At high altitude, there can be acute changes and changes due to acclimatization. -  Acute mountain sicknessDyspnoea, dizziness, tiredness, tachycardia, palpitation, nausea, vomiting etc. At higher altitudes- pulmonary oedema and cerebral oedema may occur.- Acclimatization changesHyperventilation leading to respiratory alkalosis Increased 2,3DPG- Hb-O2 dissociation curve shifts to right. Increased erythropoietin leading to absolute polycythemia with increased red cell mass. Increased renal excretion of bicarbonate Increased tissue vascularity Increased oxidative metabolism Increased diffusion capacity of the lung​ Increased myoglobin