title: 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.
  
  
  METHODS
  Prospective, unblinded clinical test evaluating 3 nerves: mixed median and ulnar across wrist (8 cm), and radial antidromic sensory (10 cm).
  
  
  METHODS
  University and private practice electrodiagnostic laboratories.
  
  
  METHODS
  One hundred six adult volunteers without known neuropathy.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  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.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indiana University Medical Center, Indianapolis, IN, USA. vevanoff@triad.rr.com
authors.forename: Van
authors.initials: V
authors.lastname: Evanoff
authors.forename: Ralph M
authors.initials: RM
authors.lastname: Buschbacher
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000368:Aged; D001917:Brachial Plexus / Q000502:physiology*; D004566:Electrodes; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction / Q000502:physiology; D011446:Prospective Studies; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values