When people travel quickly from the lowlands to mountain summits, sound health and judgment often vanish into thin air.

And Mount Rainier, which rises from sea level to 14,410 feet, is perfectly designed to punish climbers who go too high too fast.

"Rainier is an incredible mountain for provoking mountain sickness," said Dr. Tom Hornbein, a professor at the University of Washington School of Medicine and a member of the 1963 team that put the first American atop Everest. "Seventy percent of the people who climb Rainier over the course of two days will end up with some headache."

Headache is just the start. Symptoms of acute mountain sickness, or AMS, the most common mountain malady experienced above 9,000 feet, include nausea, dizziness and extreme fatigue. Sufferers also vomit, cough or have difficulty sleeping. AMS feels like the flu, seasickness or a bad hangover.

It is rarely fatal. But when climbers reach Mount Rainier's summit 24 hours after leaving sea level - the pace of most ascents - they risk two much more serious ailments.

High-altitude pulmonary edema, or HAPE, is a buildup of fluid in the air sacs of the lungs. The symptoms are coughing and shortness of breath accompanied by a fine froth of bubbles from the mouth. The bubbles don't pop readily and are sometimes tinged with blood.

Most often, HAPE is superimposed on the symptoms of AMS. Sometimes a climber's lips, ears, nose or the skin beneath the fingernails turn a bluish color, indicating cyanosis, poor oxygenation of the blood caused by the fluid in the lungs.

HAPE killed Rainier climbers Calder Bressler in 1959 and Patrick Chamay in 1968. They died spending the night on the summit, their lungs slowly filling with fluid.

High-altitude cerebral edema, or HACE, is a buildup of fluid in the brain. Symptoms are loss of coordination, confusion, sluggishness and, in rare cases, hallucinations. It, too, can be fatal, though it has caused no deaths at Rainier.

"The brain swells. And when it gets swollen enough, the end stages are coma and ultimately death," Hornbein said.

No one is immune. Fit, experienced climbers are as likely to be stricken as out-of-shape novices.

Researchers are still studying most high-altitude diseases, but they agree that all are caused by lack of oxygen.

"We live under a blanket of air, and the further down you are the thicker the blanket," Hornbein said. Air at sea level is compressed by the weight of the air above it. The higher the elevation, the lighter the overlying atmosphere, and the more air expands.

At 10,000 feet, air pressure is 69 percent of what a person would feel at sea level. At the 14,410-foot summit of Mount Rainier, it is 58 percent.

People who go higher slowly often adjust without problems. However, most Rainier climbers travel from sea level to 14,410 feet in less than two days -- seven times faster than the pace recommended for the prevention of AMS.

Atop the world's highest mountains, the thin air dulls the brain as well as the body. Higher functions such as clear thinking deteriorate first. Basic motor skills are the last to go.

"It's why people keep trudging on higher and higher. Even though they're not thinking straight, they can still walk," said Dr. Charles Houston, a retired medical professor in Burlington, Vt., who wrote "Going Higher: Oxygen, Man and Mountains" and other books on altitude disorders.

Houston said Rainier's summit likely isn't high enough to create conditions that would seriously impair a climber's judgment - a common occurrence on the world's tallest peaks.

Still, good judgment is a tricky thing to measure, even at low altitudes, said Dr. Stephen Bezruchka, an emergency physician at several regional hospitals, including Tacoma General. He wrote "Altitude Illness: Prevention and Treatment."

If one considers the decreased oxygen available atop Rainier, "It's bound to affect judgment somewhat," he said.

Those who survive HAPE and HACE will be more likely to suffer problems should they return to high altitude, doctors agree.

Humans can - and do - live at high elevations because bodies adapt over time to the decrease in available oxygen.

Drugs, such as the carbonic anhydrase enzyme inhibitor Diamox, have been shown to reduce the effects of altitude. Some doctors also believe altitude effects can be reduced by drinking plenty of fluids to compensate for the dehydration that occurs from perspiration or breathing high mountains' cold, dry air.

Yet, researchers and climbing experts agree that the best way to avoid most altitude-related illnesses on Rainier is by moving slowly up into the thinning atmosphere.

"If you can have the time to acclimate your body, you can certainly have a safe and enjoyable climb," said Jim Nelson, co-author of the book "Selected Climbs in the Cascades."

"But it takes a long time to adjust to those altitudes." (Published June 27, 1999)