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amount of data from hypobaric chamber exposures that
suggest that the physiological risk may vary somewhat
across the menstrual cycle, with a slightly elevated risk
during the first half of the cycle. Practically speaking,
even if women do have a slightly elevated physiological
risk in comparison to males, a tendency toward more
conservative practice may reduce the net risk.
Circulation. Compromised circulation resulting from
prior injury has been viewed as a possible risk factor,
but with little empirical evidence. The presence of a
patent foramen ovale (PFO) has the potential to alter
circulation by allowing a volume of blood to reach
the systemic circulation without undergoing filtration
through the lung. PFO has been identified as a risk
factor in serious DCS. Perspective is required, though,
for while the frequency of PFO is fairly high (about 25
percent of the population), the incidence of serious
DCS is low. The degree of patency varies and can be
important. PFOs are also not the only way to move
bubbles into arterial circulation. Bubbles can cross in
the lungs, particularly during exercise (while or after
climbing out of the water, for example). Dive profiles
that minimize bubble formation provide the greatest
protection since there will be no bubbles to cross over.
Biological health.
A host of factors
falling under
the category of
biological health
may influence
decompression
stress. Some
probably play
minor roles, while
others may play
important roles
that have not yet
been fully defined.
Nutritional status, for example, is important for
general health and physical fitness and may influence
the biochemical response to decompression stress.
Similarly, the potential interaction between drugs and
diving is another area with virtually no research data
but legitimate concerns. Genetic predisposition and
epigenetic expression likely also have importance that
is just beginning to receive research attention.
Acclimatization. Acclimatization is defined as
adaptive change in response to repeated natural
exposure. The effect may be positive or negative.
Repetitive diving could influence decompression
stress, and not just through the presence of residual
inert gas. Positive acclimatization could produce a
reduction in the biochemical response — effectively
a desensitization that may reduce the magnitude of
the insult. Negative acclimatization could produce a
heightened response — effectively a sensitization to
decompression stress. The published data relevant
to diving are conflicting, which may be in part a
reflection of how divers dive. The effect of positive
acclimatization could easily be masked by patterns of
increasing exposure intensity over dives in a series.
SUMMARY
Most personal factors that affect decompression stress
can be modified. Maintaining reasonable levels of
physical fitness, nutrition, restfulness and hydration
all contribute to good health and good diving health.
Good health can reduce physical limitations and the
need for medication.
When selecting dive buddies, divers should consider
compatibility of goals, risk tolerance, skills, knowledge
and capabilities. A shared understanding of both risk and
best practices can improve operations and readiness.
Thoughtful and well-informed divers know far more
than current dive computers about conditions that may
affect risk during a dive — and likely they will know
far more than dive computers for many years to come.
Being conscious in real time of conditions that may alter
risk can make it easier to build in appropriate buffers
to promote safety. Small changes toward conservatism,
when applied across a variety of factors, can enhance
safety with little impact on what can be accomplished
during a dive. AD
REFERENCES
1. Pollock NW. Factors in decompression stress. In: Pollock NW, Sellers SH, Godfrey JM, eds. Rebreathers and Scientific Diving. Proceedings of
NPS/NOAA/DAN/AAUS June 16-19, 2015, Workshop. Wrigley Marine Science Center, Catalina Island, CA; 2016; 145-56. Available at: http://www.
2. Gerth WA, Ruterbusch VL, Long ET. The influence of thermal exposure on diver susceptibility to decompression sickness. NEDU Technical Report
06-07. November 2007.