DATELINE: 17th December 2001

RATS RUN RAGGED IN DCI EXPERIMENT
Norwegian scientists have caused something of a stir in the world of hyperbaric medicine with their experiments on rats, reported in the Journal of Physiology. The results suggest that exercise prior to diving can help to prevent the onset of decompression illness in rats.
If applied to humans, this would contradict existing medical opinion that exercise before and during diving can contribute to the onset of DCI. Brubakk and Wisloff had four groups of rats which were all subjected to the equivalent of 60m dives. One group of rats was put on a six-week exercise regime, a second group ran the treadmill for two days prior to the dive, the third group had just one day of exercise, and the fourth group was left to relax.
Rats which were put on the treadmill one day before the dive experienced significantly less nitrogen bubble formation when compared to their unfit companions. However, the fitter rats on the six-week programme did not appear to gain additional benefit; just one bout of exercise the day before a dive was enough to significantly reduce nitrogen bubbles.
If the fit rats were left without exercise for two days before a dive, they were found to have formed just as many bubbles as the unfit rats.
The explanation offered by the scientists is that nitric oxide, a chemical produced by the body during exercise, "makes the inner surface of blood vessels more slippery". A slippery surface impedes the formation of bubbles. The research was greeted with cautious interest by Dr Martin Hamilton-Farrell, who runs the hyperbaric chamber at Whipps Cross, London.
"Experiments on animals are exactly that," he said. "You can't apply the results directly to humans. The science of decompression illness is highly complex. I welcome all research that can extend our knowledge, but it's far too early for divers to draw any conclusions from this."

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