Evaluation of functional capacity for exercise in children and adolescents with sickle-cell disease through the six-minute walk test

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ORIGINAL

ARTICLE

Evaluation

of

functional

capacity

for

exercise

in

children

and

adolescents

with

sickle-cell

disease

through

the

six-minute

walk

test

夽

Sandro

V.

Hostyn

_,

_Werther

_B.

_de

_Carvalho

_,

_Cíntia

_Johnston

_,

_Josefina

_A.P.

_Braga

a_{EscolaPaulistadeMedicina,UniversidadeFederaldeSãoPaulo,SãoPaulo,SP,Brazil} b_{UniversidadedeSãoPaulo,SãoPaulo,SP,Brazil}

c_{ServiceofPediatricandNeonatalPhysicalTherapy,HospitalSãoPaulo,EscolaPaulistadeMedicina,UniversidadeFederalde}

SãoPaulo,SãoPaulo,SP,Brazil

d_{DepartmentofPediatrics,EscolaPaulistadeMedicina,UniversidadeFederaldeSãoPaulo,SãoPaulo,SP,Brazil}

Received1February2013;accepted10April2013 Availableonline19September2013

KEYWORDS

Sicklecellanemia; Acutechest syndrome; Exercise; Nutritionalstatus

Abstract

Objective: Toevaluatelungfunctionalcapacity(FC)forphysicalexerciseinchildrenand ado-lescentswithsicklecelldisease(SCD)throughthesix-minutewalktest(6MWT).

Method: Across-sectionalprospectivestudywasperformedtoevaluatetheFCof46patients withSCDthroughthe6MWT.Thefollowingparameterswereassessed:heartrate(HR), respi-ratoryrate(RR),peripheralpulseoxygensaturation(SpO2),peakexpiratoryflow(PEF),blood pressure(systolicanddiastolic),dyspnea,andlegfatigue(modifiedBorgscale)atrest,inthe endofthetest,andtenminutesafterthe6MWT.Thetotaldistancewalkedwasalsorecorded. Forstatisticalanalysis,theparametricvariableswereanalyzedusingthepairedStudent’s

t-test,analysis ofvariance (ANOVA),andBonferronimultiplecomparisons,withasignificance levelsetatp_≤0.05.

Results: The 46 patients were aged age 9.15±3.06 years, presented baseline Hb of 9.49±1.67g/dL, and walked 480.89±68.70 m. SCD diagnosis was as follows: group 1-HbSS(n=20)/HbS␤0_{-thalassemia(n=3)andgroup2-HbSC(n=20)/HbS␤}+_{-thalassemia(n=3).} Regardingtotaldistancewalked,patientsingroup1walkedashorterdistancethanpatients ingroup2(459.39_±57.19vs.502.39_±73.60m;p=0.032).Therewasnostatisticaldifference regardingPEFinthethreemomentsofevaluation.TheSpO2inambientairandSpO2withO2 differedbetweengroups1and2(p<0.001vs.p=0.002),aswellastheRR(p=0.001).

Conclusion: ThesepatientsshowedalowerFCforexercisethanthatpredictedfortheagerange intheliterature.PatientsdiagnosedwithHbSS/S_{␤0-thalassemia}hadalowerperformanceinthe

夽 _{Pleasecitethisarticleas:HostynSV,deCarvalhoWB,JohnstonC,BragaJA.Evaluationoffunctionalcapacityforexerciseinchildren} andadolescentswithsickle-celldiseasethroughthesix-minutewalktest.JPediatr(RioJ).2013;89:588---94.

∗_{Correspondingauthor.}

E-mail:[email protected](C.Johnston).

0021-7557

http://dx.doi.org/10.1016/j.jped.2013.04.005

testthanthosewithHbSC/S␤+_{-thalassemiaregardingtotaldistancewalked,RR,andSpO} 2after the6MWT.

©2013SociedadeBrasileiradePediatria.PublishedbyElsevierEditoraLtda.

