The decrease in pulmonary vascular resistance provided by the inflation of the lungs means that the aortic pressure exceeds the pulmonary artery pressure during the whole cardiac cycle.
Blood continually flows from the aorta through patent ductus arteriosus into the pulmonary artery. Having passed through the pulmonary circulation the blood returns to the left atrium and left ventricle. The continual flow from the pulmonary artery to the aorta means that the pressure in the pulmonary artery - and therefore the systolic pressure in the right ventricle - is elevated. Also the flow of blood from the aorta to the pulmonary artery means that there is an increase is oxygen saturation in blood in the pulmonary artery. The right atrial and right ventricular saturations are normal.
There is a proportion of blood which is continually recirculating. As a result the left heart may become volume overloaded.
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