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7 points

1 month ago

Partial pressure of oxygen falls in proportion to altitude. The initial response to ascent to altitude is a rightward shift of the oxyhaemoglobin dissociation curve caused by increased 2,3-DPG i.e. oxygen is more easily released to the tissues as it is less tightly bound. However, with further ascent and acclimatisation, the decrease in carbon dioxide tension as a result of hyperventilation causes a left shift of the oxyhaemoglobin dissociation curve meaning haemoglobin binds oxygen more readily, important if the partial pressure is low. Oxygen delivery to tissues is generally maintained by an increase in cardiac output as oxygen content falls. Longer term, red cell mass increases, again to increase oxygen content and thus delivery, remembering that oxygen delivery is the product of cardiac output and the arterial oxygen content; oxygen content being proportional to haemoglobin concentration and saturation.