PALAVRAS-CHAVE Anemiafalciforme; Síndrometorácica aguda; Exercício; Estadonutricional

Avaliac¸ãodacapacidadefuncionalparaoexercíciodecrianc¸aseadolescentescom doenc¸afalciformepelotestedacaminhadadeseisminutos

Resumo

Objetivo: Avaliaracapacidadefuncionalpulmonar(CF)paraoexercíciofísicodecrianc¸ase adolescentescomdoenc¸afalciforme(DF)pelotestedacaminhadadeseisminutos(TC6’).

Métodos: Estudotransversal prospectivoavaliando aCF peloTC6’de 46pacientescom DF. Foramavaliados: frequênciacardíaca (FC),frequência respiratória(FR), saturac¸ãode pulso deoxigênio(SpO2),picodefluxoexpiratório(PFE),pressãoarterial(PA)sistólicaediastólica, dispneiaecansac¸oemmembrosinferiores(escaladeBorgmodificada)emrepouso,aotérmino e10minutosapósoTC6’eadistânciapercorrida.Análiseestatística:testt-Studentpareado, análisedevariânciaecomparac¸õesmúltiplasdeBonferroni,significânciap≤0,05.

Resultados: Dos46pacientes,amédia_±dpdaidadefoi9,15_±3,06anos,hemoglobinabasal 9,4±1,67g/dLe distância percorrida 480,89±68,70 m. Diagnóstico daDF: Grupo 1--- HbSS (n=20)/HbS_␤0_{-talassemia(n=3);eGrupo2---HbSC(n=20)/HbS␤}+_{-talassemia(n=3).OGrupo} 1apresentoumenordistânciapercorridadoqueoGrupo2(459,39±57,19vs502,39±73,60m; p=0,032).Nãohouvediferenc¸aestatísticaemrelac¸ãoaoPFE.ASpO2emarambienteeaSpO2 comO2(1L/min)apósotestefoimaiornoGrupo2(p<0,001ep=0,002,respectivamente).A FRfoimaiornoGrupo1aofinaldoTC6’(p<0,001).

Conclusão: EstaamostraapresentouCFparaoexercícioabaixodopreditoparaafaixaetária naliteratura. OspacientescomHbSS/S␤0_{-talassemiaapresentaram desempenho inferiorna} distânciapercorrida,FReSpO2apósoTC6,comparativamenteaospacientescomHbSC/S␤+ -talassemia.

©2013SociedadeBrasileiradePediatria.PublicadoporElsevierEditoraLtda.

Introduction

Sickle cellanemia(HbSS) is the mostcommon monogenic hereditarydiseasein Brazil,withanestimatedprevalence ofheterozygotesforHbSrangingfrom2%to8%inthe gen-eralpopulation.1_{HbSS,themostsevereformofsicklecell}

disease(SCD)isahemoglobinopathyresultingfromthe sin-gleaminoacidsubstitutionofa glutamicacidforavaline at thesixthpositionofthebeta globinchain,on chromo-some11,givingrisetohemoglobinS(HbS).2_{Thisalteration}

inhemoglobinisresponsiblefortheanomalousformof ery-throcytes,leadingtohemolyticanemia,endothelial vascu-lopathy,andvaso-occlusivephenomena,followedbytissue ischemiaandnecrosis,withsubsequentorgandysfunction, whichareresponsibleforthehighmortalityofSCD.1,2_SCD

occurswhenHbScombineswithanotherhemoglobinopathy, suchasC,D,␤-thalassemia,oranotherHbS.3

The lung is a majortarget organof acute andchronic complications in SCD; acute chest syndrome (ACS) is the second mostfrequentcauseofhospitalizationinthis pop-ulation,withhighrates ofmorbidityandmortality.4---6_Itis

anacutecomplicationusuallytriggeredbyaclinicalpicture of infection. It can be definedby a combination of signs and symptoms, which include dyspnea,chest pain,fever, cough, anda new pulmonary infiltrate.7 _{The proliferative}

vasculopathythat occursin sicklecelldiseaseis themain cause of the chronic pulmonary alterations that occur in thesepatients.8

The chronic alterations and recurrent episodes of ACS decreasethefunctionalcapacity(FC)inpatientswithSCD.

