THE EFFECT OF FOUR VOLATILE ANAESTHETIC AGENTS ON THE IMPULSE ACTIVITY OF TWO TYPES OF PULMONARY RECEPTOR

The effect of halothane, ether, chloroform and trichloroethylene on the impulse discharge of two types of pulmonary receptor has been investigated in cats and dogs under chloralose or barbiturate anaesthesia. Afferent impulses were recorded from pulmonary stretch fibres and also from slowly-conducting vagal fibres whose pulmonary endings were stimulated by hyperinflation (high-threshold inflation receptors). Ventilating the lungs with low concentrations of each agent (e.g. 1–3 per cent halothane) caused sensitization of the pulmonary stretch receptors but had no effect on the high-threshold endings. With high concentrations (e.g. 5–20 per cent halothane), pulmonary stretch receptors showed an initial sensitization followed by a reduction or abolition of activity, while the high-threshold receptors showed a marked increase in impulse activity during inflation. The possibility is discussed that the high-threshold inflation receptors may be involved in some of the reflex effects that have been observed during surgical anaesthesia with high concentrations of halothane.