Hypoxic depression of ventilation in humans: alternative models for the chemoreflexes.

The ventilatory responses of 5 volunteers to three protocols were determined. In protocol A, PETCO2 was held at 1-2 Torr above resting; and PETO2 at 100 Torr for 10 min, 50 Torr for 20 min, and 100 Torr again for 10 min. In protocol B, PETCO2 was held at 8 Torr above resting, and PETO2 varied as in protocol A. Protocol C formed a control. Each protocol was repeated at least 6 times on each subject. The data were used to evaluate four different models (models 2-5) for incorporating the depressant effect of hypoxia into a standard model (model 1) of the chemoreflex responses. In model 2, hypoxic depression was incorporated as an additive term independent of the central and peripheral chemoreflexes; in model 3 it affected the central chemoreflex gain; in model 4 it affected the peripheral chemoreflex gain; and in model 5 it affected the gain of both reflexes. From this, it was concluded only model 4 was consistent with the data; all other models were inconsistent.