With increasing altitudes the pressure of the air is reduced, and the oxygen tension becomes lower and lower. At a height of about 15,000 feet the barometric pressure is little over half an atmosphere, and the oxygen tension therefore only about 11 per cent. of an atmosphere. The presence of man at any considerable altitude necessitates an adjustment on his part so that the persistent undiminished oxygen requirement of the organism can be satisfied under the enforced changes of atmospheric conditions. Otherwise serious symptoms, which go under the designanation of oxygen starvation, may arise. They doubtless play some part in the malady familiarly known as mountain sickness.
One of the adaptations to the barometric conditions prevailing at considerable heights is an increased pulmonary ventilation. There is an augmentation in both depth and frequency of respiration. The increase in pulmonary ventilation diminishes the alveolar carbon dioxid tension, increases the oxygen tension,
GAS DIFFUSION IN THE LUNGS. JAMA. 1915;LXV(15):1284–1285. doi:10.1001/jama.1915.02580150058024