There is a fall of PO2 level at high altitudes. This lowers alveolar PO2 and consequently reduces the diffusion of oxygen from the alveolar air to the blood. So oxygenation of blood is decreased progressively. After some time, the affected person gets adjusted to the surroundings due to which the heart rate are accelerated, RBC count in the blood is increased, haemoglobin level and oxygen-carrying capacity are also increased.
