AD 2016 Q3

STEPHEN FRINK
risk of substantial bubble formation would be low. But
maintaining a low level of physical effort during the
freediving would still be advisable.
The deeper the freediving and the more intense the
exercise, the greater the recommended delay after scuba
diving. The primary issue is that bubble formation is
more likely after significant decompression stress. As a
rough rule of thumb, when a scuba dive approaches half
of the U.S. Navy no-decompression limit, the stress of
postdive freediving becomes an
increasing concern.
If the breath-hold activity is in
the “snorkel” zone (that is, with
vertical excursions of not much
more than two body lengths)
and relaxed, I would not be
concerned at all. The “relaxed”
part is subjective though, so
thoughtfulness is needed. The
risk for depths beyond 50 feet
increases before or after scuba
diving — before, because of
potential exertion and middle-ear
stress issues, and after, because of
exertion, shunting and, increasing
as a function of depth, direct
gas loading from the freediving.
Increasingly deeper depths
warrant increasingly longer
predive surface intervals.
Ultimately there is theoretical
risk that should be controlled by
conservative surface intervals
and the lowest exertion
levels possible. There is very
little outcome data, but that
should not discourage smart
practice. Shallow, truly relaxed
freediving before scuba diving probably has negligible
consequences, given a modest surface interval and
provided that equalizing during the subsequent dive is
not compromised. But even shallow, relaxed freediving
after scuba diving should be delayed if only for an
abundance of caution. More aggressive freediving
is best left for the next day. The potential negative
outcome is simply not worth the risk. AD
— Neal W. Pollock, Ph.D.
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