INTERACTION OF CO 2 AND HYPOXIC STIMULI ON VENTILATION AT HIGH ALTITUDE

The interaction of O 2 and CO 2 on the control of ventilation has been studied by a rebreathing technique in three healthy young male subjects, first under sea level conditions, then following 2 weeks' acclimatization to an altitude of 14,250 ft. The following results were observed: ( a ) at high altitude the family of response curves were shifted to lower values of alveolar CO 2 , and all response curves had a steeper gradient δV E /δP A ACO ACO2 than at sea level; ( b ) hypoxia potentiated the response to hypercapneic stimulus to about the same extent at sea level and at high altitude; ( c ) the ventilatory response to hypoxia was identical at sea level and at high altitude when P A ACO ACO2 was held at the normal air breathing value for the two conditions; but ( d ) potentiation of ventilatory response to hypoxia at high altitude occurred with smaller increments of CO 2 than at sea level. This was interpreted to mean that H + is an important factor in the mechanism of hypercapneic potentiation of hypoxic stimulus.