Separate effects of halothane and carbon dioxide on respiratory duration in vagotomized cats

The independent effects of halothane and carbon dioxide on central mechanisms regulating respiratory frequency were investigated in 12 vagotomized, artificially ventilated cats. Changes in respiratory pattern analysed from the phrenic neurogram revealed that increasing PaCO2 at a constant depth of halothane anaesthesia caused a progressive increase in TE with various changes in TI, whereas increasing the depth of halothane anaesthesia at a constant PaCO2 caused a progressive decrease in TE with various changes in TI. These results suggest that the effect of carbon dioxide on central mechanisms regulating respiratory duration is exactly the opposite of that produced by halothane and that respiratory frequency is modified by both the depth of halothane anaesthesia and PaCO2.