Status of Research in Underwater Physiology, Prepared for the Office of Naval Research, Washington, D. C. by the Physiology Group, Panel on Underwater Swimmers, Committee on Undersea Warfare (1956) / Chapter Skim
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RESPIRATORY GASES
RESPIRATORY GASES
Pages 5-12
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From page 5... ...
It is not cumulative, being consumed so rapidly in the tissues that at normal rates of decompression it is probably not possible to produce oxygen bends, even though oxygen is not eliminated from the body tissues. Where diving duration at a particular depth exceeds the practical useful period for pure oxygen, it has been considered advisable to determine the highest permissible concentrations of oxygen which can be used as a diluent of an inert gas to minimize inert gas narcosis and bends without re-introducing the problem of oxygen toxicity.
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From page 6... ...
2.1.2 Intermittent High and Low Oxygen Tension Most studies of oxygen toxicity have involved continuous exposures to pure oxygen at high pressure. If oxygen toxicity develops slowly, as indicated by the very long latent period at moderate pressures, and is rapidly reversed on lowering oxygen tension, as also appears to be the case, an alternation of high and low oxygen tensions in the respired gas mixture might conceivably extend greatly the working time at increased ambient pressure.
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From page 7... ...
Since pulmonary changes can decrease the oxygenation of arterial blood, the central nervous form of oxygen toxicity may be prevented in animals susceptible to pulmonary effects of high oxygen pressures. Much work remains to be done in elucidating the mechanism of the pulmonary damage, and ways of alleviating it must be found in order to permit more definitive studies in animals of the central nervous system effects of high oxygen pressures.
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From page 8... ...
The underlying biochemical and neurophysiological mechanisms of carbon dioxide convulsions also require study, particularly in regard to interrelationships with the convulsions of oxygen toxicity. Just as high levels of inspired carbon dioxide or the pulmonary retention of carbon dioxide can diminish oxygen tolerance, it appears from the results of animal studies that hyperventilation, with a resultant lowering of arterial carbon dioxide tension, can increase oxygen tolerance.
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From page 9... ...
This problem, now only in the early stages of investigation at positive pressure, has an important relationship, not only to primary carbon dioxide intoxication as a possible cause of "shallow water blackout" or even convulsions, but also to the pharmacology of oxygen toxicity and nitrogen narcosis, the physiology of respiratory resistance and exercise, and probably numerous other aspects of diving. Considerable information bearing upon this subject should arise in the course of general sea-level studies of the physiology of pulmonary ventilation, carbon dioxide and oxygen, exercise, respiratory control and even the respiratory effects of narcotic and stimulant drugs.
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From page 10... ...
The possibility of effects on functions other than respiration must be investigated. The exact significance of any nitrogen depression of the lower centers must be defined quantitatively relative to both oxygen toxicity and carbon dioxide intoxication.
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From page 11... ...
2.4.1 Decompression Contrary to original expectations and to information still to be found in textbooks, the use of helium does not eliminate or greatly lessen the problem of decompression in most diving situations. It provides such an advantage in long, deep dives, but in the depth-time range of practical SCUBA diving the use of helium actually appears to increase the amount of decompression time required.
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From page 12... ...
It is conceivable that high ambient pressures may influence the initial rate of carboxyhemoglobin formation but not the equilibrium amount, since the oxygen tension of respired air is also increased under these circumstances. Without definite information on this subject is is impossible to specify the safe limits of carbon monoxide content for gases used in SCUBA or even to assess the actual importance of this potential hazard.
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