The role of timing and magnitude of the vagal input in controlling the phrenic output in rabbits and baboons

Abstract

The effects of a short train of electrical impulses applied to the central stump of a cut vagus nerve at various moments of the central respiratory cycle were studied in 28 rabbits and 3 baboons. The animals were anaesthetized (halothane), vagotomized, paralyzed and artificially ventilated. Stimulation in inspiration elicited always an inhibitory effect (latency 8-9 ms) the magnitude of which increased towards the end of inspiration. The amplitude and duration of inhibition increased also with the frequency of impulses and/or the duration of the volley. Stimulation in expiration shortened this phase after latency being shorter towards the end of expiratory pause. It is suggested that excitation of thin myelinated vagal fibres has a facilitatory effect on the inhibitory response to information being conducted along thick myelinated fibres during inspiration.