Assessment of differential block of conduction by direct current applied to the cervical vagus nerve.

As investigation has been made of the adequacy of direct current to block conduction in the myelinated fibres of the cervical vagus nerve, leaving the nonmyelinated fibres conducting normally. Conduction was assessed from the compound electroneurograms, and from single fibre recording. Conduction of spontaneous activity and the responses to inflation and deflation in single fibres from lung irritant receptors and pulmonary stretch receptors were completely abolished when the A-B wave of the electroneurogram was absent but the C wave was intact. When the direct current was first applied to the nerve, and for periods lasting up to 30 s, there was sometimes a continuous discharge in the single fibres being studied. These results suggest that this method of producing a differential block of conduction in a mixed nerve such as the vagus may be superior to cooling.