MacLeanetal.,9 _{whenassessing lung function in children}

with SCD through spirometry, observed a restrictive pul-monarypatternandaprogressivereductioninlungvolume. Another prospective study,10 _{with patients aged 10 to 26}

years,foundalterationsinpulmonaryfunction,witha pre-dominanceofmixedorcombinedpattern.

Thus,theevaluationofFCshouldbepartofoutpatient monitoringofthesepatients.However,studiesassessingand addressingtheFCinchildrenandadolescentswithSCDare limited.11_{AsimpleandeffectivemethodtoevaluatetheFC}

istoapplythesix-minutewalkTtest(6MWT),whichprovides informationabout functional status,oxygen consumption, exercisetolerance, and patient survivalaccording to test performance.12,13 _{The 6MWTassesses theindividual’s}

sub-maximaleffort,similartotheeffortmadeinsomedailylife activities,representingtheirFCtoexercise.12

Although the 6MWT has not been widely studied in patients with hemoglobinopathies, especially in pediatric patients,preliminarydatasuggestthattheremaybeagood correlationamongthistest,maximumoxygenuptake,and severity of pulmonary hypertension in adults with SCD.14

There areno published articlesin the literature evaluat-ingtheFCinchildrenandadolescentswithSCD;thusthis studyaimedtoevaluatetheFCtoexerciseinchildrenand adolescentswithSCDusingthe6MWT.

Methods

Thiswasaprospectivecross-sectional studyevaluating46 children and adolescents with SCD aged between 6 and

Este é um artigo Open Access sob a licença de CC BY-NC-ND

18years, distributed according toHbSS genotype, HbS␤0 -thalassemia, HbSC, and HbS␤+_{-thalassemia. The children} whowereattendedtoatthepediatric hematology outpa-tientclinic fromAprilof2009toJulyof2010andmetthe inclusioncriteriawereevaluated.

The FC of these patients was evaluated through the 6MWT,following the guidelines of the AmericanThoracic Society.12_{ThestudywasapprovedbytheEthicsCommittee}

inResearchoftheEscolaPaulistadeMedicina/Universidade FederaldeSãoPaulo(EPM/UNIFESP).Exclusioncriteriawere patients with hemodynamic instability or neurological or orthopedicdiseasesthatlimitedexerciseperformance.

Basalhemoglobin(Hb)andhistoryofhospitalizationsfor pulmonarycomplicationswerecollectedfromthepatients’ medicalrecords.Theassessment ofbodymass(inkg)and height(inm)wasperformedinastandardizedmanner,using ananthropometricdigitalscale(Filizola®_{).Theclassification}

ofnutritionalstatuswasperformedusingZ-score distribu-tionforweight/age,height/ageandbodymassindex(BMI). The WHO AnthroPlus 2007 software of the World Health Organization(WHO)wasusedtoobtaintheBMIandZscore values.15

The 6MWT wasperformed in a 10-meter long corridor, outdoors,withmarkingsateverymeterandindicatorsonthe groundindicatingthebeginningandendofthetrajectory.It wasdecidedtoperformthetestina10-metercorridordue tothepromisingresultsinthe‘‘shuttlewalktest’’,which alsousesthisdistance.16---20

Patients received theoretical and practical training regardingtheobjectivesofthe6MWTandhowtheyshould perform it. Each patient underwent two tests (with a 30-minuteintervalbetweenthem);thetestwithbest per-formancewas considered if the differencebetween tests waslessthan10%Incaseofadifferencehigherthan10%, anewtestwouldbeperformed.Nopatienthadtoperform morethantwotests.

The6MWTwasadministeredbytwotrainedphysical the-rapists.Atthebeginningofthetest,thepatientwasatrest for15to20minutesandhadfastedforatleasttwohours.At theendofsixminutes,thepatientstoppedwherehe/she was, and one of the therapists approached him/her with achair and assessment equipment in ordertorecord the total distance walked. The number of turns was counted manually,andastopwatch (Casio®_{)wasusedtomarkthe}

time.

Waterwasofferedtothepatientsbeforeandafterthe 6MWT.Allpatientsusedoxygenduringthetest(nasal can-nula1 L/min),regardlessofSpO2 onambientair,in order

topreventhypoxemiaduringexercise,duetotheriskofa vaso-occlusivecrisiscausedbySCD.

