Climbing Mt. Everest without oxygen: an analysis of maximal exercise during extreme hypoxia.

Climbers have reached the summit of Mt. Everest without supplementary oxygen in spite of measurements at lower altitudes which suggest that this is impossible. In the present study, data obtained on the American Medical Research Expedition to Everest were used to analyze the oxygen transport system during maximal exercise at the highest point on earth. Barometric pressure was 253 Torr, giving an inspired PO2 of only 43 Torr, alveolar PCO2 was 7.5 Torr, hemoglobin 18.4 g/dl, P50 at pH 7.4 was 29.6 Torr, and base excess -7.2 mEq/L. Values for cardiac output and diffusing capacity were based on measurements previously made at an altitude of 5800 m. The analysis showed it is possible to account for a VO2 max of over 1 L/min while keeping the PO2 of mixed venous blood above 15 Torr. Differences between the present study and previous predictions of a lower VO2 max are explained. These differences include higher values of barometric pressure, ventilation and base excess than expected. The analysis shows that any rise in P50 caused by increased 2,3-diphosphoglycerate is a liability. While it is just possible for man to reach the summit of Everest without supplementary oxygen, this can only be done at the expense of extreme hyperventilation and respiratory alkalosis, and even then the arterial PO2 is less than 30 Torr.