Not avalanches, falling ice or lung problems seem to be the reasons for which many climbers on Everest die, but things like severe weather deterioration, fatigue and swelling, according to North American and British experts in medicine, physiology and meteorology. Their study is to appear in the December 20/27 print edition of the British Medical Journal, with an online issue appearing earlier.

The study by Massachusetts General Hospital, University of Toronto and three British hospitals is a unique collaboration between experts in several fields that may in fact save some lives down the road by giving people a little bit of extra evidence.

Since 1920, more than 200 people have died trying to conquer Mount Everest, one of the most dangerous places on this planet. Its highest altitude reaches 8,850 meters (29,000 feet) above sea level.

Researchers led by Paul Firth of Massachusetts General Hospital wanted to figure out the exact cause of these deaths. What they found was that when climbers made it over 26,000 feet they began to experience swelling of the brain. They were developing neurological problems, like getting confused, comatose or they were having a loss of coordination because lack of oxygen or low barometric pressure.

“At high altitude, someone said it's like being on a treadmill and breathing through a straw. There's just so little oxygen,” said Kent Moore, a University of Toronto professor who studies extreme weather in mountain areas and a co-author of the paper.

Moreover, the researchers were surprised to find there were more brain problems and fewer fatal accidents than they had expected. They found cognitive impairment and cerebral oedema, or brain swelling, were often present whereas pulmonary oedema, dealing with the lungs, was not in deaths above 8,000 meters.