Responses to severe hypoxia of phrenic and recurrent laryngeal nerve activity in vagotomized cats.

We investigated changes in activities of phrenic nerve (PN) and the recurrent laryngeal nerve (RLN) during progressive hypoxia produced by administration of a mixture of 5% O2 in N2 and a mixture of 5% O2 in N2O in 8 vagotomized, paralyzed, and artificially ventilated cats anesthetized with halothane. During progressive hypoxia produced by administration of 5% O2 in N2, both PN and RLN activities initially increased and then decreased at approximately the same rate. The relationship between PN and RLN activities during the respiratory stimulation and the relationship between PN and RLN activities during the depression due to hypoxia were both linear and were represented by the same linear regression line. The responses of PN and RLN activities to progressive hypoxia produced by administration of 5% O2 in N2O were basically similar to those observed during administration of 5% O2 in N2 although a concomitant increase in depth of anesthesia with N2O enhanced the occurrence of hypoxic respiratory depression. These results suggest that the respiratory modulation of recurrent laryngeal motoneuron activity is closely related to that of phrenic motoneuron activity and that both motoneurons share similar control mechanisms. Neither severe hypoxia nor addition of N2O to a halothane-anesthetized cat seems to affect the close linear relationship between PN and RLN activities.