Allvariableswereassessedatrest,attheendofthetest, andat 10minutesafterit.Thefollowing parameterswere measured:systolic(SBP)anddiastolic(DBP)bloodpressure withaBD®_{sphygmomanometer;respiratoryrate(RR),SpO}

2,

andheartrate(HR)withaportablepulseoximeter(Dixtal®_).

Thepeakexpiratoryflow(PEF)wasmeasuredusinganAssess PeakFlowMeter® _{device;threemeasurementsweretaken}

andthehighestwasconsidered.21 _{Dyspneaandlower-limb}

fatigue were assessed by the modified Borg scale.21 _All

variablesweremeasuredwiththepatientinthesitting posi-tion,exceptfor PEF, which wasmeasuredin the standing position.

ToanalyzethebehaviorofSCDduringthe6MWT,the sam-ple wasdivided into twogroups according tothe disease genotype.Group1consistedofpatientswithHbSS/HbS␤0

-thalassemia andgroup2 consistedof patientswithHbSC/ HbS␤+_{-thalassemia,as patientsin group 1 tend to have a}

moresevereclinicalcoursethanthoseingroup2.22,23

Statisticalanalysis

Parametricvariableswereanalyzed bypaired Student’s t-test andcontinuousmeasurementsbyANOVAforrepeated measures. Multiple Bonferroni comparisons were made between the two evaluation moments, and values were considered statistically significant whenp ≤ 0.05. Results are shown as mean±standard deviation (SD), median (minimum-maximum),frequency,andpercentage.The sta-tisticalanalysiswasperformedusingtheStatisticalPackage forSocialSciences(SPSS)release15.0.

Results

This study evaluated 46 patients with SCD with the following demographic characteristics, expressed as mean±standard deviation (SD): age 9.15±3.06 years; basal Hb 9.49±1.67g/dL; weight 30.98±11.30kg; height 1.34±0.16 m; BMI 16.63±2.40kg/m2_{; percentile} weight/age 49.29±26.57; height/age 42.83±25.92; and BMI/age 46.86±24.70. The Z-scores for all anthropo-metric indices were: weight/age 0.04±1.03; height/age 0.22±0.95; and BMI/age 0.20±1.26. The total distance walkedduringthe6MWTwas480.89±68.70m.

Patientsingroup 1andgroup 2were similarregarding age, gender, and anthropometric variables; group 1 had lowermeanHbvaluesandhigherfrequency ofpneumonia and/orACSthangroup2(Table1).Thedistancewalkedby patients in group 1 was significantly shorter than that of patients in group 2 (459.39±57.19 vs. 502.39±73.60 m, p=0.032-Table1).

Analyzingthe46patients,itwasobservedthatthe car-diorespiratory variables (HR and RR) differed only at the endof the6MWTcomparedtotheothermomentsintime (p<0.001).SBPandDBPdecreasedsignificantlytenminutes aftertheendofthe6MWT,whencomparedtomeasurements attheendofthetest(p=0.003,p<0.001)(Table2).

TherewasnostatisticaldifferenceregardingPEF(L/min) betweenthethreemomentsintime,aswellasinthe eval-uationoflower-limbstressandfatigueassessedbytheBorg scale(Table3).

Table4 presents the description of the variables mea-sured during the 6MWT (at rest, end of the test and ten minutes after the 6MWT) in groups 1 and 2. When per-formingmultiplecomparisonsofmeandifferencesbetween themomentswhencardiorespiratoryandrespiratory varia-bles were measured in Groups 1 and 2, it was observed (means of measurements/standard error; p) at rest vs. end of the 6MWT that there was an increase in HR (-10.83/2.50; p < 0.001), RR (-4.50/0.56; p < 0.001), SBP (-3.85/1.50,p=0.052)andDBP(-3.09/1.48,p=0.119);rest

vs.tenminutesaftertheendofthe6MWT,adecreasein HR(0.76/2.93,p=1),RR(0.41/0.70,p=1),SBP(1.41/2.03, p=1)andDBP(2.80/1.76,p=0.343);endofthe6MWTvs.

