Page 48 - AlertDiver_Winter2013
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WINTER 2013
nodes involved in blood-pressure
regulation, become more active
and send the brain an increased
flow of signals, which decrease the
brain’s sympathetic activity and
help reduce blood pressure. This
reduction of blood pressure was
noticed as a secondary benefit in
hypertensive patients undergoing
hyperbaric oxygen therapy for other
reasons.
However, if oxygen pressure
exceeds 3 ATA, all NO is occupied
with ROS, and none remains to
control the sympathetic nervous
system. Sympathetic activity
becomes suddenly extreme,
and levels of adrenaline and
noradrenaline in circulation
increase dramatically (the
so-called “adrenergic storm”). This
potentiates the narrowing of arteries
in the periphery and increases blood
pressure and heart rate. The arteries
of the heart may also narrow to the
point that the heart muscle does not
receive enough blood. The pumping
efficacy of the left heart fails, the
blood pressure in the pulmonary
circulation increases, pulmonary
capillaries are damaged, and gas
exchange becomes compromised.
This acute lung damage precedes
the onset of seizures. Artificial
stimulation of the parasympathetic
system (via the vagus nerve) may
counteract these effects. Indeed, a
new treatment method has been
developed for patients with epilepsy
that could not be controlled with
medication. These patients receive
an implant that provides continuous
electric stimulation of the vagus
nerve and prevents the occurrence
of seizures. Similar effects were
demonstrated using the drug
propranolol, an adrenergic blocker,
which reduces the sympathetic
activity. Unfortunately, propranolol
is not a very selective beta blocker
and may have serious side effects.
Protective effects in humans have
not been confirmed; do not use
it unless directed to do so by a
physician.
The Autonomic Nervous
System as a Key
to Understanding
Oxygen Toxicity
The role of the autonomic
nervous system in oxygen
During hyperbaric oxygen treatments, people are exposed to oxygen partial pressures
much higher than those used in diving. This is acceptable in a clinical setting as the
therapeutic benefits achieved outweigh the remote risk of central-nervous-system
toxicity. In contrast to the marine environment, the rare occurrence of seizures
during hyperbaric treatment is not associated with the risk of drowning.
STEPHEN FRINK
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cinema of dreams
800-451-3737
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