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

We investigated the effects of halothane, enflurane, and isoflurane on the activity of 43 tracheo-bronchial 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) high-threshold SARs active only in respiration. 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 particulary 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 cuased a significant decrease in activity of RARs. Our results indicate that all three halogenated anesthetics inhibit RAR at concentrations rangig from 1% to 5%.