Cardiovascular changes at birth

Question 1

Potential difference

Answer 1

Current x resistance

Question 2

Resistors in series

Answer 2

More resistors = higher total resistance

Question 3

Resistors in parallel

Answer 3

More resistors = lower total resistance

Question 4

Pressure difference

Answer 4

Flow x resistance

Question 5

Which vein carries oxygenated blood to foetus?

Answer 5

Umbilical vein

Question 6

What does the ductus arteriosus do in utero?

Answer 6

Flow to pulmonary artery is redirected to descending aorta

Question 7

What does foramen ovale do in utero?

Answer 7

Blood flows from right to left atria

Question 8

Problems with foetal circulation

Answer 8

Lungs do nothing
Placenta provides oxygenation
Brain needs best oxygenated blood

Question 9

What does ductus venous do?

Answer 9

Blood from umbilical vein straight to IVC to right atrium

Question 10

Where does most blood travel in foetus?

Answer 10

Through ovale to left atrium, ventricle, aorta and brain

Question 11

Why does right atrium normally have lower pressure than left?

Answer 11

Left ventricle has to pump blood all around body (high resistance etc)

Question 12

Where does deoxygenated blood travel?

Answer 12

From vena cava through ventricle to descending aorta and lower body

Question 13

Where does oxygenated blood travel?

Answer 13

Through foramen ovale to LA, LV and ascending aorta and brain

Question 14

What does pulmonary vasoconstriction lead to?

Answer 14

Increased resistance

Question 15

Flow, pressure and resistance

Answer 15

• Change resistance impacts flow
• Increases pressure in right atrium
• Reduces blood flow to lungs, directs blood through ductus arteriosus
• Increased r atrial pressure helps keep foramen ovale open
• Deoxygenated blood in ductus arteriosus joins descending aorta to supply lower body and preserved brains oxygen supply

Question 16

Why is it bad to be hypoxic after birth?

Answer 16

Persistence of foetal circulation

Question 17

Route of blood in foetus

Answer 17

• Majority of blood joins right atrium and streams through ovale to left atrium and ventricle, through aortic valve into ascending aorta to head
• Rest of blood goes back to placenta
• Enters via sup vena cava to right atrium and ventricle into descending aorta

Question 18

Highest oxygen pressure in foeti-placental circulation

Answer 18

4kPa

Question 19

Why is it important for baby to take first breath?

Answer 19

• First breath = oxygen rises in lungs
• Leads to pulmonary vasodilatation
• Means placental circulation ceases - flow in ductus venosus stops
• Removing placental flow means that systemic resistance increases
• High systemic resistance = L heart has to work harder
  Foramen ovale closes

Question 20

How does ligamentum arteriosus form?

Answer 20

Arteriosus flow reverses and ceases

Question 21

What does PGE2 do in pregnancy?

Answer 21

Patency of ductus arteriosus

Question 22

Why is it bad that baby doesn’t take first breath quickly?

Answer 22

• No placental circulation
• No oxygenated blood
• No blood flow to lungs
• Foetal circulation worsens hypoxia

Question 23

How does fossa ovals form?

Answer 23

Foramen ovale fuses

Question 24

How does ligamentum arteriosum form?

Answer 24

Ductus arteriosus remnant

Question 25

How does ligamentum venosum form?

Answer 25

Ductus venous remnant