Bruce Johnson is a soft-spoken man who's drawn to extremes.

He once camped on the edge of a soaring cliff in Argentina, with 40-mile-per-hour winds threatening to blow his tent away. "Like sitting behind a jet plane," he says.

As a scientist at the Mayo Clinic, Johnson has gone to some of the most forbidding places on the planet (including the South Pole) to explore one question: "What are the extremes that the human body can endure?" Monday, he takes his quest to Mount Everest.

Johnson, 54, is leading a team of scientists to "the promised land," as one colleague calls it, to study the extraordinary ways the body can change on the highest mountain on Earth.

In Nepal, Johnson and his colleagues will trek on foot for 10 days, to an elevation of 17,500 feet, to set up a Mayo outpost at Everest's base camp.

"We're bringing 1,300 pounds of medical equipment on the backs of yaks," said Johnson. "We're essentially creating a remote laboratory up there."

As part of the research, Mayo scientists will get up close and personal -- very personal -- with the members of an expedition cosponsored by National Geographic, the North Face and Montana State University. The plan is to hook everyone, climbers and staff, up to tiny sensors that will track their heart rates beat by beat. They'll test their oxygen levels, blood and urine. Even their sleep will be measured; if they wake up after a nightmare, the scientists will know it.

With luck, Johnson will return with a mountain of data -- and some lessons that could benefit patients with heart disease and other chronic conditions.

Much of the study will be broadcast live. The professional climbers are blogging about their adventures as "lab rats" for National Geographic (; Mayo is sending a member of its communication staff to cover the story online ( and on Twitter. If all goes as planned, even the climbers' vital signs will be posted on a website for all to see.

To some extent, the scientists already know what they'll find. "Any time you go above 10,000 feet," says Bryan Taylor, 29, a Mayo physiologist from Scotland, "it's putting the body under a lot of stress." At sky-high elevations (Mount Everest's peak is 29,035 feet), the effects of the cold and atmosphere are extreme: Dehydration. Fluid on the lungs. Headaches. Digestive problems. Swelling of the feet and hands. Apnea.

Many of the effects mimic the symptoms of heart failure and other chronic conditions in the elderly, Taylor said. So what they learn on the mountain may shed new light on those conditions, as well.

They're also testing a miniature heart monitor that will be embedded in the climbers' clothing. "If these devices work in extreme conditions," said Johnson, "you can probably trust them to use in [someone's] home."

Derek Campbell, 41, a North Face executive from California who's joining the expedition, got a taste of what's to come when he and a colleague arrived in Rochester in early April for preliminary tests.

Campbell's stint as a guinea pig began at night, when Mayo scientists attached electrodes to monitor him while he slept in his hotel. The next day, he was at the clinic for a battery of medical tests. By midmorning, he was racing through a series of video games designed to measure mental acuity.

He aced the games at St. Marys Hospital (elev. 1,166 feet) but knows that may change on the mountain. "I wonder what this is going to be like at high altitudes," he said. "When you're there, you know you're not functioning normally."

A few minutes later, he was covered in electrodes, with wires protruding from all sides and a snorkel-like tube in his mouth, climbing on a treadmill. "Walk as long as you can," Taylor told him. The plan was to crank up the speed and incline every three minutes. "Just go until you cannot do it anymore," Taylor coached him. "Cuss words are allowed."

Campbell, an avid hiker who has climbed peaks in Ecuador and Mexico, didn't seem worried. As the speed increased, the scientists watched his blood pressure and heart rate climb. After 11 minutes, he broke into a jog. "This is it," said Taylor. "Keep going until you're absolutely exhausted." At 14 minutes, he finally jumped off, panting. "Good job, Derek," said Taylor. "Well done."

The scientists plan to repeat the tests on the mountain (in this case, with a step-stool instead of a treadmill), and then again after the expedition returns. A month on the mountain will take a toll on their bodies; most will lose at least 20 pounds.

In this case, the scientists will face the same challenges as their study subjects. Most have scaled mountains. But Amine Issa, a pony-tailed research fellow and the team's device expert, laughed when asked if this was his first Everest trip. "First time climbing a mountain," he said. "I'm hoping I'm not the one that gets sick and has to be baby-sat."

Alex Kasak, 24, a research assistant and last-minute replacement on the team, has been loading his backpack with 35-pound weights and hiking everywhere to prepare for the trip. Johnson, who at 54 jokes that he may be the "oldest person on the mountain," says he keeps in shape by walking, cycling, swimming and "running up hills."

"None of us are, what I would say, elite climbers," said Johnson of his team. But they don't need to be, as long as they're in good shape. "It's more of a hike," he said.

Johnson admits the idea of reaching the summit is tempting. "I would have loved to give it a try," he said. But "we're going to be very busy collecting data. It's going to be hard to go out and play."

Maura Lerner • 612-673-7384