Ventilatory CO2 responses during hypocapnia in anesthetized cats.

CO2 response curves were measured in six anesthetized cats under open-loop conditions in both hyperoxia and hypoxia. Markedly nonlinear characteristics were observed with CO2 response slopes below the normal operating level almost three times that above the normal operating level. In all animals, complete apnea was observed when CO2 was reduced sufficiently. The zero ventilation intercept averaged 23.5 +/- 5.6 (SD) Torr in hyperoxia (arterial PO2 greater than 400 Torr) and 21.0 +/- 5.4 Torr in hypoxia (arterial PO2 = 52.7 Torr). These results suggest that an increased tendency for periodic breathing in hypocapnia could be due to the higher CO2 response slope.