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1 Department of Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York
When a subject inhales air containing a given concentration of CO2, the total load of CO2 is not fixed, but is increased linearly with the ventilation. The alveolar CO2 tension can never be reduced below the inspired CO2 tension, and the greater the response, the greater the CO2 load. By contrast, when CO2 is added to the inspired air stream at a constant rate, the load of CO2 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 CO2 tension is much less with fixed amounts per minute than with fixed concentrations of inspired C02. These different methods of administering CO2 were tested in two subjects, both of whom increased their alveolar ventilation equally for the same increase in alveolar CO2 tension whether the CO2 was presented as a fixed concentration or a fixed load. Furthermore, other experiments designed to change the magnitude of the fluctuations of CO2 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
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