Table1 Demographicandclinical dataanddistancewalked inthesix-minutewalk testby theHbSS/S␤0_{-thalassemia and} HbSC/S␤+_{-thalassemiagroups.} HbSS/S␤0_-thalassemia group1 HbSC/S␤+_-thalassemia group2 p Demographicdata Age(years) 9.21±3.45 9.08±2.69 0.887

Gender(%) 56.53(male) 52.17(male) 0.767a

Weight(Kg) 30.85±13.31 31.11±9.16 0.939

Height(m) 1.34_±0.18 1.34_±0.14 0.956

Bodymassindex 16.37±2.67 16.89±2.13 0.472

Hb(meang/dL) 8.26±1.33 10.70±0.90 <0.001

Hospitalizationsduetopulmonarycomplications 0.001b

PNM%(n) 47.82(11) 34.78(8)

ACS%(n) 26.08(6) 0.0

ACSandPNM%(n) 13.05(3) 8.70(2)

Nocomplications%(n) 13.05(3) 56.52(13)

Distancewalked(m) 459.30_±57.19 502.39_±73.6 0.032

Tests,Student’st-test;ACS,acutechestsyndrome;n,number;m,meters;PNM,pneumonias. a _chi-squared.

b _{likelihoodratio.}

Table2 Respiratory andcardiorespiratory variablesof children andadolescentswith sickle celldisease submitted tothe six-minutewalktest.

Variables Rest Endoftest(sixthminute) Tenminutesafterendofthetest p

HR(bpm) 91.93_±13.0 102.76_±20.3a _{91.17±12.1 <0.001} SpO2c/O2(%) 97.46±1.9 97.20±1.9 - 0.183 SpO2AA(%) 95.15±3.3 - 95.72±3.0 0.053 RR(rpm) 21.67±4.4 26.17±5.0a _{21.26±4.2 <0.001} SBP(mmHg) 99.37±11.6 103.22±15.4 97.96±11.6a _0.003 DBP(mmHg) 59.26_±10.0 62.35_±10.2 56.46_±7.9a _<0.001

bpm,beatsperminute;DBP,diastolicbloodpressure;HR,heartrate;mmHg,millimetersofmercury;rpm,respirationsperminute;RR, respiratoryrate;SBP,systolicbloodpressure;SpO2AA,pulseoxygensaturationwithambientair;SpO2w/O2,pulseoxygensaturation withoxygen(1L/min).

a_{Test:analysisofvariancewithrepeatedmeasures,withtwofactors.}

ten minutes after the end of the 6MWT, a decrease in HR(11.59/2.50;p<0.001),RR(4.91/0.56,p<0.001),SBP (5.26/1.59,p=0.004)andDBP(5.89/1.48,p<0.001).When comparingrestvs.tenminutesaftertheendofthe6MWT, therewasan increasein SpO2AA(-3.65/0.53; p< 0.001). WhencomparingGroups1and2atrestvs.sixminutesafter theendofthe6MWTtherewasanincreaseinSpO2withO2 (-1.57/0.47,p=0.002).

Discussion

Thisstudydemonstratedthat65.21%ofpatientshada his-tory of hospitalizations for pulmonary complications (ACS and/or pneumonia). People with a history of recurrent ACShavelowerpeakmaximumoxygenconsumption(VO2) and greater possibilityof chronic lung injury, which may haveanimportantimpactonFCforexercise.11 _Pulmonary

Table3 ModifiedBorgscaleandpeakexpiratoryflowofchildrenandadolescentswithsicklecelldisease submittedtothe six-minutewalktest.

Variables Rest Endofthetest(Sixthminute) Tenminutesafterendofthetest p

BorgDa _{0(0-3) 0(0-9) 0(0-4)}

-BorgLLLLa _{0(0-5) 1(0-10) 0(0-9)}

-PEF(L/min) 223.04±65.92 231.63±76.65 226.63±67.06 0.074

BorgD,Borgofdyspnea;BorgLLLL,Borgoflowerlimbs;L/min,litersperminute;PEF,peakexpiratoryflow. Test:analysisofvariancewithrepeatedmeasures,withtwofactors.

