Croatian Scientists Work on The Bends - in Diving
The following appeared in The New Scientist magazine. John Kraljic
Diver's pill could fend off the bends
17:11 26 March 04
Exclusive from New Scientist Print Edition.
Within a decade, divers will be able to take a pill that allows them to stay under water longer without risking decompression sickness when they get to the surface. That is the prediction of a team that thinks it has stumbled across a totally new way of preventing the bends.
The risk of the bends severely limits how long divers breathing compressed air can stay under water without having to make decompression stops on the way back up. At 30 metres, the safe period is just 20 minutes.
Higher pressures at depth force nitrogen from the air in divers' lungs into their blood and other tissues. If they come up too quickly the decrease in pressure causes bubbles to form, just as they do in champagne when the cork is popped. Effects range from skin rashes to death.
A team at the Norwegian University of Science and Technology in Trondheim set out to investigate anecdotal reports that being fitter reduces a diver's chances of getting the bends.
The team's animal studies showed fitness above a basic level made little difference, but that a bout of intense exercise around 20 hours before a simulated dive in a pressure chamber dramatically reduced bubble formation. "It was an accidental discovery," says team member Alf Brubakk.
A burst of exercise seems to work for people, too. Researchers at the University of Split School of Medicine in Croatia asked 12 male divers to do two simulated dives to 18 metres for 80 minutes. They exercised on a treadmill for 40 minutes 24 hours before one of the dives.
Ultrasound imaging of the heart and arteries revealed that the average number of bubbles fell from 0.98 per cubic centimetre of blood on the first dive to 0.22 on the dive after exercise. The bubbles were also much smaller.
The researchers think the exercise session works by eliminating microbubbles, or nuclei, that seed the formation of larger bubbles in the blood. Other work suggests that these microbubbles are attached to the walls of blood vessels, and exercise is known to stimulate the release of nitric oxide (NO), which not only dilates blood vessels but changes their surface properties, making them more slippery.
It is too early to recommend exercise, stresses Zeljko Dujic, head of the Croatian team. "Divers should wait for further studies," he says. And even if it does prove effective and divers are willing to make the effort, exercising in a narrow window of time around 20 hours before each dive is unlikely to be practical.
But if the Norwegian team's theory is right, it might be possible to give divers drugs to mimic the effect of exercise.
In fact, the team has now shown that giving mice an NO-releasing drug, or NO itself, reduces bubble formation. All the latest results appear in The Journal of Physiology (vol 555, p 588, p 637 and p 825).
"This is a totally novel approach," says Brubakk. Until now, all the ways of preventing the bends, such as staying within safe limits, ascending in stages or breathing gas mixtures with less nitrogen, have been designed to limit or reduce the levels of nitrogen in the body. But if you can get rid of the nuclei, bubbles cannot form even when the blood is supersaturated with nitrogen.
A drug that helps prevent the bends could be used simply to make diving safer. Some divers get decompression sickness even when they stay within recommended limits.
But Brubakk thinks such a drug would allow divers to go deeper or stay down longer. "It's not dangerous if you can prevent bubble formation," he says. A drug would not prevent bubbles forming in other tissues such as cartilage, he admits, but it is in the blood that bubbles cause the most serious forms of decompression sickness.
Many questions remain to be answered, though. Other researchers say it is plausible that exercise helps eliminate microbubbles, but question whether NO production is really the main factor.
Michael Le Page
© Copyright Reed Business Information Ltd.