Evidence for interaction between the contributions to ventilation from the central and peripheral chemoreceptors in man.

1. The question of whether there is any interaction between the peripheral and central chemoreceptor contributions to ventilation in man has been addressed. 2. Subjects were exposed to an end-tidal PCO2 of ca. 10 Torr above resting for 8 min at an end-tidal PO2 of 100 Torr. The end-tidal PCO2 was then reduced to near eucapnia. This provided a period of time when the PCO2 at the peripheral chemoreceptors would be near eucapnia, but would still be raised at the central chemoreceptors. 3. Against the background above, the effect of an hypoxic end-tidal step from a PO2 of 100 Torr to a PO2 of 50 Torr was studied, and compared with the effect of the same step when both sets of chemoreceptors were near eucapnia. 4. Three subjects were studied, each contributing twelve sets of data to each of the three protocols required for the comparisons. 5. In two of the three subjects, the ventilatory response to hypoxia was augmented when central PCO2 was high. 6. The results support the idea that there is an interaction between the central and peripheral chemoreceptors in man. The consequences of this and other possible interpretations of the results are discussed.