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I
t is generally accepted that the most important risk
factors for decompression illness (DCI) are dive time
and depth. Divers are also very interested in how other
factors such as exercise and hydration status may affect
DCI risk. Preconditioning describes the use of physiological
or pharmacological stimuli to increase resistance to
particular injuries or illnesses. In this article, we seek to
understand whether there are particular preconditioning
practices divers can employ that may reduce their risk of
DCI. We ask the experts.
The prevailing recommendation with regard to exercise
and diving is that divers avoid strenuous physical
activity around diving, but it has been suggested that
certain exercise may reduce DCI risk. How might
exercise increase or decrease the risk of DCI, and what
advice would you give divers about exercise and diving?
Constantino Balestra:
More and more researchers are
demonstrating benefits of predive exercise. The mechanisms
have not been definitively identified, but “movement” seems
to be a clue. The benefit seems to lie in the concomitant
actions of the heart, vascular system and lymphatic system.
Michael Bennett:
The relationship between exercise and
diving has become very interesting over the past few years.
The traditional view is that predive exercise is a risk factor
for DCI; this is based on the potential for increased tissue-
nitrogen uptake with hyperdynamic circulation. However,
recent evidence indicates this view may be too simplistic. Both
animal and human studies suggest a single bout of moderate
or strenuous exercise two to 24 hours before a simulated
dive can reduce bubble formation (and presumably the risk
of DCI). It is not yet clear why this should be so, but it seems
likely the generation of nitric oxide (NO) during exercise may
either favor the elimination of the nuclei where bubbles tend
to form or otherwise alter the cells that line blood vessels (the
endothelium). There are a number of alternative hypotheses,
however, and this is a very active area of research. Jean-Eric
Blatteau and colleagues postulated, for example, that the
protective effect is due to moderate hypovolemia. Currently I
advise divers there is no evidence that exercise before diving
is harmful up to about two hours before immersion, but I do
not actively advise divers to undertake exercise.
There is less controversy around the effects of exercise at
other times with regard to DCI risk. Exercise during a dive
increases nitrogen uptake and distribution to the tissues and
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SPRING 2012
Preconditioning and DCI
RESEARCH, EDUCATION & MEDICINE
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