802 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
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Application of System Dynamics to Cardiovascular System
Bicfeedback Reguiation af BP far Hypertensives
Zpv Mingjie and Zhu Zhiyuar
Department cf Autcmatic Contrat and Efectronic Engineer ing
East China University of Chemical Technatag
Abstract
The medern researches on ohysiaicay verify that there
are close refaticonships between central nervous system ¢CNS)
and autonomic nervous system (ANS? and some autonamic
functions can be regufated by CNS ta some extent. In this
paper, the mechanisms of cardicvascular system, especially
af BP reguiation, under CNS centro! are researched. A biocd
circulatory system dynamic madel iS established and aopiied
practicalfy ta treatment caf hypertensives trained with
bicfeedbak technigue, in which ouise transit time (PTT) is
employed as an indirect index of BP change. The resuit shows
that the cuartive effect of this methad is efficient far BP
comtret.
Introduction
Cardicvascutar diseases, esneciatiy hypertension, are
very commen its modern sociaty. There are evidences that
essential hypertension iS refated ta various behavioral,
sccial, and environmental conditions. Many apprceaches ta BP
reduction have been devefaned. The behavicral approaches,
such aS bicfeedback techniaue and meditation-reiaxation,
are scme caf them, with which, several disadvantages cf
medication treatment are prevented. Meaningful BP reductions
were obtained in various |iterature sources [1,2], itt Which
Subjects were trained with bicfeedback technique. Hut the
measurement of BP is Still an cbstacite for BP Bicteedpack
program, inf which it iS afsc tack of research on theory.
This paper attempts tc make scme contributions in these
aspects.
With System Dynamics, we have researched the
Physiciogical mechanisms oF cardicvascuiar system = ard
presented its dynamic mafei under CNS ceantrai. As an
application, the modet was used ta instruct the biafeedpack
training of BP requiaticn for hypertensives, in which the BP
was measured fram PTT indirectty. The resuits from chinical
Practices Shew this methad is effecient far treatment of
hypertension.
Dynamics af Cardiovascular System and BP Contre! under CNS
It is able ta analyze and madei convenientiy the
circulatery system by means af System Dynamics. In this
paper, the biocd valune is Tefered ta basic fevel variable,
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 803
and based on the process of nervous adjusting of BP, the
dynamic madef cof cardiovascuiar system is researched far
cardiac rhythm and muscte adjusting on non-invasive measure
and bicfeedback contrat.
The circulatery system inciudes beth ovlmonary and
systemic circulations. With the automaticalfy rhythmical
systefe of sinccatrial node, cardiac impuises are
transmitted ta ventricular muscte throwgh nerve fibers. In
terms of Frank-Starfing rufe, the blood flowing in heart is
completely injected inte arteries. Under the action af
pressure, biced Ffiews from ventricies to artericies,
Capifiariesveins, finality, to vein in seavence. Fram fig. t,
it can be found that there are two main factors which
affect the arterial pressure: 1) cardiac otuput @, 2)
pripheraf resistance R. The cadiac output is related to
stroke vatume (SVJ and caraica rhythm CHF),
OapycHr .
Accarding ta the Frank-Staring rufe, SV is equal ta the
Venous return, which may afsc be adjusted by humoral system.
The pripheral resistence
4
R=Byt fr
where 1 represents the blood viscosity, and f and +
denote the fength and the internal radius of the vessel.
respectively.
