Ever Wondered?

How can high altitude climbers survive with so little oxygen?

In their quest for world’s tallest peaks, many climbers use a drug to manipulate the acid-base chemistry in their bodies

January 15, 2010

Imagine unzipping yourself from the cozy cocoon of your sleeping bag, forcing your feet into numbingly frosty boots, and then propelling yourself out of the tent into the subzero night just so you can stagger a few feet away to relieve your bursting bladder.

Many high altitude climbers have to endure this “bathroom” ordeal many times a night, but you won’t hear them complaining. To them, it’s worth it. The constant need to pee is a minor hassle compared to the benefit offered by a drug they take to help acclimatize to extreme elevations.

When climbers and trekkers travel to high altitudes, between 9,000 and 20,000 feet, any extended stay leaves them at risk of developing acute mountain sickness, or AMS. At these heights in the mountains there is less than half the amount of oxygen in the air as there is at sea level, which can lead to AMS symptoms of headaches, nausea, dizziness and fatigue. If you travel upward from sea level slowly enough, gaining only a few thousand feet every day, you can avoid AMS by giving your body the chance to adjust.

According to Robert Roach, the director of the Altitude Research Center at the University of Colorado Denver, the hallmark of acclimatization is breathing more than you would at sea level. If a climber travels upward slowly enough, the body adjusts on its own and breathing speeds up, which tricks the body into thinking it isn’t at elevation.

But when a slow ascent and natural adjustment isn’t an option — like when you only have a long weekend to fly up to the mountains for a ski vacation — a boost can be found in pill form.

“The best we can do is try to mimic acclimatization,” says Roach, “and acetazolamide does that.” Also known as Diamox, this drug really gets your breathing going.

Acetazolamide works by interrupting the flow of carbon dioxide (CO2) within your body, so that you quickly build up an excess of CO2. In response, your body naturally tries to get rid of it. So, letting your lungs do the work, you begin to breathe more frequently. And because you’re breathing more quickly, you’re also inhaling more oxygen, slowing the onset of AMS.

Breathe out — bye-bye, CO2. Breathe in — hello, precious O2. But there’s a catch.

As we exhale all that CO2, the pH level in the bloodstream begins to change, forcing the body to make more fine-tuned adjustments. In order to bring balance back to the blood, bicarbonate — a simple compound that helps maintain a steady and neutral pH in our body — is shuttled to the kidneys. From there, we can easily get rid of it … by peeing it away. Having to urinate every few hours, even throughout the night, is part of what makes acetazolamide work. As long as we keep flushing away the bicarbonate, we can continue to inhale and exhale at a faster pace.

High altitude climbers have been taking acetazolamide to help adapt their breathing for over 40 years, but dosage varies depending on how much each person needs, because everyone reacts differently at altitude, says Roach. Not everyone suffers AMS to the same degree, and some of the world’s best big mountain climbers are so good at adjusting to altitude on their own that the drug doesn’t really help much.

Because there is no easy way to predict who might develop AMS, Roach says people can climb without acetazolamide to find out how the body reacts in that extreme environment, as long as they are prepared to take the drug or head back down the mountain if they get sick. For most mountaineers, that’s what the spirit of climbing high is all about: testing your own limits.

“One of the totally cool things is learning how your body does [at elevation],” Roach says, “and it’s a shame if people never, ever have that.”

About the Author

Alyson Kenward

Alyson Kenward studied chemistry at the University of Calgary. After five years of trying to keep yellow mixtures from turning orange, she decided it was time to swap her lab coat for a laptop and get down to the business of being a writer of all things science-related. Although she misses how her stir plates used to serenade her, she was happy to recall just how much she loves writing. In her spare time, she enjoys exploring the central New Jersey wilderness.



Great article. The effect of blood acidity on oxygen carriage is quite profound: http://www.altitude.org/calculators


jack greenblatt says:

It might be a good idea if travelers off to a high altitude destination go to a site in their city, e.g., a medical center, where they can experience calibrated high altitudes say from 7,000 to 14,000 feet. If the traveler has a severe reaction, it will serve as a warning sign that they need to take extra precautions. Does such a thing exist already?

rolland w amos says:

Hi! In 1955 I was a student at Mexico City College (Mexico,D.F.). The school had a mountain climbing club. With them I climbed Popocatepetl (17,750′). We drove up to the volcanic ash level at the base (maybe 12-13,000′), then climbed to the frozen snow/ice level (maybe 15,000′), then on up to the top. I knew nothing about what the lack of oxygen meant at those altitudes. I was just amazed that when we reached the snow/ice, I could only manage maybe 10 steps upward, before I had to fall and rest, yet, while resting, I noted other climbers proceeding up the volcano with nary a stop. They were obviously locals who were acclimated to the thin air. I was a gringo, who wasn’t. We started the climb at around 4-5 AM and reached the top around 1200-1300 hours. We paused there briefly, signed the guest book, then headed back down. Check Google for some good pictures. Rolland Amos, Severn MD

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