Stereotyped phrenic response to laryngeal afferent volleys: the mechanism and anesthetic sensitivity.

Abstract

The stereotyped reflex changes in phrenic discharge, produced by train(s) of electrical shocks to myelinated afferents in the internal branch of the superior laryngeal nerve (SLN), were studied in vagotomized cats and rabbits, mechanically ventilated with the mixture of oxygen and nitrous oxide. Single weak shocks caused a short latency (4-5 msec) phrenic response, an excitation followed by a slight inhibition for 10 msec, which was repeatable at a rate of 200 Hz or more. Repeated weak shocks at a rate higher than 100 Hz or single stronger shocks caused a powerful inhibition with a limited duration (25-30 msec) of both the central inspiratory activity (CIA) and short latency response. This stereotyped inhibition, which was followed by a rebound excitation, could occur every 30-50 msec with some reduction and was apparently associated with a decreased slope of integrated phrenicogram. During inhalation of halothane (0.5-1.5%), the short latency phrenic response was reduced, while the stereotyped inhibition and the reduction of phrenic augmentation were markedly enhanced when the CIA was slightly depressed by halothane inhalation. Therefore, the stereotyped inhibition produced by myelinated laryngeal afferents.