The Repeatability of Ventilatory Responses to Excess of Carbon Dioxide and Lack of Oxygen

The ventilatory responses to CO 2 without hypoxia, to hypoxia at constant P A ACO ACO2 and to CO 2 combined with hypoxia were measured in duplicate with an interval of 20 min. between the two sets of measurements. The P A ACO ACO2 threshold during the second set differed in only random fashion from that during the first set; so did the CO 2 sensitivity in the absence of hypoxia. The CO 2 sensitivity during hypoxia, however, was significantly greater during the second set of measurements. The relevance of these results to the investigation of drugs which affect respiration is discussed.