It may be fairly obvious but oxygen is a critical
factor when establishing our limitations, and the higher you go the less oxygen there
is. At high altitudes the air pressure is lower, which means there’s less oxygen in
the air you’re breathing, and the body can be pretty sensitive when it comes to oxygen
levels. In this scenario it expresses its displeasure in the form of hypoxia and altitude
sickness. This will usually start to affect you when
you pass 5,000 feet (1500 meters) above sea level. Your breathing rate increases as your
body tries to acquire more oxygen (BREATH SFX) . Despite this, your muscles still won’t
be receiving sufficient oxygen, making simple exercises like walking more difficult. You'll
start to feel tired, but you'll actually find it harder to sleep, because the sleep centers
of the brain won’t be getting enough oxygen. These conditions just get worse the higher
you go. At around 8,000 ft (2500m) these symptoms
can progress to dizziness and headaches leading to nausea or vomiting. These early forms of altitude sickness dubbed
‘Acute Mountain Sickness’ (AMS) are not usually life threatening and will normally
disappear as soon as you descend to a lower altitude. However if you continue up above 10,000 feet
(around 3000m) leaving what’s termed the ‘Physiological-Efficient Zone’, then you
run the risk of developing High Altitude Cerebral (HACE) and/or Pulmonary Edema (HAPE), where
fluid accumulates around your brain and in your lungs. Without treatment fast, this can
be fatal. If you don’t suffer Acute Mountain Sickness,
then from this height upwards the temperature will typically drop below zero and then continue
to decrease the higher you go, meaning you’re also more likely to suffer frostbite as your
blood is diverted from your extremities and towards your core. At 16,000ft you’ll be trying to survive
in temperatures of -17ºC/2ºF. Now these temperatures will vary according to the Lapse
Rate which is dictated by the humidity of the air, but it might surprise you to find
out that not only do people survive at this height but just above this at 16,700ft (5,100
m) you’ll find the highest permanent human settlement. La Rinconada is a gold mining
settlement of 50 - 70,000 people in the Andean Mountains of Peru. At this height each breath you take contains
only half the amount of oxygen of the air at sea level. So how on Earth do the residents survive in
such a harsh environment? Well there’s some debate about whether the tolerance of high-altitude
natives is genetic or a result of long term exposure, but either way they tend to have
larger lung capacities, and their bodies are able to make more efficient use of the oxygen
available, resulting in both better sleep and exercise performance. However, these traits aren’t a given among
high-altitude natives, with a syndrome called Chronic Mountain Sickness affecting nearly
a quarter of the La Rinconada population and 6-20% of all residents living over 8,000ft/2500
meters above sea level worldwide. This condition sees an excessive increase
in the body's red blood cells, which among other symptoms can result in heart failure
and death. The only cure is to descend to a lower altitude, but in some cases the symptoms
will be irreversible. While La Rinconada is the world’s highest
permanent settlement, if we push on up further to 19,520 ft (5,950 m) you’ll be at the
highest recorded height that humans can permanently tolerate. A scientific expedition in 1935 found that
Chilean miner Justo Copa lived at this altitude for 2 years. With all miners from the temporary
settlement suffering unsustainable side effects if they went any higher for extended periods
of time. The expedition team led by Physiologist David
Bruce Dill, concluded that residing at an altitude any higher was impossible. The occupants of this mine in Aucanquilcha,
Chile have since been dubbed 'The Highest Inhabitants Of The World’. But how long could you survive above this
altitude? Well, push on above 26,000 feet (8000 meters)
and you’re entering the ‘Death Zone’, so called because the oxygen deficit is so
great that the human body starts to break down and die with each minute you spend here So, with the ascent from this altitude to
Everest’s summit at 29,029 ft / 8848M taking around 7 hours how do climbers manage to stay
in the Death Zone for so many hours? For those that conquer the likes of Everest,
two big factors come into play. Acclimatization and supplemental oxygen. Most people can adapt
to altitudes if they acclimatize first. If you were suddenly transported from your
home city to the top of Everest, you’d likely be dead inside 2 minutes. Acclimatizing or acclimating allows your body,
among other things, to increase its haemoglobin, the red protein in your blood responsible
