Cardiac Physiology

Question 1

How much does the cardiac output increase during pregnancy?

Answer 1

Cardiac output increases by 30-50%

Question 2

What factors increase cardiac output during pregnancy?

Answer 2

Increase in Stoke volume and increase in heart rate

Question 3

What factors increase stroke volume in pregnancy?

Answer 3

Increased preload due to increased blood volume and reduced after load due to systemic vasodilation

Question 4

How much does heart rate increase during pregnancy?

Answer 4

By 15-20bpm

Question 5

What is the role of the umbilical vein?

Answer 5

Carries oxygenated blood from the placenta to the fetus

Question 6

What is the ductus venosus?

Answer 6

Shunts a portion of umbilical vein blood to the inferior vena cava before it reaches the liver

Question 7

Why is there high vascular resistance in the fetal lung?

Answer 7

There is no air in the alveoli, only fluid, therefore low pO2, which causes hypoxic pulmonary vasoconstriction and therefore high vascular resistance

Question 8

What is the foramen ovale?

Answer 8

The opening between the right and left atria

Question 9

Why does blood flow through the foramen ovale?

Answer 9

There is high vascular resistance in the fetal lung and this causes back pressure on the right side of the heart, causing higher pressure in the right than the left atria, forcing blood into the left atrium

Question 10

What is the ductus arteriosus?

Answer 10

A duct that allows blood to flow from the pulmonary artery directly to the aorta in the fetus

Question 11

What are the adapations of fetal circulation?

Answer 11

Umbilical vein (carries oxygenated blood)
Ductus venosus (bypasses the liver and send umbilical vein blood to the IVC)
Foramen ovale ( allows blood from the RA to move to the LA)
Ducturs arteriosus (allows blood from the pulmonary artery to flow directly to the aorta)
umbilical artery (transfers blood to the low resistance placenta to obtain oxygen)

Question 12

When should the foramen ovale close?

Answer 12

Within the first few minutes of birth

Question 13

What closes the foramen ovale?

Answer 13

Fluid in the lungs is replaced by air, the increased oxygen reduces the vascular resistance in the lungs and consequently the resistance in the right side of the heart - also more blood can flow into the lungs which means more pressure in the LA and less pressure in the RA.

Question 14

When does the ductus venosus close?

Answer 14

Within the first few days after birth

Question 15

What closes the umbilical vein after birth?

Answer 15

Placenta removed, wharton’s jelly constricts due to cooler temperature, there is high resistance and no flow, then blood clots

Question 16

What closes the ductus venous after birth?

Answer 16

Placenta removed, wharton’s jelly constricts due to cooler temperature, there is high resistance and no flow in the umbilical vein, blood clots, no flow to ductus venosus

Question 17

What causes the ductus arteriosus to close after birth?

Answer 17

low prostaglandin levels due to the placenta being removed and high oxygen in the blood due to air in the alveoli, causes the ductus arteriosus to constrict

Question 18

How long does it take the ductus arteriosus to close after birth?

Answer 18

A few hours

Question 19

Where does the umbilical artery stem from?

Answer 19

From the internal iliac arteries

Question 20

What causes the umbilical arteries to close after birth?

Answer 20

high levels of oxygen in the blood (air in the lungs), low levels of prostaglandin (placenta removed) causes the arteries to constrict AND there is high resistance due to constriction of Wharton’s jelly and no flow due to placental removal

Question 21

What are the risk factors for a patent ductus arteriosus?

Answer 21

1) low oxygen due to preterm birth (poorly developed lungs) 2) congenital rubella 3) down syndrome

Question 22

What are the signs of Patent ductus arteriosus?

Answer 22

A widening pulse pressure, “rolling thunder”, continuous heart murmur, cardiomegaly, dysponea, cyanosis

Question 23

How can PDA be treated?

Answer 23

NSAIDs - inhibit prostaglandins and therefore cause constriction to the ductus arteriosus, or surgically by ligation or coil occlusion

Question 24

What are the maternal cardiovascular changes in pregnancy?

Answer 24

More blood is pumped around the body

Increased heart rate (15-20), Increased stroke volume (increased pre-load and reduced vascular resistance), Increased cardiac output (30-50%).

Reduced blood pressure by 10% ( systolic decreases by 5mmHG and diastolic by 10mmHg) due to decreased peripheral vascular resistant (progesterone dilates smooth muscle + addition of placenta which is low resistance)

Hemodilution (physiological anaemia) - higher plasma volume

Question 25

How much does plasma volume increase during pregnancy?

Answer 25

40-50% (2600ml to 3800ml)

Question 26

How much does the red cell mass increase in pregnancy?

Answer 26

1400ml to 1650ml (18%)

Question 27

What are the maternal respiratory changes in pregnancy?

Answer 27

Increase in tidal volume, increase in minute volume, decreased airway resistance

Question 28

How does maternal CO2 and PO2 levels change in pregnancy?

Answer 28

Tidal volume increases so more CO2 lost and more O2 absorbed, and kidneys secrete increased bicarbonate to counteract the CO2 being secreted

Question 29

How does maternal renal physiology change during pregnancy?

Answer 29

Increased GFR due to increased renal flow, reduced serum urea and creatinine, dilatation of the ureters (increasing risk of pyelonephritis)

Question 30

How does GFR change in pregnancy?

Answer 30

It rises fro 140 to 170

Question 31

If there are maternal cardiac problems which previously went undetected, when would these manifest?

Answer 31

In the first 12 weeks of gestation

Question 32

What would be an abnormal murmur to hear in pregnancy?

Answer 32

A diastolic murmur