A fetus in the womb has a unique circulatory system that allows it to get oxygen from the placenta. After birth, a baby no longer gets oxygen from the placenta. Instead, the newborn must get oxygen from the lungs. Some infants cannot make this switch: The lungs’ blood vessels do not open up properly, so blood cannot flow to the lungs. This restricted blood flow in infants is called persistent pulmonary hypertension of the newborn (PPHN). “Persistent” means that the issue does not go away, and “pulmonary hypertension” refers to high blood pressure in the lungs’ blood vessels.
To understand PPHN, it’s important to know how blood circulation works in a fetus — and how it changes after birth.
The heart is made of four chambers that pump blood to different parts of the body. Upper chambers, called the right atrium and left atrium, receive blood. The bottom chambers, called the right and left ventricles, send blood to the lungs and body.
The right side of the heart receives oxygen-poor blood and sends it to the lungs to pick up oxygen. The oxygen-rich blood then flows to the left side of the heart, which pumps blood out to the rest of the body.
While in the womb, a fetus gets oxygen differently. A fetus does not breathe; instead, it gets oxygen from the placenta. The placenta is an organ that connects the mother to the fetus to exchange oxygen, nutrients, and waste. Fetal blood circulation is more complicated than normal circulation because it bypasses the lungs.
Several factors limit blood flow to the lungs’ blood vessels in a fetus. The low-oxygen environment of the womb and vasoconstrictors (substances in the body that narrow blood vessels) keep the blood vessels closed. The lungs themselves are also filled with fluid. This creates a situation where there is a lot of resistance to pumping blood into the lungs.
A blood vessel called the ductus arteriosus takes low-oxygen blood, bypasses the lungs, and channels it to the aorta, the body’s main artery. The blood travels through the umbilical cord to the placenta. There, the blood picks up oxygen. Oxygen-rich blood is sent back to the right side of the heart by the vena cava, the body’s main vein. This oxygen-rich blood can move directly from the right side of the heart to the left side through a hole called the foramen ovale. Oxygen-rich blood is then pumped to the brain and the body by the left side of the heart.
Increased blood pressure in the lungs’ blood vessels is normal in the fetus. It keeps blood out of the lungs and redirects it to the placenta.
Once an infant is born, their body must adjust to getting oxygen from the lungs rather than the placenta. The blood vessels in the lungs open up, and blood pressure falls so that blood can flow in. The ductus arteriosus normally closes in the first days of life. The hole between the right and left atrium (foramen ovale) is forced shut by increased blood pressure in the left atrium. These changes allow normal post-birth circulation to occur, so the baby can now receive oxygen from the lungs.
In rare cases, a newborn’s circulatory system might not properly switch to the lungs for oxygen. The blood vessels to the lungs stay closed, and blood still passes through the ductus arteriosus and foramen ovale. This allows low-oxygen blood to pump to the rest of the body and leads to a condition called hypoxemia (low blood oxygen).
This condition is called persistent pulmonary hypertension of the newborn. It is fatal if left untreated. Fortunately, there are several effective treatments for newborns with PPHN.
The exact cause of PPHN is currently not known. It is a rare condition, affecting an average of about 2 newborns for every 1,000 live births.
PPHN may be due to a combination of pulmonary vessels that don’t respond well to the body’s signals, thicker blood vessels that make it harder for blood to pass through, or underdeveloped lungs that don’t have enough blood vessels.
Some risk factors for PPHN include:
PPHN was previously thought to mostly affect infants who are born at term or a few weeks early. However, PPHN is being diagnosed more often in preterm and premature infants.
PPHN symptoms are caused by low levels of oxygen in the blood. They can vary from mild to life-threatening and include:
It can be tricky to tell the difference between PPHN and other heart or lung diseases in newborns. A specific diagnosis is important for providing proper care. Diagnostic tests for PPHN include:
Despite advances in treatment, PPHN is often a severe and lethal disease. Its mortality rate is between 7 percent and 39 percent. The disease’s underlying cause will direct how it is treated.
Newborns with PPHN need oxygen, warmth, fluids, nutrition, and stress management for their PPHN treatments to work. They may require antibiotics if they have a lung or blood infection. Their blood pressure needs to be monitored and treated if it gets too low. Babies with PPHN may also need medications that help the heart beat.
Medications that open narrowed blood vessels are called vasodilators. The only U.S. Food and Drug Administration (FDA)-approved pulmonary vasodilator for the treatment of PPHN is inhaled nitric oxide.
Nitric oxide is made naturally by the body to open blood vessels. Administering extra nitric oxide can be helpful when the blood vessels are closed. Other vasodilators that are not FDA approved for treating PPHN include:
Supplemental oxygen can help prevent hypoxemia (low oxygen) in infants with mild PPHN. A breathing machine can also open the lungs’ blood vessels and help newborns breathe. Doctors previously used hyperventilation (fast breathing) to treat PPHN, but studies suggest that there could be negative outcomes with this treatment. It is now considered outdated.
Lung surfactant is a material naturally made in the body that keeps the lungs healthy. It helps oxygen pass from the lungs to the blood vessels. Respiratory distress syndrome and meconium aspiration syndrome — both risk factors for PPHN — are associated with decreased lung surfactant. Giving more surfactant to newborns with PPHN may help the lungs properly exchange oxygen and carbon dioxide.
Extracorporeal membrane oxygenation (ECMO) is a last-resort therapy for severe heart and lung failure that is not responding to medical treatment. In ECMO, the newborn’s circulatory system is connected to a machine. Blood is pumped out of the body and into the machine, which removes carbon dioxide and adds oxygen. Then the machine sends the blood back into the infant’s body. ECMO bypasses the heart and lungs so that they have time to heal and the lungs’ blood vessels can open. This procedure is performed in a neonatal intensive care unit.
On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 45,800 members come together to ask questions, give advice, and share their stories with others who understand life with pulmonary hypertension.
Have you or your loved ones experienced PPHN? Share your experience in the comments below, or share your story on myPHteam.