Optimal interelectrode distance in sensory and mixed compound nerve action potentials: 3- versus 4-centimeter bar electrodes

Abstract

Objective: To evaluate the amplitude and latency for 3-cm versus 4-cm distance between the active and reference electrodes (electrode separation) used to obtain normative sensory and mixed compound nerve action potential data.

Design: Prospective, unblinded clinical test evaluating 3 nerves: mixed median and ulnar across wrist (8 cm), and radial antidromic sensory (10 cm).

Setting: University and private practice electrodiagnostic laboratories.

Participants: One hundred six adult volunteers without known neuropathy.

Interventions: Not applicable.

Main outcome measures: Peak-to-peak amplitude and onset and peak latencies.

Results: Mean onset latencies +/- standard deviation (SD) were equal for 3-cm and 4-cm separations (median, 1.6+/-0.2 ms; radial, 1.7+/-0.2 ms; ulnar, 1.5+/-0.2 ms). Mean peak latencies were also equal for 3-cm and 4-cm separation for radial (2.2+/-0.2 ms) and ulnar (1.9+/-0.2 ms) studies but differed for the median study (3 cm, 2.0+/-0.3 ms; 4 cm, 2.1+/-0.3 ms; P<.0001). Mean amplitudes +/- SD with 3-cm and 4-cm separations were, respectively, 101+/-39 microV and 103+/-39 microV (P=.0434) for the median, 47+/-17 microV and 48+/-16 microV (P=.0209) for the radial, and 52+/-28 microV and 55+/-29 microV (P=.0001) for the ulnar study. These differences were statistically significant but clinically insignificant.

Conclusions: The results support a hypothesized difference in amplitude but not latency between 3- and 4-cm separation. Clinically, however, the magnitude was insignificant.