Freediver Tanya Streeter removes a ventilator from her mouth after tests at HSPH, while Associate Professor Robert Banzett observes the collection of initial data.

Born in the Cayman Islands, Streeter practices "freediving," an extreme sport in which athletes stay underwater for extended periods of time deprived of any supplemental air. There are numerous categories in the sport, and Streeter has held nine records over the course of her ongoing career. In 2003, she broke a record when she dove to a depth of 400 feet, or more than twice the height of Building 1 at HSPH, on a weighted sled off the Turks and Caicos Islands, and resurfaced on her own power in a single breath.

What interests HSPH researchers is not the depth to which Streeter can plunge and resurface, but instead the duration for which she can hold her breath. The 2003 dive took three minutes and 38 seconds, and Streeter has been clocked at holding a single breath for six minutes and 16 seconds, her personal record. Most healthy people can hold their breath for about a minute.

But patients with lung ailments-asthma, emphysema, chronic obstructive pulmonary disease (COPD)-continually suffer from feeling like they can't get enough air at all, and their nightmarish predicament brought Streeter and her training partner Joe Tufts to HSPH and Brigham and Women's Hospital in April for a series of tests conducted by respiratory physiologists.

"The sensation of air hunger experienced by these patients is similar to what you would feel after holding your breath for a long time," explained Robert Banzett, an associate professor in the Department of Environmental Health. "We hope that by studying athletes such as Tanya and Joe, who have exceptional abilities for prolonging their breath holds, we can teach our patients how to better cope and recover from episodes of breathlessness."

Banzett specializes in the mechanics of dyspnea, or breathlessness. He and Andrew Binks, a research scientist in the Department of Environmental Health, led the HSPH experiments.

Among the tests was one designed to see just how different Streeter and Tufts are from normal subjects. Using a ventilator that controlled how often and how deeply they could breathe, the athletes began inhaling increasing levels of carbon dioxide. The ratcheting presence of the gas mimicked what happens when holding a breath-oxygen dissipates and CO2 builds in the bloodstream.

Surprisingly, Streeter and Tufts reached a level of discomfort at the same point as normal subjects, signaling for the researchers to drop the CO2 levels.

"It turns out, they're just like the rest of us," said Banzett.

While unexpected, the result may just be the break the researchers need. If athletes like Streeter and Tufts hit the same hard limit for CO2 tolerance as ordinary swimmers at the local pool, then maybe something else is going on that is not inherent to the free diver. Maybe there are lessons that can be learned without a rigorous athletic training program or aquatically gifted genes.

Banzett and Binks are developing hypotheses as to why the divers reacted as normal subjects. One purely speculative possibility is that the athletes use mental techniques to fight air hunger while in the water that they did not use in the unfamiliar lab setting. The scientists are sorting through the data collected during the divers' three-day stay and hope to submit a paper for publication in the near future.

"Not much can be done right now for patients who complain of shortness of breath, despite how common a problem it is," explained Banzett. "Unlike pain, which also affects lots of people but has benefited from well-funded research, breathlessness is an understudied and underfunded phenomenon."

Patients with emphysema and COPD often suffer until they are forced to become dependent on supplemental oxygen. Asthmatics can turn to bronchodilators, but these devices are thought to be able to mask warning signs of serious attacks, said Banzett.

"For the patient experiencing breathlessness, it becomes an ever-tightening downward spiral," said Banzett. "They begin to fear 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 the stairs, which may have not only physical but also social and psychological repercussions."

The plight of these patients is what drew Streeter and Tufts to the LMA for testing, and Streeter plans to return in the fall once the freediving season ends. "It is a huge desire of mine that the researchers may discover something about me that can help patients suffering from shortness of breath," said Streeter.