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Does the Position or Contact Pressure of the StethoscopeMake Any Difference to Clinical Blood

Pressure MeasurementsAn Observational Study

Fan Pan, MEng, Dingchang Zheng, PhD, Peiyu He, PhD, and Alan Murray, PhD

Abstract: This study aied to investigate the e!!ect o! stethosco"e

"osi#tion and contact "ressure on auscultatory blood "ressure $%P&

easureent'

Thirty healthy sub(ects )ere studied' T)o identical

stethosco"es $one under the cu!!, the other outside the cu!!& )ere

used to siultaneously and digitally record * channels o!

+oroto!! sounds during linear cu!! "ressure de!lation' For each

sub(ect, - easureents )ith di!!erent contact "ress#ures $., /.,

and 0.. Hg& on the stethosco"e outside the cu!! )ere each

recorded at - re"eat sessions' The +oroto!! sounds )ere

re"layed t)ice on se"arate days to each o! * e1"erienced listeners

to deterine systolic and diastolic %Ps $S%P and D%P&' 2ariance

analysis )as "er!ored to study the easureent re"eatability

and the e!!ect o! stethosco"e "osition and contact "ressure on

%Ps'

There )as no signi!icant %P di!!erence bet)een the -

re"eat sessions, bet)een the * deterinations !ro each

listener, bet)een the * listeners and bet)een the -

stethosco"e contact "ressures $all P >.'.3&' There )as no

signi!icant S%P di!!erence bet)een the * stethosco"e

"ositions at the * lo)er stethosco"e "ressures $P .'*- and

.'4/&, but there )as a sall $.'4 Hg, clinically

uni"ortant& signi!icant di!!erence $P .'../& at the highest

stethosco"e "ressure' The ey result )as that, D%P !ro the

stethosco"e under the cu!! )as signi!icantly lo)er than that

!ro outside the cu!! by *'5 Hg $P

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$Medicine 6-$*6&:e-.0&

Abbreviations: %P blood "ressure, D%P diastolicblood "ressure, S%P systolic blood "ressure, SD

standard deviation'

(")*+D,C)(+"

Blood "ressure $%P& is coonly easured non#invasively by anual auscultatory and autoaticoscilloetric ethods' The anual auscultatory ethod

is the gold standard !or clinical %P easureent, andreGuires a cu!!, a stethosco"e and a cu!! "ressure dis"lay'

0

A trained clinician or nurse uses the stethosco"e to listen!or the +oroto!! sounds associated )ith blood !lo)ing

through the brachial ar artery as a %P cu!! encircling theu""er ar is de!lated'

* The a""earance and

disa""earance o! sounds is associated )ith systolic anddiastolic blood "ressures $S%P and D%P& res"ectively,

and the %Ps atthese ties are read !ro a cu!! "ressure dis"lay'

Ho)ever, anual auscultation is o!ten inaccurately

"er#!ored'

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Medicine Volume 9! "um#er $9! Decem#er $%&'

As sho)n inFigure 0, * identical stethosco"es )ere used)ith one "laced under the cu!! and the other outside the cu!!on the antecubital !ossa' A s"ecially designed holder )ith as"ring scale )as used to "osition the stethosco"e outside thecu!! and then a""ly - di!!erent levels o! sin contact "ressure$., /., 0.. Hg& on this stethosco"e head' During cu!!de!lation, 0 channel o! cu!! "ressure and * channels o!+oroto!! sounds )ere siultaneously and digitally recordedto a data ca"ture co"uter at a sa"le rate o! *... H?' ;u!!"ressure )as linearly de!lated at a standard rate o! * to - Hgs' Figure * illustrates a ty"ical e1a"le o! recorded cu!!"ressure and +oroto!! sounds !ro both stethosco"es'

For each sub(ect, there )ere - re"eated sessions )ith -easureents !or each, giving a total o! 6 recordings' A tie

interval o! at least 4 inutes )as given bet)een sessions, andat least 0 inute bet)een the - easureents )ithin asession, allo)ing recovery o! cardiovascular heodynaics'For the - easureents )ithin a session, - di!!erentstethosco"e contact "ressures $., /., and 0.. Hg& )erea""lied seGuentially on the stethosco"e outside the cu!!, )ith

Pan et al

in illions o! "eo"le being)rongly diagnosed ashy"ertensive )ith attendante1"osure to adverse druge!!ects, or being deniedtreatent leading toassociated cardiovascular

conditions, includ#ing !atalstroe and !atal yocardial

in!arction'00,0* There!ore,

any "otential sall %Pdi!!erences caused by thestethosco"e "osition or thecontact "ressure a""lied onthe stethosco"e head areclinically i"ortant, and)orth !urther investigation'

