Altitude is commonly defined as:
- High Altitude: 1500 – 3500 m (5000 – 11500 ft)
- Very High Altitude: 3500 – 5500 m (11500 – 18000 ft)
- Extreme Altitude: over 5500 m
At high altitudes most illnesses and ailments are as a direct result of a lack of available oxygen. In reality the amount of oxygen in the atmosphere is constantly around 20%, but because of the way pressure is decreased at altitude it makes the oxygen molecules more spread out so they are less accessible to the body. It must work harder to obtain the same amount of oxygen. At around 5500m the total amount of oxygen available is less than half of that at sea level. But the body is often able to acclimatise to these limiting conditions, and providing the ascent is slow, can take place over a period of days.
The normal physiological changes that occur with altitude include:
- Hyperventilation (breathing fast)
- Shortness of breath during exertion
- More frequent urination
- Disrupted breathing pattern during sleep
- Disrupted sleep
- Strange dreams
When living at such conditions your oxygen-starved body can consume upwards of 5000 calories a day, but you can’t eat very much because sickness is common, and the food is often unappetizing. The body learns to increase the rate and depth of breathing in order to compensate for the smaller amount of oxygen in the air. The kidneys alter the way the blood works in order for it to become alkaline.
This allows the blood to absorb more oxygen and so transport more the body. The body’s resting heart rate is increased in order to get oxygen round to all the vital organs. Because the blood, or more specifically the red blood cells, have to work harder, the body eventually produces more, which makes the circulatory system more efficient.