Within seconds of birth, the child absorbs its own oxygen for the first time. For this to happen, their tiny lungs and circulatory systems must transform within seconds. So how does a tiny human take what might be the most challenging breath of his life just seconds after birth?
The first breath of a newborn baby
First, it helps understand how the circulatory system, specifically the lungs and heart, works in the womb. The lungs do not provide oxygen to the fetus during gestation. Instead, according to the Texas Heart Instituteduring development they are partially collapsed and filled with fluid as the baby receives oxygen through the umbilical cord from the placenta.
Because the lungs are not yet involved in providing oxygen, most of the fetal blood supply bypasses the lungs through two blood vessels unique to fetuses.
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 to the right ventricle and lungs as it does in an adult, according to the Children’s Hospital of Philadelphia.
The second vessel, called the ductus arteriosus, connects the body’s main artery and the main pulmonary artery, allowing the baby’s oxygenated blood to divert from the lungs and head to the lower part of the body, according to the American Heart Association.
Unlike an adult’s heart, “when the baby comes out, the right side of the heart is the dominant side,” said Dr. Jae Kim, a neonatologist and director of neonatology at Cincinnati Children’s Hospital. This is because it pumps oxygenated blood through these two temporary shunts throughout the body. But after birth, the circulatory system reorganizes itself.
The left ventricle becomes dominant, responsible for sending blood throughout the body, while the right ventricle takes on the new job of sending oxygen-poor blood to the lungs, according to a 2002 report published in the journal Archives of Disease in Childhood.
This transformation occurs in a series of rapid changes soon after birth. First, the cells responsible for secreting fluid in the baby’s lungs begin to absorb fluid once the baby is born, removing the fluid to make room for incoming oxygen, Kim said.
“The lungs immediately begin to fill with air.” This first breath can be so loud and dramatic that, in some cases, it blows a hole in the baby’s nascent lungs, he said.
This early inflation of the lungs dramatically decreases the pressure and resistance to blood flow in the lungs. According to a 2010 review published in the journal Physiological Reviews, low pressure invites blood pumping out of the right ventricle and redirected to the neonatal lungs.
According to the 2010 review, once pulmonary pressure is lower than systemic blood pressure, or the pressure exerted on blood vessels during heart contractions, the foramen ovale closes. Without passage between the right and left atrium, deoxygenated blood begins to flow from the right atrium to the lower right ventricle and is then sent to the lungs.
Meanwhile, low pressure in the pulmonary system draws blood away from the ductus arteriosus, the blood vessel that allows blood to bypass the lung and move to the body. No longer needed, the duct begins to narrow and close within the first two days of life.
At this point, 100% of the baby’s blood is directed to the lungs. Blood saturated with carbon dioxide is first pumped into the alveolar capillaries, small blood vessels in the lungs. The alveoli – tiny air sacs in the lungs – replace carbon dioxide in the blood with oxygen absorbed by the baby.
It takes about 5 minutes for a healthy baby born full-term to “recover” and find some sort of normality, Kim said. But the transition happens in just one breath. “It’s a truly magical moment,” she said.
Why do babies barely blink?
Look into a baby’s eyes and you may notice something strange: Babies rarely blink.
As documented by numerous studies, adults blink on average about 15 times per minute. But newborns and toddlers blink much less often, only a handful of times a minute, and some babies blink only once a minute.
“The average is two or three blinks per minute, so that’s pretty low,” said Leigh Bacher, a psychology professor at the State University of New York at Oswego.
It might seem a bit strange, but researchers believe that the baby’s blinking can reveal information about the mysterious brains of these tiny humans.
This is because blinking is regulated by the brain’s dopamine, one of the neurotransmitters that allows brain cells to communicate. Therefore, studying blinking in children could help us better understand how this important neurotransmitter works in toddlers.
Studies have demonstrated the link between dopamine and blinking, as conditions or medications that affect dopamine also change the rate of blinking. People with schizophrenia, which can be caused, in part, by too much dopamine, blink more frequently.
By contrast, in Parkinson’s disease, which is caused by the death of dopamine-producing neurons, blinking is significantly reduced. Taking drugs to increase dopamine levels brings back the blink rate.
Dopamine also underlies a diverse array of other functions, from controlling movement and hormone levels to learning and motivation. So, children’s blink rate could reveal something about the development of the dopamine system and perhaps even reflect individual differences in some aspects of children’s nervous systems, Bacher said.
“Spontaneous blinking could be potentially useful from a clinical point of view, as an additional source of information on neurobehavioral development,” Bacher said. He cautioned, however, that much more research is needed to understand infant blinking.
Spontaneous blinking is different from reflexive blinking, which serves to protect the eye from impacts from an external object, and from voluntary blinking, which we do on purpose.
Even in adults, the primary purpose of spontaneous blinking is somewhat of a mystery. It is generally thought to spread tears over the surface of the eye to keep it lubricated by removing dust and other irritants.
That’s only part of the story, researchers say. We blink more often than necessary to keep our eyes wet, so blinking must have other functions as well.
Research into the nature of spontaneous blinking goes back a long way. In 1928, two Scottish scientists, Erik Ponder and W. P. Kennedy, conducted a comprehensive study of the factors influencing the rate of spontaneous blinking in adults. In the absence of a video camera to reliably record eye blinks, scientists built a small device out of silk thread, wood and a spring connected to an electrical circuit.
They attached the device to the participants’ eyelids. Each time the participants blinked, the closing eyelids pulled the spring and caused a break in the circuit, recording a signal.
As long as the conditions were kept the same, each person’s blink rate was as regular as clockwork, the researchers found.
The blink rate was the same in both dark and well-lit rooms. Blind people blinked as often as sighted people. And anesthesia of the surface of the eye did not change the blink rate.
The speed was also independent of the humidity and dryness of the eyes. When the researchers took their subjects into the humid houses of their university’s botany department, they found that the blink rates were no different from those of people the scientists had observed in the dry saunas of various steam rooms.
The rate of blinking always increased in step with the “mental tension” of the study participants, Ponder and Kennedy found. For example, scientists found that study participants blinked more when they were excited or angry, and witnesses in courtrooms blinked faster when questioned by the opposing side.
Since one of the functions of blinking is to keep the eyes lubricated, researchers have proposed that the baby blinks less than us because his small eyes do not need as much lubrication.
Another idea is that the child, with their new vision, has to work hard to get all the visual information they need. “When you do things that are visually or attentionally demanding, you tend to blink less,” Bacher said.
A similar phenomenon is seen in adults with computer vision syndrome, a condition in which the high visual demands of computer vision cause reduced blinking and lead to dry eyes.
And then there’s the dopamine system. Some researchers have suggested that the reduced blink rate in infants is due to an underdeveloped dopaminergic system.
“I don’t think any of these are mutually exclusive,” Bacher said.
Bacher and his colleagues conduct studies to find out what they can learn about the baby by measuring his or her eye blinks. Compared to brain imaging and other techniques, a baby’s eye blink is a weak measure, but not invasive, she said. Could it serve as a measure of dopamine activity?
If so, it could help predict individual differences in personality, cognitive ability, and risk of dopamine-related conditions such as attention deficit hyperactivity disorder (ADHD) or even Parkinson’s disease later in life. These are all still speculative, Bacher said, but worth investigating.
“Searching for markers early in child development for emerging diseases later will be increasingly valuable,” Bacher said. “It’s going to take a lot of detective work to figure out what to look for, though.”
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