Only a few decades ago, premature babies born more than six weeks earlier than expected were dying at an alarmingly high rate – within a few days, sometimes within hours.

Nobody was sure why, until a mysterious ailment was discovered. It became known as the Respiratory Distress Syndrome (RDS). Tens of thousands of babies succumbed to this every year in America alone.

It turned out to simply be a basic physics problem (video above).

The root of the problem can be traced back to tiny air sacs in the lungs called alveoli, which exchange carbon dioxide for oxygen. Healthy babies have no problems here, and their alveoli are like tiny mini-inflated balloons.

But things get tricky for premature babies, and their lungs have to deal with collapsed alveoli, causing them to suffocate.

Enter physics. When we blow up a balloon, toughest part is getting the process started. LaPlace’s Law dictates that the curvier a stretched surface is, the harder it’ll squeeze the fluids inside. If you take two balloons and blow them up differently, connecting them with a straw, the smaller balloon will squeeze much harder and even blow some of its air into the other balloon.

Human lungs have the same set-up, except that healthy people don’t face trouble and their alveoli stay properly inflated, balancing the pressure between air sacs. Premature infants, however, have lungs that aren’t as developed and are unable to cope.

Doctors eventually found a way out by pumping air continuously into the babies’ lungs, preventing collapse with the help of a device called the CPAP (Continuous Positive Airway Pressure). Things have greatly improved now, and since the invention of the device, it has been estimated that more than two million babies with RDS have been saved all over the globe.