Hemodynamic and Metabolic Function in Pregnancy

8/16/2019 Hemodynamic and Metabolic Function in Pregnancy

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CONTENTS

Contents .................................................................................................................. 1

Chapter I : Introduction ........................................................................................... 2

Chapter II : Hemodynamic Change In Pregnancy.................................................... 3 Cardioascu!ar System in Pregnancy...................................................3

"eta! and #aterna! $!ood Circu!ation.................................................1%

REFERATHE#O&'N(#IC CH(N)E IN P*E)N(NC'

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CHAPTER I

INTRODUCTION

Physio!ogica! and anatomica! a!terations dee!op in many organ systems during the

course o, pregnancy and de!iery. Ear!y changes are due- in part- to the metao!ic demands

rought on y the ,etus- p!acenta and uterus andin part- to the increasing !ee!s o, pregnancy

hormones- particu!ar!y those o, progesterone and estrogen. /ater changes- starting in mid0

pregnancy- are anatomica! in nature and are caused y mechanica! pressure ,rom the

epanding uterus. These a!terations create uniue reuirements ,or the pharmaceutica!

management o, the pregnant oman.

&uring pregnancy and the puerperium- the heart and circu!ation undergo remar4a!e

physio!ogica! adaptations. Changes in cardiac ,unction ecome apparent during the ,irst 5

ee4s o, pregnancy 6Hiard- 2%178. Cardiac output is increased as ear!y as the ,i,th ee4

and re,!ects a reduced systemic ascu!ar resistance and an increased heart rate. Compared

ith prepregnancy measurements- rachia! systo!ic !ood pressure- diasto!ic !ood pressure-

and centra! systo!ic !ood pressure are a!! signi,icant!y !oer 9 to ee4s ,rom the !ast

menstrua! period 6#ahendru- 2%128. The resting pu!se rate increases approimate!y 1%

eats;min during pregnancy. $eteen ee4s 1% and 2%- p!asma o!ume epansion egins-

and pre!oad is increased.


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CHAPTER II

HEMODYNAMIC CHANGE IN PREGNANCY

2.1 CARDIOVASCULAR SYSTEM

&uring pregnancy and the puerperium- the heart and circu!ation undergo remar4a!e

physio!ogica! adaptations. Changes in cardiac ,unction ecome apparent during the ,irst 5

ee4s o, pregnancy 6Hiard- 2%178. Cardiac output is increased as ear!y as the ,i,th ee4

and re,!ects a reduced systemic ascu!ar resistance and an increased heart rate. Compared

ith prepregnancy measurements- rachia! systo!ic !ood pressure- diasto!ic !ood pressure-

and centra! systo!ic !ood pressure are a!! signi,icant!y !oer 9 to ee4s ,rom the !ast

menstrua! period 6#ahendru- 2%128. The resting pu!se rate increases approimate!y 1%

eats;min during pregnancy. $eteen ee4s 1% and 2%- p!asma o!ume epansion egins-

and pre!oad is increased.


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2.1.1 Heart

(s the diaphragm ecomes progressie!y e!eated- the heart is disp!aced to the !e,t and

upard and is rotated on its !ong ais. (s a resu!t- the ape is moed somehat !atera!!y ,rom

its usua! position and produces a !arger cardiac si!houette in chest radiographs 6"ig. 2018.

Figure. 2-1

"urthermore- pregnant omen norma!!y hae some degree o, enign pericardia!

e,,usion- hich may increase the cardiac si!houette 6Enein- 1=58.


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2.1.2 Cardiac Output

&uring norma! pregnancy- mean arteria! pressure and ascu!ar resistance decrease-

hi!e !ood o!ume and asa! metao!ic rate increase. (s a resu!t- cardiac output at rest-

hen measured in the !atera! recument position- increases signi,icant!y eginning in ear!y

pregnancy 6&ue4ot- 1==3> #aie- 1==78. It continues to increase and remains e!eated

during the remainder o, pregnancy.

&uring !ate pregnancy in a supine oman- the !arge uterus rather consistent!y

compresses enous return ,rom the !oer ody. It a!so may compress the aorta 6$ieniar?-

1=958. In response- cardiac ,i!!ing may e reduced and cardiac output diminished.

