Holding their breath for the breathless

Researchers try to get to the bottom of breathing skills  By William J. Cromie   Harvard News Office

Tanya Streeter dives as deep as 400 feet on one breath, which she can hold for more than six minutes. (Photo by Phillip Shearer, courtesy of Tanya Streeter)

Have you ever felt "air hunger"? People with asthma, emphysema, and obstructed lungs feel it often - a sensation that they can't get enough air to breathe.
Divers who attempt to hold their breath for six minutes or more and who reach depths of hundreds of feet without the help of air tanks, know the feeling well.
Somehow, they can tolerate that desperate urge to breathe better than most people.

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.

Unlike the pain these patients feel, which can be handled with the help of special drugs, no treatments exist for breathlessness. "This is primarily due to insufficient research on the physiology of air hunger," Binks notes. "We're decades behind the pain field, despite shortness of breath being so common."

"Shortness of breath, or dyspnea, is a prominent symptom of many serious diseases, especially asthma, emphysema, and pneumonia, and including heart disease," comments Robert Banzett, associate professor in the Department of Environmental Health at HSPH. "Patients with severe dyspnea say things like, 'When the shortness of breath was at its extreme, I thought I was going to die.' Dyspnea is reported by about 25 percent of the general public older than 40 years, making it one of the most common symptoms that cause people to seek medical care. It is also a predictor of early death. You are twice as likely to die early if you experience it."

Free diver Tanya Streeter breathes into a ventilator to test her resistance to carbon dioxide buildup with the help of Robert Banzett at the Harvard School of Public Health. (Photo by Suzanne Camarata)

Banzett works with Binks, a visiting scientist from the University of New England in Portland, Maine, at the Harvard School of Public Health's Department of Environmental Health. They are testing four championship free divers there. These mermen and maids include Tom Sietas, who holds the world record for a breathhold - nine minutes and 58 seconds. Most normal, healthy people average about one minute.

Another volunteer diver, Tanya Streeter, dove to a record depth of 400 feet in 2003 and returned on a single breath. She descended on a weighted sled to a point about as deep as a 35-story building is high, and resurfaced with the help of a balloon.

Streeter is 32 and jokes that she is "too old to be doing this craziness. But it's a huge desire of mine that the researchers may discover something about me that can help patients suffering from shortness of breath."

No magic bullet

Streeter and the other 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 left him and Banzett breathless.

Streeter and the other divers hit the ceiling of discomfort at the same time as untrained people. They signaled for relief from the increasing carbon dioxide as soon as everyone else. "It turns out that they're just like the rest of us," Banzett comments.

"That was both a surprise and a disappointment," Binks remarks. "There's no magic bullet for patient treatment. We have to go back to the drawing board."

Breathing tricks

The divers will return for more tests later this fall. At that time, Binks and Banzett 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. Also, hyperventilation might be too uncomfortable, making patents dizzy, even causing them to pass out. "These are questions we must answer with more tests," Binks says.

"For patients experiencing breathlessness, it becomes an ever-tightening spiral," Banzett point out. "They begin to fear any physical activity because it may trigger air hunger, so they exercise less and become even less healthy. They stop doing things like walking around the block or even up stairs. This may not only have physical but social repercussions as well."

"That," adds Binks, "is what we want to find ways to fix or avoid."

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http://www.news.harvard.edu/gazette/2005/10.13/01-divers.html