Medicine: Too Much Oxygen

The deep-sea divers working on the sunken British submarine Thetis were a scientific problem to famed Biologist J.B.S. Haldane. One day, early in World War II, Briton Haldane impetuously clapped on an oxygen mask and, breathing pure oxygen (to study its effects), “dived” in a pressure chamber to a depth of seven atmospheric pressures (200 feet). The experiment nearly killed the experimenter, but it proved to him that oxygen, under pressure, is a violent poison.

Inspired in part by Haldane’s dive, the British Navy launched a full-dress study of oxygen poisoning, now reported in the British Medical Journal. Oxygen is essential to life, but it appears that the human body can stand just so much of it (not so much as biologists once supposed). The British Navy concludes that breathing pure oxygen under more than two atmospheres of pressure (or an oxygen dive of more than 25 feet under sea water) is dangerous.

Nervous Knockout. Deep-sea divers generally have been fed pure oxygen and helium, pumped to a pressure matching the depth of their dive. Divers sometimes unaccountably passed out during relatively shallow dives (up to four atmospheres of pressure used to be considered safe). The British study, involving some 2,000 tests, proved that oxygen, forced into the tissues under pressure, somehow intoxicates the central nervous system and poisons the brain cortex. (Whales, biologists have observed, bypass the whole oxygen problem by collapsing their lungs during deep dives.)

Flashes of Light. With oxygen poisoning, the victim grows pale, feels as if he were choking, has attacks of nausea, is alternately exhilarated or depressed, has hallucinations (flashes of light, halos around everything, sounds as of bells and knocking). Finally his lips begin to twitch violently (the most common symptom); he goes into convulsions and falls unconscious. The final symptoms are much like those of an epileptic fit. But the victim quickly revives on breathing fresh air and, except for an oxygen jag lasting about an hour, shows no bad aftereffects.*

Dr. Kenneth W. Donald, the British Navy’s chief oxygen investigator, admits that he and his associates found the whole phenomenon highly mystifying. Their subjects (all volunteers) varied enormously in resistance to oxygen poisoning; and each individual varied greatly from day to day. One man was poisoned in seven minutes one day, resisted the same dose for nearly 2½ hours another day. For some unknown reason, people are more vulnerable to oxygen poisoning under water than under the same pressure in a pressure chamber. And at a pressure of one atmosphere or less (as in high-altitude flight), human beings apparently can breathe pure oxygen indefinitely without harm.

*To avoid the bends (caused by nitrogen bubbles in the blood), high-altitude flyers during the war usually breathed pure oxygen, or a mixture of oxygen and helium, for an hour or more before taking off. But they suffered no ill effects because they breathed it at ground level atmospheric pressure.