Anatomical closure of ductus arteriosus occurs at –
- 3–4 day
- 10th day
- 30th day
Circulatory adjustments at birth
- These are brought about because of a shift from placental dependance for gas exchange in the fetus to pulmonary gas exchange in neonate.
- Pulmonary circulation
- Immediatly after birth lungs expand due to first few breaths of neonate.
- This causes a fall in pulmonary vascular resistance (O2 causes pulmonary vasodilatation).
- This results in increased flow into pulmonary trunk and arteries.
- The pulmonary artery pressure falls due to lowering of pulmonary vascular resistance.
- The pressure relations between aorta and pulmonary trunk are reversed so that the blood flow through the ductus arteriosus is reversed → Instead of blood flowing from the pulmonary artery to aorta, the direction of flow through ductus, is from aorta to pulmonary trunk.
- Increasing oxygen saturation causes the muscle of ductus to constrict →
In full term neonates the ductus arteriosus closes within 10 to 25 days.
- System circulation and circulation through heart
- Loss of placental circulation and clamping of the cord after birth results in increase in systemic vascular resistance.
- This tends to increase the aortic blood pressure and the left ventricular systolic pressure.
- The loss of placental circulation results in sudden reduction of flow through ductus venosus which closes off ?→ Flow through ductus venosus disappears by the 7th day of postnatal life.
- The loss of placental flow results in a decrease in the volume of blood returning to right atrium → Right atrial pressure decreases.
- The left atrial pressure becomes higher than right atrial pressure and the septum primum which ats as a valve of fossa ovalis, approximates with the septum secundum to close off formen ovale.
- Functional closure of foramen ovale occurs very quickly.
- Over a period of months, the septum primtun and septum secundum become firmly adherent resulting in anatomical closure of the foramen ovale.
- After closure of ductus arteriosus, there is establishment of postnatal circulation : -
- The blood reaching the right atrium through IVC and SVC is emptied into the right ventricle from where it is pumped into pulmonary trunk.
- After coursing through lungs for gas exchange, it reaches the left atrium and ventricle.
- The left ventricle pumps it out for distribution in the body for oxygenation of the tissues.
- The venous return again comes back to right atrium through IVC and SVC.
- All of the blood leaving the right ventricle, after coursing through lungs, reaches the left ventricle → The two ventricles are connected in series and therefore, the output of right and left ventricles are same (in contrast to fetal circulation, where right ventricular output is more).