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."