Changes in the heart at birth
A newborn’s body undergoes many changes to adapt to life outside the womb, one of the most dramatic being the heart. Before birth, very little blood is sent to the lungs - most is diverted away from the lungs through a vessel called the ductus arteriosus. Before birth, the ductus arteriosus is as large as the aorta.
The placenta helps the baby “breathe” while growing in the womb.
Oxygen and carbon dioxide flow through the blood in the placenta
At birth, the baby’s lungs are filled with fluid. They are not inflated.
The baby takes the first breath within about 10 seconds after delivery. This breath sounds like a gasp, as the newborn’s central nervous system reacts to the sudden change in temperature and environment.
Lungs inflate and begin working, moving oxygen into the bloodstream and removing carbon dioxide (exhalation).
Lungs become distended, the capillary network dilated and their resistance is reduced drastically so that a rich flow of blood can take place.
Pressure in the right atrium sinks in comparison to left
pressure turn around in the atria causes the septum primum to be pressed against the septum secundum and the foramen secundum becomes functionally closed.
Towards the end of the first year, it has also grown together in 99% of the babies –> the hole between the left and right atrium is closed.
Fluid drains or is absorbed from the respiratory system.
Cutting of the umbilical cord gets rid of the placental low resistance area, increasing peripheral resistance in systemic circulation.
pressure in the aorta is now higher than that in truncus pulmonalis
pO2 pressure in the aorta increases since the blood is now oxygenated directly in the baby’s lungs
Triggering a contraction of the smooth musculature in the wall of the ductus arteriosus - closing
The ductus arteriosus closes within the first day or two.
However this doesn’t always happen smoothly - resulting in a congenital (from birth) heart defect - ASD (atrial septal defect)
The severity of the defect depends on the size of the hole -it may be very small (less than 5mm) with minimal leakage, allowing the individual to live a normal life. Location also plays a role in blood flow and oxygen levels.
ASDs are defined as primum (linked to other heart defects of the ventricular septum and mitral valve) and secundum defects (a single, small or large hole). They may also be more than one small hole in the septum or wall between the two chambers.
The hole may stay the same size, or grow with the rest of the heart during development and consequently will be monitored throughout childhood development, then more infrequently throughout adulthood.
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