[Effects of interelectrode separation in sensory nerve conduction studies]

Sensory nerve action potentials (SNAPs) obtained by conventional sensory nerve conduction studies are greatly influenced by the distance between exploring and reference electrodes. Changes in SNAPs were investigated in 12 healthy median nerves using the orthodromic and antidromic sensory nerve conduction studies with 1-cm, 2-cm, 3-cm, 4-cm, and 5-cm of interelectrode distances. Peak-to-peak (orthodromic) or baseline-to-peak (antidromic) amplitudes and durations between the positive peaks were measured and each value was expressed as a ratio to the recording of 1-cm of interelectrode distance. SNAPs with maximum amplitude were obtained by more than 3-cm of interelectrode distance. Duration of SNAP was increased by an increase of interelectrode distance. Change in amplitude along with the interelectrode distance was larger in the orthodromic method than in the antidromic method. Contrariwise, change in duration was larger in the antidromic method. SNAPs with long duration had a gently sloping configuration, and each peak tended to be indistinct. So, 3-cm of active and reference interelectrode separation should be recommended in performing sensory nerve conduction studies between wrist and finger, because maximum amplitude and clear visualization of peaks are available.