The team also is focusing on why climbers at high altitude experience poor sleep.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body

There have been greater numbers of climbers at high camps waiting to attempt the summit, Dr. Johnson says.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body

By means of steel cables and iron brackets anchored into rock faces, climbers reach a high-altitude world that would otherwise be seen only by hardened alpinists.

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All too often Everest hits the news for the wrong reasons - climbers left to die high on the mountain, or piles of rubbish littering the slopes - but for Luanne such rescues show the spirit of Base Camp.

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Asthma inhalers like albuterol, which work by stimulating beta-receptor cells in the lungs, were first used to treat high-altitude climbers.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body

The mountain's summit stands at 8, 848 metres high, and beyond 7, 600 metres climbers enter what is known as the "death zone" - so called because of the serious effects of oxygen deprivation on the body.

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It is, moreover, a consumer cooperative, founded 60 years ago by some climbers with no profit motive, just a need to import high-quality ice axes from Switzerland.

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