Mechanism of Nerve Block

Abstract

THE recent paper by Ochoa et al.¹ seems to imply that the only mechanism for nerve block by compression is that of direct mechanical deformation of the nerve fibres. Acute application of high pressure such as they applied (1,000 mm Hg) was first used for the production of experimental differential block of large nerve fibres by Bishop, Heinbecker and O'Leary², and no one would question the extreme case of impulse blockage due to fibre compression when the nerve is struck with a hammer. The authors have a sound point in the principle that tissue-deforming pressure, the pressure difference between the compressed and neighbouring regions, is necessary to produce deformation block. Only excessively great pressures applied to a whole nerve, essentially an incompressible liquid, produce any effect, although there are certainly clinical circumstances, like the hammer blow, where acute, focally-applied, great pressure occasions nerve damage.