Speci,ica!!y- $amer and &resner 62%%38 ,ound cardiac output at term to increase 1.2 /;min

@a!most 2% percent@hen a oman as moed ,rom her ac4 onto her !e,t side. #oreoer-

in the supine pregnant oman- uterine !ood ,!o estimated y &opp!er e!ocimetry

decreases y a third 6+e,,reys- 2%%98. O, note- Simpson and +ames 62%%A8 ,ound that ,eta!

oygen saturation is approimate!y 1% percent higher i, a !aoring oman is in a !atera!

recument position compared ith supine. Bpon standing- cardiac output ,a!!s to the same

degree as in the nonpregnant oman 6Easter!ing- 1=558.

In mu!ti,eta! pregnancies- compared ith sing!etons- materna! cardiac output is

augmented ,urther y a!most another 2% percent ecause o, a greater stro4e o!ume 61A

percent8 and heart rate 63.A percent8. /e,t atria! diameter and !e,t entricu!ar end0diasto!ic

diameter are a!so increased due to augmented pre!oad 6ametas- 2%%38. The increased heart

rate and inotropic contracti!ity imp!y that cardioascu!ar resere is reduced in mu!ti,eta!

gestations.

2.1. Circu!ati"#

Changes in posture a,,ect arteria! !ood pressure. $rachia! artery pressure hen sitting

is !oer than that hen in the !atera! recument supine position 6$amer- 2%%38. Dright and

coor4ers 61=A%8 demonstrated that enous !ood ,!o in the !egs is retarded during

pregnancy ecept hen the !atera! recument position is assumed. This tendency toard

!ood stagnation in the !oer etremities during !atter pregnancy is attriuta!e to occ!usion

o, the pe!ic eins and in,erior ena caa y the en!arged uterus. The e!eated enous


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pressure returns to norma! hen the pregnant oman !ies on her side and immediate!y a,ter

de!iery 6#c/ennan- 1=738. These a!terations contriute to the dependent edema ,reuent!y

eperienced and to the dee!opment o, aricose eins in the !egs and u!a- as e!! as

hemorrhoids. These changes a!so predispose to deep0ei thromosis.

In approimate!y 1% percent o, omen- supine compression o, the great esse!s y the

uterus causes signi,icant arteria hypotension- sometimes re,erred to as the supine hypotensie

syndrome 6inse!!a- 1==78. (!so hen supine- uterine arteria! pressure@and thus !ood ,!o

@is signi,icant!y !oer than that in the rachia! artery.

2.1.$ Re#i#% A#&i"te#'i# II% a#d P!a'(a V"!u(e

The renin0angiotensin0a!dosterone ais is intimate!y ino!ed in !ood pressure contro!

ia sodium and ater a!ance. (!! components o, this system are increased in norma!

pregnancy 6$ent!ey0/eis- 2%%A8. *enin is produced y oth the materna! 4idney and the

p!acenta- and increased renin sustrate 6angiotensinogen8 is produced y oth materna! and

,eta! !ier. E!eated angiotensinogen !ee!s resu!t- in part- ,rom increased estrogen production

during norma! pregnancy and are important in ,irsttrimester !ood pressure maintenance

6(ugust- 1==A8. )ant and associates 61=38 studied ascu!ar reactiity to angiotensin II

throughout pregnancy. Nu!!iparas ho remained normotensie ecame and stayed re,ractory

to the pressor e,,ects o, in,used angiotensin II. Conerse!y- those ho u!timate!y ecame

hypertensie dee!oped- ut then !ost- this re,ractoriness. "o!!o0up studies y )ant 61=78

and Cunningham 61=A8 and their co!!eagues indicated that increased re,ractoriness to

angiotensin II stemmed ,rom indiidua! esse! re,ractoriness. Said another ay- the

anorma!!y increased sensitiity as an a!teration in esse! a!! re,ractoriness rather than the

conseuence o, a!tered !ood o!ume or renin0angiotensin secretion. The ascu!ar

responsieness to angiotensin II may e progesterone re!ated. Norma!!y- pregnant omen

!ose their acuired ascu!ar re,ractoriness to angiotensin II ithin 1A to 3% minutes a,ter the

p!acenta is de!iered. #oreoer- !arge amounts o, intramuscu!ar progesterone gien during

!ate !aor de!ay this diminishing re,ractoriness. (nd a!though eogenous progesterone does

not restore angiotensin II re,ractoriness to omen ith gestationa! hypertension- this can e

done ith in,usion o, its maor metao!ite- AF0dihydroprogesterone.


