May 11, 2011
By C.J. Janovy
How does a fetus learn to breathe?
It's the first action a newborn baby must take, but the womb is filled only with fluids — there's nothing that really prepares a fetus to inhale a lung full of oxygen.
Still, imaging equipment allows scientists to watch as a fetus learns how to make breathing movements.
"We call it breathing, but what the baby is actually doing is exercising the diaphragm," explains Kathleen Gustafson, PhD, director of the Fetal Biomagnetometry Laboratory at Hoglund Brain Imaging Center. Gustafson says researchers believe that this exercise strengthens the diaphragm and helps develop lung function so that babies are able to breathe properly as soon as they're born.
But as a research assistant professor in the Department of Neurology, Gustafson is also interested in what these movements tell us about the brain.
"Think of the brain as a central command station. The fetus must develop ways to survive outside the womb. Even though the fetus is never awake in the way that we think of being conscious and alert, there are periods of wakefulness and quiet. We can tell the difference by looking at fetal heart rate patterns and, during those active periods, the brain is sending messages to practice important movements or behaviors."
Heart-rate patterns indicate how active a fetus is and whether its autonomic nervous system — again, controlled by the brain — is developing in a healthy way.
"When the fetus is in an active state, we can see two heart rate patterns. This is the time we can observe most of the behaviors you see outside in the world. We can see a fetus practicing sucking movements, swallowing amniotic fluids, yawning." These sorts of activities, Gustafson says, are important signs of healthy development.
What's most exciting to Gustafson is that she can now measure those heart rates in entirely new ways.
In a paper published in this month's issue of Early Human Development, Gustafson reports on a the results of a study using Hoglund's dedicated fetal biomagnetometer — a tool that measures the magnetic fields surrounding electrically active heart, brain and muscle tissue. There are only two of these devices in the United States.
"The beauty of what we have at KU is that we can see these behaviors without having to do ultrasound, without having to do anything invasive," Gustafson says. "No one has done that before."
Researchers have been able to observe these fetal behaviors in animals, but that means anesthetizing the mother, opening up her womb, inserting electrodes into the diaphragm and measuring muscle activity and tracheal fluid pressure. "These are very invasive techniques that have given us greater understanding of what happens during fetal breathing movements and helped us understand cardiac physiology in animals," Gustafson says. "But we were never really able to clearly distinguish these behaviors in the human fetus and how they affect the heart until now."
Gustafson says that's what the biomagnetometer allowed her to do.
"When we saw a distinct wave form that occurred in short bursts with a long period of silence in between, we were able to determine this was a sucking behavior, called non-nutritive suck. Then, when the fetus was born and sucked on a pacifier in front of the biomagnetometer, we could record the same waveform. The same was true with hiccups. We could measure them in utero and after the baby was born."
Measuring breathing movements was much more difficult.
"The in utero environment is fluid and fetal breathing is periodic. There are periods of movement followed by periods of silence. But then when the baby is born, it breathes just like we do — continuously. So we can't compare the two like we did non-nutritive suck or hiccups. That was the challenge: to first identify the waveform and then establish that it really was 'fetal breathing' — diaphragmatic movement — and finally look at how that affected cardiac physiology."
Her results matched perfectly with the animal studies, Gustafson says.
Most fascinating, Gustafson says, was that she saw heart rates speed up before a fetus moved. "We think the brain is signaling preparation to move, then the heart rate increases, and then the fetus moves. It's not far-fetched to think that if another activity is going to take place, such as fetal breathing, then this is also centrally controlled — the brain is signaling to initiate this breathing behavior that goes on for several minutes, then stops, then starts up again."
Which is how a fetus learns to breathe.
Being able to measure variations in fetal heart rates has important implications for doctors in the clinic, Gustafson says.
For example, research has linked abnormalities in the autonomic nervous system and cardiac regulation to sudden infant death syndrome (SIDS). Some research suggests that children who die of SIDS don't have the ability to regulate and vary their heart rates. Also, Gustafson says, measuring fetal heart rates will allow scientists to study the development of stress reactions in the nervous system. The better the brain can accelerate and then calm the heart, the healthier the baby.
Now, thanks to Gustafson's research, we have a new way to keep watch.