During the pracess of nervous adjusting of BP, autonomic
nervous contra! centers in tower fevel brain can inhibit
vasometer centers if they receive the signal of EP
increasing, sametimes, excite vagal centers, as a resuit,
the radius of vessel is expanded, the cardiac rhythm and
contraction iS weakened. Then the BP is decreased. In
generat, this kind af feedback contra! of BP is completed by
pressurereceptors in acrta. But since the pressurereceptars
may be adaptive ta hypertension, and if it remains one cr
two days for increased BP they wifi ioss their adjusting
function, It makes that they are usefuriess in treatment for
“hypertensives({33. In terms af the princinie of bicteedback
technatcgy, if BP is immediatety refiected ta CNS, the
cardiovascular contrat centers will be stimulated ta reduce
BP by the reguiating mechanisms existing betweer CNS and
ANS. In fact, the practices in bicfeedback techniave and
TeSearches cn nervous mechanisms have shown that there are.
clese retationsnins between CNS and ANS. Many autonomic
functions can be requiated by CNS with instruments cutside
body. With a BP recentar and feedback instrumerits, a new BP
comtret system —- picfeedback controf system is constructed,
ive which EP infarmation is detected continucusty arid
accurately by EP receptor and is sent efficientiy ta CNS by
ways SUCh aS audition and vision etc., and then signals are.
im turn transmitted tc ANS. Hence the vagal centers. are
excited and the stroke volume and peripheral resistance are
changed, see figeZ, The feedback instruments cutside body
804THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
take an imocrtant rote in EP reauiation instead oF
pressurereceptars MMmsSide beady. Throvoh stimufatina oF
Qratified nervous centers and training gradvaify the
Subjucts may “Tremenber’ ar ‘enforce’ the reguiating orecess
between CNS and ANS . By this way, the hypertensives can
reguiate the EP by themsetves after a periad of training sc
as ta reach the goal of fong-time treatment = for
hypertension. This system is self-fearning and is described
in the system dynamics madet.
PTT and Cardivascutar Performence
It {8 very impartant to get information about activity
oF the avtoncamic function in biefeedback contra! system,
General sphygmemancment in which koretkorf <KI seund iS Used
to determine BP fevel, cannot be empiayed in bicteedback
contrat program because of discrete and inaccurate. With ar
automated constant curf-pressure system devetaned by Dz,
Shapira et af. ([41(53, systeric braced pressure CSEPI ar
diastafic stocd pressure (DEP) fevel can be measured beat—
by-beat. But this has several disadvantages For
psychephysictogical experiments fike bicfeedback ocrogram
etc... Firstiy, it has Subjects felf uncomfartabie, ard
secondiy, the inflated cuff may cause the artery ta be
clogged cr partiy crogged. Arterial puise transit time <PTT)
has been Used as a measure af Cardiovascular perfarmences: in
past decate (63°(8], mainty as an index of BP change. In
reference [91], Inu Mingjie presente a new instrument toa
detect PTT with arte f puise wave <¢PWI and efectra-
gardiegram ECG) and established a modei tc: describe the
refationship- between PTT and BP. The regression ecwation is:
AMEP=-1. 3i3"oPTT
where MEF represents the change cf mean BP tmmHa), atic
OPTT stands for the change oF PTT (ms).
By this method, the change of BP can be detected
comtinucusty and noninvasively, which is desirabié far
bicfeedback BP comtrai experiments.
Application to Biofeedback BP Comtrat
a. Syojects and methad
2Z essential hypertensives were randcmfy assigned to
three groups A,B, and C. They were asked ta compiete
training sessicn ence daify 6 dayS a week for three weeks. A
training session ‘tock approximatety 30 minutes, Thus 18
Sessions were completed far each subject aver the training
program.
Subjects in, feedback session were Giver Feedback
information about their BP change measured with PTT
indivectsy, in pseude-feedback sessic the subjects were
given random SigaiS which were irrefevent with their BP. In
refaxation session, subjects were asked tc sit auielly,
Tefax their muscies, without feedback information. Subjects
‘THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 805
group A were trained with feedback session in whale
program, these in group Bo were trained with feedback and
relaxation Session aiternatety and in agraovp C they were
trained with oseude-feedback sessicn.
In bicfeedback sessicn, PTT was used as a measure af EP
change. The PTT was cet from the arterial nuise wavetPW) and
efectracardiogramtECG), where the PW was detected with a
phete-electranic transducer, and ECG was got from standard
fead If. *
Results
id. There are significant BP reductions in both grovo A
and group KE aver three weeks, average magnitudes are
27. B/Z2.6 maa (see fig. 3) and 24.5/18.9 inmHa,
respectively. But significant differences between them
cannet be found. .
