- Within minutes of spontaneous respiration most lung fluid is absorbed into the bloodstream and lymphatics
- Breathing leads to dilatation of the pulmonary vessels and a fall in pulmonary vascular resistance
- Clamping of the cord removes the low resistance placental circulation and causes a rise in systemic pressures
- This leads to functional closure of the ductus arteriosus and the foramen ovale is forced shut by the change in pressure