Bruce Johnson, a consultant on cardiovascular diseases at the Mayo Clinic in Rochester, Minnesota and leader of the group, said the study subjects will be a U.S. team that plans to replicate the first 1963 ascent of the mountain by a U.S. team.

That expedition put five U.S. climbers on the summit, two climbing the difficult and then-untested West Ridge route and the rest along the normal Southeast Ridge route which was used by New Zealander Sir Edmund Hillary and Sherpa Tenzing Norgay in their pioneering 1953 ascent.

Nearly 3,700 people have climbed Mount Everest, the world's highest peak at 8,850 meters (29,035 feet), since then.

"We are interested in lung physiology in high altitude, which is similar to the lung physiology in heart failure patients," Johnson told Reuters in Kathmandu, equipment scattered around him.

Johnson said each of the nine climbers, who are already at the mountain acclimatizing, will be fitted with equipment including a special wrist watch and an arm band that will allow their body to be monitored at a base camp laboratory.

The watch will measure the blood oxygen level and the specially designed arm band will show their energy expenditure and how many calories they burn.

Climbers will also be wearing the "Mayo platform," an instrument devised by the clinic that fits in a tiny pocket on the climber's clothing and will measure their cardiovascular activity, Johnson said.

Specially developed video games will also be used to test the cognitive performance of climbers, such as their ability to think at high altitude, where oxygen levels are low.

The team will set up a lab in a dome-shaped tent at the base camp, which becomes a tent city during the climbing season.

Medical research has been carried out on Mount Everest climbers in the past, and Johnson said what his team was doing would add "some incremental bits of knowledge" to the working of the human body in extreme conditions.

"The study is also very closely associated with the work we do back home with heart patients and patients with lung diseases," Johnson said.

He said the study would also add to knowledge about altitude sickness, which is a leading cause of death in high mountains.

More than 300 foreign climbers and another 400 Sherpa guides have gathered at the base camp located at about 5,300 meters (17,390 feet) to climb Mount Everest during the current climbing season which started in March.

(Reporting by Gopal Sharma, editing by Elaine Lies and Paul Casciato)

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