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Optimal interelectrode distance in sensory and mixed compound nerve action potentials: 3- versus 4-centimeter bar
Van Evanoff1, Ralph M Buschbacher
1Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indiana University Medical Center, Indianapolis, IN, USA. vevanoff@triad.rr.com
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.
