Objective
Distance between the active and reference electrodes can affect the waveform configuration and amplitude of sensory nerve action potential (SNAP). This study was purposed to determine the change of SNAP parameters with varying interelectrode distance.

Metohod: Median sensory nerve conduction study was performed in the middle finger of 40 young healthy subjects by antidromic method. To ensure firm contact with skin, strip adhesive electrode was used for recording responses. The active electrode was fixed on 1 cm distal to the proximal flexion crease of middle finger and interelectrode separation was increased from 1 to 5 cm by 1.0 cm increments. Bar electrode was fixed 14 cm proximal from active electrode for stimulation in the wrist area.

Results
As the interelectrode distance increased from 1 cm to 5 cm, onset latency remained unchanged. The peak latency increased with increasing the distance up to 3 cm but didn't change beyond 3 cm (1 cm: 2.89⁑0.89 msec, 2 cm: 2.97⁑0.89 msec, 3 cm: 3.02⁑0.19 msec, 4 cm: 3.02⁑0.19 msec, 5 cm: 3.02⁑0.20 msec). Base-to-peak amplitude significantly increased only up to 3 cm (1 cm: 30.3⁑6.7μV, 2 cm: 43.7⁑8.6μV, 3 cm: 50.8⁑10.4μV, 4 cm: 51.1⁑10.9 μV, 5c m: 51.3⁑11.4μV) but peak-to-peak amplitude sequentially increased to 5 cm (1 cm: 49.6⁑12.1μV, 2 cm: 72.8⁑14.4μv, 3 cm: 83.6⁑19.4μV, 4 cm: 91.3⁑22.5μV, 5 cm: 93.4⁑23.9μV)(p＜.05).

Conclustion: This study showed that changing interelectrode distance altered some parameters of SNAP, especially the peak-to peak amplitude.