Cen al blood p essu e om pe iphe al pulse measu emen s
Ra´ul Alonso, E ic Guisado, ´
Al a o O ega, and Pablo O iedo
Supe ised by Osca Casas
G au en Enginye ia F´ısica – Uni e si a Poli `ecnica de Ca alunya
(P ojec s o Enginee ing Physics II)
(Da ed: June 1, 2018)
In his s udy we explo e he possibili y o ob aining BP in o ma ion om PWV measu emen s.
We ha e conduc ed an analysis wi h da a om h ee indi iduals which un eils he exis ence o a clea
connec ion be ween hese wo magni udes. Mo eo e , his connec ion is in quali a i e ag eemen
wi h common exis ing models.
I. INTRODUCTION
Wi h he inc ease in li e expec ancy, ca dio ascula
diseases ha e become one o he majo causes o mo -
ali y. Fo long, i has been well-es ablished ha hype -
ension cons i u es an impo an isk ac o , and blood
p essu e (BP) measu emen s ha e been ca ied ou o
o e 100 yea s. The mos widely used echnique o BP
measu emen used o consis in he use o a sphygmo-
manome e o de e mine b achial BP (BBP). Howe e ,
di e en alues o BP a e ob ained when measu ed on di -
e en si es o he body. In gene al, whe eas dias olic BP
(DBP) seems o be simila when measu ed on di e en
si es, signi ican di e ences occu when dealing wi h sys-
olic BP (SBP) and he e o e wi h pulse p essu e (PP),
which is de ined as he di e ence be ween SBP and DBP,
wi h gene ally inc easing alues as we ge u he om
he ao a (as explained by McEnie y e . al. [1]). Recen
e idence sugges s ha cen al BP (CBP) could be a be -
e p edic o o some ca dio ascula complica ions, espe-
cially a he oscle osis and o gan damage. Roman e . al.
[2], in a s udy wi h 3520 pa icipan s, concluded ha cen-
al PP (CPP) was mo e s ongly ela ed o a he oscle o-
sis and ca o id hype ophy han b achial PP (BPP). A
s udy conduc ed by C eme e . al. [3] o e 703 hype en-
si e pa icipan s wi h low ca dio ascula isk concluded
ha 24-hou CPP measu emen was a be e p edic o
o ca dio ascula e en s in his kind o pa ien s han 24-
hou BPP measu emen . Pini e . al. [4], in a s udy wi h
398 o e -65 pa icipan s, concluded ha ca o id BP be -
e p edic s ca dio ascula e en s han BPP, also poin -
ing in he di ec ion o CBP being a be e p edic o han
BBP. This g owing e idence suppo s he use o CBP
measu emen o assess ca dio ascula isk (wi hou nec-
essa ily excluding BBP o o he measu emen s).
In addi ion, di e en BP-lowe ing d ugs, e en i hey
ha e simila e ec on BBP, may p oduce di e en ou -
comes on CBP, as shown by Williams e . al. [5], so ha
a good assessmen o hype ension ea men s would e-
qui e bo h BBP and CBP measu emen s.
All hese indings ha e led o a g owing in e es in he
de elopmen o non-in asi e echniques o CBP mea-
su emen . These echniques mus be able o es ima e
CBP om indi ec measu emen s. Some widely sp ead
me hods ely on pulse wa e analysis. These me hods con-
sis on eco ding some pa ame e s o he p essu e wa e-
o m, such as pulse wa e eloci y (PWV), om which
CBP is in e ed. To ob ain PWV, one op ion is o
ake measu emen s a wo di e en si es o he body.
These si es may be close o each o he (see, o exam-
ple, he de ice designed by Nabeel e . al. [6], in which
he measu emen si es a e a a dis ance o 23 mm), o
sepa a ed by a signi ican dis ance. In he la e case,
ca o id- emo al, ca o id-b achial and ca o id- adial mea-
su emen s a e common choices ( he comme cial Sphyg-
moCo o PWV measu emen , o example, elies on
ca o id- emo al measu emen ). The main ad an age o a
sho sepa a ion de ice compa ed o long sepa a ion de-
ices is ha i makes i easie o ha e a p ecise measu e
o he blood a eling dis ance be ween he measu emen
si es, which a e o en selec ed on he same a e y, whe eas
i s main d awbacks a e a g ea e unce ain y in ime di -
e ence and possible in e e ence e ec s. A second op ion
is o use pulse measu emen s aking om some si e in he
body and compa e hem o he ECG signal. To ob ain
he CBP om he p essu e wa e o m da a, he ans e
unc ion me hod is commonly used. This me hod con-
sis s in conside ing he CBP and he p essu e wa e as
he inpu and ou pu , espec i ely, o a linea sys em.
