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H
yperbaric oxygen therapy (HBOT) is very
effective for treating decompression sickness
(DCS), but in about one-third of cases it does
not provide complete resolution of symptoms.
In particular, divers with neurological symptoms who do
not receive immediate HBOT respond less well to it later.
A challenge in hyperbaric medicine today is to find ways to
improve the prognosis for individuals for whom HBOT is
ineffective or incompletely effective.
Furthermore, HBOT is not always available; this is true in
diving as well as in other settings. Accidents in submarines,
high-altitude aviation or space can also cause severe (and
perhaps lethal) DCS, and immediate HBOT is not generally
available in these situations. The search for therapies that can
complement or serve in place of hyperbaric therapy is ongoing.
Accepted adjunct therapies today include surface
oxygen, fluid resuscitation, management of plasma glucose,
corticosteroids, anticoagulants and management of core
temperature. Recent developments with compounds called
perfluorocarbons (PFCs) are raising hopes that we may be
close to an even more effective adjunct treatment for DCS.
The question is how close.
PFCs are synthetic “oils” made up of carbon and fluorine
atoms only. They were developed as inert insulating materials
in the Manhattan Project during World War II. PFCs are stable
and do not react with living tissues but have a large carrying
capacity for gases including oxygen, carbon dioxide and
nitrogen. The boiling temperatures of various PFCs differ. They
can be liquid at room temperature and gas at body temperature.
Uses of PFCs in humans were investigated for many years
before they were considered for treating DCS. Compounds
with their characteristics had long been sought by pursuers
of two major quests in medicine: the quest for liquid
breathing and the quest for a blood substitute.
Liquid Breathing
The quest for liquid suitable for breathing began after World
War I in the course of research into the treatment of poison-
gas inhalation. Early attempts at using saline solutions applied
to the lungs of dogs failed. The topic was resurrected after
World War II with the introduction of nuclear submarines. The
subs operated in very deep water, and if they became disabled
at depth their crews could not survive escape. Breathing a liquid
medium was studied as a possible way to increase the depth
from which crew members could be rescued.
In 1962 J.A. Kylstra and colleagues published the paper “Of
Mice as Fish,” an account of a study that showed mammals
could breathe a liquid medium. Mice survived immersed
in physiological salt solutions and compressed to 160
atmospheres (atm), which is the pressure 1 mile below the
surface of the sea. All the animals died of respiratory acidosis
because it took great effort to move liquid in and out of lungs,
and only minimal ventilation was possible. Thus, for liquid
breathing to provide sufficient oxygenation and removal of
carbon dioxide, a liquid with a large carrying capacity for
these gases was needed. PFCs met these requirements.
Leland C. Clark and Frank Gollan of Birmingham University
showed in 1966 that small mammals could survive for an
hour completely submerged in PFCs. But further studies
demonstrated gas exchange in healthy lungs is impaired in
a liquid medium relative to a gas medium. This impairment
combined with liquids’ disturbance of normal lung mechanics
brought an end to the quest for liquid breathing.
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SUMMER 2012
Perfluorocarbons
RESEARCH, EDUCATION & MEDICINE
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E X P E R T O P I N I O N S
B y B R i a n H a R p E R , W - E M T , D M T ,
a n D p E T a R D E n o B l E , M . D . , D . S c .
I S T OC K P HO T O . COM