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2.1.+ Cardiac Natriuretic Peptide'

(t !east to species o, these@atria! natriuretic peptide 6(NP8 and $0type natriuretic

peptide 6$NP8@are secreted y cardiomyocytes in response to chamer0a!! stretching.

These peptides regu!ate !ood o!ume y proo4ing natriuresis- diuresis- and ascu!ar

smooth0musc!e re!aation 6C!erico- 2%%78. In nonpregnant and pregnant patients- !ee!s o,

$NP and o, amino0termina! pro0rain natriuretic peptide 6Nt pro0$NP8 may e use,u! in

screening ,or depressed !e,t entricu!ar systo!ic ,unction and determining chronic heart

,ai!ure prognosis 6+aro!im- 2%%9> Tanous- 2%1%8.

2.1., Pr"'ta&!a#di#'

Increased prostag!andin production during pregnancy is thought to hae a centra! ro!e

in contro! o, ascu!ar tone- !ood pressure- and sodium a!ance. *ena! medu!!ary

prostag!andin E2 synthesis is increased mar4ed!y during !ate pregnancy and is presumed to


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e natriuretic. Prostacyc!in 6P)I28- the principa! prostag!andin o, endothe!ium- a!so is

increased during !ate pregnancy and regu!ates !ood pressure and p!ate!et ,unction. It a!so has

een imp!icated in the angiotensin resistance characteristic o, norma! pregnancy 6"riedman-

1=558. The ratio o, P)I2 to thromoane in materna! urine and !ood has een considered

important in preec!ampsia pathogenesis.

2.1.- E#d"te!i#

There are seera! endothe!ins generated in pregnancy. Endothe!in01 is a potent

asoconstrictor produced in endothe!ia! and ascu!ar smooth musc!e ce!!s and regu!ates !oca!

asomotor tone 6"e!etou- 2%%9> )eorge- 2%118. Its production is stimu!ated y angiotensin II-

arginine asopressin- and thromin. Endothe!ins- in turn- stimu!ate secretion o, (NP-

a!dosterone- and Nitric Oide. There are endothe!in receptors in pregnant and nonpregnant

myometrium. Endothe!ins a!so hae een identi,ied in the amnion- amnionic ,!uid- decidua-

and p!acenta 6uota- 1==2> #argarit- 2%%A8. u!andae!u- 2%138.


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2.2 eta! a#d Mater#a! *!""d Circu!ati"# i# te Mature P!ace#ta

$ecause the p!acenta is ,unctiona!!y an intimate approimation o, the ,eta! capi!!ary ed

to materna! !ood- its gross anatomy primari!y concerns ascu!ar re!ations. The ,eta! sur,ace

is coered y the transparent amnion- eneath hich chorionic esse!s course. ( section

through the p!acenta inc!udes amnion- chorion- chorionic i!!i and interi!!ous space- decidua!

6asa!8 p!ate- and myometrium .

2.2.1 eta! Circu!ati"#

&eoygenated enous0!i4e ,eta! !ood ,!os to the p!acenta through the to umi!ica!

arteries. (s the cord oins the p!acenta- these umi!ica! esse!s ranch repeated!y eneath the

amnion and again ithin the i!!i- ,ina!!y ,orming capi!!ary netor4sin the termina! i!!ous

ranches.

$!ood ith signi,icant!y higher oygen content returns ,rom the p!acenta ia a sing!e

umi!ica! ein to the ,etus. The ranches o, the umi!ica! esse!s that traerse a!ong the ,eta!

sur,ace o, the p!acenta in the chorionic p!ate are re,erred to as the p!acenta! sur,ace or

chorionic esse!s. These esse!s are responsie to asoactie sustances- ut anatomica!!y-

morpho!ogica!!y- histo!ogica!!y- and ,unctiona!!y- they are uniue.

