Within seconds of birth, the baby is taking in its own oxygen for the first time. For this to happen, his delicate lungs and circulatory system must change within seconds.
So, how can a young human take what could be the most challenging breath of his life just seconds after birth?
The lungs do not provide oxygen to the fetus during pregnancy. Instead, it partially collapses and fills with fluid during development while the baby gets oxygen through the umbilical cord from the placenta, according to the Texas Heart Institute.
Since the lungs do not interfere with the oxygen supply yet, the majority of the fetal blood supply bypasses the lung through two unique fetal blood vessels. The first, the foramen ovale, allows oxygenated blood from the umbilical cord to flow directly from the heart’s right atrium to the left atrium, instead of going into the right ventricle and lungs as it does in adults, according to Children’s Hospital of Philadelphia. A second vessel, called the ductus arteriosus, connects the main body artery and the main lung artery, allowing oxygenated fetal blood to travel away from the lungs and toward the lower body, according to the American Heart Association.
“When the fetus comes out, the right side of the heart is dominant,” said Dr. Jay Kim, a neonatologist and director of neonatology at Cincinnati Children’s Hospital. This is because it pumps oxygenated blood through these two temporary shunts to the entire body. But after birth, blood circulation is reorganized, and the left ventricle becomes dominant, responsible for sending blood throughout the body, while the right ventricle takes on the new task of sending oxygen-poor blood to the lungs, according to a 2002 report published in the Archives. Diseases in childhood.
This transformation occurs in a series of rapid changes soon after birth. First, the fluid-producing cells in the fetus’s lungs begin to absorb fluid as soon as the baby is born, removing fluid to make room for incoming oxygen. The lungs immediately move until they are filled with air.” Kim said that this first breath can be so forceful and exciting that, in some cases, it punctures a newborn’s lungs.
This is the first inflation of the lungs that significantly reduces pressure and resistance to blood flow in the lungs. The reduced pressure causes blood to be pumped out of the right ventricle to be redirected toward the newborn’s lungs, according to a review in the journal Physiological Reviews.
Once the lung pressure is lower than the systemic blood pressure, or the pressure exerted on the blood vessels during heart contractions, the foramen ovale closes. With no passage between the right and left atria, deoxygenated blood begins to flow from the right atrium to the lower right ventricle, and is then sent to the lungs.
At the same time, low pressure in the pulmonary system causes blood to be drawn from the ductus arteriosus, the blood vessel that allows blood to pass through the lung and to the body. The duct begins to contract and close during the first two days of life.
At this point, 100% of the blood supply goes to the lungs. Carbon dioxide-saturated blood is pumped into the alveolar capillaries – the small blood vessels in the lungs – for the first time. The alveoli – the small air sacs in the lungs – replace the carbon dioxide in the blood with the oxygen that the baby takes in.
Kim said it takes about 5 minutes for a healthy baby to find a normal type. But the transition happens in one breath, and it’s a “very magical moment”.