[Effect of catecholamines and propranolol on the acute acclimatization to high altitude in man]

The venous concentrations of epinephrine and norepinephrine and changes in ventilation, respiratory gases, circulation and ECG were determined in 20 young healthy male medical students during standardized stepwise ascent to 6000 m in a low pressure chamber, once without (control) and once with beta-receptor blockade (propranolol). The results show that the plasma concentration of norepinephrine increased significantly as a result of hypoxic hypoxia. The moderate increase in epinephrine was, besides the minor but significant hypoxic influence, mainly due to psychic tension. Since beta-receptor blockade does not prevent the respiratory and circulatory adjustment, beta-adrenergic stimulation is not thought to be necessary at altitude. Propranolol, on the contrary, lowers the hypoxia-induced increase in cardiac output and diminishes the ECG changes, in particular the S-T depression, significantly. By antagonizing the effects of epinephrine and by its central effects, propranolol improves subjective tolerance to altitude, and, on the other hand, by economizing the cardiac work load, the objective ability to withstand oxygen want.