As if climbing a mountain wasn’t hard enough
already, forcing the body to acclimate to high altitudes too quickly can not only stop
someone from reaching the summit, it can have dire consequences. But altitude sickness doesn’t just affect
adrenaline-driven mountaineers. The effects of altitude sickness
can be experienced at as low as 1,800 meters, only about a third of the way up to Everest
Base Camp. Oh and just because someone is young and physically
fit, doesn’t mean that they won’t get sick. Youth is no protection. Fitness is no protection. It doesn’t work that way. My name is Jan Stepanek. I’ve been at Mayo Clinic for the last 25 years,
I’m an internal medicine and aerospace medicine specialist. The biggest difference between low altitudes,
like sea level, and high altitudes, like a mountain, is actually not a lack of oxygen, it’s the
change in atmospheric pressure. We all think of oxygen merely in terms of
what is around us. 21% of the ambient air that we breathe is
oxygen. That percentage doesn’t change between sea
level and Mount Everest. The only thing that changes is the pressure
that surrounds us. It’s this pressure that drives the gas exchange
from the lungs into the red blood cells which carry oxygen to the rest of the body. So less pressure at a high altitude means
it’s harder for the body to take up the oxygen. But… Our bodies are amazing. The body can adapt to the lack of ambient
pressure at high altitude by breathing faster and elevating the heart rate. By blowing off more carbon dioxide, the lungs
are able to enrich the blood with more oxygen. It’s called sympathoadrenal drive, so your
heart rate and your cardiac output goes up and that allows your body to gradually reset
to that new altitude environment of decreased ambient pressure and you still continue to
function well without falling ill. This all happens seamlessly if you ascend
to a high altitude slowly. It’s when you jump from low to high too
quickly that the body struggles with the change. This causes the first type of altitude sickness
you’d experience called acute mountain sickness with symptoms of headache, lack of appetite, nausea, vomiting, fatigue, light-headedness, and disturbed sleep. But if you breathe too fast you can start to lower your carbon dioxide levels and there is a balance. You need normal oxygen and carbon dioxide
levels in order to function optimally. And it’s these low carbon dioxide levels
that can start to cause problems. The carbon dioxide we all think of as being
a waste gas. But we actually need certain levels of carbon
dioxide to maintain normal blood flow to regions of the brain. So if carbon dioxide levels drop too much,
blood flow to the brain starts to diminish. The changes in oxygen levels and result in changes of breathing can cause the more dangerous forms of high altitude illnesses, HACE and HAPE. We believe today, based on the pathophysiology,
that from acute mountain sickness, and if not paid attention to and people do the foolish
thing and continue to ascend despite being sick, then you can progress to high altitude
cerebral edema, which not infrequently goes hand-in-hand with a little bit of pulmonary
edema. These two edema illnesses are rare and can
be difficult to study because they often occur in high, hard to reach places where the person
either rapidly descends and their symptoms ease or they progress and cause death. In high-altitude cerebral edema, experts think
that the changes in blood flow causes an increase in the permeability of the blood-brain barrier
causing brain fluid to leak around the blood vessels. This causes the brain to swell and starts
to hinder the central function of the brain stem and other critical areas of the brain. But what exactly causes the blood-brain barrier
to leak? Million dollar question. You know, there is a lot of hypotheses. Similarly with high-altitude pulmonary edema,
blood vessels constrict in the lungs in a patchy fashion in response to lack of oxygen. This can cause the vessels to leak in a manner
similar to the blood-brain barrier resulting in pulmonary edema. And keep in mind, this is in an environment
where you already have lack of oxygen due to ambient pressure, so it gets to a point
where it just gets to be not enough for the body to be able to function and systems start
shutting down, arrhythmias start happening, and people go into respiratory arrest. So this is the worst case scenario. But for many people, acute mountain sickness
is more of an uncomfortable headache that gets better over time or after they move to
a lower altitude. You can prevent altitude sickness just by
taking more time to move from low to high elevations. You know, the biggest challenge I think that kills more
people on mountains these days than altitude sickness is bad judgment and a sense of, “I’ve
paid for this trip, it cost me a lot of money, I’m here and by gosh I’m bagging this peak.”

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