Chorionic arteries a!ays cross oer chorionic eins. "is4- 1=55> /ouet-

1=558. (,ter 1% ee4s- end0diasto!ic ,!o appears and is maintained throughout norma!


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pregnancy 6#au!i4- 1==8. C!inica!!y- these are studied ith &opp!er sonography to assess

,eta! e!!0eing 6Chap. 1%- p. 21=8.

2.2.2 Mater#a! Circu!ati"#

$ecause an e,,icient materna!p!acenta! circu!ation is reuisite- many inestigators

hae sought to de,ine ,actors that regu!ate !ood ,!o into and ,rom the interi!!ous space. (n

adeuate mechanism must ep!ain ho !ood can: 618 !eae materna! circu!ation> 628 ,!o

into an amorphous space !ined y syncytiotropho!ast- rather than endothe!ium> and 638

return through materna! eins ithout producing arterioenous0!i4e shunts that ou!d preent

materna! !ood ,rom remaining in contact ith i!!i !ong enough ,or adeuate echange.

Ear!y studies o, *amsey and &ais 61=938 and *amsey and Harris 61=998 proide a

physio!ogica! ep!anation o, p!acenta! circu!ation. These researchers demonstrated- y

care,u!- !o0pressure inections o, radiocontrast materia!- that arteria! entrances and enous

eits are scattered random!y oer the entire p!acenta! ase.

#aterna! !ood enters through the asa! p!ate and is drien high up toard the

chorionic p!ate y arteria! pressure e,ore !atera!!y dispersing. (,ter athing the eterna!

microi!!ous sur,ace o, chorionic i!!i- materna! !ood drains ac4 through enous ori,ices in

the asa! p!ate and enters uterine eins. Thus- materna! !ood traerses the p!acenta random!y

ithout pre,ormed channe!s. The preious!y descried tropho!ast inasion o, the spira!

arteries creates !o0resistance esse!s that can accommodate massie increase in uterine

per,usion during gestation. )enera!!y- spira! arteries are perpendicu!ar to- ut eins are

para!!e! to- the uterine a!!. This arrangement aids c!osure o, eins during a uterine

contraction and preents the eit o, materna! !ood ,rom the interi!!ous space. The numer

o, arteria! openings into the interi!!ous space ecomes gradua!!y reduced y cytotropho!ast

inasion. (ccording to $rosens and &ion 61=938- there are aout 12% spira! arteria! entries

into the interi!!ous space at term. These discharge !ood inspurts that athes the adacent

i!!i 6$ore!!- 1=A58. (,ter the 3%th ee4- a prominent enous p!eus separates the decidua

asa!is ,rom the myometrium and thus participates in proiding a c!eaage p!ane ,or p!acenta!

separation.


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(s discussed- oth in,!o and out,!o are curtai!ed during uterine contractions. $!e4er

and associates 61=A8 used seria! sonography during norma! !aor and ,ound that p!acenta!

!ength- thic4ness- and sur,ace area increased during contractions. They attriuted this to

distention o, the interi!!ous space y impairment o, enous out,!o compared ith arteria!

in,!o. &uring contractions- there,ore- a somehat !arger o!ume o, !ood is aai!a!e ,or

echange een though the rate o, ,!o is decreased. Simi!ar!y- &opp!er e!ocimetry has

shon that diasto!ic ,!o e!ocity in spira! arteries is diminished during uterine contractions.

Thus- principa! ,actors regu!ating interi!!ous space !ood ,!o are arteria! !ood pressure-

intrauterine pressure- uterine contraction pattern- and ,actors that act speci,ica!!y on arteria!

a!!s.

