Cardiovascular changes at birth Flashcards
Potential difference
Current x resistance
Resistors in series
More resistors = higher total resistance
Resistors in parallel
More resistors = lower total resistance
Pressure difference
Flow x resistance
Which vein carries oxygenated blood to foetus?
Umbilical vein
What does the ductus arteriosus do in utero?
Flow to pulmonary artery is redirected to descending aorta
What does foramen ovale do in utero?
Blood flows from right to left atria
Problems with foetal circulation
Lungs do nothing
Placenta provides oxygenation
Brain needs best oxygenated blood
What does ductus venous do?
Blood from umbilical vein straight to IVC to right atrium
Where does most blood travel in foetus?
Through ovale to left atrium, ventricle, aorta and brain
Why does right atrium normally have lower pressure than left?
Left ventricle has to pump blood all around body (high resistance etc)
Where does deoxygenated blood travel?
From vena cava through ventricle to descending aorta and lower body
Where does oxygenated blood travel?
Through foramen ovale to LA, LV and ascending aorta and brain
What does pulmonary vasoconstriction lead to?
Increased resistance
Flow, pressure and resistance
- 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
Why is it bad to be hypoxic after birth?
Persistence of foetal circulation
Route of blood in foetus
- 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
Highest oxygen pressure in foeti-placental circulation
4kPa
Why is it important for baby to take first breath?
- 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
How does ligamentum arteriosus form?
Arteriosus flow reverses and ceases
What does PGE2 do in pregnancy?
Patency of ductus arteriosus
Why is it bad that baby doesn’t take first breath quickly?
- No placental circulation
- No oxygenated blood
- No blood flow to lungs
- Foetal circulation worsens hypoxia
How does fossa ovals form?
Foramen ovale fuses
How does ligamentum arteriosum form?
Ductus arteriosus remnant
How does ligamentum venosum form?
Ductus venous remnant
