V1iv: Foetal circulation changes at birth and the establishment of ventilation
Foetus: conception → birth
Foetal Circulation
Parallel System
- 1 umb v (oxygenated)
↓
60% Ductus Venosus (#Shunt 1) bypasses liver & IVC /// 40% Portal V → liver/GI
↓
- RA
↓
- Foramen Ovale (#Shunt 2)
↓
- Ascending Aorta
↓
- Coronary + Cerebral circulation
↓
- SVC (deoxygenated)
↓
- RV
↓
- Pulmonary trunk
5% lungs
high PVR because
↓PaO2 & collapsed
//// 95% Ductus Arteriosus (Shunt #3)
↓
Desc Aorta
↓
Iliac Arteries
↓
2 Umbilical A
↓
Placenta
Circulatory Changes & Establishment of Ventilationa at Birth
1. Removal of Low Resistance Placenta
- Clamped umbilical cord
- ↑↑SVR
- ↑LVEDP
- ↑LAP
2. Inflation of Lungs
- Passage through birth canal squeezes fluid from lungs
- Asphyxia → activation of central + peripheral ChemoR
- First breath
- ↓PVR
- ↑Pulmonary BF
- ↓RVEDP
3. Closure Ductus Arteriosus
- ↑PaO2
- ↓Local prsostaglandin formation
- DA closure in 15hrs (local constriction of T. Media smooth m. in DA)
4. Foramen Ovale Closure
- ↑Pulmonary BF
- ↑LVEDP
- ↑LAP
- LAP > RAP = closure F. Ovale
5. Closure Ductus Venosus
- Loss of venous return from Umbilical vessels
- Closes in 1st week of life
- Open @ birth → allows umb v. catheterisation
- Remnant KA Ligamentum Venosum
Infant ventricles = smaller + ↓ compliance = HR 110 – 150bpm