Why Less Oxygen at Altitude
Breathing at Altitude
The Lungs at Altitude
Oxygen carriage in Blood
High Altitude Cough
Sleep at High Altitude
The HAPE Database
Acute Mountain Sickness
AMS, HAPE and HACE
There is so much less oxygen in the high mountains that it is not surprising that travelling to high altitude causes people to feel unwell, but how this
shortage of oxygen actually leads to altitude sickness is still not fully understood. Most people remain well at altitudes of up to 2500m, the equivalent
barometric pressure to which aeroplane cabins are pressurised. However, even at 1500m above sea level you may notice more breathlessness than normal
on exercise and night vision may be impaired. Above 2500m, the symptoms of altitude sickness become more noticeable.
If you live at altitude for many years, you may be at risk of developing another illness, called chronic mountain sickness or Monge’s disease.
Acute Mountain Sickness
The commonest illness at altitude is acute mountain sickness. This is sometimes colloquially referred to as altitude sickness or mountain sickness and in South America it is called “soroche”. Most people experience acute mountain sickness as a relatively mild, self-limiting illness.
What are the symptoms?
The most prominent symptom is usually headache, and most people also experience nausea and even vomiting, lethargy, dizziness and poor sleep. Symptoms are very similar to a really bad hangover. Acute mountain sickness can be diagnosed using a self-assessment score sheet. If you have recently ascended to over 2500m, have a headache and your total score is 3 points or more on the score sheet, then you have acute mountain sickness.
Who gets acute mountain sickness?
Anyone who travels to altitudes of over 2500m is at risk of acute mountain sickness. Normally it doesn’t become noticeable until you have been at
that altitude for a few hours. Part of the mystery of acute mountain sickness is that it is difficult to predict who will be affected. There are many
stories of fit and healthy people being badly limited by symptoms of acute mountain sickness, while their older companions have felt fine.
What causes acute mountain sickness?
How a shortage of oxygen leads to acute mountain sickness is not known. Some scientists believe that it is due to swelling of the brain but the evidence for this hypothesis is not conclusive. The theory is that In susceptible individuals, swelling could cause a small increase in the pressure inside the skull and lead to symptoms of acute mountain sickness. The swelling may be due to increased blood flow to the brain or leakiness of blood vessels in the brain.
How is acute mountain sickness treated?
It is better to prevent acute mountain sickness than to try to treat it. Ascending at a sensible rate (300m gain in altitude per day),
should mean that your body can acclimatise as you ascend and so you will be less likely to develop acute mountain sickness. However, if you
need to go up more quickly, you could consider taking a drug called acetazolamide (also known as Diamox). There is now good evidence
that acetazolamide reduces symptoms of acute mountain sickness in trekkers, although it does have some unusual side-effects: it makes your hands and feet
tingle, and it makes fizzy drinks taste funny.
by A.A. Roger Thompson
"It is essential that you should NEVER go up higher if you have acute mountain sickness"