Stethoscopes to the Streets: The First Minute of Life

Are you up for a little physiology today?  If so, read on!  Today I submitted my first article for my "independent project" elective and thought I'd share it with you.  Enjoy!! 

Have you ever gone to visit a newborn baby in the hospital?  Most of us have, but have you ever thought about the amazing changes that took place in that little body in a very short time?  I mean, the last time you “saw” that baby it was a functional parasite that breathed water and really just chilled out on the proverbial “couch” of mom’s uterus.  Now, the kid is well on his or her way to becoming an independent, walking, talking taxpayer.  Seriously, how did that happen?

            As part of my “Stethoscopes to the Streets” article series, let’s look at how a baby in the uterus (called a fetus) is different than a baby on the outside world, and the way that change takes place.  A word of warning: we are entering into the “deep weeds” of physiology and neonatology, but don’t worry, we’ll go together and I’ll be your tour guide and translator.  Ready?

            Ok first, the big difference between a baby in the uterus and a baby outside is its circulation…the way the blood flows around the body.  We’ll take a small step back and talk about how your circulation works:  your heart has a right and left side separated by a wall.  Blood comes from your body (low oxygen) to the right side of your heart, which pumps it to the lungs.  In the lungs, your red blood cells dump off carbon dioxide (a waste product from burning sugar for energy) and pick up more oxygen to take back to all the cells of your body to use in metabolic processes.  Then, the blood travels from your lungs to the left side of your heart, where it gets forcefully pushed back out the periphery (ie, your arms, brain, kidneys, the whole thing) to drop oxygen off and pick up carbon dioxide.  Great review.  Now the fetus…

            Think about it…mom is taking care of everything for the fetus while it is growing in her uterus.  Thanks to an organ called the placenta (not found in the non-pregnant state, it’s made from a combined effort of the fetus and mom’s uterus to act as an interface for the fetus to get mom’s blood), the baby receives all the glucose, oxygen, and love it could possibly want from mom’s blood.  Mom then graciously takes away baby’s carbon dioxide and waste products and takes care of them with her own organs.  Like I said, that fetus is just hanging out, stealing glucose and growing.  Because the fetus doesn’t need to breathe to get oxygen, its lungs don’t need to be open for business.  This is one way fetal circulation is markedly different from normal human circulation; blood comes up to the right side of the heart like normal but skips right through to the left side of the heart thanks to a window called the foramen ovale.  Foramen means “hole”, and ovale means oval…creative, right?  It really looks like an oval hole.  If some blood doesn’t go through the window and ends up on the path to the lungs, there is another bridge (the ductus arteriosus) that would move blood from the artery traveling to the lungs to the artery going to the whole body, thus giving another way to bypass the lungs.  So to recap, the fetus doesn’t let very much blood get to the lungs because of this hole that allows blood to skip from the right side to the left.  Whew, I told you this was in the weeds.  Any questions so far?

            Blood travel in a fetus is different in other respects too.  Remember how I told you mom takes care of all of baby’s needs through the placenta?  Well, the placenta is hooked up to the baby through the umbilical cord, which enters baby through its belly button.  The umbilical vein carries oxygenated, sugar-filled blood from mom up to the baby’s heart, mostly bypassing the liver thanks to another special vessel that goes away after birth, heading up to the heart (remember, this is oxygenated blood, opposite of how it works in your body when blood is going up to the heart, which would have low oxygen).  Once the oxygenated blood gets to the right side of the heart, it crosses over to the left side of the heart via the holes we talked about and gets pumped out to baby’s body.  When the baby takes what it needs, it ships the old, used up blood back to mom via the umbilical arteries, back to the placenta, and subsequently back to mom’s body to take care of the waste and reoxygenate it with her lungs. 

            Did you hang in there?   Because it’s about to get exciting.  We’re going to fast-forward though all the gory, gushy OB stuff (I’m much more interested in the baby end than the mom end of that story) and get to the part where the baby is delivered.  Now what?  That kid just went from an environment of a balmy 98.6 degrees to the cold room temperature.  This significant drop in temperature triggers the baby’s brain to demand the lungs to take a huge breath; the first breath that baby will ever take!  I won’t bore you with the details, but because of the rapid lung expansion and oxygenated air entry, the blood vessels in the lungs go from being shut off to being open for business.  In other words, the lungs are available to take blood from the right side of the heart (like in you and me) and oxygenate it!  This is amazing; a fetus’s lungs only gets 4% of the blood that comes back to the right side of the heart.  As soon as baby is born and takes a big breath, the lungs gets ALL of the blood that comes back to the right side of the heart. 

So what happens to that big hole that lets blood go from the right to left heart?  It seals shut, almost within minutes.  So now, the right and left sides of the heart are sealed off, which is how we like it.  Remember that other connection between right and left circulations called the ductus arteriosus?  Because of the big change in the blood highway, now with all lanes open going to the lungs, this isn’t needed anymore either and closes off pretty quickly (within a few days, at most). 

            What about that pesky placenta and umbilical cord?  Well, as you probably know, most nervous-nelly dads get to “cut the cord”, after the doctor puts on two clamps; one for baby and one for mom so no one looses too much blood.  The clamping of the umbilical cord serves to further change fetal circulation (I mean, now the kid is REALLY on his own to pump blood around, breathe to oxygenate, etc), and all those special vessels I told you about that keep blood away from the fetal liver and lungs start to close off because now blood needs to go to those places.  Interestingly, the remnants of these structures can be found in the adult body; they are just strands of tissue now, not big vessels carrying lots of blood. 

            Being a future pediatrician, I’ll quickly mention that if the baby can’t quite get it together right away and doesn’t breathe, we have lots of tricks to help them out; anything from vigorous rubbing (just incase the 30 degree temperature differential wasn’t enough to scare them straight) to oxygen supplementation to even intubation if their lungs aren’t mature yet.  It sounds scary, I know, but there is SO much that needs to happen that it’s not uncommon for a baby to struggle a bit.  In fact, about 10% of babies born will need some “support” in the first few minutes, while 1% will need full resuscitative efforts.  Pediatricians are great at this, so try not to flip out if you’re ever in the delivery room.

            So there you have it; the wonderful story of when a baby arrives in the world and takes his or her first breath.  The changes don’t stop there, but I’m hoping now you have a better understanding of how cool and complicated that one moment is in a life.  Thanks for reading this (super complicated, sorry!) edition of “Stethoscopes to the Streets!”