Effects of increasing depth of anaesthesia on phrenic nerve and hypoglossal nerve activity during the swallowing reflex in cats

The effects of increasing depths of anaesthesia on phrenic nerve (PN) activity and hypoglossal nerve (HN) activity during the swallowing reflex elicited by stimulation of the superior laryngeal nerve (SLN) were investigated in 10 cats. Swallowing induced by SLN stimulation always coincided with a characteristic brief burst of PN activity and a large amplitude burst of HN activity. These characteristic responses of PN and HN activities were not influenced by either bilateral vagotomy or neuromuscular blockade, indicating that the characteristic responses of PN and HN activities can be used as indicators of the swallowing reflex in vagotomized and paralysed animals. The results obtained in such animals showed that increasing depth of anaesthesia depressed progressively the swallowing reflex. Detailed analysis of HN activity revealed also that SLN stimulation elicited three different responses of HN activity which had different sensitivities to anaesthesia. However, the characteristic response observed during the swallowing reflex was the most sensitive to increasing depth of anaesthesia.