Physiological changes during pregnancy.

1. CARDIOVASCULAR
CHANGES IN
PREGNANCY
Dr.Nishant K. Thakur
MD Obstetrics & Gynaecology

2. ANATOMICAL
CHANGES
• Change in cardiac radiographic outline
that occurs in pregnancy. The blue
lines represent the relations between
the heart and thorax in the non
pregnant woman, and the black lines
represent the conditions existing in
pregnancy.
• Heart is pushed upward and outward
with slight rotation to left due to
elevation of the diaphragm
consequent to the enlarged uterus.

3. • Pregnant women normally have some degree of benign pericardial
effusion, which may increase the cardiac silhouette.

4. Abnormal clinical findings:
• Palpitation
• Apex beat is shifted to the 4th intercostal space about 2.5 cm outside
the midclavicular line.
• Resting pulse rate increases approximately 10 beats/min.
• A systolic murmur(apical or pulmonary area-due to decreased blood
viscosity and torsion of the great vessels)
• A continuous hissing murmur (tricuspid area in the left second and
third intercostal spaces called the “mammary murmur-due to
increased blood flow through the internal mammary vessels)

5. • Doppler echocardiography shows an increase in the left ventricular
end diastolic diameters
• The left and right atrial diameters also increase.
• A third heart sound (S3) due to rapid diastolic filling and rarely a
fourth heart sound may be auscultated.
• ECG reveals normal pattern except evidences of left axis deviation.

6. CARDIAC OUTPUT:
• CO = SV × HR
• starts to increase from 5th week of pregnancy and reaches its peak
40–50% at about 30–34 weeks. Thereafter the CO remains static till
term.
• CO is lowest in the sitting or supine position and highest in the right
or left lateral or knee chest position.
• Cardiac output increases further during labor (+50%) and immediately
following delivery (+70%) over the pre-labor values.

7. • Overall maximum CO
is seen immediately
after delivery> 2nd
stage of labor> late 1st
stage of labor> 28-32
weeks > early 1st stage
of labor.

8. • Affect of maternal
posture in
hemodynamics

9. • MAP also rises.
• CO returns to pre-labor values by 1 hour following delivery and to the
pre-pregnant level by another 4 weeks time.
• The increase in CO is caused by:
1. Increased blood volume.
2. To meet the additional O2 required due to increased metabolic activity
during pregnancy
• The increase in CO is chiefly affected by increase in stroke volume and
increase in pulse rate.

10. BLOOD PRESSURE:
• Maternal BP (BP = CO × SVR)
• Systemic vascular resistance (SVR) decreases (–21%) due to smooth
muscle relaxing effect of progesterone, NO, prostaglandins or ANP.
• In spite of the large increase in cardiac output, the maternal BP
decreases.
• Maximum decrease in BP is seen in second trimester.
• There is overall decrease in diastolic blood pressure (BP) and mean
arterial pressure (MAP) by 5–10 mm Hg.

11. • Sequential changes in
blood pressure
throughout pregnancy
in supine(blue) and in
left lateral
recumbent(red)
position.

12. VENOUS PRESSURE:
• Antecubital venous pressure remains unaffected.
• Femoral venous pressure is markedly raised especially in the later
months(It is due to pressure exerted by the gravid uterus on the
common iliac veins, more on the right side due to dextrorotation of
the uterus).
• venous pressure is raised from 8–10 cm of water in nonpregnant state
to about 25 cm of water during pregnancy in lying down position and
to about 80–100 cm of water in standing position.

13. • In pregnancy, there is no significant change in CVP, MAP and PCWP
although there is increase in blood volume, cardiac output and heart
rate. The reasons are: there is significant fall in SVR, pulmonary
vascular resistance (PVR) and colloidal osmotic pressure.

14. SUPINE HYPOTENSION SYNDROME (POSTURAL HYPOTENSION):
• During late pregnancy, the gravid uterus produces a compression
effect on the inferior vena cava when the patient is in supine position.
This, however, results in opening up of the collateral circulation by
means of paravertebral and azygos veins. In some cases (10%), when
the collateral circulation fails to open up, the venous return of the
heart may be seriously curtailed. This results in production of
hypotension, tachycardia and syncope.

15. • Uterine blood flow is increased from 50 mL/min in nonpregnant state to
about 750 mL near term.
• In a normal pregnancy, vascular system becomes refractory to angiotensin
II, endothelin I and other pressure agents.
• Pulmonary blood flow (normal 6,000 mL/min) is increased by 2,500
mL/min.
• Renal blood flow (normal 800 mL) increases by 400 mL/min at 16th week
and remains at this level till term.
• The blood flow through the skin and mucous membranes reaches a
maximum of 500 mL/min by 36th week.
• Heat sensation, sweating or stuffy nose complained by the pregnant
women can be explained by the increased blood flow.