Scientists tackle mystery mounta...(es in a potentially life-threatening sit...)

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HAPE is the most common form of altitude sickness and can kill within hours if untreated. As the illness progresses, it can cause drowsiness and lack of coordination, leading to a coma and death. As cases are not registered, nobody knows exactly how many people have died as a result of the condition.

The main treatment is descent, but this is often impossible as a sufferer may need to be carried for miles on a stretcher, only to descend a few hundred feet. Other treatments include breathing oxygen and two drugs, dexamethasone and nifepidine, which may not be available when somebody becomes ill.

Blood vessels inside the lungs constrict in response to low oxygen to such an extent that fluid is forced from the capillaries (narrow tubes through which blood cells pass), leading to flooding of the lungs air sacs.

Risk factors include rapid ascent, physical exertion and a previous history of the condition. By understanding who is most at risk, potential sufferers could take precautions such as climbing much more slowly or taking drugs to prevent the onset of the condition.