Responses of tracheobronchial receptors to halothane, enflurane, and isoflurane in anesthetized dogs.

We investigated the effects of halothane, enflurane, and isoflurane on the activity of 43 tracheobronchial slowly adapting stretch receptors (SARs) and 16 rapidly adapting irritant receptors (RARs) in 5 anesthetized, vagotomized, paralyzed, and artificially ventilated dogs. The 43 SARs were classified into 2 subtypes: (i) 17 low-threshold SARs with an expiratory discharge at FRC that were active throughout the respiratory cycle and (ii) 26 high-threshold SARs active only in inspiration. Ventilating the lungs with 5% of each anesthetic caused a significant increase in the inspiratory discharge of low-threshold SARs, whereas the expiratory discharge was inhibited or altogether silenced. While the activity of the majority of high-threshold SARs increased during the administration of the three volatile anesthetics, it decreased in those with a particularly high recruitment threshold. There was, however, a consistent increase in the pressure threshold at which all SARs were recruited. Ventilating the lungs with 5% of each anesthetic caused a significant decrease in activity of RARs. Our results indicate that all three halogenated anesthetics inhibit RARs at concentrations ranging from 1% to 5%.