High-altitude air sickness has forced a Colorado man to abandon his hopes of being part of the Cowboys On Everest expedition's assault on the world's highest peak.

Three Utahns are on the expedition, including team physician Dr. Ross Greenlee, medical director of Intermountain Health Care's Instacare in Rose Park.The other Utahns are Fred Riedman, a climber and financial consultant, and Quintin Barney, an employee with Lithograph Print. Riedman has headed for the top of the mountain, while Barney remained behind at the base camp.

Dan Pryor, base-camp manager, said 33-year-old Jim Clayton of Denver was struck with pulmonary edema, an accumulation of fluid in his lungs, and had to be taken down Tuesday from the group's 17,000-foot-high base camp.

While Clayton was in good spirits, physical weakness forced his evacuation on the only available truck in the region, Pryor said. Clayton was the team's base-camp cook and photographer.

High-altitude air sickness impairs oxygen transfer and in extreme cases can result in death by suffocation. One medical study of the disorder indicates fatality rate could be as high as 27 percent.

Clayton had been feeling ill since he arrived in base camp on Aug. 26. He had complained of severe headache, lack of appetite and severe nausea after eating.

Before moving Clayton out of the base camp on Rongbuk Glacier, crew members used a portable compression chamber that simulates a drop in altitude to alleviate his symptoms.

"Within three to four minutes, my headache was gone. The change was immediate while I was in the bag," he said.

After two hours in the chamber, where the simulated altitude was about 10,500 feet, Clayton was removed and returned to the base camp atmosphere of 17,000 feet, according to Dr. Sheri King of Pueblo, Colo.

"His symptoms returned within a half hour, but they were not as severe," she said.

"With treatment, Clayton's condition improved slightly, but the pace was too slow, his body was not getting the oxygen needed. He was OK on supplemental oxygen, but if we took him off of that, he would not do well," added team physician Greenlee.

"We did not want to keep him in the chamber for several days. We decided it was in his best interest to return to Llasa, the capital of Tibet, at 12,000 feet," the doctor said.

In an unrelated incident last week at the base-camp region, an experienced French climber died of pulmonary edema before medical equipment reached him.