Regulation of respiration and heart rate response in exercise during altitude acclimatization

¹ Departments of Physiology, University of California, Berkeley and San Francisco, and White Mountain Research Station, Big Pine, California

In three subjects pulmonary ventilation, alveolar gas, blood lactate, and heart rate were studied at rest and during two grades of treadmill exercise in four environmental conditions: at sea level breathing air or 13% O₂ (simulating altitude), and during a sojourn of 3 weeks at an altitude of 3,800 m breathing air or 33% O₂ (simulating sea level). At altitude, ventilatory response to exercise was decreased by inhalation of 33% oxygen but remained above that observed at sea level breathing air. Study of the transients at the beginning and end of exercise showed that in all four environmental conditions, the ventilatory response to exercise could be dissected into fast and slow components, interpreted as neurogenic and humoral, respectively, in accordance with the neurohumoral theory. In two subjects, the increased hyperpnea of exercise at altitude represented increases in both the neurogenic and humoral components, while in the third subject only the humoral component was increased. Study of the composition of alveolar gas at the start and end of exercise indicated that pulmonary blood flow as well as ventilation undergoes immediate change at these times. Resting blood lactate concentrations and the increment produced by exercise were higher at altitude and resting heart rate tended to increase throughout the altitude sojourn in these subjects. The increment in pulse rate produced by exercise fell progressively, as expected.

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