Oxygen Toxicity
The effects of oxygen are increased at depth so that the
maximum PO2 in diving is 1.6 ATA, and this is achieved at 218 fsw breathing
air, 132 fsw breathing 32% O2, and 20 fsw breathing 100% O2.
This is due to the effects of Dalton's Law which states
that on descent, the partial pressure of all component gases increase in
the same ratio as the total pressure. this results in the creation of the
elevated pO2 that causes the convulsions of O2 toxicity and is the direct
cause of nitrogen narcosis and along with Boyle's law, is the cause of
decompression sickness.
All O2 treatments using 100% O2 are given at 60 feet or
shallower, except for gas gangrene and CO poisoning. This effect is also
the limiting factor in the use of nitrox (increased O2 percentages) in
increasing the bottom time of "tech" divers.
The effect on the central nervous system ( the Paul Bert
effect), results in:
muscle twitching and spasm
nausea and vomiting
dizziness
vision (tunnel vision) and hearing difficulties (tinnitus)
twitching of facial muscles
irritability, confusion and a sense of impending doom
trouble breathing, anxiety
unusual fatigue
incoordination
convulsion.
Convulsion at depth in water usually results in drowning
or arterial gas embolism and is prevented by not using oxygen breathing
with SCUBA and by limiting oxygen exposure with hyperbaric oxygen therapy
100% O2 greater than 60 FSW.
Factors increasing susceptibility to O2 toxicity include:
Increasing exposure time
Increasing depth
Increasing the percentage of inspired O2 (As in nitrox mixtures)
The simple act of immersion setting off the diving reflex
Exercise increasing the metabolic rate
Increased CO2 in the tissues (May be due to cerebral vasodilation)
Cold stress (Shivering is a form of exercise)Systemic diseases
that increase the metabolic rate (such as thyroid diseases)
Pulmonary oxygen toxicity ( Lorraine Smith effect) is
a direct time /dose relationship on the lungs caused by a direct effect
of O2 on the lungs, blockage of airways, increased CO2, pulmonary surfactant
changes , enzyme interference and an inert as effect. The best treatment
is prevention and removal of pure O2 at the first signs of toxicity.
Links
to Oxygen Toxicity
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