AltitudePhysiology.org | Breathing at High Altitude

Everyone breathes faster and deeper (hyperventilates) at high altitude – it is necessary to do this in order to survive. The function of the lungs is to expose blood to fresh air, and breathing faster essentially increases the flow of fresh air past the blood. This means that whenever an oxygen molecule is taken away by the blood, it is quickly replaced by a fresh one. This means that there is always more oxygen available to be taken up into the blood. (Click to read more about the effect of altitude on the lungs.)

Carbon dioxide (CO₂) is constantly produced by the body and the lungs remove it by allowing it to diffuse into the fresh air in the lungs. Increasing the flow of fresh air through the lungs, by hyperventilating, increases the rate at which CO₂ is lost. This happens for the same reason that wet laundry dries faster in a strong wind: the wind blows away the water vapour, so there is space for more water to evaporate. You can see how hyperventilating changes the level of carbon dioxide in the blood using the altitude oxygen calculator. Simply increase the number of breaths taken per minute, and watch what happens to the CO₂.

Because CO₂ is an acid gas, losing more of it from the blood leaves the blood relatively alkaline. At altitudes up to about 6000m, the kidneys correct the alkalinity of the blood over a few days by removing alkali (in the form of bicarbonate ions, HCO₃^-) from the blood. Our oxygen calculator will allow you to remove bicarbonate ions; watch the effect on the alkalinity of the blood.

These processes have important effects on the binding of oxygen to haemoglobin in the blood. You can read more about this in our tutorial on oxygen transport.

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Breathing at High Altitude