Field of Science

Treating the Bends
Last week I wrote about the Bends, a medical problem based in an understanding of physics that results in bubbles of (primarily) nitrogen in your blood if you move from one atmospheric pressure to another to quickly, typically surfacing from depth while diving too fast.

Of course I meant to point out that decompression occurs when the external atmospheric pressure drops quickly. Most commonly this occurs in divers but also happens in astronauts. I’d never really thought about that before.

Anyway I got as far as explaining how it occurs last time. This time we are interested in how you fix it.

The therapy is actually very simple – take the person back to the depth they were diving at to force the bubbles to resolve into the blood. This immediately solves of the symptoms of the condition but is a little impractical to drive the diver back to the beach and drag them underwater. So, instead, we fake it.

In order to fix your pain I need you to please climb into this fortified chamber. What do you mean no? Credit
In order to fake depth we use a hyperbaric pressure chamber. This chamber allows us to increase the pressure of the air mixture such that the bubbles resolve. Then the operator slowly brings the pressure back to atmospheric levels to allow enough time for the patient to breathe out all the solubilised gas.

To aid this and ensure as much nitrogen as possible is extracted from the patients blood the chamber is often pumped with 100% oxygen. This generates the maximum pp (partial pressure) gradient dragging nitrogen out of the body while also providing the body and its cells with maximum oxygen to facilitate repair of any tissue damage.

The treatment is very simple but relies on an understanding of the physics that caused the problem to begin with.

Hyperbaric oxygen therapy (HBOT) is not just used to treat decompression illness though. In fact since the observation that breathing oxygen at pressure results in huge increases in the amount of oxygen found in the plasma providing a saturating level of oxygen to the tissues many conditions began being listed as ‘treatable’ by HBOT.

Of those conditions treated with HBOT a large number are infections by obligate anaerobic organisms. Conditions like gas gangrene, necrotising fasciitis and osteomyelitis show significant improvement when tissues are saturated with oxygen preventing exaggeration of the infections and even the death of the agents causing the disease.

Instead of showing you actual rotting flesh I opted for a plush gangrene toy. Thank me later. Credit
Similarly it is thought the increased oxygen carriage facilitates improved wound healing by providing the tissues with every opportunity to function normally. To this end HBOT has been employed in the treatment of diabetic wounds, radiation injury, skin graft and burns.

It’s even started to pick up such a reputation for healing that elite athletes are jumping on the bandwagon and subjecting themselves to HBOT to increase the healing of injuries.

Unfortunately it’s not all smooth sailing. HBOT does have some downsides. Apparently there is such thing as too much oxygen and its effects can be debilitating.

Oxygen poisoning can effect the central nervous system, lungs and eyes in particular. An increased oxygen hit causes the CNS to behave very strangely resulting in tunnel vision, tinnitus, nausea, muscle spasms due to increased neural activity, dizziness and personality changes toward irritated states although this might just be because how rubbish you feel with the rest of that going on. Typically these are the problems that arise in divers as they develop after short term hyperoxia.

Long term hyperoxia is more dangerous then I would have ever expected. Prolonged hyperoxia results in a burning sensation during breathing and can lead to dyspnea (shortness of breath) due to the discomfort. It has also been linked to increased blood flow to the nose and increased permeability of vascular tissues resulting in a massive chance of nose bleeds but the real problems occur in the eyes.

Whilst normally only a problem for premature babies in HBOT chambers used to assist with early life extended use may result in conditions such as myopia or even retinal detachment!

So now you know what a detached retina looks like. Obviously this is not on a premmy baby. Credit
HBOT as its uses but the tendency to use it continuously as some elite sportspeople are beginning to do may have adverse effects. Despite this its popularity will probably continue to rise while its benefits are so numerous. In the mean time for those of us that can’t afford approximately $2,000 an hour for HBOT your best option is to go diving and ascend to quickly, then you get the diving experience and your HBOT for nothing*.

Does not constitute actual advice. I’m a moron, not a doctor. Also only applies to countries like Australia where emergency medicine is supplied to those that need it and not just those that can afford it.


Vann RD, Butler FK, Mitchell SJ, & Moon RE (2011). Decompression illness. Lancet, 377 (9760), 153-64 PMID: 21215883
Acott, CJ (1999). Oxygen toxicity: A brief history of oxygen in diving. South Pacific Underwater Medicine Society Journal
Clark JM (1974). The toxicity of oxygen. The American review of respiratory disease, 110 (6 Pt 2), 40-50 PMID: 4613232
Hart, GB, & Strauss, MB (1990). Gas Gangrene - Clostridial Myonecrosis: A Review. Journal of Hyperbaric Medicine
Necrotising Soft Tissue Infections

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