When oxygen is breathed at partial pressures greater than 1.6 ATA it rapidly produces toxicity and affects the central nervous system (CNS).
The likelihood of central nervous system oxygen toxicity increases with oxygen partial pressure, exposure time, exercise, cold, anxiety, increasing carbon dioxide levels in the blood and steroid therapy.
Activities associated with increased risk of CNS oxygen toxicity include diving on air approaching and exceeding 60 meters or using gas mixtures with an increased percentage of oxygen.
Recompression treatment with oxygen for decompression illness or carbon monoxide toxicity occasionally results in oxygen toxicity.
(Occur when underwater or shortly after surfacing)
When oxygen is breathed for very long periods at partial pressures greater than about 0.6 ATA, pulmonary oxygen toxicity can result. The symptoms can include coughing, wheezing, shortness of breath and pain behind the breastbone.
It does not generally threaten the air-breathing recreational diver unless the diver requires recompression, in which case the oxygen level is reduced and monitored. However, divers breathing enriched air and technical divers need to monitor their use of high oxygen mixtures.
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