If you going to high altitude about 9000 ft from sea level , you develops some symptoms such as headache, breathlessness, dizziness, nausea, vomiting etc. this difficulty is known as mountain sickness . the reason behind is that fall of po2 level at high altitude . this wild lovers alveolar po2 and there by reduces the diffusion of oxygen form the alveolar air to blood . the oxygenation of blood is decreased progressively. The fall in oxygen level in the blood causes symptoms like head ache, vomiting, dizziness etc. when time progress the affected person becomes acclimatized to the new surrounding , by increasing the heart rate, when heart rate increases blood pumping increases .the total rbc count in the blood increases, the rbc are produced by bone marrow. By stimulating bone marrow the production of rbc increases .the oxygen carrying capability of haemoglobin also increases .the result of all these activities is that each ml of blood takes more oxygen than the usual quantity at a low concentration of po2.