Two researchers at the Harvard School of Public Health (HSPH) got the idea of studying free divers to get information that would help them help the breathless to breathe better. “We hope that by studying these athletes, we can teach patients how to better cope and recover from episodes of breathlessness,” says Andrew Binks.

Divers took a battery of tests to see why their breathing capacity is so different from that of other people. Both they and a comparison group of normals were hooked up to a mechanical ventilator that controlled how often and how deeply they breathed. This device prevented the divers from breathing faster and deeper than nondivers.

Then the subjects began to inhale increasing amounts of carbon dioxide to mimic what happens when people hold their breath. Oxygen decreased and carbon dioxide built-up in their blood until that awful feeling of air hunger started to make them uncomfortable. They wanted another gulp of air and fresh oxygen more than anything else.

“Our expectation was that normal, healthy people would reach that point much quicker than the athletes,” Binks says. But what actually happened was that divers hit the ceiling of discomfort at the same time as untrained people.

The divers will return for more tests later this fall. At that time, researchers will take a closer look at some techniques free divers use to make a single breath last so long.

One trick is hyperventilation. The diver breathes as hard and fast as she or he can, reducing the levels of carbon dioxide in their blood before a deep descent. That way the gas builds at a slowed rate.

Then there’s lung packing, or “frog breathing.” That involves taking very deep breaths and then squeezing more air into the lungs by additional breathing through the mouth. “Using a combination of hyperventilating and fuller lungs, they can postpone the onset of air hunger,” Binks explains. “The mechanical ventilator used during our tests didn’t allow them to use those techniques.”

While these tricks help experienced free divers, further tests are needed to determine if lung packing could damage the weakened lungs of the people who are ill.