What is Physiology and Hemodynamic ?
Normally, in the post-natal circulation the pulmonary and aortic circuits are in series so that the deoxygenated blood coming into the right ventricle is oxygenated in the lungs and flows back into the systemic circulation. In transposition of great arteries, the two circuits run in parallel, with the deoxygenated blood recirculating in the systemic circuit and oxygenated blood recirculating in the pulmonary circuit. Survival depends on inter-circulatory connections between these two circuits, which may be at the level of the atria (atrial septal defects), ventricles (ventricular U septa1 defects) or the great arteries (Patent ductus arteriosis or bronchopulmonary collaterals).T he presence and adequacy of these connections determine the degree j/ 1 of mixing of the desaturated systemic blood with the oxygenated pulmonary blood, which is essential for survival. The other factor which determines the natural history is the limitation to pulmonary blood flow which may occur as a result of obstruction to the left ventricular outflow tract or due to development of pulmonary vascular obstructive disease.