Effects of Oxygen at Depth
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.
Factors increasing risk of O2 toxicity
"In 1962, none other than DAN's Chief Executive Officer, Dr. Peter Bennett, while working as a research physiologist at the Royal Navy Physiological Laboratory in England, published a paper (Life Sciences; 12:721-727, 1962) testing the hypothesis that oxygen toxicity and nitrogen narcosis were caused by similar mechanisms.
He found that in rats, sympathomimetics seemed to enhance oxygen toxicity. Pseudoephedrine was not tested specifically, but it is a sympathomimetic, so we might infer that it has a similar effect. In addition, our current understanding of the mechanisms which produce oxygen convulsions would predict that sympathomimetic drugs might enhance susceptibility to oxygen convulsions. It has been shown that drugs which inhibit sympathetic stimulation seem to reduce the likelihood of oxygen convulsions in animals. No human studies have ever been done. Thus, at least a theoretical reason exists why pseudoephedrine should be avoided while diving on high PO2 dives."
Mitigation of oxygen toxicity
We often see long lists of drugs that will increase the risk of CNS and pulmonary oxygen toxicity? Are there any drugs or therapeutic measures that can be taken to reduce the risks of acute oxygen toxicity?
This is a question being studied by many for it's benefits in the area of hyperbarics and in the military for reduction of risks for users of closed circuit breathing aparatus.
Bove, p. 135. "Factors that modify the rate of development of oxygen poisoning"
Factors that Delay Onset
Adrenergic blocking drugs
Ganglionic blocking drugs
Edmonds p. 210, mentions aerosolized [recombinant human manganese] superoxide dismutase as a preventive of pulmonary O2 toxicity. He also mentions glutathione, and disulfiram, GABA, lithium (convulsions in rats), hyperventilation, hypophysectomy, adrenalectomy, adrenergic blockers, some anesthetics, magnesium and superoxide dismutase.
Some close relatives of the Carnobacterium in the Antarctic contain millimolar concentrations of intracellular Mn2+ which helps these cells to mitigate oxygen toxicity.
toxic effects of oxygen
likely are related to the unbridled formation and release of reactive
species, such as superoxide, hydroxyl radical, and hydrogen peroxide.
dismutase, catalase, glutathione, and glutathione reductase keep the
of these radicals in check until the oxygen load overwhelms the
leading to the detrimental affects on cell membranes, proteins, and
Other antioxidants used by the body include vitamins C and E, selenium,
Interleukin 1 and Polyethylene glycol-attached antioxidant enzymes have been shown to reduce the effects of O2 toxicity in rats.
Due to the other dangers of diving while on drugs, probably the safest measures to take are the intermittent periods of air breathing used quite successfully in the hyperbaric chamber. That this can not be so easily accomplished in the underwater environment should be readily apparent.
Ernest Campbell, MD, FACS All Rights Reserved.