Page 48 - AlertDiver_Spring2013

The question of whether diving can have
deleterious, long-term health effects emerges
from time to time but appears unanswered so
far. Possible neurological complications from
acute dive injuries are undisputed, but some studies show
evidence of lesions in the central nervous system of divers
with no history of decompression sickness (DCS). These
subclinical lesions or “white spots” in the brain are detected
with magnetic resonance imaging (MRI), a method very
sensitive to changes in the brain. It is not clear whether
they are more common in divers than in nondivers, nor is it
certain that their presence has any importance.
In some studies, measurements of neurological
function also indicated abnormal results in divers. These
measurements included neuropsychological assessments such
as memory and concentration tests, electroencephalograms
(EEGs), which detect electrical activity in the brain, and
single-photon emission computed tomography (SPECT)
scans, which measure cerebral blood flow. In the Geneva
“Memory Dive” study (Slosman DO et al., 2004), reduction in
cerebral blood flow and neuropsychological performance was
associated with a history of high dive frequency (more than
100 dives per year), dive depth (deeper than 130 feet) and dive
environment (cold water).
Establishing a causal relationship to diving and determining
the pathological mechanisms of these brain lesions is
difficult. Factors such as age, history of head injury, alcohol
consumption, migraines, smoking, hypertension, high blood
cholesterol, infection and presence of a patent foramen ovale
(PFO) appear associated with these findings. Often, bubbles
traveling through cardiac chambers and visualized using
ultrasound do not cause any symptoms; these “silent bubbles”
could cause the subclinical lesions.
A few studies have focused on the influence of a PFO,
an opening between the right and left atria that can vary
in size and is found in about 25 percent of the population.
Bubbles formed as a result of decompression stress could
theoretically travel from systemic circulation to the heart,
cross from the right side to the left through the PFO and
enter arterial circulation and, potentially, the brain. This
mechanism mimics paradoxical embolism, in which a clot
from a deep vein crosses through a PFO and ends up in the
brain, causing a stroke. Although the presence of a PFO
is considered a risk factor for brain lesions, so far there is
no unequivocal evidence of a causal relationship between
PFOs and silent injuries.
Additional evidence shows that breath-hold divers
exhibit central nervous system effects as well. Acute strokelike
injuries in breath-hold divers are well documented. A Swedish
study showed that prolonged voluntary apnea can transiently
increase levels of a brain-damage marker protein, even in
the absence of symptoms of acute injury (Andersson JP et
al., 2009). The researchers proposed that exposure to severe
hypoxia could cause neurological damage over time. The risk
of asymptomatic neurologic events and their possible long-
term effect in divers remains unresolved. We ask the experts.
What, if any, evidence is there for brain lesions in
divers without any history of DCS?
Richard Moon: Some studies, using MRI, observed a
greater number of brain lesions in divers compared to
nondivers. So far no relationship between the number of
lesions and the number of dives has been established, which
suggests that the lesions are not related to diving itself.
Günalp Uzun: Studies conducted in the last 20 years
aimed at illuminating the presumed correlation between
diving and brain lesions revealed conflicting results. Due
to methodological differences among the studies, it is not
possible to pool the data and reach a clear conclusion.
Consistent with some earlier reports, we found a higher
incidence of white-matter lesions in asymptomatic military
46 | SPRING 2013
Effects of Diving
on the Brain
RESEARCH, EDUCATION & MEDICINE // E X P E R T O P I N I O N S
B y J e n n a W i l e y
White-matter lesions shown on MRI. (Tamaki H, Kohshi K, et al.
“Repetitive breath-hold diving causes serious brain injury.” UHM 2010;
Vol. 37, No. 1: 8. Image reproduced with permission from
the Undersea and Hyperbaric Medical Society.)