Unde his assump ion, CBP could be eco e ed om
he p essu e wa e i we knew he ans e unc ion. The
di e en p ocedu es using his me hod make some as-
sump ions o e his ans e unc ion, bu calib a ion is
gene ally equi ed o he p ocedu e o wo k wi h each
pa ien .
An impo an di icul y ha a ises when de e mining
CBP is he ac ha CBP ob ained om a single mea-
su emen a clinical es condi ions does no seem o gi e
a good es ima e o h ough-day CBP. In his way, Bu ns
e . al. [7] compa ed 24-hou measu emen s o BBP and
CBP o single labo a o y measu emen s in es condi-
ions, and ound ha , while labo a o y measu emen s o
BBP did p o ided a good es ima e o h ough-day BBP,
hey ended o unde es ima e CBP agains 24-hou mea-
su emen s. The e o e, i seems ha measu emen o CBP
h ough non-in asi e echniques should be made h ough
24-hou epea ed measu emen s o be eliable. Mo eo e ,
classical de ices o blood p essu e measu ing, such as he
sphygmomanome e , only p o ide an a e age alue, no
bea -by-bea da a, so ha hey a e no sui able o es-
2
ima ion o CBP om pulse wa e analysis. This b ings
in he need o de ices which allow he pe o mance 24-
hou bea -by-bea measu emen s. In addi ion, i would
be con enien ha hese de ices cause as li le dis u -
bance o he pa ien as possible, as, apa om he highe
p obabili y o pa ien ejec ion, such a dis u bance could
cause some al e a ion o he pa ien , and consequen ly
a ec he measu emen ( o example, i could dis u b
he pa ien ’s sleep). Thus, an al e na i e o dis u bing
de ices (such as he commonly used cu -based de ices)
should be in es iga ed.
The e a e al eady some comme cial de ices o CBP
measu emen om pulse wa e analysis. This includes he
SphygmoCo and DiaTecne PulsePen o clinical mea-
su emen , and Heal hSTATS B-P o o 24-hou measu e-
men . They all p o ide good es ima ions o CBP, bu
hey all a e ex emely expensi e nowadays, and, excep
o B-P o, his de ices a e complex and mus be managed
by a p o essional.
In his s udy, we in es iga e he possibili y o ob aining
in o ma ion abou CBP (and BP in gene al) wi h non-
in usi e echniques wi h an a o dable de ice.
II. BACKGROUND
In his sec ion we e iew some heo y ela ed o ECG
and Impedance Ple ysmog aphy (IPG) measu emen s
and how o de i e blood p essu e om hese signals. The
basic heo y o ECG and IPG signals is ex ac ed om
Cue o’s Bachelo ’s Thesis [8].
The ECG signal is ob ained om con inuous measu e-
men o he po en ial di e ence be ween di e en poin s
on he body su ace, which allows o ob ain in o ma ion
om he hea pola iza ion. The simples e sion, which
is he one which we used in his s udy, equi es wo mea-
su emen poin s ( o example, he hands), om which a
p ojec ion o he hea pola iza ion ec o is ob ained.
A schema ic ep esen a ion o a ypical ECG signal po -
ion co esponding o one bea can be seen in igu e 1.
The mos easily ecognizable ea u e in he signal is wha
is known as he QRS complex and co esponds o en-
icula depola iza ion, which is ollowed by en icula
con ac ion. The ime in e al be ween he onse o he
QRS complex and he ejec ion o blood om he en i-
cles is known as P e-Ejec ion Pe iod (PEP).
The IPG signal is ob ained by measu ing he esis ance
be ween wo poin s o he body. Since he esis i i y o
he blood is signi ican ly lowe han ha o he su ound-
ing issue, he esis ance a ies as he pulse wa e goes
h ough he measu emen a ea gi ing ise o a a ia ion
in he a e ial olume.
F om he delay be ween some cha ac e is ic poin s o
hese wo signals, we can ge an es ima e o PWV. Fo
his pu pose, he pulse ansi ime (PTT) is de ined as
he ime di e ence be ween en icula ejec ion and some
iducial poin o he IPG signal (e.g. maximum o min-
imum). Since en icula ejec ion is no an e en ha
Figu e 1. Schema ic ECG signal wi h i s cha ac e is ic poin s.
