Page 50 - AlertDiver_Spring2013

48 | SPRING 2013
Uzun: The presence of brain lesions does not always reflect
a reduction in neuropsychological performance. However,
some studies have established a correlation between white-
matter lesions and cognitive impairment in older adults, and
some others suggested that periventricular white-matter
lesions were predictive of future development of dementia.
On the other hand, studies assessing the relationship
between brain lesions and neuropsychological performance
in divers failed to demonstrate any correlation.
Tetzlaff: Impaired executive functioning and memory
have been found to be significantly associated with white-
matter brain lesions.
How do voluntary apnea and hypoxia relate to
potential brain damage in breath-hold divers?
Moon: When breath-hold divers reach the surface, their
blood oxygen levels are often low (hypoxemia), which
causes some breath-hold divers to lose consciousness for
a few seconds. It is conceivable that repetitive hypoxic
episodes like this could cause cumulative brain damage.
Uzun: A few studies have investigated brain damage in breath-
hold divers. One recent study (Andersson et al., 2009) reported
an increase in serum levels of the S100B protein, a marker
of neural damage, immediately after voluntary apnea. The
authors postulated that hypoxia-induced neuronal damage
or temporary impairment in the blood-brain barrier could
account for this finding. Whether voluntary apnea causes
cerebral damage in the long term is yet to be determined.
Tetzlaff: Prolonged breath holding will reduce oxygenation of
the brain. There is evidence from the field of obstructive sleep
apnea that intermittent hypoxia is associated with cognitive
decline and silent brain infarcts, which predominantly involve
small-vessel cerebrovascular disease. However, unlike patients
with obstructive sleep apnea, breath-hold divers do not appear
to develop permanent sympathetic or any significant reflex
cardiovascular activation. The increase in serum levels of a
protein called S100B, a brain-damage marker, after extreme
apneas performed by elite breath-hold divers may point to the
likely disruption of the blood-brain barrier. S100B, however,
is a nonspecific marker and may be increased by extracranial
injury. Extreme apneas as performed by elite breath-hold divers
cause significant stress on the cardiovascular and respiratory
systems. It should be noted that extreme breath-hold diving
is a dangerous activity that can cause serious health hazards,
among which long-term brain damage is the least worrisome.
What risks to the central nervous system does
diving impose on a person?
Moon: The main risk, although low, is cerebral
decompression illness (DCI). This could be due to DCS
(in-situ bubble formation in tissues) producing bubbles
in blood vessels that could then reach the brain. This may
also be caused by arterial gas embolism (AGE), where
bubbles result from rupture of alveoli in the lung during
decompression caused by breath holding or lung disease.
Uzun: Scuba diving is associated with a number of
neurological risks including DCS, AGE, anoxia and high-
pressure nervous syndrome.
Tetzlaff: The major mechanism leading to central nervous
To better understand
some of the effects
of diving on the brain,
researchers at DAN are
beginning a study that
will screen divers for
acute effects of scuba
diving on executive brain
functions. Executive func-
tions include regulatory
and control processes
such as planning, prob-
lem solving, verbal
reasoning, and initiation
and monitoring of actions.
The study will use two
psychometric tests, the
Montreal Cognitive Assessment and the Clock Drawing Test (CDT),
which draw upon memory and visuoconstructional ability as well
as executive function. The CDT will employ a digital pen developed
by the Clock Consortium, an association created by researchers at
Massachusetts Institute of Technology and the Lahey Clinic. The
objective of the study is to assess possible neurological dysfunc-
tion after extreme breath-hold diving and deep scuba diving in
asymptomatic divers.
CURRENT RESEARCH
Extreme breath-hold diving may contribute to long-term
brain damage, but the data are inconclusive.
STEPHEN FRINK
STEPHEN FRINK