Table4 Descriptionofvariablesatthemoments(atrest,endofthetest,andtenminutesafterthetest)intheHbSS/HbS␤0 -thalassemiaandHbSC/HbS␤+_{-thalassemiagroups.}

Diagnosis

Variable Moment Group1(n=23) Group2(n=23)

Mean SD Mean SD

Rest 94.61 11.93 89.26 13.73

HR(bpm) Endofthetest(sixthminute) 105.65 19.44 99.87 21.25

Tenminutesafterendoftest 94.39 12.13 87.96 11.48

SpO2AA(%) Rest 93.13 3.55 97.17 1.07

Tenminutesafterendoftest 94.09 3.41 97.35 0.88

SpO2withO2(%) Rest 96.70 2.30 98.22 0.74

Endofthetest(sixthminute) 96.39 2.25 98.00 1.13

Rest 23.30 4.33 20.04 3.84

RR(rpm) Endofthetest(sixthminute) 28.30 5.34 24.04 3.66

Tenminutesafterendoftest 22.65 4.32 19.87 3.66

Rest 101.74 13.02 97.00 9.80

SBP(mmHg) Endofthetest(sixthminute) 104.78 18.55 101.65 11.65

Tenminutesafterendoftest 98.70 12.54 97.22 10.85

Rest 57.39 10.96 61.13 8.86

DBP(mmHg) Endofthetest(6thminute) 61.74 11.14 62.96 9.27

Tenminutesafterendoftest 55.22 9.59 57.70 5.75

Rest 223.04 64.77 223.04 68.50

PEF(L/min) Endofthetest(sixthminute) 234.57 78.78 228.70 76.12 Tenminutesafterendoftest 223.70 66.83 229.57 68.65

bpm,beatsperminute;DBP,diastolicbloodpressure;HR,heartrate;L/min,liters/minute;mmHg,millimetersofmercury;RR, respi-ratoryrate;rpm,respirationsperminute;SBP,systolicbloodpressure;PEF,peakexpiratoryflow;SpO2AA,pulseoxygensaturationwith ambientair;SpO2w/O2,pulseoxygensaturationwithoxygen(1L/min).

complicationsweresimilartothosereportedinliterature: 86.95%ofpatients ingroup1had ahistoryof hospitaliza-tionforpulmonarycomplications(pneumoniaand/orACS), whereasingroup2theincidencewas43.48%.Clinical man-ifestationsofSCD,in general,aremoresevereinpatients withHbSSandHbS␤0_{-thalassemia,andACSismorefrequent} inthisgroup.6,23

Thetotaldistancewalkedinthe6MWTbyhealthy chil-drenisinfluencedbyage,height,andweight:itisinversely proportionaltoweightanddirectlyproportionaltoageand height.24_{Althoughthenutritionalstatusofthepatientswere}

withinthemeannormalvalues,differingfromother stud-iesinSCDwherepatientstendtobemalnourished,25,26_the

distancewalkedduringthe6MWTwasshorterthanthat pre-dictedfor ageandheight,27---29 _{meaningthat factorsother}

thanweightandheight,suchashemoglobinvalue andthe occurrenceofACS,mayberelatedtothesefindings.

When comparingthetotaldistance walked,patientsin group 2 walkeda significantly longer distance than those ingroup 1.These results maybe relatedtothe factthat patients with HbSS and S␤0_{-thalassemia have a clinically}

moresevere formofthedisease,withlowerbasalHb val-uesand greater numberof hospitalizations for pulmonary complications,whichmayhavealsocausedasignificant dif-ferenceinthecomparisonofthetwogroupsregardingSpO2

andRRduringthe6MWT.

Liem et al.11 _{evaluated FC in 30 children and}

ado-lescentswith SCDundergoing exercise testing, and found FC limitation ranging from moderate to severe. FC for

exercise wassignificantly lowerin children witha history of recurrent ACS. and was related to the level of basal Hb (9.5±1.6g/dL), similar to values found in this study (9.49±1.67g/dL-Table1).

