Oxygen and diving

Just returned from a blinding (literally) trip to the Alps. I was part of a research team from University College London looking at the effects of low oxygen levels on the body, especially on exercise capacity and blood flow to various organs. It was blinding (literally) because I forgot my goggles, and suffered the ignominy of photokeratitis: a burn of the cornea caused by the sun’s UV rays. Luckily, it wore off after 24 hours and some medicinal single malt whisky.

But the trip was blinding (metaphorically) as well, mainly due to the sudden realisation I had of how much we owe to that mysterious gas oxygen. Once termed ‘the elixir of life’, our bodies are wholly dependent on it, and are elegantly designed to deliver it to the trillions of cells that make us up. Without it, clearly we’d die in a matter of minutes, and being deprived of it, even to a small extent (as we were at 4,500m), produces the most-unpleasant sensations of slow suffocation and despair. Where was the ‘oxygen bar’ when I needed it!

Divers, of course, are even more reliant on a failsafe oxygen delivery system. The irony is that despite being surrounded by oxygen while diving, we cannot breathe it; when it’s bonded to hydrogen to form water it’s as useful as the proverbial chocolate teapot. Until we evolve into liquid-breathing organisms we are crucially dependent on this colourless, odourless molecule in its gaseous form. But what is its story? Oxygen was discovered in 1772 by Swedish pharmacist Carl Scheele, who called it ‘fire air’. Joseph Priestley, who came across it a couple of years later, described breathing it: "the feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards”.

Nowadays we know a lot more about oxygen, and have recognised that it can be a poison as well as an elixir, a double-edged sword that can be perilous to divers in particular. Breathing pure (100 per cent) oxygen below about 7.6m can cause a convulsion, similar to an epileptic seizure, and the unconsciousness that results may be fatal.

This effect was first described by Paul Bert, a French physiologist, in 1878. He subjected various unlucky animals to different pressures in a hyperbaric chamber, and watched many of them quickly die in high concentrations of pressurised oxygen. In 1912, a sporting chap by the name of Bornstein breathed pure oxygen at 2.8 bar for 51 minutes before developing cramps in his hands and legs, early signs of central nervous system toxicity.

The British Navy conducted extensive oxygen toxicity testing in the 1940s, and naval divers during the war invented a mythical monster, Oxygen Pete, who lurked at the bottom of the Admiralty Experimental Diving Unit ‘wet pot’ (a water-filled hyperbaric chamber). Any unwary diver sustaining an oxygen toxicity hit during this time called it ‘getting a Pete’.

Always willing to be his own guinea pig, JBS Haldane’s description of his own seizure is priceless: “the convulsions are very violent, and in my own case the injury caused to my back is still painful after a year. They last for about two minutes and are followed by flaccidity. I wake in a state of extreme terror, in which I may make futile attempts to escape from the steel chamber”. One of the Navy’s tactics during the defence of Gibraltar in World War Two was to lure enemy frogmen into deep waters until they convulsed. Britannia rules the waves!
 

James Lorrain Smith was the first to report the toxic effects of oxygen on the lung, in 1899, noting pulmonary irritation in mice and birds after four days of exposure at 0.74 bar. It’s a more delayed but equally as deadly effect of too much oxygen. The other major danger with prolonged oxygen administration is damage to the retina of the eye, which is sometimes seen in premature babies who require long-term oxygen supplementation. Divers are generally not exposed to oxygen for long enough to get these problems, but as is often the case, too much of a good thing can be bad.