It is the highest, loneliest and most forbidding place on Earth. Well into the so-called "death zone" above 8,000 metres (26,250ft), the frozen South Col of Mount Everest is the final obstacle before the summit for most climbers and the last place an unfortunate few see.
It is also, in what must be the ultimate demonstration of British grit, ingenuity and downright eccentricity, where a team of mountaineering doctors from University College, London intend to set up exercise bikes and pedal their way into medical history.
The seven-strong group revealed their plan yesterday to climb Everest to conduct experiments on themselves to learn how the human body copes with extreme conditions. The doctors said the expedition would yield vital information which could explain what happens when the body touches the void - on a mountain top and in a medical emergency.
They hope the results of the tests, which include the bike experiments and the first blood samples taken on Everest's 8,850 metre (29,040ft) peak, could help treat patients who have suffered serious illness or injury.
The expedition's leader Mike Grocott, a consultant in intensive care medicine who has completed more than 30 ascents to above 5,000 metres, said: "If you reached the top of Everest without acclimatising you would be unconscious within two minutes and death would rapidly follow. Acclimatisation has allowed human beings to survive and thrive in the most extreme conditions, but it remains a poorly understood process. Our goal is to study life at the very limit."
Dr Grocott is co-director of the centre for aviation,space and extreme environment medicine at University College. Other team members include skydiver Hugh Montgomery, who leads a research group in cardiovascular genetics, Roger McMorrow, designer of a new breathing system to be tested on Everest, and Sundeep Dhillon, a GP who has extensive high altitude experience.
Space expert Kevin Fong, and diving specialist Denny Levett will provide medical support for the summit climbers.
Oxygen levels in the blood plummet at high altitudes, to a point where most people cannot survive without support. The same happens to many intensive care patients. And just as certain individuals cope with high altitudes better than others, or find it easier to acclimatise, some patients are better than others at surviving trauma.
Dr Montgomery said: "If we can understand how some patients are able to cope with that low oxygen level, and why others are not, then we may be able to make a large difference to levels of survival. The answer, we think, is to look at people climbing the highest mountains of the world, where oxygen tension is as low as can be found on the Earth's surface."
Oxygen in the body is critically balanced, even in healthy people at sea level. Although the air we breathe is 20% oxygen, it is greatly diluted in the body, falling from a normal pressure of one atmosphere to about 0.1% at the cellular level.
"Even now all of us are critically on the knife edge of dying from lack of oxygen," said Dr Montgomery, who has climbed in the Alps, Himalayas and Andes.
"What happens then when you get bad pneumonia, or unfortunately get hit by a taxi, or you get bird flu, or something goes wrong during a pregnancy and your lungs suddenly fold or your heart suddenly packs up? What happens is that oxygen levels in your bloodstream fall catastrophically and quickly. These are people who we deal with every day in our intensive care units."
The researchers are seeking between £500,000 and £1m from private sponsors to finance the Xtreme Everest expedition, scheduled for spring 2007.
They said that doing the study in a low pressure chamber at sea level would not produce data as valuable as that from Everest. It would also cost as much, or more, to operate and staff a chamber round the clock for a number of weeks.
The scientists will set up high altitude laboratories comprising the bikes, breath analysis equipment and other apparatus along the route, including at Everest's Western Cwm at 7,000 metres and the South Col at 8,000 metres.
They will use them to investigate the effects of thin air on the body, including fluid on the brain and in the lungs, and acute mountain sickness.
A separate initiative called Project Everest will recruit more than 1,000 volunteers to take part in fitness research at University College in the run-up to the expedition.
Helicopters cannot operate in the thin air around Everest so the team will have to carry all its equipment up and down the mountain.
The scientists have already teamed up with formula one engineers to design lightweight exercise bikes.
Dr Montgomery said the biggest challenge was devising a safe way to take blood samples from Dr Dhillon, who will attempt the climb without supplementary oxygen and others in the team during the brief time they will have at the mountain's peak.
They are developing a special catheter system to draw blood automatically, but it could come down to unzipping their trousers and sticking a needle into the femoral artery.
"Exposing your skin at those temperatures is a bit of a problem," Dr Montgomery said.
As one anonymous Everest summiteer answered when asked what was the hardest part of climbing the mountain: "Pissing through six inches of clothes with a three inch penis."
The history of medicine is littered with scientists using themselves as guinea pigs
· The Nigerian immunologist Jeremiah Abalaka is so convinced by his experimental HIV vaccine, he claims he inoculated himself with it and then injected himself with HIV-infected blood six times. He says he did not contract the disease, and also claims to have developed a cure that has cleared the virus from 20 infected patients. Abalaka's research was published by the British journal Vaccine last September but remains controversial.
· In a dramatic move to prove his idea that the disease pellagra, which is characterised by scaly skin, diarrhoea and mental confusion, was not contagious and was actually down to poor diet, US public health official Joseph Goldberger ate the skin scrapings and excrement of sufferers in the early 20th century.
Not so lucky was John Hunter, the 18th century Scottish anatomist and surgeon who inoculated himself with venereal pus. He rapidly developed the symptoms of gonorrhea and syphilis, which plagued him for the remaining 15 years of his life.
More recently, the Australian doctor Barry Marshall drank a flask of water full of Helicobacter pylori bacteria in 1984 to show they cause stomach ulcers.
· One of the most famous stories centres on experiments carried out in 1900 by doctors stationed with US troops in Cuba. To test the idea that yellow fever was spread by mosquitoes, scientists led by army surgeon Walter Reed allowed mosquitoes that had fed on yellow fever patients to bite their exposed arms. One volunteer, Jesse Lazear, died of the disease and two colleagues were struck down but survived. Reed took credit for the discovery, though historians subsequently discovered he refused to participate in the experiments and disappeared on the day they were scheduled.