The ai o! this study)as to investigate the e!!ecton auscultatory %Peasureent o! thestethosco"e "osition andcontact "ressure on thestethosco"e head'

A sa"le si?ecalculation )as "er!oredbased on a "aired t test !orean di!!erence' ThereGuired sa"le si?e )asestiated allo)ing !or a

ean / Hg %Pdi!!erence, )hich isconsidered to be clinicallysigni!icant, to be detected)ith a ty"ical 5 Hgstandard deviation $SD& o!%P easureent9 *0 sub(ects)ere reGuired to achieve acon!idence level o! 6/7 )itha statistical "o)er o! 5.7'Thirty healthy sub(ects $0-ale and 0B !eale& )ererecruited !ro A"ril to May*.0-, )ith ages !ro *- to3- years' There )ere 6, 0.,

and 00 sub(ects )ithin theage bands o! *. to *6, -. to-6, and 4. years and over,res"ectively' They )ereainly !ro the sta!!,students and visitors o!Freean Hos"ital ande)castle =niversity'

E1clusion criteria !orthis study included sub(ectsaged under 05 years or over5. years9 sub(ects )ithno)n cardio#vasculardisease including the atrial!ibrillation or other irre#gular heart rhyths9 andsub(ects )ho )ere"regnant'

This study receivedethical "erission !ro thee)castle I orthTyneside 8esearch Ethics

;oittee' Theinvestigation con!ored)ith the "rinci"les in theDeclaration o! Helsini'one o! the sub(ects hadany no)n cardiovasculardisease' All sub(ects gavetheir )ritten in!oredconsent to "artici"ate in thestudy' Table 0 brie!lysuari?es the sub(ectdeogra"hic in!oration,including age, se1, height,)eight, and ar circu#!erence'

Measurement

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the seGuence o! these di!!erent levels o! contact "ressurerandoised bet)een sub(ects'

BP Determination

For each sub(ect, 6 cu!! "ressure signals and 05 recordings o!+oroto!! sound $!ro - re"eat recordings o! - contact "ressures,and * stethosco"e "ositions& )ere analysed o!!#line' So!t)aredevelo"ed using Matlab *.00a $Mathor

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Spring

Three stethoscope contact pressures were applied

A

3(4,*2 &. 5A6 Dia7ram of the holder used to apply different stethoscope contact pressures! and 5B6 measurement system for8orotkoff sound recordin7.

*2S,)S

BP *epeata#ility

Statistical analysis sho)ed that there )as no signi!icant%P di!!erences $!or both S%P and D%P& bet)een the - re"eateasureent sessions, bet)een the * deterinations !ro

each listener and bet)een the * listeners $all P > .'.3&' Assho)n in Figure -, over 6/7 o! S%P and over 5.7 o! D%Peasureents had a di!!erence o! no ore than * Hgbet)een the * lis#teners'

2ffect of Stethoscope Contact Pressure andPosition on BP

2ariance analysis sho)ed that the e!!ect o! stethosco"econtact "ressure on both S%P and D%P )as not statisticallysigni!icant $P .'.B !or S%P and P .'0. !or D%P&,indicating that di!!erent contact "ressures on the stethosco"eoutside the cu!! did not in!luence %P deterination'

CuffPressure

(mmHg)

Amplitudeofkorotkoffsound(V)

Amplitudeof

korotkoffsound

Time (s)

3(4,*2 $. 2:ample of 8orotkoff sounds recorded -ith thestetho/scope outside 5middle trace6 and under 5#ottom trace6the cuff. )he sounds associated -ith systolic #lood pressure5SBP6 and diastolic #lood pressure 5DBP6 are identified. )hescales of 8orotk/off sounds ha;e ar#itrary! #ut consistent! units.

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Ho)ever, there )ere sall %P di!!erences bet)een the *stethosco"e "ositions' As sho)n in Figure 4, 0-7 o! S%Peasureents and //7 o! D%P easureents had a di!!erenceo! orehighestS%P !ro the

.'4 Hg statistically signi!icantly higher than that !ro out#side the cu!! $P .'../, 6/7 con!idence interval .'0 .'B Hg&, )hich is sho)n in Figure / and Table *'

For D%P, there )ere statistically signi!icant di!!erencesbet)een the * stethosco"e "ositions at all - stethosco"econtact "ressures $all P .'B !or both S%P and D%P di!!erences&'

D(SC,SS(+"

