March 12, 2004 -- A single session of high-intensity exercise may greatly cut the risk of decompression sickness. However, timing is critical -- exercise must be done 24 hours before scuba diving, a new study shows.
This is the first time that researchers have pinpointed pre-diving exercise as a way of preventing decompression sickness. However, further study is needed before this can be widely adopted as a predictable safeguard, writes John R. Claybaugh, PhD, an investigator with the Tripler Army Medical Center in Hawaii.
Decompression Sickness: Serious Threat
Decompression sickness following diving is a constant threat brought about by the formation of gas bubbles in blood vessels, writes lead researcher Zeljko Dujic, PhD, a professor of physiology and biophysics at the University of Split School of Medicine in Croatia. His paper appears in this month's issue of the Journal of Physiology.
"There is a growing concern that diving can lead to permanent damage to the central nervous system, even in the absence of clear signs of decompression sickness, and one of the suspected mechanisms is silent bubble formation," he writes.
The researchers had previously shown that a single bout of high-intensity exercise 20 hours before a simulated dive in rats reduced bubble formation and after the dive protected from lethal decompression sickness. Studies of human divers show bubble formation is less if they are in good physical shape.
Timing Is Everything
In this study, Dujic recruited 13 men -- all under age 40, all very experienced divers. None had ever had decompression sickness. Each was asked to do a treadmill running workout within 24 hours of their dive.
The first three minutes was at 90% maximum heart rate, then reduced to 50% maximum heart rate for two minutes. They repeated this pattern eight times for a total exercise session of 40 minutes. Maximum heart rate is calculated as 220 minus your age.
During a simulated scuba diving exercise, gas bubbles were monitored with an ultrasonic scanner every 20 minutes for 80 minutes after reaching surface pressure. Each diver performed two dives seven days apart -- one with and one without physical exercise 24 hours before.
When the men exercised 24 hours before their dive:
- None of the divers had any symptoms after diving.
- Both the number of bubbles and the size of the bubbles decreased significantly, compared with diving without exercise beforehand.
Timing and intensity of the exercise is important, he adds. Research in rats from his laboratory and others shows:
- Low-intensity exercise does not help.
- Exercising strenuously within 10 hours before scuba diving does not help.
- Exercising strenuously 48 hours before diving does not help.
Although Dujic is not sure how exercise helps protect against decompression sickenss, he speculates that nitrous oxide production during exercise is somehow involved.
The finding warrants more study before it can be recommended as a preventive before scuba diving, he adds.
SOURCE: Dujic, Z. The Journal of Physiology, March 2004: pp 637-642.