F om Mi amon es e . al. [9].
can be easily iden i ied in he ECG, he QRS complex
is used ins ead. The ime di e ence be ween he onse
o he QRS complex (i.e. poin Q) and he chosen idu-
cial poin om he IPG signal is known as he Pulse
A i al Time (PAT). Obse e ha PAT is equal o PTT
plus PEP. Fo commodi y, howe e , he maximum o he
QRS complex (i.e. poin R) is commonly used ins ead o
poin Q.
The way in which he PWV ela es o blood p es-
su e is explained by Zhang e . al. [10]. We s a wi h
Moens–Ko eweg equa ion:
PWV = sEh
2ρR ,(1)
whe e Eis he inc emen al elas ic modulus o he blood
essel, his he essel wall hickness, ρis he blood densi y
and Ris he inne essel adius. On he o he hand we
ha e he empi ical law
E=E0eaBP ,(2)
whe e E0and aa e cons an s. F om equa ions 1 and 2
and aking in o accoun ha PWV is in e sely p opo -
ional o PTT, we deduce ha BP is ela ed o PTT
h ough an equa ion o he o m
BP = α·ln PTT + β , (3)
whe e αand βa e cons an s. This is in ac a e y simpli-
ied model; we ha e assumed ha he p essu e is cons an
bo h in ime and h ough all he a eled leng h. How-
e e , i can be used o ob ain easonably accu a e mea-
su emen s o bo h SBP and DBP, as epo ed by Zhang
e . al. [10]. To ha end, coe icien s αand βmus be
de e mined o bo h SBP and DBP o each indi idual.
Mo eo e , hey mus be de e mined o a pa icula po-
si ion o he body. The adjus men o hese coe icien s
3
Figu e 2. Pho og aph showing he aking o a measu emen .
can be done by simple linea eg ession, and equi es he
use o ano he BP measu emen de ice. I is no espe-
cially impo an whe he his o he me hod p o ides only
an a e age BP alue h ough se e al seconds ins ead o
con inuous o bea -by-bea alues, as we can simply use
he mean o ln PTT h ough he measu ing ime o he
linea eg ession. To ob ain di e en pai s o alues o
he linea eg ession, he p essu e is a ia ed using di -
e en s a egies, such as doing some kind o exe cise o
pe o ming he Valsal a maneu e .
III. METHOD
The objec i e o he measu emen s was o in es iga e
he a ia ions o PTT due o exe cise and he pe o ming
o Valsal a maneu e s.
The measu emen s we e aken om a sample o 3 male
indi iduals (ages 21-22). Each measu emen consis ed
on eco ding ECG and IPG signals ob ained du ing 1-
2 minu es. Ballis oca diog aphy (BCG) and onome y
signals we e also eco ded. The measu emen s we e aken
in s anding posi ion. The ECG signal was ob ained om
wo elec odes on a handleba ha he indi iduals held
du ing he measu emen s, whe eas he IPG signal was
measu ed om oo o oo h ough senso s loca ed on a
pla o m whe e he indi iduals s ood o measu emen s.
The BCG signal was also ob ained om senso s a he
ee .
We pe o med h ee measu emen s pe indi idual. The
i s one was pe o med a es . Du ing he second mea-
su emen , he indi iduals we e asked o al e na e he pe -
o ming o Valsal a maneu e s wi h es ing pe iods. The
hi d measu emen was ob ained immedia ely a e a ew
minu es o in ense exe cise. In igu e 2 we can see a pic-
u e showing how a measu emen is aken.
The signals which we ob ained we e p ocessed using
he Pan-Tompkins algo i hm. We used Ma lab o p o-
cess he signals. The codes we e aken om Cue o’s
Bachelo ’s Thesis [8].
To analyze he measu emen s, we plo ed in each case
he p ocessed ECG signal agains he p ocessed ICG sig-
nal. We chose o use he R poin o he ECG signal
and he maximum o he IPG signal as he cha ac e is ic
poin s o de e mine PAT. We measu ed PAT by manual
explo a ion o some po ions o he plo ed signals (see
igu e 3).
Figu e 3. Cha ac e is ic poin s o de e mine PAT om ECG
and IPG signals.
