The effect of bupivacaine aerosol on the activity of pulmonary stretch and 'irritant' receptors.

1. Experiments have been done on anaesthetized, paralysed and artificially ventilated cats. 2. Vagal single afferent fibres showing discharges in phase with respiration were isolated in the neck. Two types of fibres were studied at different tidal volumes: (i) showing slowly adapting discharges from the pulmonary stretch receptors; (ii) showing rapidly adapting discharges from the lung 'irritant' receptors. The effect of bupivacaine aerosol, administered by positive pressure inflations, was recorded on the pattern of fibre discharge. 3. The pulmonary stretch fibres were further classified into low-threshold and higher-threshold fibres according to the standard criteria. Bupivacaine aerosol blocked activity in all the low-threshold and in the majority of the higher-threshold fibres. 4. Of the rapidly adapting fibres, bupivacaine completely blocked activity at some tidal volumes and markedly reduced it at most others. 5. The fibre activity data are presented. It is concluded that although bupivacaine aerosol markedly reduced impulse activity in all three types of fibres, the data suggest that there is a small difference in the ease with which low-threshold fibres on the one hand and higher-threshold and "irritant" fibres on the other hand are affected. The reasons for this difference in the behaviour are not understood.