat ions bet ween ABI - r and perform ance.1 Ot her st udies suggest t hat ABI -e could hav-e b-et t -er corr-elat ion l-ev-els, alt hough it s us-e has not b-e-en inv-est igat -ed from t h-e
perspect ive of an associat ion wit h funct ional capacit y and hem odynam ic variables.3 , 5 The SWT was chosen due t o it s st andardizat ion, less influence as t o pat ient encouragem ent , advant ages t o develop ground walking at increm ent al speeds, besides present ing m ore st abilit y in reproducibilit y
m easurem ent s.1 3
McDerm ont t et al. suggest ed t hat t he ABI m easured aft er physical act ivit y could pot ent ially have bet t er correlat ion levels wit h perform ance t han t he ABI - r, since individuals wit h POAD could have a fall of m ore t han 25% in ABI - e.5 , 1 4 I n t he present st udy, t here was a reduct ion of around 36% in t he index obt ained aft er effort , but t here was no subst ant ial correlat ion bet ween t his index and m easures of t im e, speed or dist ance of sym pt om onset or lim it ing sym pt om . Correlat ion bet ween ABI- r and funct ional variables was sm all and not significant .
St ein et al. dem onst rat ed t hat t he associat ion bet ween ABI and funct ion was st rong when t he ABI was calculat ed using t he m ean value bet ween t he dorsal foot and t he post erior t ibial art eries.2 I n t his
st udy, however, t he lowest syst olic pressure value m easured in t he lower lim b was used, because we believe t hat t he largest obst ruct ion has a great er im pact on t he funct ion of t he lim b. However,
previous st udies used t he highest arm and leg pressures t o calculat e t he ABI .1 , 1 5 Therefore, it is possible t hat variat ions in ABI recording part ly explain t he variabilit y of correlat ion values wit h funct ional m easurem ent s.
Anot her fact or t hat m ay cont ribut e t o explain t he low or lack of correlat ion bet ween ABI- r and ABI - e and SWT is t he level of physical act ivit y by part icipant s. I t has been dem onst rat ed t hat t rained pat ient s have bet t er m echanism s for oxygen upt ake and peripheral ut ilizat ion. These fact ors possibly bet t er explain sym pt om m it igat ion of claudicat ing sym pt om s in funct ional t est s, despit e not changing blood flow as est im at ed by ABI .1 I n t he present st udy, 76% of pat ient s were t aking part of a physical
act ivit y program and, t herefore, could already show peripheral adapt at ions t hat influenced t he associat ion bet ween blood flow and perform ance. Gardner et al. dem onst rat ed t hat t he increase in blood flow assessed by m eans of hyperem ic response ( 27% ) and by ABI ( 1% ) were m uch lower t han t he im provem ent in walking dist ance unt il pain onset ( 133% ) and unt il occurrence of m axim um claudicat ing pain ( 77% ) aft er a t raining program .3
Chronot ropic behavior also support s t he hypot hesis t hat t here m ay be a peripheral adapt at ion. First , t here was no st at ist ically significant difference bet ween sym pt om onset HR and lim it ing sym pt om HR, despit e t he st at ist ically significant differences in t est perform ance variables. Therefore, t his suggest s t hat perform ance during t he t est can be m ore relat ed t o abilit y of ut ilizing oxygen t han t o dist ribut ion m echanism s. I n addit ion, t here was no correlat ion bet ween sym pt om onset HR and any variable in t he walking t est , whereas shared variance ( r2) bet ween HR and variables during lim it ing sym pt om
was only 30% .
I f, on t he one hand, t here was no correlat ion bet ween blood flow im pairm ent indexes and perform ance wit h t he SWT in t his populat ion, SWT proved t o be consist ent as t o assessm ent of clinical sym pt om s. Tim e, dist ance and speed of sym pt om onset had st rong and significant
correlat ions wit h t he variables obt ained during lim it ing sym pt om ( correlat ion coefficient ranging from 0.89 t o 0.92, p < 0.05) . Thus, SWT is a feasible inst rum ent t o assess sym pt om s in pat ient s wit h POAD.
St udy lim it a t ions
Reduced num ber of pat ient s, as well as use of drugs and lack of uniform it y regarding level of physical act ivit y are issues t hat should be considered in furt her st udies, since t hey could have int erfered wit h t he result s. The m ost adequat e form of recording ABI also needs t o be invest igat ed.
Conclusions
Furt her reduct ion in ABI seen aft er effort in t his st udy corroborat es flow im pairm ent in pat ient s wit h POAD. However, low or lack of correlat ion of ABI - r and ABI - e wit h SWT perform ance suggest s t hat t he claudicat ing pat ient is able t o perform t he walking t est t hanks t o, in principle, an efficient m echanism for oxygen upt ake. SWT proved t o be consist ent in assessing t im e, dist ance and speed during sym pt om onset and lim it ing claudicat ing sym pt om . Therefore, t his walking t est is an
alt ernat ive for a consist ent and pract ical assessm ent of pat ient s in angiologic clinics. Our result s suggest t hat assessm ent of t he claudicat ing pat ient 's level of im pairm ent should not discard a funct ional assessm ent .
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Correspondence:
In•cio Cunha-Filho
Rua Ernani Agr‚cola 50/302
CEP 30455-760 – Belo Horizonte, MG, Brazil Tel.: (31) 3378.8758
Em ail: inacut ex@t erra.com .br
This proj ect was part ially funded by FAPEMI G ( research scholarship) .
