What happens to your body when you get the bends?

Reports of a man in Peru whose body swelled "doubled in size" because he got 'the bends' after diving, otherwise known as decompression sickness, are highly implausible doctors have said.

Decompression sickness happens when divers come back to the surface too quickly. As divers descend, the pressure their bodies are under doubles every 10 metres. This forces nitrogen into the bloodstream in quantities that wouldn't normally be there at surface level.

This isn't a problem while divers remain in deeper waters. But as they start to rise, the tiny bubbles of nitrogen in the blood expand. If divers come up slowly, the gas has time to gradually diffuse through the lungs and can be safely breathed out.

If a diver comes up too quickly, the bubbles expand rapidly before the gas can leave the body. The bubbles can block capillaries – tiny blood vessels – and cause immense pain.

The Peruvian fisherman Alejandro Ramos Martinez was allegedly first treated for the bends after a dive four years ago. Sites including CEN, the Mirror, the Mail Online and the Metro reported that the nitrogen had formed large sacs around his muscles, and have remained there for four years.

"Nitrogen will diffuse out of the body quite quickly. Four years down the line, it's highly, highly unlikely he would still have nitrogen blocked in his blood," Peter Karpati, a specialist doctor in treating the bends at the London Hyperbaric Medicine Healthcare centre, told IBTimes UK.

"He may have pain in the muscles from the event, but there's not likely to be any gas in sacs around the muscles any more."

Even if some nitrogen did somehow get trapped in his body, the idea that he could swell to twice his normal size doesn't make medical sense, Karpati continued.

"Gases behave according to gas laws. So if you have a volume of gas that is about the diameter of a 50p coin to start with. You could shrink it under pressure to the size of 5p coin, let's say. When it comes back to the surface it would come back to size of 50p coin again. It wouldn't be any bigger."

There are no medical case studies or peer-reviewed documents on Martinez to refer to. However, the reports claim that Martinez's doctors at the hospital San Juan de Dios in Pisco are considering removing the so-called sacs of nitrogen surgically.

"Surgically remove nitrogen? It is a gas within your blood," Karpati said. "How could you remove that surgically? It's not really possible."

The treatment for decompression sickness involves recompressing the patient temporarily and allowing time for the nitrogen to diffuse from the body. Sometimes additional oxygen is administered to aid healing of wounds in the blood vessels.

"Nothing is ever completely impossible and there's always some case that comes along to prove a centuries-old theory wrong, or changes our thinking. That's the way science works. But what is reported in those articles is really highly medically improbable," Karpati concluded.

Michael Chappell, an engineer at the University of Oxford who completed his PhD on the physics of decompression sickness, agreed that the case looked improbable.

"I've never seen anything like it. The thing that's particularly weird is that there are large gas sacs left after such a long period of time. Nitrogen readily dissolves into bodily tissues, and then it dissolves out," Chappell said. "I can't see why it would stay for a very long time."

The stories also claimed that Martinez quickly gained nearly 5 stone in weight soon after the incident.

"That wouldn't be consistent with gas, which has a very low density. If there's weight gain then it would imply there's something else going on."

Cases of decompression sickness are relatively rare. In the US, about 1,000 divers a year suffer from the condition, according to the non-profit organisation Divers Alert Network. Other studies have put the rate of cases of the bends at between 1 and 35 cases per 10,000 dives. Severe untreated decompression sickness is fatal.