Extreme sports usually mean speed, danger, or spectacular stuntsthings like snowboarding, skateboarding, rock climbing. They may reach heights (paragliding), or depths, as in free diving, whose devotees submerge themselves far below the ocean’s surface without air tanks. In 2003, free diver Tanya Streeter descended on a weighted sled to a record depth of 400 feet and, using a balloon, returned to the surface on a single breath, whichwhen standing in a pool with her face in the watershe can hold for more than six minutes.
Another diver, Tom Sietas, boasts the world record for a single-breath hold: eight minutes and 58 seconds. (The average adult can go about one minute.) Recently, Streeter, Sietas, and two other free divers came to the Harvard School of Public Health (HSPH) to help associate professor of medicine Robert Banzett and his colleague, research scientist Andrew Binks, investigate dyspnea (shortness of breath, or breathlessness). The divers’ visits were part of a larger research program run by assistant professor of anaesthesia Massimo Ferrigno.The investigators hope that studying people so adept at managing their air supply may reveal something that helps those who have trouble getting any air at all.
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| World-class free diver Tanya Streeter, submerged while outfitted in some of the gear, like extra-long flippers, that helps her dive to extraordinary depths on a single breath |
| Photograph by Paul Streeter |
Breathing troubles turn out to resemble painagonizing, hard to describe, fraught with uncertainty. They are also equally common: half the patients admitted to hospitals report dyspnea, the same number who report pain. Dyspnea is a symptom of asthma, emphysema, pneumonia, and heart disease, as well as a leading indicator of panic and anxiety disorders. One-quarter of people over 40 report breathlessness, Banzett notes, and those who experience it are twice as likely to die early.
“We don’t have ways to deal with it as well as [we deal with] pain,” says Banzett, who believes that pain management is about 20 years ahead of treatment for breathlessness. He has directed a dyspnea research lab at HSPH since the late 1980s. His group's clinic, directed by associate professor of medicine Richard Schwartzstein at Beth Israel Deaconess Medical Center, is one of only two in the country, but the field is growing. Last spring, Banzett helped organize the first international symposium on dyspnea in 40 years.
Dyspnea includes breathing with difficulty, a tightness in the chest familiar to asthmatics, and a sensation called “air hunger,” in which people feel they can’t get enough oxygen. In 1997, Banzett and colleagues mapped the area of the brain associated with air hunger and found it in the anterior insula, part of the cortex involved with conscious awareness and a place where some kinds of pain also arise. (Autonomic breathing, the kind we do when asleep, is controlled by the brainstem.)
To explore air hunger, Banzett and his colleagues control breathing with a mechanical ventilator that regulates how often and how deeply each subject breathes. In the course of several minutes, the researchers gradually add more carbon dioxide to the mix to raise CO2 levels in the subjects’ arterial blood. Every 30 seconds, subjects slide a marker over the word best describing their air hunger, from “none” to “extreme.” Afterward, they fill out questionnaires about their state of mind during the test, because mental states can strongly affect the way someone gauges both pain and dyspnea. Says Banzett, “It’s probably that emotional content that gets you to go to the doctor to have it checked out.”
The test subjects often say the sensation they feel in the lab is akin to a long breath hold. Hence Banzett and Binks, a professor at the University of New England, gave free divers (and a control group) the air-hunger test, hypothesizing that the extreme athletes would take far longer to reach a threshold of discomfort than the controls. Instead, the divers experienced air hunger at about the same time as the normal participants. “I was surprised,” says Banzett, who plans to try other tests on the divers. There may be mental adaptations that they use. One of their physical tricks is to hyperventilate for a couple of minutes before going underwater; this expands their lungs and empties them of carbon dioxide. Just before submerging, they take in as big a breath as they can, packing in even more air by gulping it with their mouth. (Such tricks, unfortunately, are hardly useful for elderly heart patients, who would likely pass out if they tried them.)
Despite the lack of a breakthrough so far, even null results like these help fill out the picture. “[The results] tell me air hunger is a primal sensation,” says Banzett. “Air hunger is our friend” because, like pain, it’s a warning sign. Yet people can live for years with pain, but no one can long ignore the need for air.
~Katharine Dunn
Robert Banzett e-mail address: dyspnea@hsph.harvard.edu
Dyspnea website: www.shortofbreath.org