Z). There i5 na significant change in average BP of
Group C aver the Prearam.
3). There i5 significant differences between bicreedback
“and refaxation in within-session, average SEP reduction
taverage reductions are 6% mmHq and 4.7 mmHa
respectively).
4), There are ne significant acress-sessicen reductions
its average: magnitutes cf BP for either reftaxation “or
pseudc-feedback Sessicr.
She Mean reduction of SEP far bicfeedback sessicn i5
Significant, magnitude is 46.9% mmHa.
Discussion
Bionifticant BP reductions of subjects trained with
bicfeedback technique successively i5 cibtained, average
magnitude is 27.8/22.6 mmHa (the fast three ta the first
three sessions). This iS supericr tc other renorted resufts
C1323 and supports the suggestion that | vaiverntary
reguiaticn cf some autonomic function! may be hefoful far
clinical treatment of the deseases caused by Stress, mainiy
hypertension, In addition, It is aisa found that there are
differences between hypertensives and nermat persons
cr the distributions af the PTT parameter and its compenents
-- the cardiac ore-ejection period PEP) and the ouvlfse
transit interval (PTI3. The PEP and PTT aise provide same
imformation about cardiovascular, berfarmence. By means af
and methead of System Dynamics, compnuter technoloay,
artificial intettigence and modern efectrenic techniques, . a
computer-aidded diagnosis and treatment system can be
constructed itt which experiences of exnéfts and various
parameters refiecting cardicvascular activity such as PTT,
PTI and etc. are useful.
806 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
References
fi] Benson, H.,et ai», Decreased SEP throvah Operant
Cond i tioning Teagchniques with Essentiat Hypertension,
Science, Val.i75, Avg.19771, pp740-74z
C2] Joarme, Le, et ata, “Hypertension Seff-camtrat with a
Portable Feedback Unit oor Meditation-Refaxation”,
Biofeedback and Seif-Reguiation, Vat.3, No.3, 1978, ppZe7-
279
C3] Guyten, A.C., "Basic Human Physictoay: Normat Function
and Mechanisms of Desease”, 2nd ed., W.B. Saunders Ccmpany,
1977
f4] Sapira, DB. "Tracking-Cuff System far Beat-to-Beat
Recording of EP", Psychapysictagy, Val.18, No.2, 1981,
pplZz9-136
CS] Tursky, &., "Automated Constant Curf-pressure System to
Measure Average Systofic ard Dyastatic Biced Pressure in
Man”, IEEE, Trans. on Bicmedicat Engineering, Volt. BME-
19, Nod, Juty 197%, ppZ71-Z76 :
{61 Weiss, T., "PTT in the Anatysis af ANS Effects on the
-Cardiovascuiar System”, Psychaphysiciogy, Vol.i7, No.3,
19780, ppZO2Z-207
{72 Pottak, MH. "Aertic-Radiat PTT and ECG G-wave to
Radiat Puise Wave Interval as Indices af Beat-py-Beat EP
Change”, Psychophysicicgy, Vol.Z0, Newt, 1983, ppzi-ze
(81 Marie, G.V., et ai., "The Retaticonshin between Arterial
BP and PTT During Dynamic and Static Exercise”,
Psychophysictogy, Vol.21, No.5, 1984, ppS2t-527
{9] Zhu Mingjie., "Hiced Pressure Made and its Application
te Bicfeedback BP Reduction in Hypertensives”, Master
Thesis, East China University of Chemicai Technofonay, Juty,
1986
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA'807
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Fig2: Viagram of biofeedback control of BP
=
t Training Session
6 8 © 2 hh 6 B
2
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39 “=~ DBP
Fig.3: Changes of 8P during the program
Conese S— Cardiovascula
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Humorel, 7 \ me R Pressurereceflor PIT
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