Explanation

At height above 8000 m from sea level, the partial pressure of oxygen in air is decreased. As a result, less haemoglobin is formed and the person suffers from dizziness, breathlessness, etc. This is called mountain sickness. A continuous exposure to this height increases ventilation to about 3 to 7 times than normal by significant increase in RBCs count and haemoglobin content in blood and breathing becomes normal.