Sep 8 2008
Scientists in the U.S. say an athlete's ability to sweat may do more than keep the body cool but might also prevent the development of exercise-induced asthma (EIA).
EIA is a common respiratory condition among trained athletes and according to the researchers athletes with EIA produce less sweat, tears, and saliva than those who do not have breathing problems.
Lead study author Dr. Warren Lockette says it is unclear why so many elite athletes have exercise-induced asthma.
Dr. Lockette who is an advisor to the University of Michigan's NCAA Division I women's swimming team and has worked with many Olympians and future professional athletes with EIA, suggests it is possible that sufferers manifest symptoms of exercise-induced asthma simply because their levels of exertion and breathing rate are so high compared with the average, competitive sportsman.
Dr. Lockette, head of clinical research at San Diego Naval Medical Center and a former medical officer with the U.S. Navy, says a diagnosis of asthma would preclude many young sailors from becoming divers or special warfare operators.
He and a team of investigators wanted to understand the mechanisms by which asthma attacks are precipitated during exercise in otherwise healthy individuals.
Lockette and his colleagues analysed the relationship between fluid secretion rates, sweat, saliva and tears, in 56 athletic subjects suspected of having EIA. They measured the air movement through the lungs in the otherwise healthy volunteers before and after the administration of methacholine, a drug that can cause airways to constrict in patients with EIA.The researchers then measured responses to the application of pilocarpine, an agent used to induce sweating and saliva production.
They found the individuals who were most sensitive to methacholine, were the least sensitive to pilocarpine - induced sweat secretion - meaning, those subjects who had the most hyperreactive airways tended to sweat the least. The sweating rates were found to be significantly higher among those subjects who were relatively unresponsive to methacholine and who showed no signs of EIA. The researchers also found a correlation between the net sweat fluid excretion and net sweat sodium excretion, with sodium excretion rates being higher in subjects who were unresponsive to methacholine compared with those who were responsive.
Another significant correlation was found between sweat secretion and unstimulated salivary gland flow rates and tear secretion.
Dr. Lockette says there were many Olympic hopefuls whose competitive chances were potentially limited by exercise-induced asthma but they found that by controlling air quality during workouts, as well as by providing individualized attention to athletes' hydration and nutrition, the limitations imposed by hyperreactive airways in many individuals could be reduced.
Although Dr. Lockette and his team were not able to establish a cause-effect relationship between the increased incidence of EIA and diminished sweat sodium excretion, they speculate that the mechanism responsible for determining sweat volume is the same mechanism responsible for the volume of water secreted by the airways. As a result, individuals who sweat less also have drier airways.
Dr. Lockette says it now appears that how much fluid your airways secrete could determine a persons protection from exercise-induced asthma, so if athletes sweat, drool, or cry, at least they won't gasp.
The research appears in the September issue of CHEST.
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