Our study has Guantitatively sho)n that D%Ps easured

)ith the stethosco"e under and outside the cu!! )ere di!!erent' To

the best o! our no)ledge, this is the !irst clinical study tosiultaneously co"are the %P di!!erence !ro di!!erentstethosco"e "ositions' ;onsidering the cu!! "ressure de!lation rateo! * to - Hgs, an overall *'5 Hg D%P di!!erence suggeststhat there is on average a""ro1iately 0 beat di!!er#ence bet)eenthe easureents !ro the stethosco"e under and outside the cu!!'This D%P easureent di!!erence, a!!ected by stethosco"e"osition, "rovides !urther evidence that it is di!!i#cult to easure

D%P accurately'5

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Pan et al Medicine Volume 9! "um#er $9! Decem#er $%&'

comp

arisons

%o

f

A

comparisons

%o

f

B

3(4,*2 . isto7ram of -ithin/su#0ect systolic #lood pressure5SBP6 5A6 and diastolic #lood pressure 5DBP6 5B6 differences#et-een the $ listeners. 3or each sound recordin7! themeasure/ments from the $ listeners -ere compared. A total of&%=% comparisons 5from % su#0ects! $ stethoscope positions! contact pressures! repeat recordin7 sessions and $ BPdeterminations on separate days6 -ere made.

siultaneously recorded signals, )hich ay also suggestdi!!er#ent echanical behaviour o! the brachial arteries at the *

"ositions during %P easureent'0B

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comparisons

%o

f

16

A

comparisons

%o

f

16

B

3(4,*2 '. isto7ram of -ithin/su#0ect systolic #lood pressure5SBP6 5A6 and diastolic #lood pressure 5DBP6 5B6 differences#et-een the measurements taken under the cuff and outsidethe cuff. A total of &%=% comparisons 5from % su#0ects!

contact pressures! repeat recordin7 sessions! $ listeners and$ BP deter/minations on separate days6 -ere used.

SBP DBP

cuff

Bloodpressuredifference

betweenunderandoutsidethe

(mmHg)

3(4,*2 . +;erall mean and SD of -ithin/su#0ect systolic #loodpressure 5SBP6 and diastolic #lood pressure 5DBP6 differences

#et-een the measurements taken from the stethoscopes under andoutside the cuff. Differences at contact pressures on the outsidestethoscope head 5? % mm 7! M? % mm 7! ? &%% mm 76 are7i;en. Si7nificant difference! P< %.%.

;o"yrightC*.04 olters +lu)er Health,

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Medicine Volume 9! "um#er $9! Decem#er $%&' 2ffect of Stethoscope on Blood Pressure Measurement

)AB2 $. +;erall Blood Pressures Measured @ith Stethoscope ,nder and +utside the Cuff 3rom % Su#0ects. )heir @ithin/Su#0ect Differences Are Also 4i;en. 3or 2ach Su#0ect! the A;era7e BPs 3rom *epeat *ecordin7 Sessions! $ isteners and$ BP Determinations on Separate Days @ere ,sed

S%P $ Hg&

D%P $ Hg&

, M, and H: contact "ressure on stethosco"e head is ., /., and 0.. Hg'Signi!icant di!!erence, P HK, OJ%rien E' A%; o! hy"ertension' Part , i" >KH, OJ%rien E' A%; o! hy"ertension: blood"ressure easureent: "art < s"hygoanoetry: arte!acts

coon to all techniGues' %ML' *..09-**:65065/'

4' ;ushan ;, ;oo"er +M, Horne 8A, Meydrech EF' E!!ect o! bac

su""ort and stethosco"e head on seated blood "ressure deterinations'A L Hy"ertens' 066.9-:*4.*40'

/' etea 8T, enders LM, Sits P, Thien T' uidelines !or anageent o! hy"ertension: re"ort o! the

!ourth )oring "arty o! the %ritish Hy"ertension Society' L Hu

Hy"ertens' *..4905:0-605/'

0.' Handler L' The i"ortance o! accurate blood "ressure easureent'Per L' *..690-:/0/4'

00' Lones D, A""el L, She"s S>, et al' Measuring blood "ressure

accurately: ne) and "ersistent challenges' LAMA' *..-9*56:0.*B

0.-.'

0*' e)ington S, ;lare 8, Ni?ilbash , et al' Pros"ective studies

collaboration' Age#s"eci!ic relevance o! usual blood "ressure to

vascular ortality: a eta#analysis o! individual data !or one illion

adults in 30 "ros"ective studies' ancet' *..*9-3.:06.-060-'

0-' Murray A, Zheng D, %o)ers EL, et al' Physiological causes o!

variability in blood "ressure easureent'ecture ote Series,

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