Mostchildrenandadolescentsadapttotheincreased car-diacdemandcausedbychronicanemia,andgenerallyhave a50% to75%reducedexercise capacity.30 _{Chronicanemia}

can leadtolowertissueoxygenation,mainly during exer-cise, inwhich theuse ofoxygen isincreasedtomeet the demandforenergy.InSCD,somecompensatorymechanisms prevent thisfrom occurring, suchasincreased heart rate duringexercise, increasedsystolicvolume,anddecreased peripheral vascular resistance, reducing the resistance of sickle erythrocytes in capillary transit and oxygen supply tothetissues, thus allowingclosetonormalsaturation in themixedvenousblood.31,32_{Thiscouldexplainthepresent}

resultsofasignificantincreaseinHRattheendofthe6MWT withoutsignificantchangesinSpO2.

The study by Campbell et al.32 _{concluded that the}

exercise-induced SpO2 decrease was more related to the

degree of anemia and hemolysis than to previous history of ACS and severe pain. Lammers et al.33 _demonstrated

thatSpO2varieslittleduringthe6MWTinhealthychildren,

whereasthereisanincrease inHRandRR.Inthepresent study,asignificantincreaseinHR,RRandSpO2withO2was

observedattheendofthe6MWT.

SBPinpatientswithSCDisdescribedasnormalandDBPas decreased,resultinginalowermeanarterialpressure.34_The

tenminutesafterthe6MWT,mayberelatedtothedecrease in HR and consequent decrease in cardiac output, main-tainingvasodilationforaperiodoftimeaftertheexercise, whichwasalsodescribedinotherstudies.35,36

Asubjectivemethodofdyspneaandfatigueassessment isthroughtheBorgscale.21_{TheBorgscalecanbeusedasan}

aidtothe6MWT,allowingfortheevaluationofthedegree ofrespiratorydistressaccordingtothepatient’sperception throughsubjective indices.12 _{In thisstudy, therewere no}

significantchangesinrespiratorydistressofpatientsduring the6MWT,whichmayhavebeenduetotheoxygensupplied topatients(nasalcannula1L/min)duringthe6MWT.

WhenevaluatingPEF,therewasnostatisticaldifference amongthethreemomentsintime(Table3).LowerPEFin asthmaticchildrenisrelatedtodiseasesymptomsandthe riskofexacerbation.37_{Inthepresentsampleofchildrenwith}

SCD,therewasnodifferencebetweengroups1and2when PEFwasevaluatedatrest.

Regardingthevariablesanalyzedduringthetest,itwas observedthatSpO2inambientair(AASpO2)andSpO2with1

L/minofO2wereonaveragesignificantlyhigheringroup1

thaningroup2.Significantdifferenceswerealsofoundfor RR,andhighervalueswereobservedingroup1regardless ofthetimeofevaluation.Thesefindingsmayberelatedto thefactthatpulmonarycomplicationsweremorefrequent ingroup1.

This is a novel study; however,it hasthe limitationof using a 10-meter corridor to performthe 6MWT, whereas theATSrecommendsa30-metercorridor.12_Despitethe

rec-ommendationoftheATS,somestudies38---40_{applieddifferent}

lengthsforthe6MWT.Sciurbaetal.40_{statedthatthelength}

ofthetrackisnotthemostimportantfeatureofthe6MWT. The standardization of theshuttle walk test recommends theuse ofa 10-metercorridor,19 _{andthereisa reference}

value for the distance traveled (544.28±131.13 meters) forBrazilianchildren(meanage±SD:11.28±1.85years).20

Thisstudysampleshowedlowpredictedvaluesforthe dis-tancewalkedin the10-metercorridor,whencomparedto healthyBrazilianchildren.

It can be concluded that this sample of children and adolescentswithSCDhadFC for exercisebelowthat pre-dictedfortheagerangewhencomparedtohealthychildren. PatientsdiagnosedwithHbSS/S␤0_{-thalassemiahadaworse}

performanceregardingtotaldistancewalked,HR,andSpO2

after 6MWT when compared to patients with HbSC/S␤+-thalassemia. It is suggested that other studies should be conducted with similar designs for evaluation of FC in patientsofthisagegroupwithSCD,astheyshowalterations inFC,whicharerelatedtothediseaseprognosisandquality oflife.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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