2.2. Cardi"a'cu!ar S3'te(

The ,eta! circu!ation is sustantia!!y di,,erent ,rom that o, the adu!t and ,unctions unti!

irth- hen it is reuired to change dramatica!!y. "or eamp!e- ecause ,eta! !ood does not

need to enter the pu!monary ascu!ature to e oygenated- most o, the right entricu!ar

output ypasses the !ungs. In addition- the ,eta! heart chamers or4 in para!!e!- not in series-

hich e,,ectie!y supp!ies the rain and heart ith more high!y oygenated !ood than the

rest o, the ody. Oygen and nutrient materia!s reuired ,or ,eta! groth and maturation are

de!iered ,rom the p!acenta y the sing!e umi!ica! ein. The ein then diides into the ductus


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enosus and the porta! sinus. The ductus enosus is the maor ranch o, the umi!ica! ein

and traerses the !ier to enter the in,erior ena caa direct!y. $ecause it does not supp!y

oygen to the interening tissues- it carries e!!0oygenated !ood direct!y to the heart. In

contrast- the porta! sinus carries !ood to the hepatic eins primari!y on the !e,t side o, the

!ier- and oygen is etracted. The re!atie!y deoygenated !ood ,rom the !ier then ,!os

ac4 into the in,erior ena caa- hich a!so receies !ess oygenated !ood returning ,rom

the !oer ody. $!ood ,!oing to the ,eta! heart ,rom the in,erior ena caa- there,ore-

consists o, an admiture o, arteria!0!i4e !ood that passes direct!y through the ductus enosus

and !ess e!!0oygenated !ood that returns ,rom most o, the eins e!o the !ee! o, the

diaphragm. The oygen content o, !ood de!iered to the heart ,rom the in,erior ena caa is

thus !oer than that !eaing the p!acenta.

In contrast to postnata! !i,e- the entric!es o, the ,eta! heart or4 in para!!e!- not in

series. De!!0oygenated !ood enters the !e,t entric!e- hich supp!ies the heart and rain-

and !ess oygenated !ood enters the right entric!e- hich supp!ies the rest o, the ody.

These to separate circu!ations are maintained y the right atrium structure- hich

e,,ectie!y directs entering !ood to either the !e,t atrium or the right entric!e- depending on

its oygen content. This separation o, !ood according to its oygen content is aided y the

pattern o, !ood ,!o in the in,erior ena caa. The e!!0oygenated !ood tends to course

a!ong the media! aspect o, the in,erior ena caa and the !ess oygenated !ood ,!os a!ong

the !atera! esse! a!!. This aids their shunting into opposite sides o, theheart. Once this

!ood enters the right atrium- the con,iguration o, the upper interatria! septum@the crista

diidens@pre,erentia!!y shunts the e!!0oygenated !ood ,rom the media! side o, the

in,erior ena caa through the ,oramen oa!e into the !e,t heart and then to the heart and rain

6&aes- 1=928. (,ter these tissues hae etracted needed oygen- the resu!ting !ess

oygenated !ood returns to the right atrium through the superior ena caa.

The !ess oygenated !ood coursing a!ong the !atera! a!! o, the in,erior ena caa

enters the right atrium and is de,!ected through the tricuspid a!e to the right entric!e. The

superior ena caa courses in,erior!y and anterior!y as it enters the right atrium- ensuring that

!ess e!!0oygenated !ood returning ,rom the rain and upper ody a!so i!! e shunted

direct!y to the right entric!e. Simi!ar!y- the ostium o, the coronary sinus !ies ust superior to


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the tricuspid a!e so that !ess oygenated !ood ,rom the heart a!so returns to the right

entric!e. (s a resu!t o, this !ood ,!o pattern- !ood in the right entric!e is 1A to 2% percent

!ess saturated than !ood in the !e,t entric!e.

(!most =% percent o, !ood eiting the right entric!e is shunted through the ductus

arteriosus to the descending aorta. High pu!monary ascu!ar resistance and comparatie!y

!oer resistance in the ductus arteriosus and the umi!ica!p!acenta! ascu!ature ensure that

on!y aout 1A percent o, right entricu!ar output@5 percent o, the comined entricu!ar

output@goes to the !ungs 6Teite!- 1==28. Thus- one third o, the !ood passing through the

ductus arteriosus is de!iered to the ody. The remaining right entricu!ar output returns to

the p!acenta through the to hypogastric arteries- hich dista!!y ecome the umi!ica!

arteries. In the p!acenta- this !ood pic4s up oygen and other nutrients and is recircu!ated

through the umi!ica! ein.


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Harert )# +r- Corne!! )D- /itt!e,ie!d +$- et a!: #aterna! hemodynamics associated ith

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)yneco! Inestig =:392- 2%%2

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Hemodynamic and Metabolic Function in Pregnancy