AD 2018 Q1

outpouchings of the lungs; these are called blebs. The
spots are weaker than the normal lining of the lung and
can occasionally break and cause air to leak from the
lung into the chest cavity. When this happens, the result
is a spontaneous pneumothorax: unexpected rupture of
alveoli (lung air sacs).
Such a lung collapse can occur without provocation
and with no warning. Often the individual is
exercising, straining while lifting or performing some
other physical task, but sometimes the person is doing
nothing out of the ordinary.
Since barotrauma can occur with hyperinflation
of lung tissue, a diver’s lungs must be able to tolerate
rapid changes in volume and pressure. Fibrotic or
scarred tissue is of particular concern to the scuba
diver because it offers reduced compliance in its
interface with normal lung tissue. Any weakness in
lung structure or architecture may be predisposed to
rupture from even minimal overinflation. Pulmonary
barotrauma usually happens near the end of a dive.
Escaped gas from the lungs can enter one of
three places:
1. the mediastinal area around the heart (causing
pneumomediastinum or mediastinal emphysema)
2. the pleural space between the lung and the chest
wall (causing pneumothorax)
3. the bloodstream (causing arterial gas embolism)
Presence of blebs and smoking seem to be risk factors
for spontaneous pneumothorax. A person who has
had a spontaneous pneumothorax has a 30 percent
chance of having another within two to three years.
There is a further 30 percent chance of recurrence
after three years, with a 60 percent long-term risk for
another pneumothorax. These statistics are based on
the finding that a person who has pleural blebs usually
has more than one, and all blebs are prone to leaking at
some point.
Diving, unlike above-water activities, involves
pressures likely to stimulate a bleb to rupture and leak
air into the chest cavity. A spontaneous pneumothorax
that occurs underwater is much more likely to be
fatal than one that occurs above water. Because of the
increased risk of such an event during a dive and the
possibility of a severe pneumothorax if gas expands
in the chest during ascent, the expert consensus
is that people who have ever had a spontaneous
pneumothorax should not dive. AD
— Frances Smith, EMT-P, DMT
N
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