In the womb, the pathway of your baby’s blood circulation is different than it is after birth. In the uterus, a baby’s circulation bypasses the lungs. The lungs are not needed to exchange oxygen because the placenta (the organ that nourishes and protects your developing baby) supplies the baby with oxygen through the umbilical cord. The pulmonary artery—which, after birth, will carry blood from the heart to the lungs—instead sends blood directly back to the heart through a fetal blood vessel called the ductus arteriosus.
Normally, when a baby is born and begins to breathe air, his circulatory system quickly adapts to the outside world. The pressure in the lungs changes as air enters and inflates the lungs. As a result, the ductus arteriosus, which previously supplied the fetal heart with blood, permanently closes. Blood returning to the heart from the body can now be pumped into the lungs, where oxygen and carbon dioxide are exchanged. The blood is then returned to the heart and pumped back out to the body in an oxygen-rich state.
Understanding Persistent Pulmonary Hypertension of the Newborn (PPHN)
In a baby with PPHN, however, the fetal circulatory system doesn’t “switch over.” The ductus arteriosus remains open, and the baby’s blood flow continues to bypass the lungs. Even though the baby is breathing, oxygen in the breathed air will not reach the bloodstream. Because the blood returning from the body is unable to enter the lungs properly—and instead flows through the still-open ductus arteriosus—it returns to the heart in an oxygen-poor state. This condition is known as persistent fetal circulation, or PFC.
“The baby’s circulation has not made the normal transition from fetal circulation to normal newborn circulation because pressure in the lungs is increased, and this causes distress,” says Neal Cohn, MD, a pediatrician. Depending on the degree of PPHN causing the persistent fetal circulation, the oxygen in the air your baby breathes into his lungs is not adequately picked up and carried by the blood to other areas of the body that need it (such as the brain, kidneys, liver, and other organs). These organs soon become stressed from a lack of oxygen.