Andy Chapman above 6,000-meters in the Cordillera Blanca, Peru.
As a result of the lower barometric pressure at high altitude, the air (and the oxygen in it) becomes less dense (fewer molecules per unit of volume), so you cannot get as much of it into your lungs. Have you ever put a bag of chips in your car and then driven over a pass? The bag that was about half full of air will be bursting at the seams by the time you’re a few thousand feet higher. Though the amount of air in the bag hasn’t changed, it’s under less pressure than it was at a lower elevation. That expansion is similar to what’s happening to the air around you when you climb a peak. However, while the atmosphere around you is expanding, your lungs are the same size, so each breath you take has a lower percentage of oxygen than it did at a lower elevation.
As you near the poles, the atmosphere becomes less deep (there’s less distance from sea level to the edge of the toposphere at the poles than there is near the equator). So, comparable air density decreases happen at lower altitudes at the poles than they do at the equator. As a result, altitude changes have larger physiological impacts near the poles. For example, 20,000 feet in Alaska feels higher than 20,000 feet in Peru.
No matter where you are, you have to take more breaths at a higher elevation to make up for the lack of oxygen in your body, so even just walking around feels like you’re running. This lower barometric pressure and decreased oxygen may cause a number of life-threatening illnesses, so proper acclimatization is key on any trip to a big peak.
Threats of Altitude
High altitude does all kinds of stuff to the human body—none of it good. It’s important to know what’s happening to yourself and your climbing partner, so you understand how serious the situation is and what can be and should be done about it.
Acute Mountain Sickness (AMS):
AMS is essentially a mild case of high altitude cerebral edema (discussed later) with symptoms that often mimic the flu. Things like headache, loss of appetite, fatigue, nausea, and dizziness all indicate AMS. While AMS itself is not life threatening, its symptoms can be a sign of oncoming HACE, which can put a serious kink in your climb. Mild AMS usually goes away after a day or two if you don’t go any higher, and most climbers just deal with the symptoms during quick technical climbs where stopping for a day or two isn’t an option. If the symptoms get worse, however, going down is the best move.
High Altitude Pulmonary Edema (HAPE):
High Altitude Pulmonary Edema results when fluid leaks from your pulmonary capillaries and builds up in the lungs. As the amount of fluid in the lungs becomes greater, it prevents you from making full breaths, which leads to less oxygen intake and makes the situation even worse. In essence, your body will slowly suffocate due to the lack of oxygen. With less oxygen available to the brain, a victim will experience ataxia (loss of coordination) and hallucinations. Shortness of breath, serious weakness, confusion, and irrational behavior are all signs of HAPE, so keep an eye on the guy roped to you. If anyone starts hacking up something with blood in it, they’re in trouble and need to descend immediately.
High Altitude Cerebral Edema (HACE):
The decreased barometric pressure at high altitudes can lead to fluids leaking from your body’s internal tissues. When this fluid leak results in swelling brain tissue, it’s known as High Altitude Cerebral Edema. Headaches, ataxia, hallucinations, loss of consciousness, and eventually coma and death result if someone with HACE isn’t brought to a lower altitude in a reasonable amount of time. Do not take any form of edema lightly. Head down immediately if the terrain and weather permit it.
High Altitude Flatus Expulsion (HAFE):
Changes in barometric pressure cause increases in rectal gasses, and, well, basically cause you to fart far more often than you normally would. This isn’t exactly life threatening, but it’s a real bummer when you get storm bound in a tiny bivy tent for a couple days. Sorry, it’s just part of the deal.
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Tags: alpine climbing, outdoor survival
You need to review your first two paragraphs. You’re talking out your ass.
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“Many people seem to think that there’s less air at high altitudes. The reality is that there’s the same amount of air, but as a result of the lower barometric pressure, the air (and the oxygen in it) becomes less dense, so you cannot get as much of it into your lungs. ”
No. That’s ridiculous. The definition of density mass per volume. If the air is less dense, there will be less air per volume. So yes, there is “less air” up there, keeping volume constant. Any other interpretation of “less air” (variable volume) is just silly and meaningless.
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Thank you both for your comments. I especially appreciate Shoo’s comment explaining the amount of air in terms of mass per volume. I’m a climber, not a physicist, and the issue was clearly hard for me to explain. What I was trying to get at by saying that there is the same amount of air is the fact that the percentage of oxygen that makes up the atmosphere remains the same (approx. 21%), but less of it is available for you to breathe because the air is less dense. I tried to incorporate the issue of volume with the potato-chip bag example, but it seems that my analogy came up short.
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