Effect of CO₂ on respiration using a new method of administering CO₂

When a subject inhales air containing a given concentration of CO 2 , the total load of CO 2 is not fixed, but is increased linearly with the ventilation. The alveolar CO 2 tension can never be reduced below the inspired CO 2 tension, and the greater the response, the greater the CO 2 load. By contrast, when CO 2 is added to the inspired air stream at a constant rate, the load of CO 2 and the challenge to the respiratory control is fixed and independent of the response, as it is in muscular exercise. The ventilatory response necessary to maintain a normal alveolar CO 2 tension is much less with fixed amounts per minute than with fixed concentrations of inspired C0 2 . These different methods of administering CO 2 were tested in two subjects, both of whom increased their alveolar ventilation equally for the same increase in alveolar CO 2 tension whether the CO 2 was presented as a fixed concentration or a fixed load. Furthermore, other experiments designed to change the magnitude of the fluctuations of CO 2 tension which must occur in the arterial blood during the respiratory cycle also failed to alter the subjects' ventilatory responses. respiration control; ventilation; exercise Submitted on January 21, 1963