Fo he i s measu emen o each indi idual ( he one
aken in es ing condi ions) we simply chose a po ion
o he signal whe e 10 consecu i e pulse signals could be
clea ly iden i ied o bo h ECG and IPG and calcula ed
PAT as he a e age o he PAT o hese 10 consecu i e
pulses.
Fo he second measu emen o each indi idual (when
he Valsal a maneu e s we e pe o med) we analyze a
agmen o he signal co esponding o he pe o ming
o a Valsal a maneu e and he ollowing eco e ing ime.
Fo he hi d measu emen o each indi idual, we chose
di e en po ions co esponding o 10 consecu i e pulses
a signi ican ly sepa a ed imes o s udy he e olu ion o
PAT.
IV. ANALYSIS OF THE RESULTS
The esul s ob ained o PAT a es ing condi ions can
be ound in able I.
4
Indi idual PAT (ms)
1 257
2 315
3 330
Table I. PAT a es ing condi ions.
Figu e 4. E olu ion o PAT o indi idual 1 du ing and a e
he pe o mance o a Valsal a maneu e .
In igu es 4 and 5 we plo ed he e olu ion o he ob-
ained PAT o indi iduals 1 and 2, espec i ely, o a
po ion o he second measu emen , co esponding o he
pe o ming o a Valsal a maneu e and he subsequen
eco e ing ime. Each alue o he plo ed signal esul s
om a e aging each measu ed alue wi h he p eceding
and he ollowing measu ed alues, i.e.
x0
n=xn−1+xn+xn+1
3.
As we can see in bo h g aphics, he ob ained PAT de-
c eases du ing he pe o mance o he Valsal a maneu e
and i g adually e u ns o alues a es condi ions a e -
wa ds. This ag ees wi h he heo e ical model exposed
in sec ion II: as a consequence o he Valsal a maneu-
e , BP inc eases, so ha he elas ici y o he a e ies
dec eases and PWV inc eases.
In able II we can see he PAT ob ained o each in-
di idual om he measu emen aken a e in ense exe -
cise. In he able we see wo alues pe indi idual, he
i s one ob ained om a po ion owa ds he beginning
o he eco ded signal and he second one ob ained om
a po ion owa ds he end o he eco ded signal, in bo h
cases om he a e age o 10 consecu i e bea s. As we can
see, he ob ained alues a e smalle han ha ob ained a
es ing condi ions, which again ag ees wi h he heo e -
ical explana ion in sec ion II, as p essu e inc eases wi h
exe cise. We can also obse e ha he second alue o
PAT is g ea e han he second one, showing he eco e y
a e exe cise.
We also conduc ed an analysis based on ime di e -
ences using BCG ins ead o ECG. In his case, he min-
ima o he BCG signal we e used as he cha ac e is ic
poin s o measu e ime di e ences. The quali a i e be-
Figu e 5. E olu ion o PAT o indi idual 2 du ing and a e
he pe o mance o a Valsal a maneu e .
Indi idual PAT 1 (ms) PAT 2 (ms)
1 212 228
2 267 285
3 301 312
Table II. PAT a e exe cise.
ha io o hese ime di e ences u ned ou o be simila
o ha o PAT p e iously desc ibed.
Apa om he measu emen s we ha e jus analyzed,
we also ook some measu emen s using he DiaTecne
PulsePen. This de ice allows o de e mine CBP om
a se o pe iphe al measu emen s a di e en si es o he
body. In pa icula , only as an example o how he de ice
wo ks, we ook some measu emen s a he ca o id. We
could expe ience he di icul y o aking a good-quali y
signal wi h his kind o de ice, which adds o i s ob ious
dependence on he managing by he ope a o .
V. CONCLUSION
F om he pe o med measu emen s and he subsequen
analysis, we can conclude ha he e exis s an ac ual con-
nec ion be ween PAT (and so PWV) and BP, poin ing o
he possibili y o ob aining in o ma ion abou BP om
PWV analysis. Mo eo e , his connec ion ag ees quali a-
i ely wi h he model exposed in sec ion II. To de e mine
he quan i a i e alidi y o his model, we would need a
e e ence me hod o ob ain BP alues, bo h o adjus -
ing he coe icien s o he model and o checking he
p ecision o he alues o BP ob ained om PAT mea-
su emen s once hese coe icien s ha e been de e mined.
This was beyond he aim o his s udy. Ne e heless,
he esea ch g oup/labo a o y whe e we ha e made he
measu emen s will begin a s udy o ob ain hose coe i-
cien s ha ela e he empo al changes wi h changes in
p essu e.
5
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