The effect of halothane on phrenic and chemoreceptor responses to hypoxia in anesthetized kittens

We examined the effect of halothane on phrenic never and carotid sinus discharge during hypoxia in anesthetized kittens. In 12 animals, phrenic amplitude was measured during normoxia, during isocapnic hypoxia, and after a return to normoxia, both with and without halothane. Without halothane, all animals had an increase in phrenic amplitude during hypoxia. With halothane, half the animals showed an increase in phrenic amplitude followed by a decline. In a second group of animals, recordings were obtained from single or a few fiber strands of carotid sinus nerve. Without halothane, an increase in chemoreceptor discharge frequency during hypoxia was seen. With 1.0% halothane, frequency was decreased during normoxia and did not increase during hypoxia. Thus, halothane's effect on the ventilatory response to hypoxia, as measured by phrenic discharge, is at least partially explained by an effect on peripheral chemoreceptors.