Effect of Altitude on Oxygen Transport
At sea level, the partial pressure of oxygen in the atmosphere is just over 20kPa, and the partial pressure of oxygen in an alveolus is about 13kPa.
If however, a person climbs up a mountain to a height of 6500 metres, then the air pressure is much less.The partial pressure of oxygen in the air is only about 10kPa, and in the lungs about 5.3kPa.This means that haemoglobin will be only 70% saturated in the lungs
If someone travels quickly, over a period of just a few days, from sea level to a very high altitude, the body does not have enough time to adjust to this drop in oxygen availability, and the person may suffer from altitude sickness. The symptoms of altitude sickness frequently begin with an increase in the rate and depth of breathing, and a general feeling of dizziness and weakness
However, if the body is given plenty of time to adapt, then most people can cope well at altitudes up to atleast 5000 metresAs the body gradually acclimatises to high altitude, a number of changes take place.The number of red blood cells increases: whereas red blood cells normally make up about 40-50% of the blood, after a few months at high altitude this rises to as much as 50-70%. However, it takes time. There is no change in the number of red blood cells for atleast two or three weeks at high altitude. People who live permanently at high altitude often have especially broad chests, providing larger lung capacities than normal. The heart is often larger than in a person who lives at low altitude, especially the right side, which pumps blood to the lungs. They also have more haemoglobin in their blood than usual, so increasing the efficiency of oxygen transport from lungs to tissues.
In 1979, two mountaineers climbed Mt. Everest without oxygen, returning safely despite experiencing hallucinations and feelings of euphoria at the summit.