for transporting oxygen around your body. This can then absorb more oxygen. This doesn’t
necessarily negate all of the previous symptoms we’ve talked about, it just gives you a
better chance of making it to the top. Most that suffer from altitude sickness ascend
too quickly, the key is to climb slowly, with progressional stops at different altitudes
for days at a time. The climb to summit Everest usually takes 2 months. But even with the most comprehensive acclimatization
route, at 23,000feet most climbers will begin to tackle Everest with the assistance of oxygen
bottles, and when you’ve entered the Death Zone at
26,000 feet, acclimation becomes impossible and nearly everyone uses auxiliary oxygen. "EVEN IF YOU’RE ON OXYGEN AT EXTREME ALTITUDE,
YOU CAN’T GET NEARLY ENOUGH OXYGEN TO FEEL GOOD OR BE COMPLETELY SAFE,"
"WITHOUT OXYGEN, YOUR BODY IS SLOWLY DYING." While needing a consistent supply of oxygen
bottles doesn’t exactly fit the bill for a survivable height, there are an elite group
of climbers who have pushed past 26,000 ft and summited the highest point on our planet
without the assistance of extra oxygen. At these heights each breath of air that you
took would only contain about a third of the oxygen you would normally be inhaling back
at sea level. “UP THERE, YOU DO SOMETHING THAT’S TOO
AEROBIC ALL OF A SUDDEN AND YOU LAY THERE FOR 10 MINUTES TRYING TO CATCH YOUR BREATH." Ed Viesturs who has climbed all 14 of the
world’s highest mountains above the Death Zone mark, is 1 of only 200 people to have ever summited
Everest without supplemental oxygen. This elite club accounts for only 3 percent
of the total Everest summits, but 22 percent of the 111 deaths that have occurred above
26,000 feet. Understandably, most people tend to take in
the view, get a selfie and start heading back down out of the Death Zone,
but Babu Chiri Sherpa decided to settle in for a while longer, remaining at the top for an incredible 21
hours! Unsurprisingly this is the longest recorded time anyone has spent at the summit. But is there a limit beyond the world’s
highest peak of 29,000 feet (29,029 ft / 8848M) without extra oxygen? Well Professor Mike Grocott, an expert on
the physiological effects of altitude, estimates that the top of Everest is actually pretty
close to our limit… “I’D GUESS THE LIMIT WOULD BE ABOUT 9,000
METERS.” However, for obvious reasons we can’t physically
try to climb any higher than the Earth’s highest summit, but what if we weren’t climbing, what if we hopped on a passing balloon and
travelled up toward the stratosphere, what’s the absolute height we could survive to? Well
with oxygen continuing to decrease you’d need to get up there pretty quickly. As we established earlier, the reduced amount
of oxygen within each breathe is due to the decrease in pressure- something that also
continues to decrease the higher up we go. Above 49,000ft or 15,000m the pressure is
so low that even supplemental oxygen won’t help you. “...AT THIS ALTITUDE THE PRESSURE IS SO
LOW THAT THE CARBON DIOXIDE IS REMOVED FROM THE BLOOD FASTER THAN IT IS PRODUCED BY THE
BODY. THIS LEADS TO THE BLOOD BECOMING TOO ALKALINE [CAUSING] ALKALOSIS, DAMAGING THE
DELICATE STRUCTURE OF PROTEINS, WITH FATAL RESULTS. This decrease in pressure also lowers the
boiling point of fluids. You may be familiar with the concept that on top of Everest instead
of boiling at 100ºC/212°F water will boil at around 68°C/154 °F. Well head up a little
further to above 60,000ft, around 18,000 meters, and the average body temperature of 37ºC
/ XXºF will become the new boiling point, causing the surface fluids in your mouth,
on your eyes, as well as the air sacs in our lungs to vaporize and rapidly escape our bodies. The common misconception that blood contained
within your circulatory system will also boil however is not true, as your internal blood
pressure is still higher than the external pressure. Nonetheless, survival here will be extremely
short lived unless you are urgently repressurized. Humans are only able to survive above these
heights with the use of specialized pressure suits or pressurized cockpits. Named after Harry G. Armstrong (Founder of
the US Army's Department of Space Medicine), the 60,000ft or 18,000 meter Armstrong Limit
or Armstrong Line is considered the absolute limit of human survival. Despite the name
however, it is not actually a hard line, due to variations in the human body temperature,
effects could occur as low as 55,000 ft/17,000 meters, so you might want to take a thermometer
with you to be sure. This video is part of our human survival series,
with another video out soon! But in the meantime thank you to our The Great
Courses Plus who have made this video possible.
