r 62
The Last Resource
years ago the Navy experts tested its own and other diving schedules,
they found that the schedules were inadequate for dives of more
than an hour much below 100 feet. Since then the decompression
schedules have been modied, but generally speaking they err on
the safe side rather than provide the fastest possible decompression.
It is quite possible that for general working dives the rate of ascent
will never progress much beyond an average of one foot every
ten
minutes. At this rate, a prolonged dive at 1,000 feet requires almost
a week of decompression.
Since the ultimate factor governing the speed of ascent is the rate
at which the inert gas escapes from the tissues, most efforts to make
diving safer and decompression faster depend on manipulation of
the way the gas is used during deep dives. According to Professor
C. ]. Lambertsen of the University of Pennsylvania, the most useful
single measure for improving decompression rates will continue to
be the use of maximum tolerable oxygen. This limits the uptake of
inert gas during descent and at diving depth, increases the 0utward
gradient for the elimination of inert gas during decompression, and
nally aids the treatment of bends when or if it occurs.
On theoretical grounds, gas mixtures composed of several inert
gases including argon, helium and neon should enable faster
decompression. Each gas in the mixture behaves as though it is the
only one present, thus giving the effect of a considerable reduction
in pressure. Unfortunately, once the smallest bubble forms in the
tissues, it grows in response to the total pressure of all the gases as
well as of the carbon dioxide, oxygen and the water vapour also
present. However, the idea of using several inert gases during a dive
has not been entirely discarded; by alternating the gas in the
breathing mixture, one inert gas can be eliminated from the tissue
while a second one is being taken up. Switching from one mixture to
another during descent and ascent has already led to some rapid
deep dives.
A further possibility is the use of chemicals which reduce the
bends. Dr C. W. Crowdey has shown that the incidence of bends in
experimental animals during rapid decompression can be remarkably
reduced by treating the animals with the drug PDHA (partially
depolymerized hyaluronic acid). The precise action of the drug is
unknown, but Dr Crowdey has suggested that the PDHA demo—
lishes a coating of fat which covers and strengthens each nitrogen
bubble and so speeds up dispersal of the gas.
The Last Resource
years ago the Navy experts tested its own and other diving schedules,
they found that the schedules were inadequate for dives of more
than an hour much below 100 feet. Since then the decompression
schedules have been modied, but generally speaking they err on
the safe side rather than provide the fastest possible decompression.
It is quite possible that for general working dives the rate of ascent
will never progress much beyond an average of one foot every
ten
minutes. At this rate, a prolonged dive at 1,000 feet requires almost
a week of decompression.
Since the ultimate factor governing the speed of ascent is the rate
at which the inert gas escapes from the tissues, most efforts to make
diving safer and decompression faster depend on manipulation of
the way the gas is used during deep dives. According to Professor
C. ]. Lambertsen of the University of Pennsylvania, the most useful
single measure for improving decompression rates will continue to
be the use of maximum tolerable oxygen. This limits the uptake of
inert gas during descent and at diving depth, increases the 0utward
gradient for the elimination of inert gas during decompression, and
nally aids the treatment of bends when or if it occurs.
On theoretical grounds, gas mixtures composed of several inert
gases including argon, helium and neon should enable faster
decompression. Each gas in the mixture behaves as though it is the
only one present, thus giving the effect of a considerable reduction
in pressure. Unfortunately, once the smallest bubble forms in the
tissues, it grows in response to the total pressure of all the gases as
well as of the carbon dioxide, oxygen and the water vapour also
present. However, the idea of using several inert gases during a dive
has not been entirely discarded; by alternating the gas in the
breathing mixture, one inert gas can be eliminated from the tissue
while a second one is being taken up. Switching from one mixture to
another during descent and ascent has already led to some rapid
deep dives.
A further possibility is the use of chemicals which reduce the
bends. Dr C. W. Crowdey has shown that the incidence of bends in
experimental animals during rapid decompression can be remarkably
reduced by treating the animals with the drug PDHA (partially
depolymerized hyaluronic acid). The precise action of the drug is
unknown, but Dr Crowdey has suggested that the PDHA demo—
lishes a coating of fat which covers and strengthens each nitrogen
bubble and so speeds up dispersal of the gas.