Posted by . on December 11, 2001 at 10:01:46:
http://www.nature.com/nsu/011213/011213-4.html
Physical exercise could stave off decompression sickness.
10 December 2001
TOM CLARKE
Physical exercise before a simulated dive protects rats from developing the nitrogen bubbles in their bloodstream that lead to the bends, Norwegian researchers have shown
The finding could help to reduce divers' risk of decompression illness (DCI). It may also point to previously unknown effects of exercise on the flow of blood and gases around the body.
Nitrogen dissolves in the blood during dives, but comes out of solution if divers return to normal pressure too rapidly - like bubbles coming out of champagne when the bottle is uncorked. Nitrogen bubbles under the skin or around the spinal cord and the brain cause effects ranging from skin rashes to seizures, coma and death.
Changing exercise regimes, in rats at least, "can turn an unsafe dive into a safe dive", says physiologist Alf Brubakk, of the Norwegian University of Science and Technology in Trondheim.
Brubakk and his colleague Ulrik Wisloff compared unfit rats with those given a six-week, two-week or one-day exercise regime on a treadmill. One day later the rats were sent on the equivalent of a 60-metre dive - the limit for human recreational divers is 30 metres - in a pressure chamber.
Nitrogen bubbles only formed in the blood of unfit rats, the duo found. But one bout of exercise was just as beneficial as six weeks. And fit rats sent on dives two days after stopping exercise developed as many bubbles as unfit rats.
The researchers think that nitric oxide is the key to DCI. The body produces this chemical during exercise; it is crucial to regulating breathing and blood flow.
There is also evidence that it "makes the inner surface of blood vessels more slippery", says Brubakk. Nitrogen bubbles are seeded like crystals on rough surfaces: the smoother the blood vessels, the harder it is for bubbles to form.
Valerie Flook, a physiologist at the University of Aberdeen in Scotland, agrees, but cautions that the amount of exercise needed, and the duration of the benefit, will probably be very different between rats and humans. "It is necessary to be cautious before applying these results to humans," she says.
Under pressure
The result runs counter to received wisdom about DCI. Although some research has shown that fit divers are less likely to get the bends, strenuous exercise during dives increases the risk of illness, and exertion is discouraged before or during dives.
"It's certainly not a result you'd expect," says Martin Hamilton-Farrell, who runs the dive-medicine unit at Whipps Cross Hospital in London, England.
Brubakk and Wisloff are working with pigs to investigate how different exercise regimes at different times before diving affect bubble formation, and to see how nitric oxide affects DCI.
The finding that even short bursts of exercise can affect the circulation of gases should be of interest to the medical community in general, says Wisloff. "We believe we're on the track of something very important to exercise physiology."