Video - Pulmonary changes at high altitude and altitude sickness

At high altitudes, the air pressure decreases and as a result the pressure driving oxygen through alveoli and into circulation also decreases. As a result, people can become hypoxic which causes many problems including increased pulmonary vascular resistance.

As people spend much time at high altitudes, the body adapts and produces 2,3-bisphosphoglyceric acid, which helps decrease hemoglobin’s affinity for oxygen, allowing more oxygen delivery to oxygen-deprived tissues. The kidneys also increase the release of erythropoietin to stimulate the bone marrow to produce more red blood cells.

When people ascend to high altitudes too quickly, the body hasn't got time to adapt to low air pressures, and this can result in altitude sickness. Symptoms include headache, fatigue, shortness of breath, nausea, and loss of appetite. In severe cases, it can lead to high-altitude cerebral edema (HACE) or high-altitude pulmonary edema (HAPE), both of which are life-threatening conditions.