Surface recording of orthodromic sensory nerve action potentials in median and ulnar nerves in normal subjects.

Reference values of sensory nerve compound action potentials (CAP) were established in 50 healthy subjects by examination with surface electrodes placed in a transverse and a longitudinal position at the wrist. Longitudinal electrodes record potentials of larger amplitude and shorter duration than transversally recorded CAPs. Both amplitude and duration were increased by an increase of interelectrode distance. The use of amplitude and duration as variables is encouraged by the well-defined biologic variation obtained when fixed interelectrode distance is used and when values are corrected for age and temperature. The strong correlation between amplitude and duration might indicate that the decrease of amplitude with age is caused by the reduction of conduction velocity rather than axonal loss. The ulnar nerve CAPs differ from those of the median nerve mostly with regard to influence of age and temperature. The reasons for this are discussed.