You are about to attend your first delivery of a baby. Which of the following circulatory changes normally takes place in the newborn within five minutes after bih?
Decrease in systemic aery resistance
Increase in pulmonary aery resistance
Closure of the foramen ovale
Closure of the ductus aeriosus
With the first breath of life, pulmonary aerial resistance drops dramatically. This is due to the oxygenation of the lungs causing vasodilatation of the pulmonary vessels. Clamping of the umbilical cord doubles peripheral resistance and causes an increase in aerial blood pressure. As soon as right atrial pressure drop below left atrial pressure, the foramen ovale will close (valve-like mechanism), establishing the adult type blood circulation. The rising systemic and falling pulmonary aery pressure cause a flow reversal through the ductus aeriosus from right to left to left to right within minutes of bih. Complete closure of the ductus aeriosus appears to be due to a decline of local prostacyclin levels and usually drops within 24 to 48 hours after bih. The ductus venosus closes even later. Ref: Bashore T.M., Granger C.B., Hranitzky P., Patel M.R. (2013). Chapter 10. Hea Disease. In M.A. Papadakis, S.J. McPhee, M.W. Rabow (Eds), CURRENT Medical Diagnosis & Treatment 2013.