[Physiological basis of fetal and neonatal circulation]

The extremely reduced nature of the pulmonary circulation, the parallel arrangement of the right and left sides of the heart, and the mixture of oxygenated umbilical blood with the rest of the venous return in the right atrium endow the foetal circulation with its "relatively protected" nature. Thus the majority of cardiac and pulmonary malformations have no effect or cause only minor circulatory disturbances. The transfer of respiratory function from the placenta to the lungs which becomes necessary as soon as the cord is clamped is a highly disturbing event. The pulmonary circulation must be established, the communications of foetal life close (Botal's foramen, ductus arteriosus), and the right and left heart function in series. Such adaptations, certain of which are essential to immediate survival, may require several weeks before completion. Any disease in the newborn, congenital or acquired, respiratory, circulatory, metabolic or other, is accompanied by numerous interwoven consequences. In particular, return to a foetal type circulation by increase or absence of pulmonary resistances could induce a right-left shunt through a fossa ovale which is only asking to open, or even through a ductus arteriosus which is only asking to reopen. Congenital diaphragmatic hernia is no exception is no exception to this rule.